EX RPT & DWGS - 26149 2013 SevenTubesReplacementRED.pdf

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[ I r1 WATER LEVEL CONTROL STRUCTURE REPLACEMENT

I I HYDRAULIC REPORT

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SHIAWASSEE FLATS DAM - SEVEN TUBES

SHIAWASSEE RIVER STATE GAME AREA

ST. CHARLES, MICHIGAN

PREPARED FOR THE

MICHIGAN DEPARTMENT OF NATURAL RESOURCES

AND THE

MICHIGAN DEPARTMENT OF TECHNOLOGY, MANAGEMENT AND BUDGET

FILE NO. 751/08274.RWG - INDEX NO. 86930

APRIL 30, 2013

BY

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Table of Contents

1. Introduction ................................................................................................................................... I

2. Methods of Analyses ........................................ ,

3. Modeling Limits

4. Variables, Coefficients and Modeling Strategies

5. Modeling Results Discussion

6. Hydraulics Analysis Conclusions

7. Temporary Cofferdam Hydraulic Impact

8. Temporary Spoils Stockpile Hydraulic Impact

Appendices

Appendix 1 - Existing Conditions Photographs

Appendix 2 - Site Maps, Locations and Modeling Limits

Appendix 3 - River Flow Data, Monthly Flows & Annual Flood Frequency

Appendix 4 - Project Plans, 2013 Water Level Control Structure Replacement

Appendix 5 - WLCS Discharge Rating Curves, Seven Tubes vs Tilting Weir

Appendix 6 - Dam Discharge Rating Curves, Existing vs Proposed

Appendix 7 - Flow Distribution Graphs, Existing vs Proposed

Appendix 8 - Hydraulic & Energy Grade Profiles, Existing vs Proposed

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1. Introduction

Project Name:

Shiawassee Flats Dam 'Seven Tubes' Water Level Control Structure Replacement

Project Address:

Prepared By:

Prepared For:

Responding To:

Project Location

Shiawassee River State Game Area Field Office 225 East Spruce Street St. Charles, Ml 48655

Jerry J. Powell, PE Williams & Works, Inc.

Office Telephone: 616-224-1500 E-mail Address: powell@williams-works.com

Michigan Department of Natural Resources, and Michigan Department of Technology, Management and Budget File No. 751/08274.RWG- lndexNo. 86930

MDEQ's March 25, 2013 Correction Request related to JPA #13-73-0007-P

The Shiawassee River State Game Area is located within Swan Creek, St. Charles and James Townships, in Saginaw County, Michigan, at the confluence of the Shiawassee River, the Bad River, and several smaller tributary creeks. The Shiawassee River drainage basin size is listed as 625 sq. mi. The Shiawassee Flats Dam Radial Gates Water Level Control Structure (Radial Gates WLCS) is located in the SW quarter of Section 34 of Swan Creek Township; TllN, R3E, at 43° 18' 51.4" N latitude and 84° 06' 12.3" W longitude. The Shiawassee Flats Dam Seven Tubes WLCS was located in the NW quarter of Section 35 of James Township; Tl lN, R3E, at 43° 19' 17 .8" N latitude and 84° 05' 29.3" W longitude.

Hydraulic System Overview The Shiawassee River State Game Area is owned and operated by the Michigan Department of Natural Resources (MDNR), Wildlife Management Division (WMD). The State Game Area (SGA) includes an earthen dam which separates the Shiawassee River flats from the Bad River, known as the Shiawassee Flats Dam, Dam ID #1819. This 15,000 ft. long dam and its water level control structures are critical components of the State Game Area seasonal flooding operations - allowing MDNR to control the impoundment water levels of the SGA's Waterfowl Hunting Zones and wildlife management areas south of the Bad River, and supplying water for the Waterfowl Hunting Zones and wildlife management areas north of the Bad River. The gates are typically closed each year for the fall season beginning on September l '\ and are reopened in December to drain the impoundment.

The dam's original principal spillway, the Seven Tubes Water Level Control Structure (Seven Tubes WLCS), was installed in 1963 to control flow from the Shiawassee River flats into the Bad River. The dam's impoundment normally stores 2,500 ac-ft. of water, with a maximum storage of 9,100 ac-ft. The

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I I f I f I f I i1 dam's Emergency Spillway is located approximately 2,900 ft. southwest of the Seven Tubes to provide extra discharge capacity during high stage flood flow conditions. The Seven Tubes WLCS consisted of seven 36" CMPs with a stoplog overflow weir inlet structure for regulating the impoundment water level (see 1963 ST plan sheets). By 1977 it had become evident that the Seven Tubes did not provide sufficient flood flow capacity, and the larger Radial Gates structure was installed about 4,375 ft. southwest of the Seven Tubes.

