What is a Watershed?
Overland flow moves only a short distance over the ground before it gathers into minute threads of water. These threads merge with one another, forming rivulets capable of eroding soil and shaping a small channel. This system of channels is called a drainage network, and it represents nature’s most effective means of getting water off the lands. The area feeding water into the drainage network is the drainage basin, or watershed.
Modern land development often alters drainage networks by altering natural channels, and man-made channels, or by changing the size of drainage basins. Deforestation, agriculture, and land development may initiate soil erosion, gully formation, and expansion of the drainage network. Discharges are in turn larger, higher flows occur with more frequency, erosion is greater, and water quality can be expected to decline.
Primer on Hydrology
Dick Ford, former manager of the Lake Association, offers this brief primer on hydrology
The basic hydrologic cycle consists of rainfall, runoff, recharge, evaporation, and condensation. Rainfall on natural undisturbed soils becomes surface runoff or ground/soil water recharge, from which evaporation and transpiration losses to the atmosphere are driven by the Sun’s energy. Surface runoff is readily apparent for a brief period after a rainfall. Local water bodies rise and fall as the runoff flows through the watershed. Groundwater recharge however is not as readily apparent. Water is absorbed like a sponge by the soil and transmitted downward into saturated formations referred to as ground water aquifers. Aquifers are often interconnected with water bodies. Unlike surface runoff, ground water flows more slowly discharging over time into surrounding streams and lakes. Groundwater discharge guarantees that streams and lakes will be able to maintain year-round flows and levels, not surface runoff.
Cazenovia Lake has few significant year-round tributaries contributing surface water inflows to the lake. In addition to outflows to Chittenango Creek, Carpenters Pond, irrigation, and domestic water intakes, about one-half of the annual rainfall within the watershed is lost to surface water evaporation and vegetative transpiration. The most important source of water available to sustain the lake level is groundwater. Without sufficient groundwater recharge, there would be insufficient groundwater discharge to sustain the lake during periods of low rainfall.
As the Cazenovia Lake watershed is developed and subjected to ever increasing human activity, the watershed is becoming less pervious to groundwater recharge and more susceptible to storm water runoff. Every new roof and driveway, parking lot and road removes another square foot of potential groundwater recharge for our lake, our streams, and our wells. We need to mitigate and manage human activity in order to protect our lake, its watershed, and aquifers.