WSP12495

• File Number: 8221.109
• Description: Colorado River Basin Projects - Long Hollow
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 9/1/2003
• Author: Wright Water Engineers - Ecosphere
• Title: Long Hollow Reservoir - Feasibility Study-Biological Assessment and Addendum
• Water Supply Pro - Doc Type: Publication

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TABLE OF CONTENTS

Page

0.0 EXECUTIVE SUMMARy...... ............................ .......... ............. ................. ....... ................1

1.0 INTRODUCTION................................. ......... ................................................................... 7

2.0 PROJ ECT LOCATION ............................... ..................... ................. ......... .......... ............ 7

3.0 PURPOSE AND NEED ....... ............................ ......... ......... ..................... .........................8

4.0

PROJECT DEseRI PTION ....................... .............................. ......................... .............. 10

4.1 Reservoir Construction................................... ~................................... ............................... 12
4.1.1 Dam Foundation.............. ...................................................................................12
4.1.2 Embankment Design ............. ......... .......... .............. ............ ............. ...... ........ .... .12
4.1.3 Outlet Works Tunnel..........................................................................................13
4.1 .4 Emergency Spillway.. ........................... ............... ............................................... 13
4.1 .5 Reservoir Area........... .................................................. ............................. .........13
4.1.6 On-Site Borrow Sources ....................................................................................13

4. 1 . 7 Topsoil... ......................................... .. ......... ................ .... ..... ................................ 14

4.1 .8 Schedule..................................................................................................... .......14

5.0

DEPLETIONS ANALYSIS ... .......................... ........................ ........................ ............... 14

5.1 La Plata River Flow Characteristics...................................................................................14
5.2 La Plata River Flow Model.................................................................................................15
5.3 Depletions Attributable to Long Hollow Reservoir .............................................................16

6.0

CHANGE IN STREAM FLOWS ....................................................................................17

7.0

RESERVOI R OPERATIONS............. ........................ ..................................... ............... 18

AL TERNA riVES............ ........... ............... ......... ............ ............ ....... ............. ....... ......... 18

8.0

9.0

PROJ ECT AREA ENVIRONMENT ... ..... ........ ...... ................. ....................... ................. 19

9.1 Topography....... ............ ................................................. .............. ........ ..... ...... ................... 19

9.2 Geology ............................................................................................................................. 19

9.2.1 Bedrock........................................................................................................... ...20

9.2.2 Valley Bottom Alluvium and Alluvial Fans ..........................................................20

9.3 Hydrology.......................................................................................................................... .21

9.4 Groundwater...................................................................................................................... 21

9.5 Surface Water.....................................:............................................................................. .21

9.6 Soils................................ ......... ......................................................................................... .22

9.6.1 Fluvaquents, Sandy, Frequently Flooded ..........................................................22
9.6.2 42-Lazear-Rock Outcrop Complex, 12 to 65 Percent Slopes ............................22
9.6.3 44-Mikim Loam, 3 to 12 Percent Slopes ............................................................23
9.6.4 48-Panitchen-Dominguez Variant Silty Clay Loams ..........................................23
9.6.5 70-Ustic Torriorhents-Ustollic Haplargids Complex, 12 to 60 Percent S/opes...23
9.6.6 73-Vernal-Sedillo Complex, 3 to 12 Percent Slopes ..........................................24
9.6.7 76-Witt Loam, 3 to 8 Percent Slopes .................................................................24
9.6.8 81-2yme Clay Loam, 3 to 25 Percent Slopes ....................................................24