1

1.1 Energy

The internationally accepted SI system of units defines energy and power by distance, time and mass as follows. As long as a force f causes acceleration a, a distance d is covered in a certain time t. Multiplying f by s produces the yielded energy fs, expressed in joules.
Energy per time t gives the performed power fs/t expressed in watts (see Fig. 1).

Speed and acceleration suppose distance and time:
d (distance)	d	d
	-- = v (velocity)	-- = a (acceleration)
t (time)	t	t²
Linear momentum and force persuppose mass, velocity and acceleration:
	d	d
m (mass)	-- m = i (momentum)	-- m = ma = f (force)
	t	t²
	x distance	/ time
	d²	d²
	-- m = e (energy)	-- m = e/t = p (power)
	t²	t³
Energy is expressed in joules (J), power (energy per second) in watts (W)
	J=kg*m²/sec²	W = J/sec
Old measures should be replaced as follows:
k= kilo(*10³)	kWh = 3.6 MJ	kWh/year = 0.1142W
M= mega(*10⁶)	kcal = 4.186 kJ	kcal/day = 0.0485W
G= giga(*10⁹)	pk.h = 2.648 MJ	pk = hp = 735.5 W
T= tera(*10¹²)	ton TNT = 4.2 GJ	PJ/year = 31.7 MW
P= peta(*10¹⁵)	MTOE = 41.87 PJ	J/sec = 1 W
E= exa(*10¹⁸)	kgfm = 9.81 J
	BTU = 1.055 kJ	W (watt) could be read as watt*year/year.
	watt*sec = 1 J
The equivalent of 1 m³ natural gas (aeq), roughly 1 litre petrol, occasionally counts 1 watt*year:
Occasionally:	m³ aeq = 31.5 MJ and	aeq/year = 1 W, or
Occasionally:	Wa = watt*year = 31.5 MJ	1 W = 1 watt*year/year
	1 MJ = 0.031709792 Wa 1 GJ = 31.7 Wa 1 TJ = 31.7 kWa 1 PJ = 31.7 MWa	‘a’ from latin ‘annum’ (year) Wa is watt during a year ‘k’ (kilo) means 1 000x ‘M’ (mega) means 1 000 000x

Fig. 1 Dimensions of energy

A year counts 365 x 24 x 60 x 60 = 31.536 Msec. So, 1 watt*year = 31.5 MW*sec = 31.5 MJ = 1 Wa.
Occasionally the equivalent of 1 m³ natural gas (aeq) counts approximately 31.5 MJ as well. So:
m³ aeq = watt*year = Wa = 31,5 MJ (energy) and m³ aeq / year = watt = W (power).

So, read ‘Wa’ and think ‘1 m³ natural gas’ or ‘1 litre petrol’ or ‘1 kg coal’ and
read ‘W’ and think ‘1 m³ natural gas per year’ or
read ‘kW’ and think ‘1000 m³ natural gas per year’ and
read ‘kWh’ and think ‘one hour of 1000 m³ natural gas per year’.

So, 1 Wa = 1watt*year =
8 769 watt*hour (Wh), because there are 365 x 24 = 8 769 hours in a year, or
8.769 kilowatt*hour (kWh), becauses ‘k’ means 1 000, or
31 536 000 Ws (J), because there are 31 536 000 seconds in a year, or
31 536 kJ, 31.5 MJ or 0.0315 GJ, because k = 1 000, M = 1 000 000 and G = 1 000 000 000.

This Wa measure is not only immediately interpretable as energy content of roughly 1 m³ natural gas, 1 litre petrol or 1 kg coal, but via the average amount of hours per year (8 775) it is also easily transferable by heart into electrical measures as Wh or kWh (and then via the number of seconds per hour (3 600) into the standard Ws=J). Moreover, in building design and ~management the year average is important and per year we may write this unit simply as W (watt). So, in this chapter for power we will use the usual standard W, known from lamps and other electric devices while for energy we will use W*year or Wa (‘a’ derived from latin ‘annum’, year). If we know the average use of power, energy costs depend on the duration of use. So, we do not pay power (in watts, joules per second), but energy (in joules, wattseconds, watthours, kilowatthours or wattyears): power x time.

A quiet person uses approximately 100 W per year, the equivalent of 100 m³ natural gas. That power is the same as the power of a candle or pilot light or the amount of solar energy/m² on our latitude. That is a lucky coincidence as well. The power of solar light varies from 0 (at night) to 1000W (at full sunlight in summer) around an average of approximately 100 W. Burning a lamp of 100 W during a year takes 100 watt*year as well, but electric light is more expensive.[1]

Crude oil is measured in barrels of 159 litres. So, if one barrel costs € 25, a litre costs € 0.16. However, a litre petrol (1 Wa) from the petrol station after refining and taxes costs more than € 1. Natural gas needs less refinary. Because 1 m³ natural gas (1Wa) now costs approximately € 0,30 [a], a year burning of a pilot light (100 Wa) costs approximately € 30,-. However, an electric Wa costs approximately € 0.70, more than 2 times as much as natural gas. Why?

1.1.1 Entropy

Electric energy is more expensive than energy content of gas or coal because the efficiency of electricity production can utilise approximately 38% from the energy content of fossile fuels only. The rest is necessarily lost as heat. That heat could be used for space heating, but transport of heat appeared to be too expensive more than once. Enterprises needing electricity and heat as well could gain a profit by generating both on their own (warmtekrachtkoppeling, WKK [b]). The electrical yield is expressed as ‘kWh_e’ (‘e’ = electric), the yield of heat as ‘kWh_th’ (‘th’ = thermic).

Here we meet the working of two main laws of thermodynamics. No energy gets lost by conversion (first main law of thermodynamics), but it degrades (second main law of thermodynamics). By any conversion only a part of the original energy can be utilised. The rest is dispersed, mostly as heat. So, it is no longer applicably concentrated in a point of application. Without ‘help from outside’ (in a ‘closed system’) energy conversion can only partly direct energy on any application, concentrate energy bearing particles, but by any conversion in total the disorder (entropy) grows.

In Fig. 2 all possible distributions of n = {1,2,3,4) particles in two rooms are represented. If one marks every individual particle by A, B, C, D, one can count the possibilities of configuration per state k. These determine the probability P(n,k) this state will occur. Extremely high of low values of k represent concentration in one room or the other.

Fig. 2 The distribution of particles in two rooms

When the numer of particles grows (for example from 10 to 100) the normal distribution becomes narrower (Fig. 3). That means the state k = n / 2 (sprawl) becomes more probable.

Fig. 3 The decreasing probability of concentration with a growing number of particles

In Fig. 3 below a probable and an improbable distribution of 100 particles within a cylinder without external influences are drawn. The probability of a defined state of dispersion has a positive relation with entropy S, dependent on the integrally summed heat content Q per temperature T:

This formula shows that a higher heat content increases entropy S, but a higher temperature decreases it. If we keep heat content the same and increase volume, then concentration, pressure and temperature decrease (Boyle-Gay Lussac), so entropy will increase. Storage (concentration) decreases entropy.

The (change of) force by which a piston is pushed out of a cylinder is equal to the proportion of (change of) energy and entropy Fig. 4.

Fig. 4 Carnot-engine

In a cylinder engine, alternating states of dispersion are used to convert imported disordered energy (heat) partly into directed movement. It is only possible by exporting part of the heat in an even more dispersed form (cooling). The necessary event of cooling makes an efficiency of 100% impossible and increases entropy in a larger environmental system. The reverse, adding rotating energy to this engine the principle can be used for heating (heat pump) and cooling (refrigerator).

1.1.2 Energetic efficiency

The proportion of the applicable part from total energy content of a primary source is the efficiency of the conversion. In Fig. 5 some conversion efficiencies are represented.

Device or process	chemical->thermic	thermic->mechanisal	mechanical->electric	electric->mechanical	electric->radiation	electric->chemical	chemical->electric	radiation->electric	thermic->electric	efficiency
100%
electric dynamo
electric motor
90%
steam boiler
HR-boiler
80%
c.v.-boiler
electric battery
70%
fuel cell
60%
50%
steam turbine
40%
electric power station
gas turbine
30%
car engine
neon lamp										20%
solar cell
10%
thermocouple
0%
Gool and e.a. (1986)
Fig. 5 Energy conversion efficiencies

An electric power station converts primary fuel (mostly coal) into electricity with approximately 38% efficiency. Fig. 5 shows that such a power station combines 3 conversions with respecitive efficiencies of 90, 45 and 95%. Multiplication of these efficiencies produces 38% indeed.[2] The step from chemical into electrical power could also be made directly by a fuel cell (brandstofcel)[c], but the profit of a higher efficiency (60%) does not yet counterbalance the costs.

The table shows the solar cell as well. The efficiency is between 10 and 20% (maximum 30%). Assuming 100W sunlight per m² Earth’s surface average per year in The Netherlands (40 000 km² land surface) we can yield at least 10W/m².

The average Dutch household uses approximately 375 wattyear/year or 375W electricity.

In a first approach a household would need 37.5 m2 solar cells. However, a washing machine needs also in periods without sunshine now and then 5000W. So, for an autonomous system solar electricity has to be accumulated in batteries. According to Fig. 5 such batteries have 70% efficiency for charging and discharging or 0.7 x 0.7 = 50% for total use. The needed surface for solar cells doubles in a second approach to at least 75 m² (37.5 m² / (0.7 x 0.7)).

However, most domestic devices do not work on direct current (D.C.) from solar cells or batteries, but on alternating current (A.C.). The efficiency of conversion into alternating current may increase the needed surface of solar cells into 100 m² or 1000 W installed power. Supposed solar cells cost € 3,‑ per installed W, the investment to harvest your own electricity will be € 3 000,‑. In the tropics it will be approximately half.

Electricity from the grid amounts to € 0.70 per Wa. So, an average use of approximately 375 W electricity approximately amounts to € 250 per year. In this example the solar energy earn to repay time exclusive interest is already approximately 3000/250 per year = 12 year. Concerning peak loads it is better to cover only a part of the needed domestic electricity by solar energy and deliver back the rest to the electricity grid avoiding efficiency losses by charging and discharging batteries. It decreases the earn to repay time.

The costs of solar cells decreased since 1975 (€70 per installed watt) a factor of approximately 23 (€3). Their efficiency and the costs of fossile fuels will increase. To pass the economic efficiency of fossile fuels as well the price of solar cells has to come down relatively little (Fig. 6).