By 2001 the original Seven Tubes structure had aged and degraded to the point that MDNR elected to decommission it in place. Since that time the 40-foot wide Radial Gates structure has been the principal spillway. See Appendix 1 for photographs of the existing conditions. However, the Radial Gates structure was not originally designed to operate alone, and doing so reduced flow capacity, increased discharge velocity and produced excessive scour of the outlet channel. The primary goal of this project is to replicate the 'Seven Tubes' WLCS flow regime, capacity and level control functions, while reopening a natural watercourse of the Shiawassee River.

Previous Investigations & Work History In March of 2008, the Dam Safety Program of the Michigan Department of Environmental Quality (MDEQ), Land and Water Management Division (LWMD), conducted an inspection of the Shiawassee Flats Dam. The inspector identified significant erosion of the Radial Gates outlet channel and recommended in his report, in part, that MDNR:

"Further investigate the erosion problem on the stream banks just downstream of the radial gates structure by December 31, 2008. On the basis of this study, install appropriate measures by December

31, 2009."

In November of 2008, the MDTMB hired Williams & Works (W& W) on behalf of the MDNR to perform the recommended investigation of the outlet channel erosion, and to identify suitable erosion control measures. On April 6, 2009, W& W issued its Erosion Control Measures Preliminary Design Report for MDTMB/MDNR review. In that report, W& W presented its review of the radial gates hydraulics that had caused the observed erosion, examined a wide array of corrective measures, and developed recommended strategies for corrective action as follows:

" ... review of the past operation and the current hydraulic conditions indicate that the Radial Gates structure was not originally designed to operate alone. The decommissioned 'Seven Tubes' structure provided additional flow capacity and level control that was an important component of the dam's hydraulic system. Given this background, the radial gates hydraulics were evaluated, hydraulic bases of design were selected, erosion repair/control alternatives were developed and evaluated, and three main strategies were identified to improve the situation, as follow:

1. Emergency Erosion Control Measures to minimize further scour/erosion, stabilize the Radial

Gates structure, and avoid a complete failure of the Shiawassee Flats Dam,

2. Long Term Erosion Control Measures and Improvements to the Radial Gates to repair the existing damage and better protect it from the increased velocities and flows, or

3. Long Term Erosion Control Measures, Improvements along with Capacity Enhancements to return flow capacity and level control that was lost when the 'Seven Tubes' structure was decommissioned."

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Based on the detailed recommendations in the Erosion Control Measures Preliminary Design Report, MDNR obtained a grant from the U.S. Fish & Wildlife Seivice under the Great Lakes Fish and Wildlife Restoration Act, and has implemented the following repairs:

1. Emergency Radial Gates inlet channel erosion repairs in 2009 (permit 09-73-0029-P), and

2. Long Term Radial Gates outlet channel erosion repairs in 2011 (permit 10-73-0026-P), The grant also provided funding to implement the third strategy by constructing the proposed new auxiliary spillway to replace the decommissioned Seven Tubes water leveVflow control structure.

The specific concern identified in the 2009 Study is that the Radial Gates were designed as flood gates to supplement the limited flow capacity of the Seven Tubes. The Radial Gates open along their bottom edge and are not designed to be opened under the high head of a full impoundment. Doing so, releases jets of pressurized water under the gates at extremely high velocity, resulting in excessive erosive forces in the outlet channel. The Seven Tubes structure was originally designed to gradually lower the impoundment level before the Radial Gates (flood gates) were opened; thereby controlling the erosive power of the stored water. Once the impoundment is drained, the Radial Gates and the Seven Tubes would remain open throughout the winter, spring and summer.

Project Overview The proposed project will implement strategy number three of the recommended corrective actions -replacement of the decommissioned Seven Tubes water leveVflow control structure with a modern auxiliary spillway in the same location, along with renovation of the outlet channel. The decommissioned 'Seven Tubes' structure allowed water to cascade over the stoplog 'weir' gradually draining the impoundment as stop logs were removed, while dissipating energy within the concrete inlet structure. To replicate this function, a tilting weir style gate has been selected. Tilting weirs, or overshot gates, are used to control water level in much the same way as a stoplog structure; providing a continuously variable weir height, but without the heavy lifting of multiple stop logs and the danger of falling into the water. This new water leveVflow control structure with a tilting weir will allow for a more controlled, less erosive, annual release of the impoundment waters. See Appendix 4, Project Plans, 2013 WLCS Replacement.

