FLOOD05142

• County: Dolores
• Community: Rico
• Basin: San Juan/Dolores
• Title: Floodplain Information Report
• Date: 9/1/2000
• Prepared For: Rico
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
I

Table 1-2. Peak Discharges and Area-discharge Data for this Study
Area (A) Peak Discharge, Q (cfs)
Location (sq mi) lOO-year Q/A 500. year Q/A QoooIQUlO
Dolores River 85 2800 33 6000 71 2.1
at Rico
Dolores River 105 2655 25 3183 30 1.2
below Rico
freq. analysis
Scotch Creek 11 400 36 700 63 1.7
Silver Creek 7 350 50 500 71 1.4

Hydraulic Analyses

Water surface profiles were computed using the Army Corp of Engineers' HEC-2
computer program (ref. 8). The iterative program applies the standard step method to
solve energy and head-loss equations for one-dimensional steady or gradually varied
flow. Subcritica1 conditions were assumed.

Cross-section geometry for this study was determined from recent 1: 1 ,200 scale
topographic maps with 2-foot contour intervals (ref. 9). The data was refined and
verified by field measurements. Bridges and culverts were measured in the field.
Cross section locations are indicated by flood water elevations on the flood map.

Initially, Manning's roughness coefficients ("n-values") were estimated based on field
observations and standard ranges of values (ref. 10). However, due to the high
gradients of the channels, roughness coefficients were adjusted to conform with data
from similar high-gradient streams in Colorado (ref. 11). The previous study found a
strong correlation between slope and hydraulic radius with roughness for high-gradient

4