Pond Study CSS version

Pond Watersheds


       The watershed (= catchment, or drainage basin) of a pond consists of land which conveys surface runoff and groundwater in the direction of the pond (Fig. 15). The boundary of the watershed (shown as a blue line) is usually determined from a topographic map as the set of ridges or other high ground surrounding the pond. The watershed shown in Figure 15 has moderately steep slopes surrounding the pond. The steepness and vegetation cover of land directly surrounding the pond help determine inputs of sediments and nutrients, and thus strongly affect pond infilling and susceptibility to excessive plant/algal growth (see Sections J and U below).
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Fig. 15. The watershed of a pond in East Nantmeal Township, showing 30-m elevational contours.


        The size of the watershed relative to the size of the pond itself can be a useful index of land use impacts; ponds with higher ratios of watershed areas (Ad) to pond area (As) may be especially prone to inputs of nutrients and other materials and are often hyper-eutrophic as a consequence. An example of the relationship of watershed area to pond area for local ponds (Fairchild et al. 2005) is shown in Figure 16. Some ponds had very large watersheds relative to their size, falling below and to the right of the regression line in the figure (e.g., HH), while others had very small watersheds relative to their size, and fall above and to the left of the regression line (e.g., NH). In general, ponds nearer the upper left of the diagram are expected to be less prone to sediment infilling and/or algal/weed proliferation stimulated by excessive nutrients.
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Fig. 16. Pond area (As) vs. watershed area (Ad) for 13 ponds in Chester County. Ponds more likely to be negatively impacted by excessive nutrient loading from their watersheds are located below and to the right of the line of best fit (e.g., HH), while better protected ponds are located at the upper left (e.g., NH).