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<br />Dolores River near Dolores, Colorado
<br />Flood Insurance Study
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<br />HYDROLOGY REPORT
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<br />Table of Contents
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<br />I. Purpose.......... ..., .......... ............ ,... ............ ... ........., ............... ........... ................... ,..,.., I
<br />2, Scope. ............ ............... .." ........... ,. ,............., ......... ....... ......... .,., ............. .......... I
<br />J. Summary.............. .........." ................. ............ .......... ...... ........ ..... ....... ,..., ................... 2
<br />4. References .............." ..........,. .............." ............ ......... ................... .........,. .., ............... 3
<br />5. Descriptive Information ...........,...........,.........................,...........",...,..,................... 5
<br />5. I General Characteristics ...., ............. ..........., ...... ........ ............ ........... ................ 5
<br />5.2 Topography.. ...""..""."".. .".........",... .""".. ......,. ....", .....""". ."............ .....,.... 7
<br />5.3 Geology and Soils............................,........"............................,............., 8
<br />5,4 Climate ....... ,. ............ ..............., ............ ......", ...., ......... ... .......... ...................,.. 8
<br />5.5 Precipitation,. .............., .............. .................... ........, ......... .." .......... ................. 9
<br />5.6 Storm and Flood Characteristics..........................."........................................ 11
<br />5.7 Flood llistory ......".. ........., ............, ............ ..................................................... 14
<br />6, Ilistorical Flood Analysis and Model Development...,............................................. 15
<br />6.1 Ilydrologic Analysis - General.........._......,................,.........._......................... 15
<br />6,2 Previous Model Development.. ............ .......... ......_....... ........... ,............... ,._.,... 16
<br />6.3 Current Flood Insurance Study ModeL,.....................................,.,................. 16
<br />6.4 Loss Rates .......... ..., .......n' ............, ......................... ,......................." ............... 18
<br />6.5 Base Flow ..............................................."..........."...,...........18
<br />6.6 Unit Hydrograph for Historic Flood Reproduction .........................,............19
<br />6.7 Stream Routing Parameters...... .................... ......._....... .......... ................., ..." ... 20
<br />6.8 Precipitation Used for 1970 Flood Reproduction .................."....................... 22
<br />6.9 Model Validation for Flood Simulation.........................,................................ 23
<br />7. Modeling the 1% Flood Evenl..............,..........,......................................,................. 24
<br />7.1 Previous Stoml Modeling ...............,.............................................,................24
<br />7.2 1% Chance Precipitation Data ....................................................................... 24
<br />7_3 Stoml Centerings .................... ........................., ................................ ,.... ,.., ,... 25
<br />7.4 Storm Distribution .........................................................................................26
<br />7.5 IIMS Basin Parameters for 1% Stonn ........................................................... 27
<br />7.6 1% Flood Hydrographs,...."................"..""""""........""....."".."........."""", 28
<br />8. Flo\\-. Frequency Analysis ............,......................................................"....................28
<br />8.1 Upper Dolores Basin StrcamOow Records................................."................. 28
<br />8,2 Rainflood and Snowmelt Records ................................................................. 29
<br />8.3 Flood Frequency Analysis ................_......_.....................................................31
<br />8.4 Flo\\,' Frequency Curves .........__...........,.......,.........................................,........ 32
<br />8.5 Flow Comparison - HMS Model and Flow Frequency Records ................... 33
<br />9. 10/0 Peak Flo\v Comparison....................................................................................... 35
<br />10. McPhee Reservoir ...........................................,....................................................... 38
<br />10.1 Hypothetical Routings of Historic Floods ................................................... 40
<br />10.2 Hypothetical Routings of 1% Chance Rainflood............u........................... 42
<br />II. Conclusions............ .......................... ._....... ......... ..................................,.. ................. 37
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