Agriculture Reference
In-Depth Information
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Figure 8.9
Watersheds delineated on contours adapted from a USGS quad map with arrows showing direction of surface
water flow
In Figure 8.10-A is a rural pond created by the farmer to impound
(store) water for irrigation and farm animals. The pond was formed by
the construction of an earthen dam across the valley floor to capture
rainwater. In effect, the farmer created a watershed that is utilitar-
ian and provides a convenient water source. The rainwater previously
flowed down the valley in a slow-moving stream into a larger stream
several miles away. Hypothetical contours have been drawn of the same
pond scene shown in Figure 8.10-A to help the reader visualize what the
contours might look like in a topographic map.
A watershed is considered a topographic and hydrological phe-
nomenon; however, the concept of creating a closed catchment surface
is commonly used in site grading. The concept of a watershed has been
used in devising a way of collecting and disposing of surface rainwater
on the university campus plaza shown in Figure 8.11. All rainwater that
falls within the dashed outline of the watershed flows to a central catch
basin. Rainwater that falls outside the dashed line flows to other catch
basins or to landscaped areas where the water is collected, or perhaps
allowed to percolate into the soil or be carried by a swale or sheet flow to
some other nearby area.
