In the ecology and management of the North Pond our main goals were to determine the watershed and the bathymetry. This includes dimensions of the pond, land use of the surrounding area and drainage patterns. Watershed is the total area of drainage that leads to a river or a body of water. In studying the watershed and its drainage we also determined the bathymetry to help us determine the total area and dimensions of North Pond. Our first step was to determine where and how big of an area the water was coming from, entering the North Pond. We were also trying to figure out if the depth of the pond was increasing or decreasing and the reason for its change (if there was any at all) And finally, we were trying to figure out the dimensions of the pond at high water level to see if the bulge in the 1998 pond dimensions connect with the body of water to the west. We intended to accomplish finding the specific area and watershed of the pond.
On September 20, 1998 at 1300 hours we began our study by observing North Pond and its surrounding area, which is located in the Calvin College Ecosystem Preserve. In 1989 the water level was just below the cement blocks that support the deck. The first day of our study we measured the water level to be 2 inches above the top of the cement support. We routinely measured the water level with a tape measure on the cement deck supports. Our next step was to obtain a topographic map of the Calvin College Ecosystem Preserve. We met with the Calvin College architect, Frank Gorman, who provided us with a suitable map that had contour lines for determining the flow pathways of surface water leading to the North Pond area.
On November 7,1998 at 1050 hours we took the canoe out to take measurements of the pond depths using the secchi disk on a marked string showing measurements in decimeters. We first dropped the anchor to keep us from drifting due to the wind. We selected six locations that corresponded to the locations on the Bathymetry map of 1989 to see if there was any significant change in the water level of the pond. After determining the depths of the six locations selected, we walked around the pond westward to see if North Pond connected to the neighboring body of water, at the ponds high water level mark. Using the maps provided by the college architect, we applied hydrologic principles of water flow in drawing arrows from the contour lines showing the directional flow. To verify the water flow paths we walked around the area of our determined watershed. After drawing out our watershed area on the topographic map, we used the planimeter manufactured by Leitz model number 3651-30, to determine the area of the watershed and the pond areas from 1989 and 1998. The planimeter is a tabletop device that measures the area by tracing the perimeter of the areas of the watershed and the ponds on the map giving us a scale that can be calculated into the actual area.
In our study, using the planimeter, we determined the watershed of North Pond to be 860,857.96 square feet We also determined the areas of the pond in 1989 to be 64,671.12 square feet and in 1998 it was measured to be 156,186.85 square feet . The total change in the surface area of the pond is 91,515.73 square feet In comparing the bathymetry of the pond in 1989 to 1998 the water level rose three decimeters.
For 7 consecutive days (October 5-1 1), we measured the water level compared to the cement supports of the deck. The water levels correlated to the amount of precipitation or rainfall. Within that week the water level rose from being 3/4 of an inch above the cement to 2 1/2 inches above the cement. When looking at the fall, 1998 weather summary we find that 58mm (2.28 inches) of rainfall fell during that week.
The 1998 North pond has the same basic shape as it did in 1989, except at high water level it spills over and connects with the small pond northwest of it and a shallow bulge is formed towards the west. We found that it does not connect with the body of water to its west.
The water inputs in North Pond have remained the same the past ten years, but the water level has been steadily increasing due to a clogged main sewer drain. Rainwater that lands in the North Pond watershed is a 19.76 acre area almost entirely to the east of North Pond. This area drains to the west and flows over privately owned property on its way to the pond. This could potentially cause a problem if the private landowner introduced pollutants into the watershed from his backyard. North Pond is essentially a retention basin, a low area where the flowing groundwater connects. The only way water can leave this system is through ground water seepage, or evaporation. Because of the steady increase in spring water level, North Pond has joined a small pond to the northwest at high water level. If the water level continues to rise, it will overflow its current boundaries and encompass the body, of water northwest of the pond. This season, we concluded that it came close to connecting but did not quite reach. Our evidence for the boundary of how far the bulge went was the boundary line between the tall grass and matted vegetation. We also found mudcracks that had formed as the water receded and the soil dried up. We came to the assumption that the map of North Pond from 1989 was a typical representation of the area year round. The shape could remain constant because the sewer drain was cleaned out every year allowing for excess water to drain quickly. But, the spring 1998 map was larger because the sewer drain has been clogged with muck, leaves, mud, sticks, etc. and has not been cleaned out. The North Pond has become seasonal in its water level with high spring levels as the snow melts and spring rain, and low levels in the hot, dry, summer. This seasonal aspect of North Pond could affect the bordering vegetation.
Figure 1. click on image to view full size. Only figure 1 is available
Watershed of North Pond. Arrows indicate the drainage pathways.