After Maycock cited by Brown, Kane et al. (1993)

Fig. 6 Decreasing costs of solar cells

The efficiency of solar cells is rather high compared with the performance of nature. Plants convert approximately 0.5 % of sunlight in temporary biomass (sometimes 2%, but overall 0.02%), from which ony a little part is converted for a longer time in fossile fuel. Biomass production on land delivers maximally 1 W/m² being an ecological disaster by necessary homogeneity. In a first approach a human of 100 W would need minimally 100 m² land surface to stay alive. However, by all efficiency losses and more ecologically responsible farming one could better depart from 5000 m² (half a hectare).

1.1.3 Global energy

There is more than 6 000 times as much solar power available as mankind and other organisms use. The Earth after all has a radius of 6Mm (6 378 km) and therefore a profile with approximately 128 Mm² (p x 6 378 km x 6 378 km = 127 796 483 000 000 m²) capturing sunlight. The solar constant outside atmosphere measures 1 353 W/m², on the Earth’s surface reduced to approximately 47% by premature reflection (‑30%) or conversion in heat by watercycle (‑21%) or wind (‑2%). The remainder (636 W x 127 796 483 000 000 m² of profile surface unequally distributed over the spherical surface) is available for profitable retardation by life or man. However, 99.98% is directly converted into heat and radiated back to the universe as useless infrared light. Only a small part (-0.02%) is converted by other organisms in carbohydrates and since some billion years a very small part of that is stored more than a year as fossile fuel.

		Earth	The Netherlands
radius	Mm	6
profile	Mm²	128
spherical surface	Mm²	509	0,10	0,02%

solar constant	TW/Mm²	1353	832,99	61,57%[d]
solar influx	TW	172259	33,83	0,02%
from which available
sun 47% or 100W/m2	TW	80962	10,00[e]	0,01%
wind 2%	TW	3445	0,68	0,02%
fotosynthesis 0,02%	TW	34	0,01	0,02%

Fig. 7 Globally and nationally received solar power

The biological process of storage produced an atmosphere livable for much more organisms than the palaeozoic pioneers. Without life on earth the temperature would be 290^oC average instead of 13^oC. Instead of nitrogen (78%) and oxigen (21%) there would be a warm blanket of 98% carbon dioxide (now within 100 years increasing from 0.03% into 0.04%). By fastly oxidating the stored carbon into atmospheric CO₂ we bring the climate of Mars and heat death closer, unless increased growth of algas in the oceans keep up with us.

The actual energy use is negligible compared with the available solar energy (compare Fig. 7 and Fig. 8).

		Earth	The Netherlands
coal	TW	3	0,02	0,45%
oil	TW	4	0,03	0,77%
gas	TW	2	0,05	2,14%
electricity	TW	2	see fossile
traditional biomass	TW	1
total	TW	13	0,10	0,73%

Fig. 8 Gobal and national energy use[f]

Concerning Fig. 6, Fig. 7 and Fig. 8 making a plea for using wind or biomass is strange. Calculations of an ecological footprint based on surfaces of biomass necessary to cover our energy use have ecologically dangerous suppositions. Large surfaces of monocultures for energy supply like production forests (efficiency 1%) or special crops (efficiency 2%) are ecological disasters.

Without concerning further efficiency losses Dutch ecological footprint of 0.10 TW (Fig. 8) covered by biomass would amount 10 times the surface of The Netherlands yielding 0.01 TW (Fig. 7). However, covered by wind or solar energy it would amout 1/7 or 1/100. However, efficiency losses change these facors substantially (see 1.1.4).

To compare energy stocks of fossile fuels with powers (fluxes) expressed in terawatt in Fig. 7 and Fig. 8, Fig. 9 expresses them in power available when burned up in one year (a = annum).

		Earth	The Netherlands
coal	TWa	1137	0,65	0,06%
oil	TWa	169	0,03	0,02%
gas	TWa	133	1,60	1,20%
total	TWa	1439	2,28	0,16%

Fig. 9 Energy stock

By this estimated energy stock the world community can keep up its energy use 110 years.

However, the ecological consequence is ongoing extinction of species that can not keep pace with climate change. Forests can not move into the direction of the poles in time because they need thousands of years to settle while others ‘jump from the earth’ flying for heat.

For the contribution of different kinds of energy supply scenarios are made (Fig. 10).

After RIVM (2000)

Fig. 10 Energy scenarios

The small contribution solar energy and the great confidence in fossile fuels and biomass are remarkable.

1.1.4 National energy

According to CBS (2003) Dutch energy use (Fig. 11) approaches 0,1 TW (100 000 MW)[g] from which 0.01TW_e[h].

Fig. 11 Development of Dutch energy use 1988-1998

An ecological footprint on the basis of nearly 7 times as much wind looks favourable, but how efficient wind can be harvested? How useful is the power of 680 000 MW (0,68 TW) blowing over The Netherlands? The technical efficiency of wind turbines is maximally 40%, practically 20%. The energy from wind principally can not be harvested fully because the wind then would stand still behind the turbine. At least 60% of the energy is necessary to remove the air behind the turbine fast enough. Technical efficiency alone (R1) increases the wind based footprint of 1/7 into more then ½. But there are other efficiencies (see Fig. 12) together reducing the available wind energy from 0,68 TW available into maximally 0.02 TW useful.

Putting the Dutch coast from Vlaanderen to Dollard full with a screen of turbines and behind it a second one and so on until Zuid Limburg, these screens could not be filled by more than 80% with circular rotors (R2). In the surface of the screen some space has to be left open between the rotors to avoid non productive turbulence of counteracting rotors (R3). In a landscape of increasing roughness by wind turbines the wind will choose a higher route. So, in proportion to the height the screens need some distance to eachother (R4). The higher the wind turbine, the higher the yield, but we will not harvest wind on heights where costs outrun profits too much (R5). Decreasing height could be compensated partly by increasing horizontal density (R6) though local objections difficult to be estimated here can force to decrease horizontal density (R7).

R1 technical efficiency	0,20	R5 vertical limits	0,30
R2 filling reduction	0,80	R6 horizontal compensation	2,50
R3 side distance	0,25	R7 horizontal limits	P.M.
R4 foreland distance	0,85	PRODUCT TOTAL	0,03

Fig. 12 Reductions on theoretical wind potential.

By these efficiency reductions the ecological footprint on basis of wind appears not to be 1/7, but at least 5. For an ecological footprint on the basis of solar energy there are only technical and horizontal limits. A comparable ecological footprint then is 1/10. In both cases efficiency losses should be added caused by storage, conversion and transport, but these are equal for both within an all-electric society.

The ecological footprint based on biomass depends on location bound soil characteristics and efficiency losses for instance by conversion into electricity. A total efficiency of 1% applied in the comparance of Fig. 13 is optimistic.

			W/m²
rounded total Dutch energy use including	100000	MW	1,00
rounded Dutch electricity use	10000	MW	0,10

WIND
over The Nederlands blows at least	680000	MW	6,80
after reduction by 0.03	17340	MW	0,17
required surface	577%

SUN
The Nederlands receives	10000000	MW	100
after reduction by 0.1	1000000	MW	10
required surface	10%

BIOMASS
The Nederlands receives	10000000	MW	100
after reduction by 0.01	100000	MW	1
required surface	100%

Fig. 13 Comparing the yield of wind, sun and biomass

What are the costs? In Fig. 14 for wind, sun and biomass the required surface is represented only. The environmental costs are not yet stable. Environmental costs of new technologies are in the beginning always higher then later on. For coal, uranium and heavy hydrogen the environmental costs are calculated, the required surface is negligible (Jong, Moens et al. (1996)).

	total		per inh.
Actual Dutch energy use	95890	MW	5993	W
yielded by
solar cells	10	x 1000 km2	0,06	ha
wind	564	x 1000 km2	3,53	ha
biomass	96	x 1000 km2	0,60	ha
surface of The Nederlands inclusive Continental Plat	100	x 1000 km2	0,63	ha
Actual use electric	10432	MW	652	W
remaining heat	26080	MW	1630	W
yielded by
coal	20864	mln kg coal	1304	kg coal
waste	62592	mln kg CO2	3912	kg CO2
waste	835	mln kg SO2	52	kg SO2
waste	209	mln kg NOx	13	kg NOx
waste	1043	mln kg as	65	kg as
uranium	8346	kg uranium	0,001	kg uranium
waste	3452992	kg radio-active	0,216	kg radio-active
heavy hydrogen (fusion)	10432	kg h.hydrogen	0,001	kg h.hydrogen
waste	10432	kg helium	0,001	kg helium

Fig. 14 Environmental costs of energy use

The environmental costs of oil and gas are less than those of coal, but concerning CO₂-production comparable: the total production is approximately 30kg per person per day! That makes clear we have to avoid the use of fossile fuels.

The contribution of non fossile fuels is increased substantially (Fig. 15), but it is not yet 1000 from the yearly used 100 000 MW. The growth of 0,5% into 0,8% is mainly due to the use of waste including biomass unused otherwise.

After CBS (2003)

Fig. 15 Contribution of sustainable energy sources 1990 en 1999

The growth of the contribution of wind, heat pumps and sun (Fig. 16) is impressive on itself, but not yet responsible for 0.1% of total energy use.

CBS (2003)

Fig. 16 Contribution of wind, sun and heat pumps

between 1990 en 1999

Why develops solar energy so slowly while so much energy can be gained while solar cells are 23 times as cheap as 30 years ago? The fast decrease in price of Fig. 6 would be due to efficiency improvements in peripheral equipment. Just before passing the economic efficiency of fossile fuels basic barriers loom up. Which basic barriers are that? The oil industry has collected patents and studies that question. Scenarios still depart from a small contribution of solar energy in 2030. The development of the steam engine lasted 40 years. Are the barriers larger? Any way, the consequences are larger than those of the industrial revolution. Many people will loose their jobs or investments, but use of energy, depletion of resources, mobility would no longer be environmental problems. Only basic ecological problems remain: from the 1.5 mln known species 100 000 are lost, 80% of the human population is not healthy.

1.1.5 Power supply

Electric power stations in The Netherlands have a capacity of approximately 15 GW_e (15 000 MW_e), from which at average 10 GW_e is used (the rest is necessary to receive peak loads). These plants produce in the same time approximately 15 GW_th. From that heat only a small part is used.
Electric power stations can not be switched off immediately. Temporary overproduction is sold cheaper at night or into foreign countries (for example to pump up water in storage reservoirs). Approximately 2% is generated by nuclear power, 1% sustainable, the rest by fossile fuels.

The use of electricity only takes up a small part of our total consumption of primary energy sources. The Dutch energy balance is represented in the flow diagram of Fig. 17.

