FLOOD08228

• County: Boulder
• Community: Boulder
• Stream Name: Boulder Creek
• Basin: South Platte
• Title: Urban Drainage and Flood Control District
• Date: 3/1/1990
• Prepared For: Boulder Creek
• Prepared By: Goerge V. Sabol
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

f:,
f
fl
f1
fJ
fJ
f
fl
f1
f
f\
I!
Ii
i1
i1
i

~

I
'i
il

Hydrologic Design Manual
for Maricopa County

Rainfall Losses

6. Determine the land-use and/or soil cover for the drainage area and use
Table 4.1 to estimate the surface retention loss (IA).

B. When soils data are not available:

1. Estimate the CN based on data for similar watersheds or regional ex-
perience. Estimate the percent vegetation cover.

2. Use Figure4.11 to estimate XKSAT based on CN and hydrologic condition.

3. Use Figure 4.11 to estimate XKSA T for bare ground.

4. Use the bare ground XKSAT and Figure 4.12 to estimate PSIF.

5. Use the bare ground XKSA T and PSIF with Table 4.2 to estimate DTHET A.

C. Alternative methods:

As an alternative to the above procedures, Green and Ampt loss rate
parameters can be estimated by reconstitution of recorded rainfall-runoff
events on the drainage area or hydrologically similar watersheds, or
parameters can be estimated by use of rainfall simulators in field experiments.
Plans and procedures for estimating Green and Ampt loss rate parameters by.
either of these procedures should be approved by the Flood Control District
and the local agency before initiating these procedures.

4,5.2 Initial Loss Plus Uniform Loss Rate Method
A, When soils data are available:

1. Determine the soil texture classification and/ or the hydrologic soil group.
Soils reports such as those of the Soil Conservation Service can be used if
available, or laboratory analysis of appropriate soil samples from the
drainage area can be used to classify the soil if adequate documentation
on the sampling and laboratory procedure is provided and approved.

2. Use values of CNSTL and IL from Table 4.3 if the losses are to be based on
soil texture classification.

3. Use values of CNSTL and lL from Table 4.4 if the losses are to be based on
hydrologic soil group.

4. Determine the land-use and/ or soil cover and use Table 4.1 to estimate the
surface retention loss (IA).

5. STRTL = IA + lL.

_:-;1'#';~.;.;.:,};<<<<-},..;.;.;.;<<{~;.;.>;;.~-x-:-x-",*;.;.:.;.>>};.:.;.;{-:-:.~:.;.}:.:.;,:,:-~;,>=<<,~:-;,;.:*::.;,;,,,,:_,;,:,;,;,;,;';'>>;';f;';-}:-;':':';.>>;';':.;':',;.};.:,;.;.;.:-..--:.;.:<:.",.;t:-;.;~_>>w.'=-';.;:-:-:.;.:.>>;.;.;.:-;.;x;.:.;..N;':-}~M<<-:W;.f;.>>*.---:-;;}:_:.:-:-
65