Over the years since the original Seven Tubes structure was decommissioned, its outlet channel has filled with silt and sediment. See the upstream existing conditions photographs in Appendix 1. So the project also includes dredging, reshaping and partial armoring of the restored outlet channel. Replacing the decommissioned Seven Tubes structure will also reopen a natural watercourse of the Shiawassee River from January through August of each year.

Scope of Investigation During Preliminary Design, W& W investigated the hydraulic performance of the original Seven Tubes WLCS with an eye towards designing the new WLCS with improved hydraulics and flexibility. This report includes a summary of those design activities used to select and size the new Tilting Weir WLCS.

This report also presents our investigation of the hydraulic performance impacts of adding the selected Tilting Weir WLCS to the dam's existing Radial Gates WLCS. More specifically, a Federal Highway Administration HY-8 model was used to analyze the 'through-dam' flow capacity, with and without the new WLCS, at various representative flows up to the stage where the dam is overtopped. Using this stage/flow data, we compared the projected 'through-dam' flow capacities before and after the proposed construction to document the decreased flood stage and the increased flow capacity resulting from adding the proposed

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Tilting Weir WLCS. These numeric evaluations were performed for the 'full open gates' condition in order to determine the maximum flow/stage relationships without operator intervention.

It should be noted here that MDNR staff can operate the existing Radial Gates to restrict flow through the dam and to thereby establish a desired impoundment stage. Maximum stage is based on the sharp-crested weir flow over the closed Radial Gates. The proposed Tilting Weir WLCS will be slightly taller than the Radial Gates, but much lower than the top of dam embankment, and it will not change the sharp-crested weir performance of the closed Radial Gates. So the upriver stage with the gates closed will be unchanged.

That is, addition of the proposed Tilting Weir WLCS will not allow the operators to select any higher impoundment stages, only lower stages.

Also, it should be noted that the upstream side of the dam consists of a very large, flat, river delta lacking a clearly identifiable floodway. In fact, the dam embankment is nearly 3 miles long in order to span the river's mouth. Since the 10 ft. wide Tilting Weir WLCS is effectively an added culvert where there is no FEMA identified floodway, a new floodway delineation has not been prepared.

For clarity, references herein to the 'Seven Tubes' WLCS refer to the defunct original 7 culvert water level control structure. References to the Tilting Weir WLCS refer to the proposed box culvert with a tilting weir control gate proposed in the same location.

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2. Methods of Analyses

The primary goal of this project is to replicate the 'Seven Tubes' flow regime, capacity and level control functions, while reopening a natural watercourse of the Shiawassee River. During Preliminary Design, W& W investigated the hydraulic performance of the original Seven Tubes WLCS with an eye towards designing the new WLCS with improved hydraulics and stage control flexibility. After the new Tilting Weir WLCS was designed, modeling of the dam's overall hydraulic capacity was performed to confirm the increased capacity.

Tilting Weir WLCS Preliminary Design To evaluate the flow capacity of the original 'Seven Tubes', a model of the original multi-culvert system was prepared, and a discharge rating curve was developed. Another model was prepared for the proposed box culvert with an open tilting weir and a short span bridge crossing. In both cases the dam embankment is generally perpendicular to the direction of river flow, has a rather uniform cross-section, and minimal openings or culverts. The existing and proposed outlet channel cross-sections are also rather simple and readily modeled with a minimum number of data points. Due to the relative simplicity of the culvert/bridge systems to be modeled and the expectation of reduced flood stages, the Federal Highway Administration HY-8 model was selected.

During the course of the WLCS Preliminary Design several culvert sizes were evaluated. Based on the cross sectional area and peak flow of the original Seven Tubes, box culverts of 6 ft., 8 ft. and 10 ft. widths were evaluated; some with beveled inlet edges. Rating curves were developed for comparison to the original Seven Tubes rating curve.

The FHwA HY-8 model allows multiple sets of culverts, but not more than 6 sets. For this reason, the original Seven Tubes WLCS model consisted of 5 simple culverts plus 1 compound culvert consisting of 2 barrels.

All models utilized 90 degree wing walls to be consistent with the original Seven Tubes WLCS design, and to produce conservative flow data for the proposed Tilting Weir WLCS design. The actual Tilting Weir WLCS design utilizes 45 degree wing walls for slightly improved inlet hydrodynamics.

