53:171 Water Resources Engineering
Problem #4
Areal-Average Precipitation for Ralston Creek (June 1972 storm)
Hourly rainfall data for five stations in the North Branch of Ralston Creek are provided for a flood that occurred on 17-18 July 1972. The areas associated with the five Thiessen polygons are given below.  Use this information to complete are storm analysis for this event.

NumberStationArea
(sq mi)

1

Ruppert0.641

2

Donovan0.482

3

Hunter0.819

4

Larsen0.638

5

Kessler0.430

  1. Create the Thiessen polygons for the watershed.
  2. Estimate the areal average rainfall (in inches) for each hour using the arithmetic average method.
  3. Compute the Thiessen Polygon weights (wi).
  4. Compute the areal average rainfall (in inches) for each hour using the Thiessen polygon method and the total storm precipitation for the drainage basin (Use a spreadsheet if you'd like).
  5. Plot the the areal average rainfall (in inches) computed using the Thiessen polygon method (part d) versus time (A bar graph looks best. Note that this is commonly referred to as the incremental rainfall hyetograph).
Last changed on 01/30/14 by Gabriele Villarini.