CBS (2003)

Fig. 17 Energy flows through The Netherlands, 1999 (x PJ or 31.7 MWa)

A summary like Fig. 17 is made every year[i]. Adding “winning” (extraction) and “invoer” (import) while subtracting “uitvoer” (export), “bunkers” (stocks) and “verliezen en verschillen” (losses and differences), one has left “verbruikerssaldo” (balance of use). Subtracting from that balance of use what power companies need themselves, one has left the quantity customers can use. On the way to the customer losses have to be subtracted to find what really lands to the customer, the ‘finaal gebruik’ (final use).

Calculating back these figures per inhabitant, expressing them into the individual human power during a year (100 Wa), one gets a figure like the number of ‘energy slaves’ people have to their disposal. The balance of use comes down to 57 energy slaves per Dutch(wo)man. Power companies need 11 of them to produce the rest. So, 46 remain for final use. From these 46 energy slaves industry takes 19, transport 8 and 19 are needed for offices and dwellings. From these 19 natural gas delivers 13, oil 3 and electricity 3 as well.

In 1982 the average inhabitant had 11 energy slaves in his own home, 10 of them needed for heating. At that time there were 2.8 inhabitants per dwelling. So, at average approximately 3000 m3 natural gas per year was needed for heating a house.

1.1.6 Local energy storage

Sustainable energy sources fluctuate per season or per 24 hour. That is why their supply does not stay in line with demand. Therefore, energy storage is of overriding importance for succes of these sources, but also for mobile applications like cars.[3]
In Fig. 18 some kinds of storage are summed up with their use of space and efficiency. If you lift up 1000 kg water (1m³) 1 meter against Earth’s gravity (9.81 m/sec²), you need 1000 kgf or 9810 newton during 1 m and 9810 newton*meter is 9810 joule or 0.0003109 watt during a year (Wa, see Fig. 1, page 9). Now you have got potential energy you can partly gain back as electricity any time you want by letting the water flow down via a water turbine and a dynamo. The efficiency is approximately 30%. So, you can gain back maximally some 0.000095 watt*year/m³ electricity. If you have a basin of 1km² where you can change the waterlevel 1m you can deliver 95 W_e[j] during a year, 190 W_e during half a year or 34722 W_e (0.00003472 GW_e) during a day. To deliver 1 GW_e you need 1/ 0.00003472 km² = 28800 km² (see Fig. 18). That is nearly three-quarter of the Netherlands! A larger fall (of 10m for example) improves both storage and efficiency of the turbine by increased speed of falling water.

	Storage[4]	Efficiency		Surface for 1 GW_e during
	gross	(max.)	net	24 hours	half a year
	Wa/m3	%	Wa/m3	km²	km²
Potential energy
water (fall = 1 m)	0,0003	x30%	=0,0001	28800	5259600
water (fall = 10 m)	0,003	x75%	=0,002	1152	210384
water (100 m)	0,03	x90%	=0,03	96	17532
50 atm. pressed air	1,3	x50%	=0,6	4	789
Kinetic energy
fly weel	32	x85%	=26,9	0,10	18,56
Chemical energy
natural gas	1	x80%	=0,8	3,42	625,00
lead battery	8	x80%	=6,3	0,43	78,89
hydrogen (liquid)	274	x40%	=109,5	0,03	4,57
petrol	1109	x40%	=443,6	0,01	1,13
Heat
water (70^oC)	6	x40%	=2,5	1,08	197,24
rock (500^oC)	32	x40%	=12,7	0,22	39,45
rock salts(850^oC)	95	x40%	=38,0	0,07	13,15
After Lysen (1980)and Hermans and Hoff (1982)
Fig. 18 Storage capacity (for conversion into electricity) from some systems

From the row ‘50 atm. pressed air’ on, the last column of Fig. 18 simply departs from a surface with a built height of 1m needed to deliver 1 GWe (1 000 MWe) during 24 hours or half a year continuously. By doubling the height of course you can halve the needed surface. Space for turbines and dynamos is not yet included. Fossile fuel like petrol still stores energy most efficiently.

However, in normal storage circumstances this surface is estimated too large for two reasons. Firstly energy production by some differentiation of sources never falls out completely. So you can partly avoid storage. Secondly, the average time difference between production and consumption is smaller than half a year or 24 hours. So, you need a smaller capacity. However, you have to tune the capacity to peak loads and calculate a margin dependent on the risks of non-delivery you want to take. These impacts can be calculated as separate reductions of the required storage

The actual Dutch energy use amounts nearly 100 GW, partly converted into electricity. So, you do not need 100x the given surface per GW to cover this use from stock. After all, in the total figure losses of conversion from fuel into electricity are already calculated in, and these are calculated in Fig. 18 as well.

1.1.7 References to Energy

Brown, L. R., H. Kane, et al. (1993) Vital Signs The trends that are shaping our future (London) Earthscan Publications Ltd.

CBS (2003) Homepage URL http://www.cbs.nl/.

Gool, v. and e.a. (1986) Poly-energie zakboekje (Arnhem) Koninklijke PBNA.

Hermans, L. J. F. and A. J. Hoff, Eds. (1982) Energie. Een blik op de toekomst. (Utrecht) Het Spectrum.

Jong, T. M. d., R. Moens, et al. (1996) Energie, water en mineralen Monografieen Milieuplanning SOM 25 (Delft) TUDelft Faculteit Bouwkunde: 128.

Lysen, E. (1980) Eindeloze energie Alternatieven voor de samenleving (Utrecht) Het Spectrum B.V. ISBN 90 274 5354 3.

RIVM (2000) Insights for the third Global Environment Outlook from related global scenario anlayses (Bilthoven).

1.2 Sun

1.2.1 Looking from the universe (a, b and latitude l)

The earth orbits around the sun in 366.25 days at a distance of 147 to 152 mln km. The radius of the earth is only maximally 6 378 km. So, the sunlight reaches any spot on earth by practically parallel rays. The surface covering that practically circular orbit is called the ecliptic surface. The polar axis of the Earth has always an angle a = 23,46^o with any perpendicular on that ecliptic surface.

On December 22^nd (Fig. 19) the angle b between polar axis and the line from Sun into Earth within the ecliptic surface equals 90^o+ a. On March 21^st b = 90^o, on June 21^st b = 90^o- a and on September 23^rd again b = 90^o. Arrows a in Fig. 19 show the only latitudes where sunrays hit the Earth’s surface perpendicular at December 22^nd and June 21^st. So, the sunlight reaches the earth perpendicular only between plus or minus 23,46^o latitude from the equator (tropics). Anywhere else they hit the Earth’s surface slanting. At December 22^nd the sunlight (sunray b in Fig. 19) does not even reach the north pole inside the arctic circle at 90^o – 23,46^o = 66, 54^o latitude (arctic night).

Fig. 19 The orbit of the earth around the sun

The sunlight reaching the earth’s atmosphere has a capacity of 1353 W/m² (solar constant). Some 500 km atmosphere reduces it by approximately 50%. So, any m² of sunrays reaching the surface of the Earth distributes say 677 W over its slanting projection on the earth’s surface. In Fig. 20 (left) the solar capacity of 1m² (677W) is distributed that way over the larger surface SN. That 1 m² capacity divided by hypotenuse surface SN equals cos(l). So, 1m² Earth’s surface in P receives cos(l) x 677W.

Fig. 20 The received sunlight average per year at latitude l; daily fluctuations with the hour angle h.

On March 21^st or September 23^rd it happens 24 hours on the whole latitude l circle because these days polar axis is perpendicular to the sunrays. That circle with radius r of latitude l (‘parallel’), seen from the Sun is a straight line with 2r length. On both days the Sun continuously delivers cos(l)*677W on any m² of that line. In 24 hours that capacity is distributed over a larger circular surface length 2pr of the whole latitude circle. So, the 24 hour average is that capacity divided by p. We do not yet have to calculate more cosinuses for every hour (Fig. 20 right) to conclude that 24 hour average. And March 21^st or September 23^rd offer useful averages for the whole year as well.

1.2.2 Looking from the Sun (culmination g and declination d)

The University of Technology in Delft is positioned around 52^o latitude, a global parallel crossing the building for Electrotechnical and Civil Engineering on its campus. The cosine of 52^o is 0.616. So, there the year average solar capacity at noon is 417 W per square meter earth surface. Averaged again per 24 hours it is 417/p = 133 W (not concerning Dutch weather conditions). This value is reached only as daily average on March 21^st or September 23^rd. At other dates it varies symmetrically around that average. The day period between sunrise and sunset varies and throughout the year the sunlight reaches the earth’s surface at noon by a varying maximum angle g (‘culmination’ related to the Earth’ surface, not to be confused by declination d related to its polar axis, see Fig. 22). After all, seen from the sun the earth nods ‘yes’ (Fig. 21). Bending to left and right does not matter for locally received sunrays.

Fig. 21 The yearly nodding earth with a parallel l=52^o seen from the sun.

December 22^nd the earth is maximally canted a = 23.46^o backwards related to the sunrays. At noon we receive: 677 * cos(52^o + a) = 170 W/m². Canting forward on June 21^st we have to subtract a: 677 * cos(52^o – a) = 595 W/m². Inbetween we need a variable ‘declination’ {d | +23.46^o ≤ d ≤ –23.46^o } instead of a. In Fig. 22 declination d is positive in June, so now we can write 677 * cos(l – d) W/m² for any day at noon at any latitude. From Fig. 22 we can derive visually: g + l - d = 90^o or l - d = 90^o - g.

Fig. 22 Declination d

Declination d could be read from Fig. 22 or calculated according to Voorden (1979) by d = 23.44 sin(360^o x (284 + Day) / 365). As ‘Day’ we fill in for instance:

Mar21 = 31 + 28.25 + 21 = 80.25

Jun21 = 31 + 28.25 + 31 + 30 + 31 + 21 = 172.25

Sep21 = 31 + 28.25 + 31 + 30 + 31 + 30 + 31 + 31 + 21 = 264.25

Dec22 = 31 + 28.25 + 31 + 30 + 31 + 30 + 31 + 31 + 21 + 31 + 30 + 22 = 356.25

1.2.3 Looking back from Earth (azimuth and sunheight)

But how is that capacity distributed per hour? The earth turns 360^o in 24 hours ousting the Old World by the New Word all the time. That is 15^o per hour, drawn in Fig. 21 (left) by 12 visible meridians of 15^o.

The distribution on a constant latitude l is not only affected by a declination d varying day by day but also by the hour angle h visibly varying every minute. From Fig. 23 we derive the hour angle of sunset and sunrise: cos(h_sunset)= h x cot(b)/r x cos(l), while h = r*sin(l).



Fig. 23 Sunset and sunheight at noon varying with b and hour angle h on one parallel circle.	Fig. 24 Looking back to the universe in the Autumn.

Within that formula, r plays no rôle and cot(b) = tan (90^o – b) = tan(d), see Fig. 22. So, we can write:

sunrise = acos(sin(l) x tan(d) / cos (l)) / 15^o and sunset = 24 hour - sunrise.

Now we can move our field of vision down to earth looking back to the universe as Copernicus saw it, reconstructing the preceding model from what he saw. Then we see any star moving daily in perfect circles around, the Pole Star (Polaris) standing still. So, we see the Great Bear and some ‘circumpolar’ constellations througout the year turning around Polaris (Fig. 24). Other constellations disappear daily behind the horizon, be it seasonly at an other moment of the day and therefore in some seasons by day not visible behind the brightness of the Sun. Polaris is a star 1600 times more powerful than the Sun, but on a distance of 300 light years. Occasionally it stands in our polar axis apparently standing still that way, moving too little (1 degree) to take into account.

The Sun makes its daily circles shifting approximately 1 degree per day (the year circle of 360^o is called eclipse) against a more stable remote background of 12 constellations (the Zodiac), according to its yearly wave seen by a nodding Earth.

Turning ourselves 360^o we see a lamp on our desk describing a circle around us as well. Bowing our head backward 23.46^o while turning around we see the lamp low in our field of vision. When we stay turning around and in the same time walk around the lamp keeping our head in the same polar direction (slowly nodding forward until we are half way and than again backward) we experience how we see the sun during the year starting from December 22^st. When we had a third eye in our mouth we would have a complementary view from the southern hemisphere as well.

Such circles we can draw as sun bows in a sky dome using b as deviation from the polar axis (Fig. 25).

Fig. 25 Sun bows 3D in a sky dome, map and cross section.

The circular parallel sun bow divided in hours has to be projected as an ellipse on the Earth’s surface (see Fig. 26). The hours in the Azimuth angle then decrease in the direction of sunrise and sunset.


The hour angle h in the parallel surface	projected	on the Earth’s surface.
Fig. 26 The hour angle transformed into Azimuth.

To transform the hours of the parallel surface into hours on the Earth’s surface we can observe two triangles perpendicular to the surface SouthZenithNorth (see Fig. 27) the first with two equal sides SunM and MD (r sin b), the second with two equal sides SunP and PD ( r) as well, and a common third side. The first triangle has an angle SunMD=180^o-h. So, we can use the cosine rule two times to calculate the square of the third side SunD in both triangles and angle SunPD = arc p. Spherical cosine rules applied on the spherical triangle SunZenithD produce Sunheight and Azimuth as angles.


		Spherical cosine rule: cos a = cos b cos c+ sin b sin c cos A
Cosine rule: a² = b² + c² - 2bc cos A

Fig. 27 Two isosceles triangles and a spherical one

However, Voorden (1979) in his Appendix A and C (see Enclosure 2) derives by more difficult transformation rules the usual and easier formulas:

Declination = 23.44^o x sin(360^o x (284+Day)/365))

Sunheight=

asin(sin(Latitude) sin(Declination(Day)) – cos(Latitude) cos(Declination(Day) cos(Hour x 15^o)

Azimuth= asin(cos(Declination(Day) sin(Hour x 15^o))/cos(Sunheight(Latitude, Day, Hour))

1.2.4 Time on Earth

On a meridian 1^o East of us (68 km on our latitude) local solar time is already 4 minutes later. If we used the solar time of our own location we could only make appointments with persons living on the same meridian. So, we agreed to make zones East from Greenwich of ± 7.5^o around multiples of 15^o (1026 km on our latitude), using the solar time of that meridian. However, between the weekends closest to April 1^st an November 1^st we save daylight in the evening by using summertime. By adding an hour around April 1^st in the summer, 21.00h seems 22.00h on our watch and it is unexpectedly light in the evening. So, to find the solar time from our watch we have to subtract one hour in the summer and the number of degrees of longitude x 4 minutes West of the agreed meridian. In the Netherlands we use the solar time of 15^o East of Greenwich (time zone 1), but live between 3^o and 8^o.

http://www.squ1.com/index.php?http://www.squ1.com/solar/solar-position.html

Fig. 28 Time zones

So, on the Faculty of Architecture in Delft (4^o 22.5’ easter longitude = 4.38^o) in winter we have to subtract 15 x 4 minutes from our watch time and add 4.38 x 4 minutes (-10.62^o x 4 minutes = -48.48 minutes) to find an approximate solar time. In summertime we have to subtract an extra hour.

In addition to these corrections we have to add or subtract some minutes (time equalization E) amongst others due to differences in travel speed (29.3 km/s in summer, 30.3 km/s in winter) around the Sun according to Fig. 29.

Fig. 29 Time equalization per day of the year

So, instead of the Hour we read on our watch (WHour with minutes decimally added) in the formulas for Sunheight and Azimuth we should fill in Sun Hour (SHour) from:

SHour(WHour,Timezone,Longitude,Summertime,Day) = WHour - Timezone + Longitude/15^o – Summertime + E(Day)/60

As Timezone we fill in 1, 2, 3 and so on with a maximum of 23. As Summertime we fill in daylight saving yes=1, no=0 and E(Day) we read or calculate from Fig. 29.

Finally, atmospheric refraction of 34’ and sun radius of 16’ (together nearly 1^o) shows us sunrise nearly 4 minutes earlier and sunset 4 minutes later, but by day this effect approaches to zero at noon.

1.2.5 Calculating sunlight periods

Putting the formulas we found in an Excel Sheet (download http://www.bk.tudelft.nl/urbanism/team, publications 2003 Sunsheet), we can check them by observing shadows.

Input
Date		Time		Latitude		Longitude
Date	Days	Hour	Minute	Degrees	Minute	Degrees	Minute	Timezone	Summertime
18-apr-03	108,25	11	45	52	0	4	30	1	yes

Fig. 30 Data needed for solar calcuations

We need date, time, geographical coordinates, the time zone and wether or not we have to take summer time into account. The Sheet brings them into a decimal form and adds a time correction to calculate the hour angle in radians. Excel needs radians to calculate sine, cosine and tangent.

Calculated	hour	h	m	deg	rad
Watch time	11,75	11	45
TimeCorrection	-1,69	-2,00	19
Sunhour	10,06	10	4
Hour angle				151	2,63

Timezone	1
Summertime	1
Latitude				52,00	0,91
Longitude				4,50	0,08

Fig. 31 Restating data in dimensions needed

The sheet then calculates the declination of the day and at what time on our watch we can expect sunrise, culmination and sunset neglecting atmospheric influence from –4 to + 4 minutes. Finally the sheet calculates Azimuth and Sunheight. Azimuth is calculated from South, but a compass gives the number of degrees from North (180 – Azimuth).

Calculated	hour	h	m	deg	rad
Declination				10,6	0,18

Watch Sunrise	6,77	6	46
Watch Culmination	13,69	13	41
Watch Sunset	20,61	20	37
Azimuth				40	0,70
On Compass	(180 - Azimuth)			140
Sunheight				42	0,74
Prediction
Height	10,00
Shadow	10,97

Fig. 32 Solar calculations

The height of an object on the Earth’s surface given, the sheet calculates the length of its shadow. Now we can check these results by putting a pencil in the sun. Measure its height, the length of its shadow and Azimuth as the angle of its shadow with a North-South line (using a map or reliable compass, not disrupted by iron in the neighbourhood!) (Fig. 33).

Fig. 33 Fast indoor check of shadow.

Outdoors you can measure angles copying, folding and cutting the paper instrument of Fig. 34 to get the sunheight and the height of buildings. To measure height of buildings you need a mirror or mirroring piece of glass. Measuring Azimuth you need a compass or map as well.





Fig. 34 Measuring Azimuth, sunheight and building height outdoors

Fig. 34 shows a compass directed to the sun by adjustment to the shadow line of a vertical object. It indicates 106^o from North, which is 74^o from South (Azimuth). Sunheight appears to be 39^o on the paper instrument. Turning the instrument 180^o partly covered by a piece of glass we read an angle of 40^o (tangent 0.84) to the upper edge of the mirrored building. According to our distance meter that building is at 8.37m distance. However, when we measure it by tape measure it appears to be 10.30m, occasionally just like the shadow . So, we do not trust the electronic divice. It apparently has measured the tree closer by. The height of the building must be 10.30 x 0.84 = 8.65m above the table surface from which we took the measurement (35cm above ground level). So, the building should be 9m high. That could be right, because the building has 2 storeys (3 layers). Now we can fill in the measurements in http://www.bk.tudelft.nl/urbanism/team, publications 2003 Sunsheet.xls (Fig. 35) and check its prediction.

date	09-06-03	dd-mm-yy
Watch time	10.15	hour.minute
Building height	9	metres
Shadow	10.30	metres
Azimuth	74	degrees
Sun height	39	degrees
Building height and Shadow would indicate (calculated):
Azimuth	74	1.29
	degrees	radians
Sunheight	41	0.79

Fig. 35 Checking shadows in http://www.bk.tudelft.nl/urbanism/team, publications 2003 Sunsheet.xls.

The sun height may be measured a quarter earlier. Then it was calculated as 39^o indeed. The shadow was predicted to be 10.27m elsewhere in the sheet So, the measurement agrees with the calculation rather well.

1.2.6 Shadow

Fig. 36 shows the length of shadows on June 2^nd from an object of 10m height for every hour. Download http://www.bk.tudelft.nl/urbanism/team, publications 2003 Sunsheet, and try other dates.

At noon - 13h40min. - shadows are smallest. Turning the figure with that point North we got some idea (not precise, see Fig. 26!) of the shadows to be expected throughout the day. The figure is symmetrical around that point and the centre. It does not seem so because the graph rounds off on full hours, sunrise is at 5h31min., sunset at 21h50min. and noon inbetween. So, we can put the figure on a map of same scale with that orientaton and shift it on a line with given height to get som idea of the shadow caused by a building block, a line of trees and so on. East~ and westward shadows are symmetrical.


http://www.bk.tudelft.nl/urbanism/team, publications 2003 Sunsheet
Fig. 36 Shadows throughout the day June 2^nd	Fig. 37 A garden on June 2^nd at 12 o’clock

From an urbanistic point of view shadow is important for climate and lighning of outdoor space, gardens and public spaces. Fig. 37 shows a South garden with two small trees at the southern border (above) throwing shadow. The Northern part has sunlight all day and ants clearly undermine the pavement there. There is a substantial damage on pavements by ants in towns. However, the continuously shadowed Southern part of the garden is more moisty and the pavement is filled by rough moss. At the Eastern and Western part of the circle inbetween the tiles (20x20cm) grass and flatter kinds of moss find their optimum. In the sunny Northern side sun loving plants like grape (Fig. 38 left) find their optimum, in the Southern shadowed borders you find shadow loving plants like ferns (Fig. 38 middle).



