E V A L U A T I O N A N D S E L E C T I O N R E P O R T

EVALUATION AND SELECTION REPORT CDRL A018 EAST LOCUST CREEK WATERSHED, RW-1 NEAR MILAN, MISSOURI SULLIVAN COUNTY

Prepared For:

U.S. Department of Agriculture Natural Resources Conservation Service, Missouri State Office 601 Business Loop 70 West Parkade Center, Suite 250 Columbia, Missouri 65203 Task Order Number AG-6424D-10-007 IAW Basic PIIN AG-3A75-C-09-0022 Contract 53-7335-3-124 January 2014

URS Corporation 8181 East Tufts Ave. Denver, CO 80237 URS Project 41009852

TABLE OF CONTENTS

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Executive Summary ............................................................................................................................... ES-1

Section 1 ONE Introduction ..................................................................................................................... 1-1

1.1 Summary and Purpose ............................................................................. 1-1 1.2 Authorization ........................................................................................... 1-1 1.3 Project Personnel ..................................................................................... 1-1 1.4 Description of Project .............................................................................. 1-2 1.5 Project Objectives .................................................................................... 1-2

Section 2 TWO Alternatives and Evaluation and Selection .................................................................. 2-1

2.1 Geology Summary ................................................................................... 2-1 2.1.1 Previous Investigations ................................................................ 2-1 2.1.2 Geologic Investigation ................................................................. 2-2

2.2 Soil Mechanics Summary ........................................................................ 2-7 2.3 Embankment Layout and Design ............................................................. 2-9 2.4 Structure Alternatives .............................................................................. 2-9 2.5 Recommended Alternative..................................................................... 2-10

Section 3 THREE Hydrology and Hydraulics ............................................................................................. 3-1

3.1 Stream Flow Augmentation ..................................................................... 3-1 3.2 Spillway Hydraulic Design ...................................................................... 3-2

3.2.1 Spillway Design Criteria .............................................................. 3-2 3.2.2 Wave Action ................................................................................ 3-4 3.2.3 Labyrinth Weir With Notch Spillway .......................................... 3-4 3.2.4 Spillway Chute ............................................................................. 3-5 3.2.5 Spillway Stilling Basin ................................................................ 3-6

3.3 Reservoir Routing .................................................................................... 3-6 3.4 Downstream Hydrology and Hydraulics ................................................. 3-7

3.4.1 Downstream Hydrology ............................................................... 3-7 3.4.2 Frequency Storm Hydraulic Analysis .......................................... 3-8

3.5 Breach Analysis and Inundation Mapping ............................................... 3-8

Section 4 FOUR Concept Design of Recommended Alternatives .......................................................... 4-1

4.1 Preliminary Design Drawings .................................................................. 4-1 4.2 Cost Estimate ........................................................................................... 4-2 4.3 Final Design Considerations .................................................................... 4-2

Section 5 FIVE References ...................................................................................................................... 5-1

TABLE OF CONTENTS

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List of Tables. Table 2.1 Borrow Summary

Table 3.1. Stream Flow Duration Analysis using Area-Reduced Flow from Gauge 06901500

Table 3.2 Structural Data with Planned Storage Capacity for RW-1

Table 3.3 Labyrinth Weir Discharge Rating Table

Table 3.4 Stilling Basin Calculation Summary

Table 3.5 Reservoir Routing Summary

Table 3.6 Frequency Storm Maximum Weir Depth Overtopping at Downstream Bridge Crossings

Table 3.7 Breach Summary

Table 3.8 Dam Breach Maximum Weir Depth Overtopping at Downstream Bridge Crossings

Table 4.1 Index of Drawings

Table 4.2 Cost Estimate Summary

List of Figures Figures 2.1 Combined Principal and Auxiliary Spillway (Ogee Crest) Structure Alternative

Figures 2.2 Combined Principal and Auxiliary Spillway (Labyrinth Weir) Structure Alternative

Figures 2.3 Multi-Gated Outlet Works Structure Alternative

Figures 2.4 Outlet Works with Submerged Intake Tower Structure Alternative

Figures 3.1 Labyrinth Weir Discharge Rating Curve

List of Appendices Appendix A Geology Report Selected Sheets

Appendix B Hydrology and Hydraulics

Appendix C Drawings

Appendix D Cost Information

Executive Summary

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The recommended alternative for the East Locust Creek RW-1 site consists of a zoned earthen embankment, a concrete labyrinth spillway, and a multi-level gated outlet works structure. A single conduit through the embankment will be used to convey stream augmentation flow, construction floodwater discharge, and municipal releases to a downstream control structure.

Alternatives were evaluated and selected based on cost, geologic and soil mechanics information from site and laboratory investigations, hydrology and hydraulic evaluations performed for this study by URS, and evaluations previously completed by the Natural Resource Conservation Service Missouri Office (NRCSMissouri).

Other structure alternatives considered included the following:

Conventional reinforced concrete ogee spillway on left abutment designed as a combination spillway for both principal and auxiliary flows.

Conventional ogee or labyrinth spillway on the left abutment designed only for auxiliary spillway flows, in conjunction with a two-chambered combined outlet works/principal spillway tower.

The combined spillway option was chosen for the project and is the least costly because the auxiliary and principal spillway crest elevations differ by only 2.4 feet. Construction of two different crests within the same structure is relatively simple and is advantageous from both construction and maintenance cost perspectives. The multi-gated outlet works tower allows for a smaller, single penetration through the embankment to pass municipal flows and stream augmentation. A low-flow tube near the base and a low-level gate are included in this option for construction dewatering. Of the two alternatives for a combined overflow spillway, the labyrinth is the least costly attributable to lower reinforced concrete and backfill concrete quantities as compared to the conventional ogee spillway.

The embankment will be approximately 78 feet high at the maximum section with a crest width of 22 feet, and will be approximately 2,700 feet in length. It has been designed with a vertical cutoff trench, clay blanket, grout curtain, and cement-bentonite slurry wall for underseepage control. The cross section is zoned to take advantage of the borrow materials available at the site, with a central low-permeability core with exterior shells comprised of other, more permeable soils available. Borrow soils appear to be plentiful, but some selective borrow operations will likely be required to segregate materials for appropriate zoning. Riprap for upstream slope wave protection and for spillway and outlet works channel bank lining will be required from off-site sources, as well as sand/gravel for internal drainage systems. Staged embankment construction will be required due to lower shear strengths in valley alluvial soils. A total of 1.2 million cubic yards of earth materials are required for the embankment construction.

SECTIONONE Introduction

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1. Section 1 ONE Introduction

1.1 SUMMARY AND PURPOSE The purpose of this Evaluation and Selection Report is to document and describe the development of the recommended alternative for a new multipurpose reservoir in Sullivan County, 4 miles north of Milan, Missouri. The structure has been given the designation of East Locust Creek RW-1 by NRCS-Missouri.

The East Locust Creek Watershed Revised Plan Environmental Impact Statement (NRCS, 2007) prepared and issued by NRCS-Missouri (in conjunction with the local sponsor group consisting of Locust Creek Watershed District, North Central Missouri Regional Water Commission, Sullivan County Soil and Water Conservation District, Putnam County Soil and Water Conservation District, Sullivan County Commission, and Putnam County Commission) dated 25 January 2007, describes the justification, impacts, and