HydroZogicaZ effects resulting from water management systems

geological and topographic conditions (Gustafsson

et al,

1970). Among other problems there could be the risk of pollution in a groundwater lake intended for recreation, bathing, fishing, etc.

There are in this case many additional problems related to water circulation, biological activity and the choice of suitable material to be used for the shore.

11-3.3.4 A special groundwater problem illustration

A special groundwater problem that has occured in Stockholm is worth mentioning because it ill- ustrates the influence of urbanization on hydrological processes. When the subway was built in Stockholm large quantities of water were pumped in order to drain the construction works. This pumping contributed considerably to the settlement problem mentioned earlier. However, a large volume of water is constantly withdrawn from groundwater and is used for air conditioning inst- allations and power stations in Stockholm. At least 8 O00 m3 daily are used during maximum cooling demand. During the 1960s the temperature of the groundwater rose 1 to 1.5OC in cities and at present the temperature is about 10.5 to ll°C. A large increase in temperature has occurred near the infiltration plant which explains the fact that the groundwater sources nowadays have an increased temperature. The water which is discharged to the infiltration wells after being heated during its passage through the cooling plants flows beneath the cellar floors to the groundwater sources without being appreciably cooled. In this way the cellars will have too high a temperature. One important consequence of this is that one of the groundwater consumers could not use water when its temperature exceeded f12OC. The result is that the groundwater temperature has to be continuously controlled (Nordstrom, 1970b).

11-3.3.5 A reclamation problem

The handling of solid wastes is a serious problem in Sweden as in many other countries. In the Malmö area, in the south west of Sweden, there is a plan for extensive reclamation by moving the shoreline outwards by filling with solid wastes, suitably pretreated. The land area created in this way will be about 1000 hectares of which 600 hectares will be used for an extension of the harbour area and 400 hectares will be used for recreation. The filling of the area is plan- ned to be completed in 4 stages by the year 2000. However, many questions have been raised about this enterprise. The most serious one is associated with the possible risk of pollution from the solid wastes. Will there be any leakage through the sea defence dikes. This problem is comparable with the contamination risk at a site for solid waste disposal on land. Another important question is whether the ground beneath the fill is sufficiently waterproof to prevent filtrat- ion. Infiltration of polluted water would endanger the so-called Alnarp stream which flows bel- ow the surface in the immediate vicinity of the proposed land fill area, and is one of the most important sources of groundwater for south western Sweden.

11-3.3.6 Thermal effects of heated effluents in Lake Mälaren

Some interesting features have been observed at a power plant situated at one of Sweden's largest lakes; Lake Mälaren. A 200 MW capacity power station belonging to the National Power Ad- ministration and also the 300 MW combined district heating and power station of the Aroskraft Corporation is situated at Vasteras Bay. The cooling water discharges from these two stations are 14.5 m3/sec with a temperature increase of 8 $0 9OC and 5 to 6 m3/sec with a temperature increase of 8 to 9OC respectively. The bays at Vasteräs nave a combined surface area of about 5 0 km2 and a volume of about 3 3 5 ~ 1 0 ~ m3- There is a very limited renewal of water in the bays and this is mainly due to wind influence (Ehlin, 1970; Carlsson, 1970). Temperature conditions in the Västeräs bays have been observed continuously.

water discharged into a water bay during winter is cooled quickly and sinks. If the lake is sufficiently large, the effect on the ice will be limited to a small open area caused by melting. But if the volume of the lake or bay is relatively small, as also is the renewal, a very different situation may be expected. The Västeräs bays are good examples of this situation. In 1970, when other parts of Lake Mälaren were covered by ice, the Vasteras bays were largely ice-free.

significant heat discharge was occurring, the heat content was 3.3 x losi4 cal.

1969 it was 4.8 x 1014cal and in March 1970, it was 6.5 x 1014cal.

A specially interesting situation arose in the winter of 1969-1970. Generally, cooling

Observations of the heat content showed th t in 1968, when no In March

101

Water

suppiiy effects

The consequences of this extensive ice melting are not wholly understood. As far as is known at present, one positive consequence seems to be that the earlier melting of ice in the nearby bays had an advantageous effect on the oxygen balance due to the reduced period of ice cover. A negative effect is the fact that the lake cannot be used for skiing or ice-skating.