Fig. 38 Full sun, filtered shadow and full shadow

On the other side of the building (Fig. 38 right) there is full shadow all day with high trees catching light in their crowns only and slow growing compact shrubby vegetation in a little front garden. Such fully shadowed spaces are suitable for parking lots. “Keep pavements in the shadow” may be a sound rule.

Trees filter sunlight by small openings projecting images of the sun on the ground as Minnaert noted in the first article of his marvellous book in three volumes on physics of the open air. You can see it best when an eclipse of the sun is projected thousendfold on the ground (Fig. 39). Most solar images are connected to vague spots and sometimes the openings in the foliage are too large to get clear images. Leaves of a tree are composed differently into a so called leaf mozaic (Fig. 40).



Fig. 39 Eclipse of the sun August 11^th 1999	Fig. 40 Leaf mozaic

That roof of public space is worth more attention. People love the clairobscur of filtered light with local possibilities of choice for full sun and full shadow meeting their moods. It challenges their eyes more then one of the extremes continuously. Urban designers should be aware of the importance of light and its diversity in cities. None of them ever makes a shadow plan, though any painter knows that shadow makes the picture. The same goes for artificial city light in the evening and at night. Dry engineers calculate the minimum required amount of light for safety to disperse streetlamps as equally (economically) as possible over public space.

Nature’s diversity is primarily based on competition for light. Some plants grow as high as possible to outrun neighbours. Others are satisfied by less light growing slower, using more years to reproduce. By very closed foliage some trees do not leave any light to plants on the ground like spruces and beeches. They are the trees of dark forests. Trees of light forests are not stingy with light for plants growing below, like birches. They need helpers there to get the right minerals from soil. So, trees are different in light permeability (Fig. 41).


weeping willow (treurwilg)	poplar(populier)	alder(els)	lime(linde)

plane(plataan)		elm(iep)

Fig. 41 Light permeability of trees

How do we measure such differences? The absolute force of visible radiation (the part of radiation we call ‘light’) produced by a 1/60 cm² black body with the temperature of melting platina (2047^oK) under specified pressure in any direction is 1 candela (cd). The sun has many candelas. It is a measure characterising the source of light in its point of departure, not its dispersing impact as flow elsewhere, at any distance or surface. However, sampled in 1 spherical m² at 1m distance or in 100 spherical m² at 10m distance (radius) around the source (surface or distance do not matter, only their proportion called ‘spherical radius’ or ‘sr’ matters) 1 candela produces a power (continuous flow) of 1 lumen (lm). So, 1lm = 1cd x 1sr. But how much dispersing power actually reaches your book? Lightning power of 1 lm per m² on a specific location is 1 lux (lx). So, 1lx = 1 cd x sr /m².

And you need 300 – 1500 lux to read a book. Lux is something we can measure easily by a lux meter. Fig. 42 shows how shifting the meter 10cm can decrease lightning power from 2500 to 1100 lux.



Fig. 42 Impacts of distance to source and direction of surface on local lightning power

Turning the lux meter 90^o (Fig. 42) diminishes the available power further to 300 lux. So, distance to source and orientation of surface to light in the neighbourhood of the source (here approximately 30cm) make much difference. On larger distance the impact is less dramatic. Besides to this, the colour differences between the photographs show the differences a camera can not compensate like our eyes do by perception with brains near by.

Fig. 43 shows a plot division of 19 dwellings taking shadow into account (download www.bk.tudelft.nl/urbanism/TEAM publications 2003 standaardverkaveling.exe). All of them have the same plot area of 120m², but the Southern dwellings have narrow and deep plots to make front gardens possible and make the back gardens accessible for sunlight at some distance of the buiding. However, the Northern dwellings with South gardens have shorter and wider plots and parking lots instead of front gardens and public green. Eastern and western buiding blocks have no sun in the street in the morning or evening but at noon they have. But at the back they have a different character. Western blocks have sun in the garden and living room in the morning, Eastern blocks in the evening. Having breakfast or dinner in the sun attract (or create) other kinds of people.


Jong (2001)	Hotzan (1994)
Fig. 43 Plot division taking shadow into account	Fig. 44 Avoiding shadow by neigbours according to German regulations

The value of dwellings can decrease when neigbours are not limited in building on their plots by regulation removing sun from other gardens. So, many urban plans regulate building on private plots.

1.2.7 References Sun

Hotzan, J. (1994) DTV-Atlas Stadt. Von den ersten Gründungen bis zur modernen Stadtplanung (München) Deutscher Taschenbuch Verlag GmbH&Co. ISBN 3-423-03231-6.

Jong, T. M. d. (2001) Standaardverkaveling 11.exe.

Voorden, M. v. d. (1979) Bezonning. Stedebouwfysica gc 49 (Delft) Technische Hogeschool Delft, afdeling der Civiele Techniek: 70.

1.3 Temperature

1.3.1 Long term variation

The power of the sun fluctuated in periods of 100 000 years or less, causing ice ages and great differences in wind, water, earth and life stored and named in layers of soil (Fig. 45).

Sticht.Wetensch.Atlas_v.Nederland (1985)page 13

Fig. 45 Temperature fluctuations in The Netherlands in the past 3 million years

These impacts are readable from the topographic history of The Netherlands (Fig. 46).

-200000

-150000

-75000

-40000

-10000

-5500

-4100

-3000

-2100

-1000

-200

600

1000 vloed

1000 eb

1100

1300

1550

1675

1800

1850

1930

1960

1989

Universiteit van Utrecht 1987 commisioned by Nederland Nu Als Ontwerp

Fig. 46 De topographic history of The Netherlands

The Dryas and Alleröd Periods (from 10,000 years BC)

In the famous Lascaux caves, people have made images of mammoths and long haired rhinos. These animals became extinct during the last Ice Age. In Scandinavian countries this period is known as Weichsel and in the Alpine countries as Würm. A tundra plant ‘dryas octopetala’ grew in our part of Europe at that time and gave its name to the last cold period of the Weichsel.

15 000 – 10 000 b.C. Older Dryas period

[T.M. de1]

University of Utrecht 1987

Vedel and Lange (1974)

Fig. 47 The end of the Weichsel ice age, the Dryas Period

Fig. 48 Vegetation during the Dryas Period

10 000– 9 000 b.C. Alleröd period [T.M. de2]	9 000 – 8 000 b.C. [T.M. de3]
Vedel and Lange (1974) p 216
Fig. 49 Sub-divisions of the Dryas

The PreBoreal and Boreal Periods (from 8,000 BC)

In the warmer periods that followed the Dryas, people learnt how to hunt smaller animals using correspondingly smaller stone tools. The Mesolithicum, the Middle Stone Age, had already started, and peat was also beginning to form due to the warmer climate.

About 8,000 BC the oceans began to rise again, because of the melting ice, and the North Sea filled with water again.In the Netherlands, peat formation began late in the Boreal Period, after the cold extensions of the Dryas and Pre-Boreal, and this continued into the warm and humid Atlanticum. The rising sea levels flooded western parts of the country.

Pre-Boreal (8,000 BC)	Early Boreal (7,000 BC)

Vedel and Lange (1974)
Fig. 50 The landscape of the Pre-Boreal and Early Boreal

Approximately 5,500 BC the sea formed off-shore bars that during the ebb tide were blown higher, forming dunes. In the Waddenzee, behind the dunes, fine sand and silt were deposited, successively, on top of the peat base. The silt became the ‘old’ or ‘blue’ marine clay of (the provinces of) Holland.


University of Utrecht(1987)	Vedel and Lange (1974)
Fig. 51 The Boreal landscape. (from 5,500 BC)

Atlanticum (from approx. 4,000 BC)

While ever the sea continues to rise, the coast and the peat advance. Approx. 3,000 BC the rise in sea level began to slow down; the off-shore bars remained intact and these broadened out seawards to form a strong coast.

A new row of dunes was laid down in front of the old ones and the peat that had grown on top of the blue marine clay, in so far as the sea had not washed it away, was dug out later. Peat streams first became estuaries and then reverted back to peat streams again. The sea cut into the Sub-Boreal peat leaving channels in which fine sand was deposited. Subsequent drainage caused a reversal in relief.

Atlanticum (4,100 BC).	Atlanticum (3,000 BC)


Vedel and Lange (1974)		University of Utrecht (1987)t
Fig. 52 The landscape of the Atlanticum.

The Sub-Boreal (from approx. 2,000 BC)

Approx. 2,100 BC, rivers carred fresh water into the lagoon behind the off-shore bars, causing widespread peat formation


University of Utrecht (1987) and Vedel and Lange (1974)
Fig. 53 The sub-Boreal landscape.

Late Boreal and Sub-Atlanticum, from 1000 BC.

Approx. 1,000 BC: The stagnation of water from streams also causes hoogveen (i.e. peat formations above the water table) to develop on the lower parts of sandy ground (e.g., the Peel and Drente).

Approx. 200 BC: peat erosion also occurs along the shores of the Almere lake (Zuiderzee area), thereby extending the lake.

Late Sub-Boreal, 1000 BC	Sub-Atlanticum, 200 BC


Vedel and Lange (1974)	University of Utrecht (1987)
Fig. 54 The Sub-Boreal landscape and subatlanticum

The Roman period and early Middle Ages, from 100 BC.

Approx. 100 BC: The sea attacked again and large areas of the laagveen (i.e. peat formations below the water table) were washed away: this continued for centuries. Bloemers, Kooijmans et al. (1981) and Klok and Brenders (1981) describe Roman relics from this period in The Netherlands like Corbulogracht (Fig. 56).

Approx. 600 AD: The sea first broke through in the North to create the Waddenzee and the Zuiderzee.


University of Utrecht	Bloemers, Kooijmans et al. (1981) page 99
Fig. 55 The landscape of the Early Middle Ages, 600 AD.	Fig. 56 Roman sites

1.3.2 Seasonal variation

Latitudinal differences account for the largest global variations (from approx. -40°C to 30°C) in average monthly temperatures (Fig. 57 and Fig. 58).


	Wolters-Noordhof (2001) page 180
Fig. 57 Global winter temperatures	Fig. 58 Global summer temperatures

Latitudinal differences account for most of the average monthly temperature variations in Europe, but these are moderated by the sea from approx. -15°C to 25°C (Fig. 59 and Fig. 60).


