Questions about Schoharie Reservoir 1. The current mean residence time of the Sc
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Questions about Schoharie Reservoir
1. The current mean residence time of the Schoharie Reservoir is about 55 days. Water input into the reservoir can come from precipitation directly onto the reservoir surface or from runoff originating from the surrounding watershed. Considering the current residence time, which contribution (inflow from watershed or direct precipitation) is likely to be larger? Justify your answer by considering the typical precipitation amounts in this region (you can find typical precipitation amounts in Larry Mays book Figure 7.2.5). [Tip: One way to approach this is to assume that the only input comes from precipitation under steady state conditions and test what residence time you would get]
2. (A by-hand watershed delineation exercise) Assume that your firm is building an open reservoir type rainwater harvesting system next to Route 322 in Worth Township, Center County along Laurel Run. Figure 3 shows the location along the stream where it should be located. In order to correctly size the reservoir, you must calculate the amount of water that will flow into the reservoir from the watershed. The first step is therefore to determine the area of land that drains to that point. Delineate the watershed boundary upstream of the Stream Crossing. You do not need to calculate the area of the watershed, just determine the boundary by plotting it on Figure 3.
Proposed Stream Crossing N033 ORTH Figure-3: Port Matilda & Sandy Ridge USGS 7.5 minute series quadrangles available at www.pasda psu.eduExplanation / Answer
1. Residence time is the average time that a substance spends in a physical system: the substance can be any particle flowing with water. So , this indicates the time between the inflow and outflow of water at an instant of time.
given, Current mean Residence Time = (Resevoir Volume/ Amount of inflow or outflow ) = 55days
volume = 74.2x106 m3 , inflow = from( direct precipitaion + runoff)
assume a steady direct precipitation of 2mm , then volume of direct precipitation = 4.9x106 x 0.002x365 = 23577000m3 / day
Current Residence Time = (74.2x106 m3 / 3577000m3 / day) = 21 days
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