INTRODUCTION - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 4

discrete rural communities. Therefore, pollution problems of surface waters in such types of
watersheds are likely to be complex due to the presence of combined sources of pollution in the form
of point and non-point sources based on different types of land use.
1.3. WATER QUALITY PROBLEMS IN CONNECTED CATCHMENT - SHALLOW LAKE SYSTEMS
One of the most important problems associated with irrigated watersheds is the non- point source of
pollution resulting from agricultural practices, introducing various pollutants to the drainage network
such as phosphorus, nitrogen, metals, pathogens, sediment, pesticides, salt, trace elements (e.g.
selenium). This is in addition to the pollution load from domestic untreated wastewater, fisheries
waste loads, and other point sources of pollution from inadequately treated industrial and domestic
wastewater. In irrigated agriculture, the conservation of water by the efficient conjunctive use of
irrigation and drainage water may provide an economically sound solution to the problem of irrigation
water deficiency in countries with limited water resources. Reuse of drainage water either directly or
by mixing with irrigation water is one of the agricultural practices in irrigated watersheds. However,
this practice has its limitations and drawbacks. Deterioration in of the quality of drainage water by
different pollution sources has direct negative effect on irrigation water quality, agricultural crops and
local farmers. Coastal deltaic regions with rare rainfall are usually a good example of such types of
watersheds.
The Nile Delta region in Egypt, could be referred to here as a typical example, the region is divided
into a number of irrigated agricultural watersheds that comprises drainage catchments connected to
coastal shallow lakes, which act as drainage system outlets to the sea. All human activities that take
place in the catchments, has its effect on the whole watershed. Irrigation in the Nile Delta depends on
drainage water reuse, as a second important source after surface irrigation. Rainfall on the
Mediterranean coastal strip decreases eastward from 200 mm/year at Alexandria to 75 mm/year at
Port Said. It also declines inland to about 25 mm/year near Cairo. Rainfall occurs only in the winter
season in the form of scattered showers. Therefore, it cannot be considered a dependable source of
water. Therefore the surface water pollution sources are mainly originating from agricultural drainage
water in addition to industrial and untreated domestic wastes. The pollutants are transferred from the
drainage network to the coastal shallow lakes. These pollutants are mixed with another source which
is the wastewater from aquaculture or fish ponds that usually surrounds coastal lakes. The ecosystems
of such lakes usually face eutrophication problems due to excess nutrient loadings into the lakes. Also,
there are usually unbalanced quantities and species of aquatic vegetation due to existing pollution
problems.
The pollution problems in such watersheds, especially in developing countries including the Nile
Delta catchments, are increasing due to the lack of formal sanitation and treatment facilities,
population growth, continuous urbanization and the lack of public awareness on the extent of the
problems and the importance of pollution prevention. In these watersheds, which are subject to
different pollution sources, there is an urgent need for effective management of the surface water
quality. Management tools are needed in order to ensure compliance of surface waters with the
different water quality objectives for various uses. Environmental management problems associated
with water quality in such watersheds are inherently complex and difficult to analyze due to the
interaction of physical, chemical and biological processes and the consequences of anthropogenic
activities. Further, finding good management alternatives becomes exceedingly difficult due to
conflicting issues such as cost, environmental impact and equity that need simultaneous consideration.
The solution of these problems is compounded by a very complicated system that includes different
types of water bodies, categories of land use and sources and types of pollutants. Therefore, the
solution requires an integrated approach to the modeling, analysis and management of such types of
watersheds in order to manage their surface water quality.