Lab:  Color Me A Water Table

Color Me a Watershed



 Background:  Learning about the past helps us with our current perspectives and helps us plan for the future.  Historical, sequential maps provide graphic interpretations of watershed history.  By comparing past and current land-use practices, we can recognize trends in development.  This knowledge can help us appreciate the importance of watershed management.


Resource managers and policy makers use maps to monitor land-use changes that could contribute to increased amounts of runoff flowing into a river.  Vast amounts of public and private time, energy, and money have been invested in research projects that were specifically designed to collect land-use data.  Land uses that are monitored include urban (residential, parks, & businesses); agriculture (pastures and production of corn, soybean, wheat, sunflower, tomato, pineapple and lettuce); industry; transportation systems (roads, railroads, and trails); and public lands (refuges, parks & monuments).


Land-use changes can have significant effect on a region’s water resources.  Streams, lakes, and other bodies of water collect water drained from the surrounding land area, called a watershed or drainage basin.  After periods of precipitation or during snowmelt, surface water is captured by the soil and vegetation, stored in ground water and in plants, and slowly released into the collection site, i.e. a stream.

Resource managers are developing and using Geographic Information Systems (GIS) to store data and to generate land-use maps electronically.  Although the process of collecting the data is tedious work, generating usable maps and map overlays is significantly eased by technology.  For example, a water manager could generate a map that shows a river’s watershed and major tributaries, the floodplains, and the locations of urban dwellings (homes and businesses), displaying areas likely to be affected by floods.  This information is valuable to local governments, planners, realtors, bankers, homeowners, and others.  The map could also be compared to similar land-use maps from 10, 20, or 30 years ago.

One way that watershed managers study drainage basins is by measuring stream flow.  Determining how much water a watershed discharges usually involves measuring the amount of water (volume) that flows past a certain point over a period of time (velocity).  Stream flow is measured in cubic feet per second (cfs) or cubic meters per second (cms).

By measuring the amount of water flowing through a stream channel over a period of years, scientists can calculate the average stream flow.  When stream flow changes significantly from its normal qualities, watershed managers investigate the reason for the change.  The amount of water discharged by a watershed is influenced by soil conditions, vegetative coverings, and human settlement patterns.  Wetlands, forests, and prairies can capture and store more water than can paved roads and parking lots.  So, urban areas will have more runoff than areas covered with vegetation.

Water managers carefully assess land-use changes and set development policy accordingly.  For example, in areas that are susceptible to erosion, the incorporation of soil conservation measures (planting cover crops on farmland and establishing grassed waterways) can significantly reduce erosion and stream sediment load.  Managers may designate lands so highly susceptible to erosion that landowners are required to plant vegetation on them.  Local urban governments may set aside natural areas to serve as filters for runoff storm water after they examine runoff data and problems of stream water quality.  In each situation, using maps to understand past and present land use helps scientists and managers better predict future problems.


Color Me a Watershed Updated2

© lbranch 2013