According to some preliminary plans it is intended to locate a nuclear power plant not far from Stockholm with a thermal effect of 1550 MW. The cooling water needed is estimated at 30 m3/sec and the water will be heated to approximately 10°C.

that the plans are only preliminary. Some preliminary studies have been made on the expected effects O € this plant on the environment. Of special interest here is a study made on the effect of temperature distribution from cooling water discharge.

ice cover, even at some distance from the proposed discharge points, because deeply injected cooling water will be conveyed to the surface by circulation (Sprinchorn and Ehlin, 1971).

It should be emphasized

Preliminary calculations indicated that the cooling water may cause weakening of the

11-3.4 WATER SUPPLY EFFECTS

11-3.4.1 Urban public supply withdrawals

An estimate of the net annual precipitation shows that per capita this amounts to about 27 O00 m3 and of this quantity about 3% will be consumed.

age will rise to 5% in the year 2000 and that industry will use 80% of the total amount (Royal Ministry of Foreign Affairs/Royal University of Agriculture, 1971).

With the aid of statistical data concerning Swedish municipal water works (Swedish

Central Bureau of Statistics/National Swedish Environment Protection Board, 1969), it has been possible to render an account of the use of groundwater and surface sources respectively in urban areas (19681, Table 19. The data, which are as complete as possible, are arranged according to cdunties ipdicated by letters. The figures in the col-mns of the table represent-

ing groundwater and kurface water supply show that about 47% of the requirements of urban areas is derived from groundwater whereas about 53% is obtained from surface water. However, the individual figures for each county indicate that there is a great variation in the rela- tion between groundwater use and surface water use. The use of groundwater in Swedish cities is increasing (Winquist, 1968).

of groundwater in Sweden. The groundwater abstraction capacity of a Swedish esker may rang'e from approximately 10

abstraction capacity is less. From Table 19 it can be seen that the water requirements for domestic and industrial use amount to about 62% and 20% respectively of the total annual abstraction. The column entitled 'remaining' and 'losses' includes all abstraction for general public use (street cleaning, fountains, etc.). (Table 19 is on Page 99.)

follows.

It is expected that this percent-

Although the superficial deposits are generally thin they are extensively used as a source m3 per second to some 100 1i3 per second. In sedimentary rocks the

According to Sweden's national report (Jansson, 1971a) the future water use will be as

Table 20. Future water use

Use iñ million m /year 3

Year

Indus try Urban areas Pulp

and

paper Total Total

End of 1960's 3 200 4 O00 870

2 O00

2000 6 700

The quantities given in Tables 19 and 20 do not take into account the fact that water may be re-used several times along a water course. Furthermore, the water use in urban areas in

Water suppZy effects

the year 2000 is based on the assumption that the population in Sweden will have increased from 8 to 10 million. Moreover, it is expected that of the 10 million people 90% will live in urban areas compared with the present 80%.

The figures also include an allowance for an assumed increase in water usage, per person.

11-3.4.2 Independent industrial water abstractions

In Sweden, large industries use surface water drawn almost exclusively from their own supplies.

The largest water user is the pulp and paper industry: the next largest are the mining and metal industries. Industrial water usage has been approximately doubled in the past ten years.

The water requirement for cooling use in Sweden is small at present. Only one experi- mental nuclear power plant (65 MW) is in use. In 1973 a nuclear power plant (760 MW) will be

in operation and this plant will later be expanded to 3000 MW. In 1974 another nuclear plant will be developed (1000 MW). In 1980 it is supposed that 75 O00 MW will have been installed.

Of hydrological interest are the thermal pollution effects of this activity.

problem has already been discussed in Section 3.3.6. It is generally estimated that a power plant of 3000 MW uses about 150 m3/sec of cooling water and that the need for cooling water is proportional to the size of the nuclear plant. Most likely, nuclear power stations in addition to those already agreed upon will be located on the coasts where water is readily available. Exceptionally, some may be located in the vicinity of lakes.

and the planning of their location is an important part of the preliminary work of a national physical plan. It is difficult to predict the volume of abstraction but it seems likely that by the year 2000 the rate of abstraction will be about 2000 m3/sec.

water discharge will be contributed by ten plants along the coasts of Southern Sweden. This quantity corresponds approximately to four times the discharge of the Göta River, the largest Swedish river and will almost certainly cause local hydrodynamic effects on the water circulation. Abstraction of water from groundwater sources is likely to be extremely small.

