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Drainage Design Manual, Hydrology - Flood Control District of ...

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<strong>Drainage</strong> <strong>Design</strong> <strong>Manual</strong> for Maricopa County<br />

<strong>Hydrology</strong>: Application<br />

Using the above procedure, T c as a function <strong>of</strong> i for each <strong>of</strong> the Clark subbasins is as follows:<br />

Subbasin ID Length miles K b Weighted<br />

Adjusted Slope<br />

ft/mi<br />

T c as a<br />

Function <strong>of</strong> i<br />

S2 4.11 0.045 224.5 0.860<br />

S3 3.91 0.021 220.1 0.568<br />

S4 3.40 0.020 197.0 0.534<br />

S5 2.29 0.035 157.5 0.629<br />

S6 2.06 0.033 144.2 0.595<br />

S7 1.74 0.039 214.1 0.527<br />

S8 2.36 0.040 201.6 0.634<br />

S9 1.66 0.035 307.0 0.435<br />

S10 1.83 0.025 294.8 0.389<br />

S11 2.98 0.064 126.3 1.051<br />

d. Develop a subbasin-only HEC-1 model using the 6-hour rainfall data, the procedures<br />

and example from Section 9.1, and the rainfall loss parameters from the procedures<br />

and example in Section 9.3 to compute rainfall excess (HEC-1 output for subbasin S2<br />

follows). Use an estimate for T c . The purpose <strong>of</strong> the model is to compute rainfall<br />

excess, not peak discharge.<br />

Note: For the purpose <strong>of</strong> this example, only the HEC-1 model for subbasin S2 is provided.<br />

e. Sort the incremental rainfall excess values from the HEC-1 output from highest to lowest<br />

and tabulate the ten (10) highest values as follows:<br />

Time, hours &<br />

minutes<br />

Incremental<br />

Excess<br />

Rainfall,<br />

inches<br />

0:00 0.15<br />

0:05 0.15<br />

0:10 0.15<br />

0:15 0.11<br />

0:20 0.11<br />

0:25 0.11<br />

9-54 August 15, 2013

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