	Wolters-Noordhof (2001) page 71
Fig. 59 Winter temperatures in Europe	Fig. 60 Summer temperatures in Europe

Latitudinal differences account for most of the average monthly temperature variation in the Netherlands, but they are moderated by the sea, especially in winter, from approx. 3°C to 17°C (Fig. 61 and Fig. 62).


	Wolters-Noordhof (2001) page 43
Fig. 61 Winter temperatures in the Netherlands	Fig. 62 Summer temperatures in the Netherlands

In the Netherlands, on 3rd March 1976, the differences in local temperatures, within metres of each other, ranged from -2°C to 62°C (Fig.34). The air temperature at a height of 1 metre (Fig. 63) was 11.8°C.

Barkman and Stoutjesdijk (1987) citing Stoutjesdijk (1977)

Fig. 63 Surface temperatures along a line perpendicular to edge of a forest

There are few pioneering plants that begin to flower in July, and, likewise, there are few plants growing on rough ground that flower before March; few trees flower after May and few shoreline and water plants before this month. In the table below, a number of plants are mentioned in the month in which they can first be encountered in the Netherlands.

	pioneering-plant		ruderaal
jan
	Chickweed (vogelmuur)	Groundsel (klein kruiskruid)
feb
	Common Whitlowgrass (vroegeling)	Coltsfoot (klein hoefblad)
march
	Shepherd’s-purse (herdertasje)	Purple Dead-nettle (paarse dovenetel)	Giant Butterbur (groot hoefblad)
april
	Dandelion (paardebloem)	Rape (koolzaad)	Cow Parsley (fluitekruid)
may
	Greater Plantain (grote weegbree)	Oxe-eye Daisy (margriet)	Comfrey (smeerwortel)
june
	Biting Stonecrop (muurpeper)	Persicaria/Red Shank (perzikkruid)	Rosebay Willowherb (wilgeroosje)
july
			Tansy (boerenwormkruid)
			Kelle and Sturm (1980)
Fig. 64 Flowering times pioneers and ruderals

	grass land	wood/forest
jan
	Daisy (madeliefje)	Hazel (hazelaar)	Snow Drop (sneeuwklokje)
feb
	Lesser Celandine (speenkruid)	Alder (zwarte els)	Cornelian Cherry (gele kornoelje)
march
	Ground Ivy (hondsdraf)	Silver Birch (ruwe berk)	Wood Anenome (bosanemoon)
april
	Lady’s Smock/ Cuckooflower (pinksterbloem)	Poplar (populier)	Broom (brem)
may
	Meadow Buttercup (scherpe boterbloem)	Common Oak (zomereik)	Herb-Robert (robertskruid)
june
	Tormentil (tormentil)		Wild Honeysuckle (wilde kamperfoelie)
july
	Water Mint (watermunt)		Hop (hop)
			Kelle and Sturm (1980)
Fig. 65 Flowering times on grass land and in forest

	wetand	water
may
	Yellow Iris/Yellow Flag (gele lis)	Yellow Water-lily (gele plomp)
june
	Bulrush (lisdodde)	Arrowhead (pijlkruid)
july
	Common Reed (riet)	Spiked Water-milfoil (aarvederkruid)
			Kelle and Sturm (1980)
Fig. 66 Flowering periods wetland and water

The plants listed above occur so widely that it is well worth while getting to know them. If one comes across pioneer vegetation in a certain season, then one can assume that the ground has been recently disturbed. If one comes across plants that grow on rough ground, then one can assume that the soil was disturbed one or more years previously. If one encounters woodland vegetation, then the soil has remained undisturbed for a longer time. Grassland plants indicate frequent mowing, however, from the nature of grassland vegetation and on the basis of the above table, one should be cautious about drawing conclusions regarding the mowing period.[5]

Londo (1987) page 103

Fig. 67 The effect of mowing on various species. (Londo 1987: 103)

For more than 10 years already there has been a mowing policy in Zoetermeer that is directed towards ensuring that the food content of roadside vegetation is drastically reduced by regularly removing biomass:

Vos (1990)

Fig. 68 Mowing management in Zoetermeer

Over a period of 10 years, impoverishing the soil does not appear to lead to a large increase in the number of species growing there. Obviously, more time is needed for this to happen.

1.3.3 Daily variation

Plants receiving shadow throughout the day in the growing seasons grow larger and narrower then the same species receiving more sunlight. They look for light rising as high they can. Plants are long term indicators of local climate (sun, wind, water, soil) while occasional measurements give a random indication of moments.

Vogel, Günter et al. (1970) page 198, 199

Fig. 69 The influence of variations in light

1.3.4 References Temperature

Barkman, J. J. and P. Stoutjesdijk (1987) Microklimaat, vegetatie en fauna (Wageningen) Pudoc Wageningen ISBN 90-220-0917-3.

Bloemers, J. H. F., L. P. Kooijmans, et al. (1981) Verleden land (Amsterdam) Meulenhoff Informatief ISBN 90-290-9992-5.

Kelle, A. and H. Sturm (1980) Prisma Plantengids (Utrecht/Antwerpen) Uitgeverij Het Spectrum.

Klok, R. H. J. and F. Brenders (1981) Reisboek voor Romeins Nederland en België (Haarlem/Antwerpen) Fibula-Van Dishoeck/Standaarduitgeverij ISBN 90-228-3614-2.

Londo, G. (1987) Natuurtuinen en -parken (Zutphen) B.V. W.J. Thieme & Cie ISBN 90-03-95000-8.

Sticht.Wetensch.Atlas_v.Nederland (1985) Atlas van Nederland. Deel 13. Geologie (Den Haag) SDU ISBN 90-12-05013-8.

Vedel, H. and J. Lange (1974) Bomen en struiken in bos en veld (Baarn / Antwerpen) Moussault's Uitgeverij Standaard Uitgeverij.

Vogel, Günter, et al. (1970) Sesam atlas bij de biologie (Baarn) Bosch en Keuning ISBN 90.246.6909.x; 90.246.6910.3.

Vos, J. G. (1990) "Bloemrijke linten door Zoetermeer. Het resultaat van 10 jaar maaien en afvoeren?" Groen 90(2)

Wolters-Noordhof, Ed. (2001) De Grote Bosatlas 2002/2003 Tweeënvijfstigste editie + CD-Rom (Groningen) WN Atlas Productions ISBN 90-01-12100-4.

1.4 Planting (Prof.dr.ir.C.M. Steenbergen; Drs. M.J. Moens)

1.4.1 Introduction

The key thing to remember when designing and using planting elements is that you are dealing with living material. Architects work with dead material; buildings are not living organisms. Trees grow, and young trees have a different form than mature trees. They look different in winter and change under the influence of climatic conditions. A plane tree, for example, has a pyramidal form when young and then ‘sags’ when older. Trees attain their typical growth form when they are 15 to 20 years old and keep it until they are 80, but by then they will have acquired an individual ‘character’. Shrubs usually achieve their mature form after about 10 years. Perennials and roses reach maturity in just 2 to 3 years.

Planting effects

The following illustrations give an impression of the wealth of effects that can be achieved with planting.






Fig. 70 Visual effects of planting

Conceptual framework

Introduction

The conceptual framework is a language to express and convey planting effects. To describe a particular effect we can draw from the themes and related visual forms described below. The overall effect. Depends on the role of each theme.

Themes

The degree of screening

Height is an important consideration when deciding on planting elements. Their height determines how much of the objects behind the planting can be seen. The degree to which they are hidden is called the degree of screening.

The degree of transparency

The visibility of objects behind the planting also depends on how much can be seen through the planting. This is referred to as the degree of transparency.

The degree of uniformity

When looking at a planting element we can examine the diversity of species in relation to the height of the composition to determine vertical variation in texture.

The degree of continuity

In the same way, the diversity of species along the length of the planting element can be examined. The horizontal variation in texture is important.

Structure

The manner in which trees and shrubs are placed to create a unified composition has a strong influence on the other themes. Structure plays a major role in creating the overall effect.

Edge profile

In urban areas planting elements are usually narrow and consist, essentially, of two edges. The profile of these edges has a major influence on the appearance of planting elements.

The degree of naturalness

The mood or atmosphere created depends to an important extent on whether the composition has a formal, artificial appearance or an informal, ‘natural’ feel.

Characteristic Forms

Each theme can manifest itself in different ways characteristic forms. These can be clearly indicated by introducing terms for all the possible forms.

The degree of screening




Fig. 71 Edge: maximum planting height 0.5 m		Fig. 72 Articulation: planting height between 0.5 and 1.5 m



Fig. 73 Partition: planting height between 2 and 5 m		Fig. 74 Screening: planting is higher than 5 m

The degree of transparency




Fig. 75 Wall: the planting blocks all vision		Fig. 76 Curtain: even, partial visibility through the planting



Fig. 77 Window: opening in the planting

The degree of uniformity




Fig. 78 Even: no clear vertical variation in texture		Fig. 79 Layered: clear vertical variation in texture

The degree of continuity



Fig. 80 Constant: no horizontal differences in texture		Fig. 81 Rhythm: differences in texture at regular intervals


Fig. 82 Accentuation: random striking differences in texture

Edge profile




Fig. 83 Receding		Fig. 84 Upright



Fig. 85 Overhanging

Degree of naturalness




Fig. 86 Straight and ‘hard’: the planting has straight contours and ‘hard’ boundaries		Fig. 87 Ragged and ‘soft’: the planting has irregular contours and vague edges

Structure



Fig. 88 Trees	Fig. 89 Trees with occasional shrubs	Fig. 90 Shrubs with occasional trees



Fig. 91 Shrubs	Fig. 92 Trees with a shrub margin	Fig. 93 Trees with a shrub layer

Design tools

Each of the characteristic forms described above can be created using different design tools:

Edge

· Native stock trimmed to form a hedge

· Low-growing non-native plants

Articulation

· Native stock trimmed to form a hedge

· Smaller, non-native shrubs

Partition

· Native shrubs with or without trimmed edges

· Larger non-native shrubs

Screening

· Tree planting, no crown raising

· Tree planting with shrub layer; the trees and shrubs must intertwine

Wall

· Native species with a dense, compact habit

· Non-native evergreen species

· Wide spacing and sufficient thinning to allow full growth and the development of complete foliage cover

· No crown thinning, branch reduction or crown raising

· Broad plant bed

Curtain

· Species with an open and loose habit

· Small distances between plants, which encourages them to grow upwards

· Crown thinning, branch reduction and crown raising is possible

· Narrow plant bed

Window

· Native shrubs pruned to the right height

· Low, non-native shrubs

· Widely spaced shrubs for full growth and good foliage cover

· Trees with upright crowns

· Trees with raised crowns

Even

· Large number of species, individually mixed

· Small number of species with very similar textures

· One species

Layered

· A few layers with very different textures

· Each layer consists of one species or a few species with very similar textures

Constant

· In species-rich planting the length of the planting element must be many times its height (minimum 100 m)

Rhythm

· Striking individual trees or shrubs planted at regular intervals

Accentuation

· Striking individual trees or shrubs at irregular intervals

Receding

· Free growth along the edge

· Shrub margin in front of tree planting

Upright

· Use of woodland planting as hedge

· Tree planting with low branching crowns

Overhanging

· Edge pruning in a margin of trees and shrubs

· Crown raising in an margin containing only trees

Straight and hard

· Pruning for shape

· Straight, clearly defined edges

· Rhythmic or striking accentuation along the edge

· A sharp silhouette

· Layered

Ragged and soft

· Vague, ill-defined edges; abundant herbs in the edge

· Individual mixing of striking species

· Ragged silhouette

The effect over time

Planting schemes can be grouped according to the way they develop from the time of planting until they reach full maturity.

