intro

Stormwater run-off?

The monsoon brings with it very welcome showers. The earth sings with joy after a hot summer. People feel a great relief from heat and from the suffering of lack of water. We all welcome rain with open arms.

Yet, many a times, the rain which we wait for so longingly becomes a curse, a problem. There are floods. some manageable and some unmanageable .resulting in destruction, health hazards, epidemics and what not. If nothing else, it results in water-logged areas near the habitation creating major incon-veniences in access and mobility and become breeding houses for mosquitoes, flies and every other germ and bacteria.

Thus the gift can turn into a curse.

Rainwater, has a cycle. The way the water moves through the landscape decides very much how the land and people live. Does the water move fast and cause erosion ? Does the water meander and thus is beneficial ? What does it carry with it and what does it bring with it ?

As one can see in the picture, runoffs from roofs move into open spaces and streets around the house sites. From there, following the slope of the land, they collect and drain into the nearest water bodies.

Managing this water run-off can be very beneficial. It would mean increasing the time the water takes to reach the water bodies, the speed with which the water moves towards them, what it carries with it etc.

What is Storm Water Runoff?

Storm water runoff is the volume of water generated by a storm that does not infiltrate into the ground or is not retained in storage as surface water. As the name suggests, it runs off. Runoff flows overland during and following a rainfall, picking up material along the way as it moves downgrade to a river, stream, lake or reservoir. The volume of storm water runoff is related to the amount of impervious surface areas in a watershed. Impervious areas are those areas which do not allow water to seep into the ground. Urbanization and the resulting increase in land area devoted to parking lots, rooftops, and additional roads is the primary source of increases in storm water runoff.

Why Be Concerned with Storm Water Runoff?

Storm water runoff occurs over a very small percentage of the total land area, yet it is responsible for a majority of the surface water pollution. As urbanization occurs, the speed with which a drop of water in a remote area of the watershed can make its way to the receiving surface water (i.e., streams or lakes) is increased considerably. Not only is it quicker for water to flow over paved surfaces versus natural soil, but storm sewers further expedite drainage into the nearest lake or river. A drop of water that used to take hours or days to make its way through a watershed to a channel is now there in a matter of minutes or hours.

Effects of increased storm-water runoff

The increase in storm water runoff has its consequences. The increased speed with which the storm water runoff enters the receiving rivers and streams means that channels flood more frequently in response to relatively small storm events.

This concept is easily illustrated by a stream hydrograph, a measure of the amount or volume of water passing by a point on a stream over time. As seen on the conceptual hydrographs presented in Figure 1, increased runoff causes the volume of water to increase rapidly, pushing the peak discharge of the stream much higher for the same storm event.

The higher the discharge the more power the stream has for erosion, and thus the channel becomes unstable and begins to incise or widen to accommodate the new peak discharge. Unstable channels jeopardize the stability of bridges and other structures located along stream channels.

The same storm event results in two different runoff regimes. Increased development increases the area cove red by impermeable surfaces, so the volume of storm water runoff increases and also reaches its peak volume sooner after the initiation of the runoff event.

Storm water itself is a concern when present in large quantities. Storm water can be detrimental to the environment due to the sheer volume of water that falls into an area.

Stormwater also carries with it many pollutants which eventually reach the different

water bodies and also permeate into the ground. Good stormwater management

practices can eliminate or reduce such pollutants.

Table 2: Common Pollutants in Storm Water

Storm Water Pollutant	Sources	Impacts
Sediment	Construction sites, disturbed areas, streambank erosion, sand treatment of roadways Degradation/wearing of paved surfaces	Accumulates in rivers and reservoirs. Suppresses populations of fish, mussels, and aquatic in-vertebrates. Brings in excessive nutrients which are adsorbed by sediment particles.
Nutrients	Fertilized fields, agricultural applications, leaking sewers and septic tanks	Causes unchecked growth in aquatic systems followed by deadly anoxic conditions. Indicated by unusual algal blooms in lakes and rivers.
Bacteria	Animal waste from cattle, goats etc., leaking sewers, combined sewer overflows	A major health hazard to humans. Destroys recreational potential of waterways, causing economic losses. Increases water treatment costs.
Oil and Grease	Automobiles, industrial areas, illegal dumping, garages and mechanic sheds, petrol bunks, warehouses etc.	Limits the interaction of surface water and air by covering a body of water in a film of oil. Can be deadly to aquatic life and humans in large amounts.
Trace Metals	Automobile wear, exhaust, industrial areas	Are long lived in the environment. Often work their way into the food chain and are passed from one organism to another. Have toxic effects when built up in a system over time.
Road Salt	Roads, parking lots, Home applications	Is lethal to aquatic organisms in high concentrations
Chemicals	Pesticide applications, accidental spills, automobiles, illegal dumping	Lethal to aquatic organisms and often build up in the environment causing problems later on

source

Storm water runoff picks up a variety of pollutants that degrade the quality of surface waters. Sediment is by far the most visible and common pollutant carried by storm water runoff into rivers and streams. Sediment has drastic effects on aquatic life living in the stream and also causes increased dredging and decreased reservoir capacity over the long term. The impacts to our waterways from unchecked storm water runoff are substantial. The consequences are not only biological, but economic as well as aesthetic. Populations of fish and other aquatic organisms decrease, the capacity of the waterbodies to store water decreases, waterbodies get polluted etc.

When I run, I pick up more dirt, I dont get a chance to settle down into the ground.