This type of

The problems of locating a nuclear power plant close to an urban area have been studied This volume of cooling

11-3.4.3 Present and anticipated public and industrial water supply problems

If the mean water supply per capita in Sweden is calculated, taking into account the estimated increase of population until the year 2000, the future sources appear to be sufficient to meet the demand. However, the practicalities of organising the supply are more difficult since the natural occurrence of water does not coincide with the distribution of the population. As already mentioned, the total annual precipitation is estimated to be 27 O00 m3 per capita of which about 3% is uged for water supply. The normal minimum demand averages

5 500 m3 The uneven distribution of population is such that about 80%

of the population lives in the southern part of the country. In this area the annual mean runoff, 300 mm, is the equivalent of 7 O00 m3 per capita, which is much lower than the national average of 27 000 m3 per capita.

the rest of the country and because sources are scattered it is difficult to make efficient use of them. Resort has been made to regional distribution to meet requirements (Swedish Government Official Report, 1965-8). In order to guarantee a sufficiently large water supply for the metropolitan Malmö-Lund-Helsingborg in the south west of Sweden, water will be trans- ferred from the River Lagan through an 80 km tunnel from Lake Bolmen. The water will be dis- tributed to five cities through three mains with a total length of about 300 km. This project will be completed by 1978 or 1979. During the planning of this work calculations were made

to study the possibilities of supplying water to the Hamburg area of north Germany. The so- called Bolmen project has been extensively debated, and a strong public resistance to this project has been expressed, including the opinion that the groundwater resources have not been thoroughly surveyed.

Sweden appear to be sufficient to maintain supplies at least until the year 2020.

method has been studied by a special group (Swedish Board for Technical Development, 1970).

It has been found that a ditional water may be produced through a distillation process at a cost of about 0.70 Skr/m

per capita per year.

The southern part of Sweden must be considered as a region short of water compared with

According to preliminary calculations the resources for southern An alternative for the future would be to supplement supplies by desalination. This

9 ’

(

=

14 cents/m3).

103

Z Zution

effects

11-3.5 POLLUTION EFFECTS

11-3.5.1 Organic, inorganic and thermal aspects

The present total discharge of oxygen-consuming organic substances for 6he whole of Sweden is estimated at 670 000 tonnes BOD7 per year (Andersson, 1972). Of this quantity, about 270 000 tonnes will be discharged to inland waters and about 400 O00 tonnes to coastal waters. Forest industries are responsible for about 83% of the total discharge and urban areas for about 14%. Most of the coastal discharge comes from forest industries whereas the disposal of organic pollution in inland waters comes from urban sources.

Total phosphorus discharge has been estimated at 13 O00 tonnes per year for the whole of Sweden. Of this quantity 59%, or 7 7 0 0 tonnes per year is discharged to inland waters and, 41% or 5 200 tonnes per year, to coastal waters. Calculations show that about 58% of the total discharge originates from urban areas, about 30% comes €rom industry and the remaining 12% from forest and arable land. Urban areas are responsible for about 71% of the discharge into inland waters and industry and urban areas account for 51% and 46%, respectively , of the discharge to coastal waters.

whole of Sweden and of this sum 77 O00 tonnes or 83% is discharged to inland waters and the remaining 16 000 tonnes or 17% to coastal waters. The leaching of nitrogen from agricult- ural and forestry areas is assumed to contribute 65% of the total nitrogen discharge. Urban areas are responsible for about 27% and industry for about 8%. The discharge from urban areas into coastal waters amounts to about 48% of the total nitrogen discharge.

11-3.5.2 Pollution from urban sewer systems

The disposal of total nitrogen has been estimated at 93 O00 tonnes per year for the

Storm water overflow and urban storm runoff are considered potentially harmful to the environment under Swedish law. The legislation requires individual authorization before the construction of new sewerage works and the extension of existing ones. The discharge of wastewater from urban areas is mainly effected by combined or separate systems.

