FLOOD01902

• County: Pitkin
• Community: Aspen
• Title: Drainage Facility Capacity Analysis of City of Aspen
• Date: 9/1/1998
• Prepared For: Aspen
• Prepared By: WRC Engineering, Inc.
• Floodplain - Doc Type: Project

hourly temperature over the course of a day, The energy-budget method requires

values of shortwave radiation, the dewpointtemperature, and wind speed overtime.

b. Theory
The degree-day method of estimating snowmelt used by HEC-l incorporates the
following equation:

Snowmelt = C *(Temp - 32"F)

(8)

Where:

C

=

0,07

Temp, =

Air Temperature

HEC-l is capable of using several different types of synthetic unithydrographs, For

this study the Soil Conservation Service (SCS) dimensionless unit hydrograph

method was chosen. The time-to-peak and the peak flow are calculated as follows:

T, = 05* ~t+ TLAG

(9)

Where:

T,
At

=

Time to peak of unit hydrograph
Duration of excess rainfall

=

TLAG

=

0.6 * T c = Lag between the center of
mass of the excess rainfall and the peak
of the unit hydro graph,
Time of concentration

T,

=

A
Q, = 484*-
T,

(10)

Where:

Qp
A

=

Peak flow of the unit hydro graph
Sub-basin Area

=

c, Input Data

The temperature data used by the model was based on actual temperature data

recorded on Aspen Mountain and recovered from the Colorado Climate Center

via the Internet. Two recording stations have been located on Aspen Mountain.

Station 50370 (Aspen) recorded from 1900 to 1979, and climatic data collected

from 1980 to 1997 from the second station, 50372 (Aspen 1 SW), was also used.

This data was combined for this study, The mean monthly maximwn

18