BOARD01965

• Board Meeting Date: 3/22/2005
• Description: Flood Section - Presentation of the CWCB's Draft Rules and Regulations for Regulatory Floodplains in Colorado
• Board Meetings - Doc Type: Memo

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'{~ 1988 THE PUBLlC RECORD CORPORATION
ALL RiGHTS RESERVED

!lCR1,1-88

F=iage 9

1 evees, at conf1 uence:; with tri butari es, and at all f1 ow
control structures. In genera;, more cross sections are
needed to define energy losses in urban areas than in rural
areas, where steeper slopes are encountered, and on smaller
streams. Based on computed results, addit~ona1 cross
sections may be required if the slope of_the energy 9rade
line between successive cross sections decreases by more
than 50 percent.or increases by more than 100 percent. The
location of the crcss-secti6ns shall be shown on the work
maps.

MaD Accuracy. Vertical map accuracy shall De such that
at least 90 percent Df all contours are within 1/2. of the
contour interval, and the remaining contours are not in
error by more than 1 contour intervi1l.. HOI'izonta1. map
accuracy shall be such that at le~st 90 percent of the
planimetric features are plotted to within 1/40 inch as
measured at the map scale, and the remaining features are
plotted to within l/~O inch.

In areas where the ground is completely obscured by dense
brush or tree cover, .contours shall be plotted as
accurately as possible from the stereoscopic model, while
making full use of spot elevations obtained where the
ground is visible. Spot elevations shall have the same
vertical. and horizontal tolerance as the contours. Where
applicable, the work map shall carry the statement: "This
map complies with National Map Accuracy Standards."

B. Hydrologic Analysis

8..

1. Freouency. The hydrologic ana1ysis shall include, at a
mlnlmum, calculations for the 10-, 50-, and 100-year
frequency flood peak discharges. The Board recommends that
the peak discharge for the SOO-year floOd b~ calculated in
addition to the other discharges.

2. Methodo1oQY. Peak discharges developed .from hydrologic
analysis for floodplain management purposes shall be
determined by one or more of the following methods
depending on the length of systematic records available:
statistical. analysis .or regional regression analysis of
stream gage dat~, including historic flood data;
comparisons with similar watersheds; or flood estimates
using hydrologic models and precipitation records
(synthetic analysis). All available streamflow data from

THE CODE OF COLORADO REGULATIONS

2 CCR 408-1