The HY-8 model does not allow for custom culvert shapes or irregularities. Insertion of the tilting weir into the proposed box culvert creates a 0.75 ft. step in the bottom of the WLCS channel. For this reason, modeling of the proposed Tilting Weir WLCS factored the step into the overall bottom slope of the culvert.

Dam Hydraulic Capacity Analysis Once the Tilting Weir WLCS Preliminary Design was completed, models of the Radial Gates alone and the Radial Gates combined with the proposed Tilting Weir WLCS were prepared, and several discharge rating curves were developed for comparison. In both cases the dam embankment is generally perpendicular to the direction of river flow, has a rather uniform cross-section, and minimal openings or culverts. The existing and proposed outlet channel cross-sections are also rather simple and readily modeled with a minimum number of data points. Due to the relative simplicity of the culvert/bridge systems to be modeled and the expectation of reduced flood stages, the Federal Highway Administration HY-8 model was selected.

As discussed above, one of the primary design goals was to increase the dam's hydraulic capacity compared to both the original and current conditions - thereby decreasing the stage at the control structure for any given flow rate. And when stage is reduced at the control, the upriver stage will also be reduced. Early

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. j modeling runs confirmed this expectation that the 'Combined WLCS' would operate at reduced stage compared to the Radial Gates WLCS alone. Therefore, numerical evaluations of the upriver stages and water surface profiles are not required in order to make a determination that the upriver stage will be reduced. Also, there is no FEMA identified floodway, no available survey of the Shiawassee River flats, and it is beyond the scope of this project to perform such a large survey. For all of these reasons, no upriver water surface profiles have been calculated. Representative hydraulic and energy grade profiles through the existing Radial Gates WLCS and the proposed Tilting Weir WLCS are provided in Appendix 8.

Although the FHwA HY-8 model allows multiple sets of culverts, it will not self-calculate the tailwater level(s) for more than one outlet channel. For this reason, when modeling the combined Radial Gates and Tilting Weir WLCS system a range of fixed tailwater elevations were evaluated. The same fixed tailwater elevations were also used when modeling the Radial Gates WLCS alone to develop comparable rating curves.

Similarly, due to the HY-8 models inability to self-calculate the tailwater level(s) for more than one outlet channel, it does not calculate the energy grade line (EGL) properly. An Excel spreadsheet was used to calculate the EGL's for the 'Existing Radial Gates WLCS' and the 'Proposed Combined WLCS' systems.

The HY-8 models for the 'Existing Radial Gates WLCS' and the 'Proposed Combined WLCS' systems also included the Emergency Spillway. Although the models provided flow distribution data for the spillway, they did not provide the hydraulic and energy grade profile data over the weir. So an Excel spreadsheet was used to calculate the HGL's and EGL's for the Emergency Spillway. Since the Emergency Spillway is a constant feature in both systems, more detailed analyses are not warranted.

All models utilized 90 degree wing walls to be consistent with the current Radial Gates and the original Seven Tubes WLCS designs, and to produce conservative flow data for the proposed Tilting Weir WLCS design. The actual Tilting Weir WLCS design utilizes 45 degree wing walls for slightly improved inlet hydrodynamics. Sensitivity analyses indicated that the improvement was minor, on the order of 0.1 ft.

The HY-8 model does not allow for custom culvert shapes or irregularities. Insertion of the tilting weir into the proposed box culvert creates a 0. 7 5 ft. step in the bottom of the WLCS channel. For this reason, modeling of the proposed Tilting Weir WLCS factored the step into the overall bottom slope of the culvert.

During the Radial Gates Erosion Control Measures study in December of 2008, the MDEQ Land and Water Management Division (L WMD) provided the Shiawassee Flats Dam flood event frequency data presented in the table below. See Appendix 3 for a copy of MDEQ's correspondence. We have recently requested MDEQ confirmation that these values remain valid. The average discharge rate of the Shiawassee River is based on a Williams & Works analysis of the nearest upstream USGS gauging station at the Fergus Road bridge, gauge #04145000, for the record period from March of 1940 through June of 2007.

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Event Frequency Discharge (%) (Years) (cfs)

- Average 457 50 2 3,600 20 5 4,900 10 10 5,700

4.0 25 6,800

2.0 50 7,600

1.0 100 8,300

0.5 200 8,900

0.2 500 9,800

The design discharge for the overall dam is the 1 % (100 yr.) flood discharge, which MDEQ indicates as 8,300 cubic feet per second (cfs).

The FEMA Flood Insurance Study and Map indicate that the 100 year flood stage is at elevation 594 feet.

