Montgomery Soil and Water Conservation District
Helping People and Communities Care for Land and Water
Just like human society has political boundaries (city, township, county, etc.), nature has boundaries too. Unlike the typical straight lines dividing counties or states, natural boundaries are determined by the shape of the land (topography).
The land area that drains into a particular stream, river or lake is called a watershed. Both surface and (under) ground water flow to the lowest elevation in its watershed. Streams are often connected to ground water.
Many human activities can alter the flow, amount, and quality of surface or ground water within a watershed. The most drastic alteration involves construction of buildings, roads, and other hard surfaces that increase the amount of surface runoff. Artificial storm water systems are then designed to direct the flow of surface waters through a system of pipes, culverts, ditches, etc. This flow, known as storm water runoff, is eventually delivered directly to streams and rivers, without treatment of the water to remove pollutants, referred to as Nonpoint Source (NPS). NPS pollutants include nitrates (from fertilizers, leaking sewer pipes, failing septic systems), petroleum products from automobiles, road salt, and heavy metals from automobile brake linings. The term nonpoint means that it comes from many sources instead of a single identifiable location such as a pipe from a factory.
The idealized drawing below will help you visualize the three-dimensional aspect of a watershed: