C150094 Feasibility Study

• Contract/PO #: C150094
• Contractor Name: La Plata Water Conservancy District
• Contract Type: Grant
• Water District: 0
• County: La Plata
• Bill Number: HB02-1152
• Loan Projects - Doc Type: Feasibility Study

TABLE OF CONTENTS
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1.0 EXECUTIVE SUMMARY ................................................................................................1
2.0 PROJECT DESCRIPTION AND PURPOSE ................................................................7
2.1 Project Location and Description .........................................................................................7
2.2 Project Purpose ...................................................................................................................8
2.3 Study Objective ....................................................................................................................9
3.0 DESIGN DATA .....................................................................................:.......................11
3.1 Topography and Feasibility Level Study Drawings .................................:..........................11
3.2 Reservoir Inflow ................................................................................................................ .12
3.2.1 Water Rights ......................................................................................................12
32.2 Surface Water ..:................................................................................................. 12
3.2.3 Groundwater Recharge ...................................................................................... 14
3.3 Dam Hazard and Size Classification .................................................................................15
3.4 Hydrology ................................................................................. .....................16
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3.4.1 Background ........................................................................................................ 16
3.4.2 Probable Maximum Precipitation .....:................................................................. 16
3.4.3 Unit Hydrographs ............................................................................................... 17
3.4.4 HEC-1 Rainfall Runoff Simulations .................................................................... 19
3.5 Outlet Operating Criteria .................................................................................................... 21
3.6 Engineering Geology ......................................................................................................... 21
3.7 Geotechnicallnvestigation ................................................................................................. 22
4.0 INSTITUTIONAL ASPECTS ......................................................................................... 28
4.1 National Environment Protection Act ................................................................................. 28
4.2 Threatened and Endangered Species ............................................................................... 28
4.2.1 Federally Listed Species Considered and Evaluated ......................................... 28
4.2.2 Sensitive Species ............................................................................................... 30
4.2.3 San Juan River Basin Recovery Implementation Plan ....................................... 31
4.2.4 Summary of Conclusions of Threatened and Endangered Species Evaluation 31
4.3 Wetlands ............................................................................................................................ 32
4.3.1 Direct Impacts .................................................................................................... 32
4.3.2 Preliminary Wetlands Mitigation Plan ................................................................. 33
4. 3. 3 Permitting ........................................................................................................... 33
4.4 Cultural Resources ............................................................................................................ 34
4.5 Local Consultations ........................................................................................................... 35
4.6 Indian Trust Assets ............................................................................................................ 36
4.7 Findings of Regulatory and Institutional Investigations ...................................................... 37
5.0 DAM AND APPURTENANT STRUCTURES .............................................................. 38
5.1 Introduction ........................................................................................................................ 38
5.2 Reservoir ........................................................................................................................... 39
5.3 Spillway .............................................................................................................................. 40
5.3.1 Spillway Type ..................................................................................................... 40
5.3.2 Spillway Flow ...................................................................................................... 41
5.3.3 Hydraulic Control Sections ................................................................................. 42
5.4 Dam ................................................................................................................................... 43
5.4.1 Embankment Section ......................................................................................... 43
5.4.2 Minimum Freeboard ........................................................................................... 44
5.4.3 Seepage Control Measures ............................................................................... 45
5.4.4 Earthwork ........................................................................................................... 45