MDEQ has informed us that the FEMA flood elevation is actually "only the flood elevation of the Shiawassee Flats; ... with a 1 % flood elevation of 593.9; that is what FEMA has mapped." In any case, the flood elevation is more than 4 ft. above the Dam's normal embankment elevation of 589.35 ft. (NGVD29).

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3. Modeling Limits

Tilting Weir WLCS Preliminary Design The FHwA HY-8 culvert modeling program was used to evaluate the performance of the original Seven Tubes WLCS in order to design the proposed replacement Tilting Weir WLCS. Therefore, the upstream modeling limit is located immediately upstream of the WLCS inlet. The downstream modeling limit was either an idealized cross-section of the outlet channel shape or a specified tailwater elevation, depending on modeling purpose.

The lateral modeling limits extend for roughly 3,000 ft. along the Shiawassee Flats Dam embankment, beginning at the Emergency Spillway 2,900 ft. southwest of the Seven Tubes to 100 ft. northeast of the Seven Tubes. But the design modeling didn't need or include stages influenced by the Emergency Spillway.

So the maximum modeling stage was limited to the Emergency Spillway crest elevation of 586.35.

Dam Hydraulic Capacity Analysis The FHwA HY-8 culvert modeling program was used to evaluate the performance of the existing Radial Gates WLCS system compared to the combined system of the Radial Gates WLCS and the proposed Tilting Weir WLCS. The Emergency Spillway was included in both system models. Early modeling runs confirmed the expectation that the 'Combined WLCS' system would operate at reduced stage compared to the existing Radial Gates WLCS system. Therefore, the upstream modeling limit was located immediately upstream of the dam. The downstream modeling limit was a group of representative fixed tailwater elevations. Specifically, the original Seven Tubes design tail water of 579 .15 ft., the current Ordinary High Water Mark of 582.25, and the crest of the Emergency Spillway at 586.35 were modeled.

The lateral modeling limits extend 6,000 ft. along the Shiawassee Flats Dam embankment beginning 1,100 feet southwest of the Radial Gates to 550 feet northeast of the original Seven Tubes. The dam's Emergency Spillway is located between the Radial Gates and Seven Tubes, approximately 1,400 ft. northeast of the Radial Gates, and is included in these models. See Appendix 2, Site Maps, Locations and Modeling Limits.

The maximum modeling stage was not limited in these models. The maximum modeling flow was limited to 8,500 cfs, well above the 1 % (100-yr) frequency flood flow of 8,300 cfs.

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4. Variables, Coefficients and Modeling Strategies

Tilting Weir WLCS Preliminary Design As previously discussed, the original Seven Tubes WLCS was modeled in 'like new' condition to obtain a baseline design goal for the proposed Tilting Weir WLCS. Maximum WLCS flow was determined for the 'full open' condition at a stage equal to the crest of the Emergency Spillway, 586.35 ft. And a rating curve was developed for the 'full open' condition. Coefficients and variables used in these calculations were:

► Culvert size/shape - 7 ea. 36" round per the original design plans, ► Inlet Invert Elevation - 578.1 per the original design plans (survey datum adjusted), ► Slope - 2.77% as surveyed in 2012, ► Roughness Coefficient - Manning's 0.024 for corrugated steel pipe, ► Contraction/Inlet Orifice - "Conventional - Square Edge Headwall" with 90° wing walls, ► Tail water Elevations - As determined by program based on outlet channel section .

The proposed Tilting Weir WLCS was modeled at various sizes and shapes to achieve hydraulic performance similar to the Seven Tubes, with increased capacity throughout its operating range. All channel shapes were box section to accommodate the proposed tilting weir. Maximum WLCS flows were determined for the 'full open' condition at a stage equal to the crest of the Emergency Spillway, 586.35 ft.

Rating curves in the 'full open' condition were developed for several of those size/shape combinations.

Coefficients and variables used in these calculations were:

► Channel size/shape - 10' high by 6', 8', 10' and finally 9.5' wide per tilting weir design, ► Inlet Invert Elevation - 577.25 per the existing Radial Gates invert elevation (survey), ► Slope - 2.03% overall to account for the step created by the open weir, ► Roughness Coefficient - Manning's 0.012 for new concrete, ► Contraction/Inlet Orifice - "Conventional - Square Edge Headwall" with 90° wing walls, ► Tailwater Elevations - As determined by program based on outlet channel section.

