FLOOD06564

• County: Boulder
• Community: Boulder
• Stream Name: Goose, Wonderland, Elmer's Twomile, 2-mile, 4-mile
• Basin: South Platte
• Title: Major Drainageway Planning Volume 1, Part B
• Date: 4/1/1969
• Prepared For: Boulder County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

14

RAINFALL

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The lOa-year design rainfall was determined from the nine isohyetal
maps presented in the Rainfal I Part of the DRCOG Storm Drainage
Criteria Manual, Figure IV-I is the Depth-Duration-Frequency curve
for the North Boulder area for the 2, 25, 50, and lOa-year storms,
Table IV-I tabulates the lOa-year storm from Figure IV-I. The last
column in the table represents the rearranged rainfall increments that
were used for design purposes.

TABLE IV-l
NORTH BOULDER lOa-YEAR DESIGN RAINFALL
Total Incremental Design
Rainfall Rainfall Rainfal I
,00 ,00 .00
1.37 1.37 .02
1.82 .45 ,04
2.18 ,36 .07
2.30 .12 .12
2,40 ,10 1.37
2,50 ,10 .45
2.57 ,07 .36
2.64 ,07 .10
2,69 ,05 .10
2,74 ,05 .07
2.78 ,04 .05
2,82 ,04 .05
2.86 .04 .04
2.90 .04 .04
2,94 ,04 .04
2,96 .02 ,04
2.98 ,02 ,02
3,00 ~ ,02
3.00 3.00

Time from
Beginning of
Storm

o
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180

TOTALS

Infiltration

Part of the rainfall that occurs infiltrates into the ground and does
not become part of the immediate storm runoff. As North Boulder
develops the overall infiltration rate will change because large
areas will become impervious due to building and paving, and other
areas will change from pasture to lawn grass. In some cases, the
infiltration will increase, and in other cases it will decrease.

The infiltration rates used in this study are based on the probable
future land cover. To obtain these rates, numerous field infiltration