Problems caused by poor drainage are a grave environmental issue. With urbanisation spreading like wildfire, even the villages are developing into townships. A good drainage system is of paramount importance to ward off diseases especially during the monsoons and floods.
Clogged drainage is the worst thing that can happen to a city or township. It can lead to outbreak of diseases, growth of mosquitoes and make urban life hell. Removing stormwater and household wastewater – sometimes called ‘sullage’ – is an important environmental health intervention for reducing disease. Poorly drained stormwater forms stagnant pools that provide breeding grounds for disease vectors. Because of this, some diseases are more common in the wet season than in the dry season.
Household wastewater may also contain pathogens that can pollute groundwater sources, thereby increasing the risk of diseases such as lymphatic filariasis. Poor drainage can lead to flooding, resulting in property loss, and people may even be forced to move to escape floodwaters. Flooding may also damage water supply infrastructure and contaminate domestic water sources.
Public health at risk
What always happens is that in areas where drainage and sanitation are poor, water runs over the ground during the rains, picks up faeces and thus contaminates water sources. This contributes significantly to the spread of diseases such as typhoid and cholera, and may increase the likelihood of contracting worm infections from soil contaminated by faeces. Flooding itself may displace populations and lead to further health problems.
Drains from irrigated fields should also be properly designed and maintained, since the introduction or improvement of irrigation is often associated with an increase in the numbers of people with schistosomiasis (infection caused by some parasitical flukes). This is particularly true where earth-drains are used and the water supply and sanitation are inadequate. Lining and properly grading the drains, removing aquatic weeds and building self-draining structures are all important measures for reducing health and environmental risks.
Need for planning
The drainage system is an integrated system of tributaries and a trunk stream which collects and funnel surface water to the sea, lake or some other body of water. The total area that contributes water to a single drainage system is called a drainage basin. This is a basic spatial geomorphic unit of a river system, distinguished from a neighbouring basin by ridges and highlands that form divides. Thus, river basins are natural units of land. They are regarded as the fundamental geomorphic as well as hydrological units for a systematic study of the river basins.
A geometric arrangement of streams in a region determined by slope, differing rock resistance to weathering and erosion, climate, hydrologic variability, and structural controls of the landscape is known as a drainage pattern. In other words, drainage pattern refers to a design which a river and its tributaries form together, from its source to its mouth. The factors controlling the pattern of drainage in a region include the topography, slope, structural control, and nature of rocks, tectonic activities, supply of water, and above all, the geological history of that region.
Designing and constructing drainage systems require expert advice from engineers to make sure that water flows away quickly and smoothly and is disposed of in a surface watercourse or soak away. Drainage installed by one community should not create problems for other communities downstream, nor should it affect ecologically important sites. Environmental considerations should be given adequate attention since long-term changes to the environment may lead to greater health problems in the future.
The detailed design of stormwater drains should be carried out by engineers and take into account climatic and hydrological data. These data may be scarce, or may not cover the community where work is to be carried out. In such cases, the community can help by describing where major flood problems occur in the village and by providing information about previous floods. Stormwater drains should be designed to collect water from all parts of the community and lead it to a main drain, which then discharges into a local river. The size of the drains should be calculated according to the amount of water they would be expected to carry in a rainy season.
If drains are designed to carry only the amount of water expected from an annual flood, they will not be able to cope with the flow of water from heavier floods, which may occur as often as every 2-3 years. This may make flooding problems worse and increase the health risks. Stormwater drains are best constructed using a concrete lining. Earth-drains are more likely to become clogged and overgrown, and cause problems with stormwater flow during minor floods. This can lead to the formation of stagnant pools and result in breeding grounds for disease vectors, such as mosquitoes, increasing the risk of malaria and schistosomiasis and also increasing the risk of snails.
The drains must also be properly maintained and cleaned: it is common to find that new drains become dumps for solid waste or even sewage because of inadequate maintenance. The community should, therefore, establish how often drains are to be cleaned and who will be responsible for the maintenance. Often, the best solution is for the community members themselves to take responsibility.
(Read the full article in the November 2015 issue of Safety Messenger Magazine)