Dam Hydraulic Capacity Analysis The dam's overall hydraulic capacity was modeled in the existing and proposed configurations for comparison. The baseline condition consisted of the existing Radial Gates WLCS and Emergency Spillway as recently surveyed, with the Radial Gates in the 'full open' condition. The system was modeled at several fixed tailwater elevations, and rating curves were developed from O to 8,500 cfs for each tailwater condition.

Coefficients and variables used in these calculations were:

► Radial Gate size/shape - 2 ea. 20' wide by 9' high per the original design plans, ► Channel size/shape - 2 ea. 20' wide by 11.35' high to bottom of bridge per plan, ► Inlet Invert Elevation - 577.25 per the existing Radial Gates invert elevation (survey), ► Slope - 0.0% per the original design plans, and as surveyed in 2011, ► Roughness Coefficient - Manning's 0.012 for new concrete, ► Contraction/Inlet Orifice - "Conventional - Square Edge Headwall" with 90° wing walls, ► Tailwater Elevations* - Fixed at

• 579.15 per Seven Tubes 1963 design plans,

• 582.25 at current OHWM, and

• 586.35 at Emergency Spillway crest.

► Emergency Spillway Top Width - 210 feet perpendicular to flow, ► Emergency Spillway Top Length - 12 feet in direction of flow.

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The proposed condition consisted of the existing Radial Gates WLCS and Emergency Spillway as recently surveyed, plus the proposed Tilting Weir WLCS. Both the Radial Gates and the Tilting Weir were modeled in the 'full open' condition. The system was modeled at the same fixed tailwater elevations as the baseline modeling, and rating curves were again developed from O to 8,500 cfs for each tailwater condition.

Coefficients and variables used in these calculations were:

► Radial Gates, 2 ea. - baseline coefficients and variables listed above, ► Tilting Weir size/shape - 1 ea. 9.5' wide by 9.35' high per the proposed design plans, ► Channel size/shape - 1 ea. 9.5' wide by 12.75' high to bottom of bridge per plan, ► Inlet Invert Elevation - 577.25 per the existing Radial Gates invert elevation (survey), ► Slope - 2.03% overall to account for the step created by the open weir, ► Roughness Coefficient - Manning's 0.012 for new concrete, ► Contraction/Inlet Orifice - "Conventional - Square Edge Headwall" with 90° wing walls, ► Tailwater Elevations* - Fixed at

• 579.15 per Seven Tubes 1963 design plans,

• 582.25 at current OHWM, and

• 586.35 at Emergency Spillway crest.

► Emergency Spillway Top Width - 210 feet perpendicular to flow, ► Emergency Spillway Top Length - 12 feet in direction of flow.

*Note: For Fixed Tailwater models the outlet expansion and channel friction/roughness coefficients are not used .

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5. Modeling Results Discussion

Tilting Weir WLCS Preliminary Design While the Shiawassee River annual average flow is just 457 cfs, the flood flows are 10 to 18 times greater than that value, prompting the installation of the Radial Gates in 1977. After the Radial Gates were installed, the main function of the Seven Tubes became the annual draining of the impoundment in December of each year.

HY-8 modeling of the original Seven Tubes WLCS was performed to obtain a baseline design goal for the new WLCS. The maximum WLCS flow for 'full open' condition at a stage equal to the crest of the Emergency Spillway (586.35) was calculated to be 466 cfs. The monthly average river flow for December is 423 cfs and the historic standard deviation in flow during December is 286 cfs, resulting in a 'Mean+ 1 SD' flow of 709 cfs. This flow rate at a maximum headwater of 586.35 was selected as the practical design peak flow for the new Tilting Weir WLCS.

HY-8 modeling of the proposed Tilting Weir WLCS was then performed to ensure a maximum hydraulic capacity greater than 709 cfs. The maximum Tilting Weir WLCS flow for 'full open' condition at a stage equal to the crest of the Emergency Spillway (586.35) was calculated to be 761.6 cfs for any tailwater level from O ft. up to 7 .5 ft. (el. 584.0 ft.). This meets and exceeds the 709 cfs design goal by 52.6 cfs, or 7 .4%.

HY-8 modeling was also performed to ensure proposed hydraulic performance similar to the original Seven Tubes throughout its operating range. Discharge rating curves for the nominal 6 ft., 8 ft. and 10 ft. wide channels were developed in the 'full open' condition. The proposed 8 ft. and 10 ft. wide WLCS rating curves were plotted along with the curve from the original Seven Tubes WLCS. See Appendix 5 for the Seven Tubes/Tilting Weir Discharge Rating Curves Comparison. It is clear from the rating curves comparison that the proposed nominal 10 ft. wide WLCS meets the 'stand-alone' performance criteria.

