Exercise 3:



Homework 1

Fluxes, Flows and Volumes

#1

Make a plot of the discharge at the five stations for this period

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#2

At a daily time interval, calculate the cumulative volume (acre-ft), incremental volume (acre-ft) and the daily mean discharge (cfs) for each gage for the period of record.

Cumulative volume is calculated by multiplying the average instantaneous flow over the time interval by the length of the timestep and adding it to the previous value. For i = 1, 2, ….

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Incremental volume is calculated for each timestep (daily in this case) by subtracting the cumulative volume from the previous timestep (previous day).

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Daily mean discharge in cfs is calculated by dividing the total volume over the timestep by the total time of the timestep (daily) and converting to the proper units.

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#3

Calculate the runoff in mm/day occurring in each subwatershed for the period of record (i.e. the daily value of runoff coming from the subwatershed into the stream system for each day, Jan 1 through Jan 10)

For each watershed, a “horizontal” water balance is first performed to calculate the amount of water contributed by the watershed as opposed to upstream rivers. For Blanco @ Wimberley, Plum Creek at Lockhart, and San Marcos at San Marcos, this is trivial as there are no upstream contributors. For the other gauges, the incremental inflows must be subtracted from the incremental outflows to get the cumulative volume contributed from the watershed over this timestep.

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The cumulative volume contributed from the local watershed must be divided by the area of each watershed to get the implied runoff from the watershed for each interval

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