In Sweden, there is a total of about 8 O00 km of combined conduits and they constitute about 21% of the total conduit system. Storm sewers comprise 24% and sanitary sewers about 5S% of total conduit length.

When a combined system is used a hydraulic surcharge may result from snow melt and in- tensive rainfall occurrences. During severe overloads water is discharged by means of overflow weirs to stream courses. The quantity which added in this way to the water courses is estimated at 3 to 5% of the total pollution from an area with a combined system. This implies (Ulmgren, 1971) that pollution by overflow constitutes 30 to 50% of the total discharge of pollutants which is discharged annually from a treatment plant after combined biological and chemical treatment (which means a 90% reduction of BOD as well as phosphorus).

The instantaneous quantity of pollutants from the overflow may in many instances be much higher than the discharge of pollutants from the sewage treatment plants despite the fact that, +e discharged water is diluted by storm runoff water.

culated according to certain rules. These stipihlate that biological and chemical treatment processes shall not bb loaded in excess of 2 Qdim. Greater quantities are rejected through overflows. It has been shown that with a load of 4 @im, for instance, much better treatment will be effected if the biological and the chemical stages are each loaded with 2 Qdim rather than to dispose of 2 Qdim and only treat the remaining 2 Qdim biologically and chemically. Separate, small treatment plants for urban storm runoff treatment have been built in some cities in Sweden.

aining in the effluent from biologically treated sewage, derived from an urban area of comparable population density. The authors found that urban storm water contained a higher proportion of suspended material and bacteria but smaller amounts of BOD, phosphorus and nitrogen than in the treated water. Thus, if the standard of treatment of effluent is im- proved then the relative importance o€ storm runof€ pollutants will increase.

worthy of note. They paid particular attention to the pollution effect of snow in urban In Sweden, the dimensioning hydraulic load, Qdirnr at a waste treatment station is cal-

A comparative study was made of the pollutants in urban storm water with those rem-

In this connection another pollution problem observed by SÖderlund and Lehtinen 1970b is

Po

ZZution èffects

areas, In Stockholm, for example, where the mean annual precipitation is about 555 mm of which an equivalent of 120 mm is from snow, about 850 O00 m3 of snow is deposited in the Lake Malaren every year. The authors found that the percentage of suspended matter was con- siderable. The conclusion drawn was that there may be a stabilizing mechanism involved in the dispersal system of sand and water. Such a mechanism may indicate that an adsorption of bitumen, oil products and light hydrocarbons occurs. One consequence is that a consid- erable quantity of sand will enter the treatment process along with the oil products. These products should have been separated off in the grit chamber. Another consequence of the stabilization mechanism is that sand, with its attached oil and bitumen products, etc., will be carried to stream courses without treatment.

To Compensate for the negative effects of the discharges mentioned, great efforts axe made to provide municipal sewage plants with facilities for biological and chemical treatment. The present annual investment in treatment plants alone amounts to 230-300 million Swedish Crowns (equal to about 45-60 million US dollars). in 1970 about 20% of the urban population was not served by any sewage treatment while some 30% were connected to plants with only sludge separation. About 50% were connected to plants providing more advanced treatment. In 1975 the sewage from almost the entire urban population will be discharged to treatment plants according to present plans. One half of the population will be served by sewers connected to chemical, or combined chemical and biological treatment works, and more than 30% by sewers connected to biological treatment worlts, cf., (Royal Ministry of Foreign Affairs/Royai University of Agriculture, 1971)

.

11-3.5.3 Disposal of solid wastes

Detailed information about the quantity of total municipal wastewater solids in Sweden is not available. It is generally assumed that conventional treatment, on average, will result in 9 0 g (dry weight) per day per person. By 1975, because of an extended programme of treat- ment for the whole country this quantity may be increased to about 120 g per day per person.

The sludge is processed by drying, settlement in lagoons, spray-irrigation on farmland or incineration.

Sweden does not dispose of sewage sludge by dumping it at sea. Incineration is the principal method of waste disposal employed for large city areas. About 20% is incinerated at present but this proportion is increasing. However, it must be mentioned that open b u m -

Dans le document of urbanization (Page 98-103)