Dam Hydraulic Capacity Analysis After establishing that the proposed nominal 10 ft. wide WLCS meets the 'stand-alone' performance criteria, the overall hydraulic capacity of the dam was modeled in the existing and proposed configurations for comparison. Discharge rating data for the Radial Gates WLCS alone and in combination with the proposed Tilting Weir WLCS were developed in the 'full open' condition at 3 fixed tailwater elevations.

Proposed Combined System Capacity vs Existing System Capacity

TW=579.15 ft. TW=582.25 ft. TW=586.35 ft.

Headwater Existing Proposed Existing Proposed Existing Proposed Elev. (ft.) Flow Flow Flow Flow Flow Flow

582.25 1,146 1,445 - - - -

586.35 2,886 3,591 2,886 3,591 - -

589.20 7,430 8,300 7,430 8,300 7,341 8,300

It is clear from this rating data comparison that the proposed Combined Radial Gates and Tilting Weir WLCS system exceeds the performance of the existing Radial Gates system. Specifically, depending on tailwater elevation the proposed system's flow capacity increases as follows:

► Headwater elev. at Ordinary High Water Mark 582.25 => Flow capacity increases by 26%, ► Headwater elev. at Emergency Spillway crest 586.35 => Flow capacity increases by 24%, ► Headwater elev. at Dam Embankment top 589.20 => Flow capacity increases by 12% to 13%, II r I r I

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The table below presents comparative system headwater elevation or stage data for the proposed 'Combined WLCS' system versus the existing Radial Gates system over a wide range of flows and tailwater conditions.

Proposed Combined System Headwater vs Existing System Headwater

Flood Flow TW=579.15 ft. TW=582.25 ft. TW=586.35 ft.

Freq% cfs ExHW PropHW ExHW Prop HW ExHW Prop HW

0 579.15 579.15 582.25 582.25 586.35 586.35 850 581.40 580.80 582.68 582.51 586.47 586.43 1700 583.84 582.87 583.94 583.29 586.77 586.64 2550 585.90 584.60 585.90 584.59 587.15 586.93 3400 587.04 586.15 587.04 586.15 587.55 587.27

50 3600 587.18 586.43 587.18 586.43 587.64 587.35 20 4900 588.03 587.47 588.03 587.47 588.24 587.88 10 5700 588.47 587.93 588.47 587.93 588.6 588.21 4 6800 589.00 588.51 589.00 588.51 589.06 588.65 2 7600 589.25 588.87 589.25 588.87 589.27 588.96 1 8300 589.34 589.17 589.34 589.17 589.34 589.22

It is clear from this headwater data comparison that the proposed Combined Radial Gates and Tilting Weir WLCS system reduces the system headwater elevation compared to the existing Radial Gates system alone.

Specifically, depending on the tailwater elevation, the proposed system's stage decreases as follows:

► 50% Frequency flood flow of 3,600 cfs => Stage decreases by 0.29 ft. to 0. 7 5 ft., ► 20% Frequency flood flow of 4,900 cfs => Stage decreases by 0.36 ft. to 0.56 ft., ► 10% Frequency flood flow of 5,700 cfs => Stage decreases by 0.39 ft. to 0.54 ft., ► 4% Frequency flood flow of 5,700 cfs => Stage decreases by 0.41 ft. to 0.49 ft., ► 2% Frequency flood flow of 7,600 cfs => Stage decreases by 0.30 ft. to 0.38 ft., ► 1 % Frequency flood flow of 8,300 cfs => Stage decreases by 0.12 ft. to 0.17 ft.

And for the sub-flood flow rate of 2,550 cfs with tailwater at or below OHWM (582.25) the 'Combined WLCS' system stage decreases by 1.3 ft. compared to the Existing WLCS system. See Appendix 6 for graphs of the Dam Discharge Rating Curve Comparison at each of the representative tailwater elevations.

As noted above, the Shiawassee River Flats is a wide river-delta-like area immediately upstream from the Shiawassee Flats Dam. Multiple river flow paths approach a main canal that runs parallel to the dam along its upstream bank. Currently this canal feeds all river flow to the Radial Gates WLCS and/ or the Emergency Spillway for discharge to the Bad River side of the dam. The proposed replacement of the old Seven Tubes WLCS with a new Tilting Weir WLCS will have negligible impact on the upstream river and canal system, as no construction or encroachment is proposed in that area. On the downstream side of the dam, the historic outlet channel of the old Seven Tubes WLCS will be dredged and renovated to pass the Tilting Weir flow. This work will rehabilitate one of the Shiawassee River's main flow channels, improving flow through the river flats and dam.