The first group consists of planting schemes with a pronounced static character. Stated simply, the effect of such planting schemes changes little over time, they just become higher and fuller. These planting schemes are simple, containing just a few species which each have a clear place and contribute to the overall long-term effect.

In contrast, the second group consists of planting schemes with a distinctly dynamic character. A typical example is traditional woodland planting schemes: species-rich, individually mixed planting. The roles of the individual species constantly change, creating a succession of visual effects over time.

The final group of planting schemes are those with a cyclical development. The visual effect is obtained by periodic rigorous pruning back to restore the same visual effect.

Design techniques

Each of the planting groups described above can be linked to a number of specific design techniques to choose from.

Static planting
· The structure of the planting and the role played by each species in the visual effect is determined beforehand. · The way the visual effect will develop is clear from the start; specific maintenance work will need at certain times to achieve this effect. · When the planting has reached maturity the purpose of maintenance work is to maintain vitality and a tidy appearance. · Radical rejuvenation measures are delayed as long as possible. · The ‘nurse crop’ system cannot be used.[k] · Use of long-lived species. · Rows of different species.
	Fig. 94 Static planting technique

Dynamic planting
· Indicate the characteristic forms that will determine the appearance of the planting (e.g. transparency)The structure of the planting and the role of each species in creating the visual effect are not fixed in advance. During the growth of the planting there are certain moments when the designer and technical maintenance staff have to decide how the planting scheme will continue to develop. The choice is influenced by the previous visual forms. · The ‘nurse crop’ system can be used. · Plants may be individually mixed. · Species with different life cycles may be mixed together, although this makes maintenance more complex and expensive. The most manageable system is to keep to the life cycle of the main plants. · The plant bed must be at least 50 m wide; any narrower and it is extremely difficult to manage the visual effect. The planting will acquire a ragged appearance with, in places, considerable differences in height, texture and transparency.
	Fig. 95 Dynamic planting technique

Cyclical planting

· The appearance of the planting is fixed beforehand.

· The desired appearance develops too quickly but is repeated; the effect is dominated by periodically cutting back to just above ground level.

· The timing of pruning is based on the fastest growers – depending on their rate of growth, once every three to seven years.

· The ‘nurse crop’ system cannot be used.

· Only species amenable to hard pruning can be used.

· A wide range of species can be used because species do not have the chance to suppress other species (see section 0).

Restrictions on the choice of plant material

Both the nature of the plant material and the environment in which it is planted impose a number of limitations. If these limitations are not properly taken into account in the design, the desired visual effect will not be achieved.

The range of influential factors can be divided into two groups:

· The characteristics of the plant material itself, called ‘iron laws’.

· Environmental influences, in this case the urban environment.

Iron laws

Introduction

The native species available for planting differ widely in two respects:

· Light requirement

· Rate of growth

These differences drive two processes that are always at work in woodland planting schemes:

· The natural process of forming open spaces in woodland

· Process of species supressing other species

Because these processes always occur they are often called referred to as ‘iron laws’.

The natural process of forming open spaces in woodland

Under natural conditions, herbs are in time overgrown by shrubs, which in turn are eventually shaded out by trees. The planting ‘hollows out’, as it were, from the middle. Eventually, the middle of the planting area will consist mainly of trees; shrubs can maintain themselves only along the edges. What develops is, in effect, a natural woodland profile. This process repeats itself when trees die and fall. In the open spaces where sunlight reaches the ground, herbs spring up again, only to be overgrown by shrubs, etc.


This profile does not develop in artificial urban environments because the plant beds are usually far too narrow. This means that in urban areas ‘woodland planting’ based on this natural process can only contain a segment of the natural profile of the woodland edge. There are a number of possibilities:

	Fig. 96 Woodland profile

These are called ‘planting forms’ – in effect, no more than combinations of trees and shrubs derived from the natural woodland edge.

	Fig. 97 Planting forms

If the process is not the basis of the design, a further option can be added to the list:


In such a planting scheme the process must be continually checked, which requires intensive maintenance. The appearance easily degrades if maintenance work is not carried out on time.

	Fig. 98 Tree layer with a shrub layer

Each of the planting forms has specific planting and maintenance requirements. These are listed below.

Tree layer


Dimensions: · minimum width of the plant bed: 15 metres · in narrower compartments one or two rows of nursery-grown standard trees

	Fig. 99 Tree layer

Tree layer with occasional shrubs


In addition to the recommendations for the tree layer above: · the shrubs must tolerate shade · the trees must cast as little shade as possible

	Fig. 100 the tree layer with occasional shrubs

Shrub planting


Giving each shrub less space encourages rapid vertical growth. Constraining horizontal growth, though, usually reduces the robustness of each individual shrub.

	Fig. 101 Shrub planting

Shrub planting with occasional trees


· the trees should cast little shade · trees should be nursery-grown standards planted at least 20 metres or more apart the shrubs must grow more slowly than the trees

		Fig. 102 Shrub planting with occasional trees

Tree planting with a shrub margin


The recommendations made for the tree layer and for shrub planting apply here; tree planting with a shrub margin is actually these two forms joined together. Again, some additional recommendations can be made:



Fig. 103 Tree planting with a shrub margin

Dimensions

· minimum width of the plant bed for a symmetrical profile: 25 metres

· minimum width of the plant bed for an asymmetrical profile: 20 metres

· 15 metres is sufficient width for a row of nursery-grown standard trees and a row of nursery-grown shrubs

Plant selection and situation

· sun-loving shrubs can only be planted on open south-facing sites

· a continuous strip of shrubs on north-facing edges is not possible: only a few dispersed shade-tolerant shrubs will be able to survive

· eastern and western edges should be planted with shade-tolerant shrubs

Fig. 104 This is necessary to ensure sufficient daylight penetration

Process of species suppression by other species

The environment into which new plants are put (bare soil) is ideal for pioneer species [l] However, planting schemes often involve planting pioneer species and climax species^a in the same bed. The pioneer species thrive in this environment and soon outgrow the climax species.

We can deal with this in different ways:

· accept the suppression of species

· prevent the suppression of species

Working against the suppression of species is not really possible. Maintaining a rich mixture of pioneer and climax species ‘whatever the cost’ involves a considerable amount of work. The visual effect is highly vulnerable to any delays in maintenance work.

Accepting the suppression of species

When some slow-growing species have only a temporary role to play in the visual effect, the suppression of species presents no problems. When the planting is still young these species can maintain themselves without difficulty and enhance the appearance of the planting for a while. When the plants grow up they are eventually suppressed and the fast growing species dominate.


This means that: · the appearance of the planting changes quite a lot during its development, in a sequence of intermediary forms · this planting type requires relatively little maintenance

	Fig. 105 Intitial species	Fig. 106 suppressed later

Preventing the suppression of species

If a limited number (1 to 3) of species with the same growth rate are planted none of them will be suppressed. During its development each species plays the same role in the overall effect.


This means that: · the appearance of the planting changes little over time · such planting schemes require relatively little maintenance

	Fig. 107 Small number of species	Fig. 108 not suppressed later

Artificial succession

A totally different way of dealing with different growth rates is to use the nurse crop system. Pioneer and climax species are planted together, the pioneers (the nurse crop) protect the climax species when they are young. Once the pioneers have fulfilled their function they are cut, allowing the climax species to develop further.




Fig. 109 Nurse crop	Fig. 110 removed	Fig. 111 leaves climax species

This approach means:

· the appearance of the planting changes considerably and suddenly over time; in effect there are two stages, each with its own appearance

· this type of planting requires a relatively high level of maintenance

· the appearance degrades if maintenance falls behind schedule

Urban areas

Introduction

Besides the influences of the plants themselves, the influences of the physical environment surrounding the planting also play a role: in this case, the urban environment.

Data on a number of these factors are available, for example on:

· the soil (profile, mineral composition, organic matter content)

· water management regime

· traffic engineering requirements (sightlines)

· mains services, cables and pipes

· building control (distance to outer wall)

· pollution (exhaust gases, road salt)

· gusts and downdraughts

A few important aspects are discussed below. These are:

· the limited space

· the limited amount of daylight

· informal use (wear and tear)

Limited space

It is only really the width of a plant bed that sets firm limitations on the use of woodland planting in urban areas. The plots in urban areas are often too narrow. Native species in particular need plenty of horizontal space to grow freely. Shrubs can easily achieve a diameter of 5 meters and the crowns of the biggest trees can be as much as 10 metres across or more, given time.

The minimum width of a pant bed must be greater than the width of a spreading shrub because after woodland planting has been thinned the margin will never consist of a straight row of plants.

Minimum width of the plant bed

· Shrubs in woodland planting require a plot at least 6 metres wide.

· A woodland planting that includes trees requires a plot at least 15 metres wide.

Plant beds narrower than 6 metres wide

· Only suitable for woodland planting if at a later stage the margins are continually cut back or pruned.

· Straight row of nursery-grown shrubs or trees.

· The required width can then be reduced to 5 metres. If the margins are also cut back the plot may be even narrower.

· Non-native species with a narrower growth form.




Fig. 112 Plant beds narrower than 6 metres wide

Besides a sufficiently wide plant bed, a generous margin is needed if plants are to grow freely and reach their full width.

Edges

On edges you should leave space for later development.




Fig. 113 Leaving space	Fig. 114 for later

Another possibility is to plant up the whole plot and remove the outside row at the first thinning.


An unplanted strip should be left along the margin of the plant bed. This can be temporarily filled with grass, herbs or ground cover plants.

