11-5.5 WATER QU?iLITY
The influence of urbanization on natural water quality mainly depends on the Eollowing fac- tors :
(a) release of wastewater from industrial enterprises situated within urban areas;
(b) release of municipal wastewater;
(c) contamination of precipitation water;
(d) pollution of surface runoff from urban areas.
The release of industrial wastewater should be considered separately since this problem is not regarded as the direct consequence of urbanization.
Apart from industry , urbanization leads to pollution of the environment, which is closely connected with the number of inhabitants and the size of an urban area. In cities the volume of sewage water may range from several dozens to hundreds of thousands of m3 per day. Depending on the water content of the city river, sewage water can constitute a con- siderable portion of its natural runoff.
The release of sewage water may influence considerably the biochemical qualities of the natural water in an urban area. The sharpest increase is observed in the content of dissol- ved and suspended organic substances, biogenic elements and dissolved gasses. The extent of bichromatic oxidation of water , which characterizes the total content of dissolved organic matter subject to oxidation, may become four times greater. Approximately the same rise is observed in the biochemical need for oxygen. The content of nitrogen and phosphates in- creases 3 to 10 times.
oxygen content is reduced to 30-70% of saturation near sites of sewage water discharge.
which are widely used in domestic washing. Such substances make water quality considerably worse and cause foam formation which seriously hinders the work of the sewage and water- supply systems.
As to the gas content, marked changes are observed in the amount of dissolved oxygen.
One of the specific types of water pollution is that produced by synthetic substances
11-5.5.1 The influence of surface runoff from urban areas on water quality
Until recently, due attention was not paid to this pollution problem and watex discharging from streets into storm water drains was regarded as relatively clean. Special investigations
(Lvovich, 1964) showed that this water contained a substantial amount of organic and mineral substances, washed out of the atmosphere and from the surface of urban areas.
Due to ail- pollution , precipitation falling on urban areas contains rather complicated solutions of salts, acids and organic matter, and also includes a variety of suspended par- ticles.
1964) , precipitation falling on a sq km of the earth's surface over a year brings 5 to 15 tons of dissolved matter in rural areas and 2 0 to 30 tons in urban areas.
surface of urban areas is equivalent to 8-15% of the corresponding vaLues of pollution of municipal sewage water which form at the same place.
According to computations in the USSR, on the basis of observational data (Lvovich, The total amount of pollutants discharged into water bodies and water courses from the
11-5.6 POLLUTION AND SELF-PURIFICATION OF WATER IN RIWñS , LAKES AND RESERVOIRS
The influence of urbanization on water quality also depends on the type of natural water body receiving the sewage water and on the conditions of its self-purification.
At present, when making plans for water management and water quality control it is essential to take into account not only the possibilities of improving sewage water purifi- cation but the self-purification which takes place in water bodies as well. This will pro- vide on the one hand a better outline for the development of productive forces within indi- vidual countries and regions, and on the other hand permit a more rational use of water resources.
tion of natural water bodies. In this case it is important to study not only the rate of It is essential to make a detailed field investigation of pollution and self-purifica-
Re ferences
pollution of the water body as a whole, but to investigate in detail the zones of pollution in reservoirs , and to evaluate the conditions of self-purification within these zones. Using field investigation data in hydrological and hydrodynamical computations , it is possible to develop general and specific recommendations to improve water quality and to regulate water use.
lem of man's influence on the hydrological environment, especially on surface water quality, are observational studies of water pollution , and the development and improvement of general theoretical models of pollution and self-purification processes. These models should be re- garded as a basis for the improvement of existing computation methods and for the development of new ones.
Application of the techniques of hydrological investigations and a detailed study of individual factors depend on the hydro-meteorological regime and location of the water body under study.
water pollution consequences and inadequacies of sewage and purification works, as well as for the development of mthods for computation of self-purification and for verification of
exis ting techniques.
In the USSR, the most popular and well-developed methods of computation of wastewater dilution in rivers, lakes and reservoirs are based on the general differential-equation of turbulent diffusion. Design methods have been developed for steady and unsteady diffusion.
Detailed methods have been developed for the dilution of polluting admixtures in rivers, characterized by both high and low rates of mixing. Special methods have been developed for lakes and reservoirs to take into account the pollutant storage at the discharge site, its transference and diffusion. It is planned to study the possible effect of wind-wave turbu- lence on dilution. Supplementary design considerations make it possible to analyse the de- composition of destructable substances and settlement of suspended pullutants , and to obtain characteristics of recurring water pollution due to the disturbance of polluted sediments caused by hydrodynamical effects.
for the practical estimation of pollution and self-purification in rivers, lakes and reser- voirs (Anon, 1970b). This publication presents an analysis of the following problems:
A w n g the most important tasks of a programme of international co-operation on the prob-
Actual results obtained may be used for economic planning, for timely prediction of
In the USSR, the State Hydrological Institute has developed and published recommendations
(1) classification of water bodies with respect to conditions of wastewater dilution;
(2) recommendations on how to select a method for estimating dilution for different (3) selection of the initial hydrological values and hydraulic elements necessary for (4) description of detailed and simplified methods for estimation of wastewater dilu-
ways of discharging wastewater;
the estimation of dilution in rivers, lakes and reservoirs;
tion in rivers , lakes and reservoirs.
11-5.7 REFERENCES
Anon , 1970a. ' Gidroenergetica i kompleksnoye ispolzovanie vodnykh resursov SSSR' (Hydro- energetics and complex usage of water resources in the USSR) . Moscow , 'Energia'.
Anon , 1970b. Prakticheskie rekomendatsii PO raschetu razbavleria stochnykh vod v rekakh , ozerakh i vodokhranilishchakh (Practical recommendations for the computation of dilution of sewage water in rivers, lakes and reservoirs) , Hydrometeorological Publishing House , Leningrad.
m o n , 1971. Chislennost , razmeshchenie , vozrastnaya structura , unrovon obrasovania , matsio- ralny sos tav , yazyki i is tochniki srodstv sushchestvovania naselenia SSR podanaym Vsesoyuxnoy perepisi nesslenia 19709. (Size settling, age structure , standard of education, national bodies , languages and means of subsistence of the USSR population according to the ALL-Union
Census of 1970)
.
Moscow ,Statistics.
Dekhtyarev A. P. 1964.
cities)
,
Moscow, 1968.and keep clean the reservoirs of the capital) , Goredskoe khoz-vo Moskvy, No.5;
Voprosy vodosnabzhenia krupnykh gorodov (Problems of water supply of Basaev I.A. Berech i solerzhat v chistots vodoemy stolitsy (Conserve
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