FLOOD01787

• County: Boulder
• Stream Name: South Boulder Creek
• Title: South Boulder Creek/ Flatirons
• Date: 12/5/1997
• Prepared For: Boulder
• Prepared By: Consultants
• Floodplain - Doc Type: Community File

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Table 111-1

HYDROLOGY PARAMETER COMPARISON
1977 CORPS' INVESTIGATION VERSUS CURRENT LOCAL PRACTICE

Item Corps' Boulder and Boulder and UDFCD Effect If Boulder and
South Boulder Creek Manual or Other Local UDFCD Values Would
Studies Studies Be Used
6 hour Rainfall Values' 2.8 to 3.8 inches Same magnitude None
1 hour Rainfall Values' 1.4 to 1.9 inches 2.14 to 2.7 inches Significant increase in
peak flow and volume
Peak Rainfall Intensity 30 minute increment at 5 minute increment at Significant increase of
intensity of 2.7 intensity of greater flow in local tributaries,
inches/hour than 8.0 inches/hour small effects on main
stream because of
timing and routing
Percentage Impervious 5% 25 to 50 % Increase peak flow
from urban areas in
particular
Impervious Area 0.3 inches 0.05 to 0.10 inches Minor increase, mainly
Detention (by ground volume
surface depressions)
Mountain Infiltration 1.0 inches steady state Not reviewed Not reviewed
Urban Infiltration 0.5 inches steady state 3 inches per hour Would reduce volume
decaying to steady of runoff
state 0.5 inches

. Before Area Reduction Factors or Expected Probability Corrections.

Review of the Corps' sensitivity studies along Boulder Creek through Boulder to
above South Boulder Creek indicate the magnitude of variation for various
parameters given in Table 111-2.

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