FLOOD10395 ‎(2)‎

• County: Montezuma
• Community: Dolores
• Stream Name: Dolores River
• Title: Dolores River near Dolores, Colorado, Flood Insurance Study
• Date: 5/1/2004
• Prepared For: Dolores
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

e,1

Dolores River near Dolores, Colorado
Flood Insurance Study

HYDROLOGY REPORT

Table of Contents

-'

1. Purpose................................. .... ......... ............................ ............................. ............... 1

2. Scope............................................................... .......................................................... 1

3. Summary.. .. .. . . . .. .. .. . . .. .. .. . .. .. .. .. .. .. . .. .. .. .. . . . .. .. . .... . . . .. .. .. .. . .. .. .. .. .. .. . .... .. .. .. .. . .. ... . .. ... .. .. .. .. . 2

4. References........... .... ................................. ............................... .................................. 3

5. Descriptive Information .................................................................................. ........ 5
5.1 General Characteristics............................................ ........... .................... ........ 5

5.2 Topography..................................................................................................... 7

5.3 Geology and Soils........................................................................................... 8

5.4 Climate ............................................ ............................................. .................. 8

5.5 Precipitation..................... .................................... ...................................... ..... 9

5.6 Storm and Flood Characteristics..................................................................... 11

5.7 Flood History.................................................................................................. 14

6. Historical Flood Analysis and Model Development................................................. 15
6.1 Hydrologic Analysis - General....................................................................... 15
6.2 Previous Model Development........... ..... .............. ......... ..................... ............. 16
6.3 Current Flood Insurance Study ModeL.......................................................... 16

6.4 Loss Rates..................... ..................................... ............... .... .......................... 18

6.5 Base Flow . ............................................................................. 18

6.6 Unit Hydrograph for Historic Flood Reproduction ...................................... 19
6.7 Stream Routing Parameters....................... ................... .............................. ..... 20
6.8 Precipitation Used for 1970 Flood Reproduction ........................................... 22
6.9 Model Validation for Flood Simulation.......................................................... 23
7. Modeling the 1 % Flood Event .................................................................................. 24
7.1 Previous Storm Modeling ....... ......... .............................. ................... ............. 24
7.2 1% Chance Precipitation Data ....................................................................... 24

7.3 Storm Centerings ............................. ........ ................... ................ ........ ........... 25

7.4 Storm Distribution ................ ................................ .......... ........... ............. ....... 26
7.5 HMS Basin Parameters for 1 % Storm ........................................................... 27
7.6 1 % Flood Hydrographs.... .......... ............. ............................ ........................... 28
8: Flow Frequency Analysis........... .............................................................................. 28
8.1 Upper Dolores Basin Streamflow Records ....................................................28
8.2 Rainflood and Snowmelt Records .................................................................29
8.3 Flood Frequency Analysis ............................................................................. 31
8.4 Flow Frequency Curves..... ......... ............. ........................ ............... ............... 32
8.5 Flow Comparison - HMS Model and Flow Frequency Records ................... 33
9. 1 % Peak Flow Comparison.... ............... ........... ........................................ ................. 35

10. McPhee Reservoir ................................................................................................... 38

. 10.1 Hypothetical Routings of Historic Floods ................................................... 40
10.2 Hypothetical Routings of 1 % Chance Rainflood......................................... 42

11. Conclusions.............................................................................................................. 37

e

1