	Fig. 115 Initial planting	Fig. 116 thinning	Fig. 117 for growth


The stems of the shrubs in the outside row should be no less than 2.5 metres from the edge of the plant bed		When trees are included in the planting they should be at least 5 metres from the edge of the plant bed.

	Fig. 118 Shrub distance		Fig. 119 Tree distance

Planting patterns

A regular pattern of rows is the most preferred option for the long narrow plots usually found in urban areas; it permits mechanised planting and hoeing and systematic thinning.
An irregular pattern requires more complex maintenance and makes the visual effect more difficult to control; in narrow plots the planting can easily take on a patchy appearance.
Rows can either be planted to form a square or triangular grid; an important feature of the triangular pattern is that after the first systematic thinning the remaining plants are equal distances apart, which is highly beneficial for their subsequent development.


Fig. 120 Planting patterns

Limited daylight penetration

The way the edges of the planting develop is heavily influenced by the amount of light. Two aspects play a role here:


The orientation of the edge in relation to the sun. The location of any nearby objects; other planting and buildings often cut out a lot of light.

Fig. 121 Sunlight orientation

We can deal with these effects in various ways:

· Appreciate the positive aspects of the differences between margins resulting from differences in daylight penetration.
For example, the differences between a north-facing edge and a south-facing edge can be seen as a special feature. On the shaded side you can look between the stems into the planting; in the background the sunlight filters through the foliage on the other side in a soft green haze. On the sunny side you look at a dense mat of foliage; a few small patches of the darkness beyond are occasionally visible.

· Give all edges the same profile through the careful choice of species.
If the aim is to ensure a good edging with shrubs, different species will have to be planted along the eastern and western edges than along the southern or northern edges.

· Careful siting of plants in relation to nearby objects.




Fig. 122 Siting of plants

- Trees and shrubs can become straggly and thin if the distance between the plant bed and a nearby object is less than the height of that object.

- Spreading, well formed trees and shrubs and a dense margin can develop where the distance between the plant bed and a nearby object is greater than the height of that object.

Informal use (wear and tear)

Plants in urban areas are exposed to heavy use. Paths may be worn by people walking through planting elements and children may play in them.

Such wear and tear can be resisted. This is often desirable for planting elements in semi-public spaces, such as residential courts, where residents can exert informal social control to prevent damage to planted areas. Narrower strips of planting are particularly vulnerable and the survival of the whole planting element could be at risk.

· Preventing informal use

- The first step is to locate the planting element with sufficient care: study the walking routes and level of use in general; maybe even cancel the planting altogether.

- Plant species that are hard to walk through, such as thorny bushes, but do not forget that these can severely hamper maintenance work and are not suitable near schools or playgrounds.

- Another option is to add exotic species to the woodland mix. These give the planting a more graceful appearance which can evoke greater respect from the public, particularly if they feel attached to the area.

Instead of preventing informal use there may be opportunities to make use of it. This may be possible in planting with a clear public function in a more anonymous location. In such places, informal use of planting elements can enrich the functional value of the public domain. Moreover, planting areas in public spaces are usually larger and so informal use is no threat to the survival of the planting element as a whole. Plots accessible to the public must be at least 25 to 30 metres wide (deep).

· Accepting informal use

- When managing a fait accompli, e.g. surfacing a short cut worn through regular use, the special qualities (e.g. a certain sense of secrecy) of cutting through the vegetation is destroyed.

- Not replanting open spots in the planting.

- Use species that are resilient to wear and tear.

- Opportunities can be created, for example by tipping a pile of sand in the planting area so that children can make a mountain bike arena.

1.4.2 Planting and Habitat

Factors

The suitability of planting depends on climatological conditions (wind, light, seasons) and physical conditions (soil, groundwater level, air and the space available above and below ground). A different selection of plants is needed behind the dunes along the coast than on a site in a fenland polder or on the sandy soils of Noord-Brabant.

As a designer, you will at first be tempted to base your choice of plants on spatial qualities to do with dimension, form (habit), colour and structure. A further consideration is whether the site is in a rural or an urban environment, where there are special restrictions.

Whatever the scale at which you are working, the final detailing is crucial. Financial resources will often be an important consideration (particularly if planting or transplanting older trees is involved).

Climatological conditions

Wind

Wind, usually from the sea, is an important factor in the west and north of the Netherlands; frost in the east and south. The effects of wind must be fully considered as it exerts considerable pressure on twigs and branches (in leaf). In rural areas, the direction of the prevailing wind can often be read from the shape of the trees.

Poplars grow rapidly and quickly make a spatial impact, but are ‘not solid enough’. At about 40, branches tend to split and so many trees are felled at around this age. Poplars are not the trees to plant if you want them to be around in 100 years time, although they can live for a long time. As solitaires, it may be worth the extra work, but not for an avenue.

Unfortunately, many a good tree succumbs to our autumn storms; the poorest specimens have by then lost their leaves, but those that still have a good leaf cover are exposed to the full force of the wind.

But wind is not restricted to rural areas. The taller buildings built in recent years create considerable ‘downdraughts’. In front of the Robeco building in Rotterdam some trees have been planted to absorb these downward gusts so that passing cyclists are not literally blown through the air! Climatological conditions, therefore, do play a role in urban planting.

Light

Light pollution (albeit only at high levels) and salt (road salting in winter, fish stalls on the market) are disastrous for trees. Light requirement and ‘drip damage’ are more important factors affecting shrubs, and trees with dense crowns permit only a very little undergrowth. The so-called ‘woodland planting’ (plots with trees and shrubs) dating from the 1970s often cause problems now. The trees are large and the undergrowth is dying off purely due to insufficient light. Of the original large plots full of trees and shrubs, only the edges will eventually remain, the planting being hollow under the tree canopy in the middle. If you want the shrubs top remain, plant the trees far apart or choose trees with open crowns that let a lot of light through. ‘Drip damage’ can be a significant problem; some hedges (e.g. Yew) are very susceptible to drip damage, other, like Beech or Sycamore, are unaffected.

Seasons

Planting should look attractive the whole year round. Some trees and plants bloom in winter. Autumn colouration can also add variety.

Spring (flowering)

· Trees: Alder and Willow (March); Cherry and Magnolia (April); Apple, Horse Chestnut, Hawthorn (May)

· Shrubs: Hamamelis, Forsythia (March); Currant, Rhododendron (April); Azalea (May)

· Bulbs/tubers:

· Early: (February/March): Snowdrop, Crocus

· Late: (April/May): Narcissus, Tulip

Summer

· Trees: Horse Chestnut, Catalpa (July); Golden Rain (June)

· Shrubs: Hibiscus, Hydrangea, roses and perennials

Autumn (colours)

· Trees: Sycamore, Birch, Hornbeam, Sweet Chestnut, Hawthorn, Honey-Locust, Oak

· Shrubs: Whitebeam, Currant, spindle

Winter

· Berries: Hawthorn, Privet, Ornamental Apple

· Evergreen shrubs: Rhododendron, Holly, Viburnum

· Shrubs with berries: Currant, Whitebeam, Ivy, Privet, Rose

Winter (flowering)

· Tree: Prunus subhirtella ‘Autumnalis’ (flowers November/December and again in April)


`

Fig. 123 Lime (summer)	Fig. 124 Lime (winter)

Physical conditions

Soil

Roughly speaking, soil in the Netherlands can be classified into clay, peat and sandy soils (and all the intermediary forms). Plants on sandy soils – often in windy locations – have adapted by reducing the size of their leaves (e.g. Sea Buckthorn, Juniper), by growing hairs on their leaves (Mullein) or by taking on light or greyish colours.

Examples of coastal trees:

· Alder

· Poplar

· Oak

· Willow

· Rowan

Because of their structure, clay and loamy soils retain water for a long time. They are often cold in spring, and less oxygen is available than in sandy soils.

Examples of trees on clay/loam soils

· Alder

· Horse Chestnut

· Birch

· Cherry

Another important factor is the presence of calcium, which supports a different type of vegetation; a base-poor dune vegetation contains different plants to calcareous dune valley vegetation. Peaty areas are acid and always moist; nutrient levels are a crucial factor. Alder and Rowan do well in nutrient-rich peat, Birch in nutrient-poor peat. Well-known shrubs suitable for acid soils are Rhododendron and Azalea. If they are planted in other soil types, peat will always have to be added to the soil.

The above also applies, in principle, in rural areas, where plants still have a ‘feel’ for the soil. Clearly, in purely urban environments the original soil is less important for plants, particularly trees.


Sea clay River clay Peat Sandy soils Loamy soils
	Fig. 125 Soils of The Netherlands

Groundwater

If the water table is too high, few trees and shrubs will be able to survive. Tree roots will develop poorly and not anchor the tree well in the ground; as a result they are easily blown over. Of course, too little groundwater is not good, either; the plants wilt.

Trees which can grow in wet conditions are: Alder, Birch, Poplar and Willow. Trees that can grow in dry conditions are a few Maple species, Birch, Hornbeam, Acacia and a few Poplar species. During the growing season (May to August) tress take up large quantities of water from the soil.

In an urban environment, trees depend on a number of sources of water:

· Groundwater

· Capillary water (‘sucked’ up from the groundwater through the soil)

· Pendular water (precipitation that clings to the surface of particles in the aerated zone)

The demand for water in summer is greater than the amount of pendular water. The extra is drawn from the groundwater; the water table falls in summer, but it is replenished again in winter from rain and snow.

Much water in the city goes straight into the sewer; the more ‘porous’ the paving is the better this is for the trees. But the water must remain for as long as possible in the pendular water zone. Humus is a valuable component in the soil because it retains a lot of water.

The best situation is a water table that fluctuates around 1.25 m under the soil surface (1.50 m in the summer and 1 m in the winter). Under these conditions trees can become well established and firmly anchored. If a tree cannot take up enough water, the roots go in search of more. The root ball of a healthy tree reflects the size of the crown.



1. Soil containing humus 2. Capillary zone 3. Water table
Fig. 126 Spring	Fig. 127 Autumn



Fig. 128 Groundwater level approx. 1.25 m:Roots and branches: above ground = below ground	Fig. 129 Deep groundwater level: roots ‘search out’ water

Air

Trees in built-up areas – except trees in parks and gardens – grow in a habitat that simply cannot be compared with a site in a wood or open landscape. The soil in the country is open (to air and water) and fallen leaves provide a supply of nutrients. Conditions in urban areas are very different. Paving requires well compacted soil; but trees need open soils. Air is kept out by the closed road surface and compacted soil, which leaves almost no pore volume for air to penetrate.