Flow Distribution Analysis In the existing conditions there are two paths of water flow before the dam is completely overtopped. Flow passes through the Radial Gates WLCS (when open) until the water level reaches the crest of the l l n i I '. l

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Emergency Spillway at elevation 586.35. At that level the water begins to flow over the Emergency Spillway.

The table below presents flow distribution data for the 'Existing WLCS' system in low tailwater conditions.

Existing WLCS System Flow Distribution*

Flood Inlet HW Total Radial Emergency Freq.% Elevation Flow, cfs Gates Spillway

579.15 0 0 0

581.40 850 850 0

583.84 1700 1700 0

585.90 2550 2550 0

586.35 2749 2749 0

587.04 3400 3069 331

50 587.18 3600 3136 464 20 588.03 4900 3542 1358 10 588.47 5700 3752 1948 4 589.00 6800 4033 2767 2 589.25** 7600 4163 3437 1 589.34** 8300 4204 4096

Notes: *Tailwater elevation= 579.15, **Top of Dam= 589.20±

In the proposed condition there are three paths of water flow before the dam is completely overtopped.

Flow will pass through the Radial Gates WLCS and the Tilting Weir WLCS (when open) until the water level reaches the crest of the Emergency Spillway at elevation 586.35. At that level water begins to flow over the Emergency Spillway. This next table presents flow distribution data for the proposed 'Combined WLCS' system in the same low tailwater condition. See Appendix 7 for graphical presentations of the existing and proposed flow distribution data.

Proposed Combined WLCS System Flow Distribution*

Flood Inlet HW Total Tilting Radial Emergency Freq.% Elevation Flow, cfs Weir Gates Spillway

579.15 0 0 0 0

580.80 850 180 670 0

582.87 1700 360 1340 0

584.60 2550 551 1999 0

586.15 3400 740 2660 0

586.35 3515 766 2749 0

50 586.36 3600 776 2786 38 20 587.47 4900 909 3270 721 10 587.93 5700 970 3495 1235 4 588.51 6800 1044 3767 1988 2 588.87 7600 1092 3961 2546 1 589.17 8300 1132 4118 3050

Note: *Tailwater elevation = 579.15

The 'Combined WLCS' system data indicate that the proposed Tilting Weir WLCS captures approximately 21.5% of the total flow for stages below the crest of the Emergency Spillway (<586.35). For stages at and above the Emergency Spillway, the Tilting Weir's percentage of flow drops off gradually to approximately 13.6% of the total flow .

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Comparing the 'Combined WLCS' system data to the 'Existing WLCS' system data above highlights the reduced headwater elevations required for the proposed 'Combined WLCS' system and the resulting reduced Emergency Spillway flow rates. For example, at the 1 % (100 yr.) frequency flood flow the 'Existing WLCS' system pushes 1,054 cfs more flow through the Emergency Spillway and over the top of the dam than does the 'Proposed Combined WLCS' system. And the 'Existing WLCS' system inlet headwater elevation is 0.17 ft. higher than the Proposed system, and 0.14 ft. higher than the top of the dam. In summary, the 'Proposed Combined WLCS' system will pass the 1 % (100 yr.) flood flow without overtopping the dam, and will operate at noticeably reduced stage compared to the existing system.

It should also be noted that when both WLCS' are 'fully closed', the discharge and stage characteristics of the Shiawassee River will be unchanged from the existing 'fully closed' condition.

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6. Hydraulics Analysis Conclusions

This evaluation of the existing and proposed Shiawassee Flats Dam water level control structures has confirmed that the proposed 'Combined WLCS' system will operate at noticeably reduced stage compared to the 'Existing WLCS' system. But the complexity of the dam's multiple discharge paths does not lend itself to a single table presentation of the hydraulic and energy grades. That is, the Radial Gates, Emergency Spillway and Tilting Weir each have their own existing and proposed hydraulic and energy grade lines for each flood flow and tailwater elevation combination. Multiple tables and profiles are presented in Appendix 8 for the Radial Gates, Emergency Spillway and Tilting Weir at each of the six flood flows utilizing the Ordinary High Water Mark tailwater elevation of 582.25.

Reviewing the existing and proposed hydraulic and energy grade profiles indicates that both the hydraulic and energy grade levels will be noticeably reduced by the addition of the proposed Tilting Weir WLCS.

This is evident throughout the range of flood flows evaluated. As discussed in the Introduction, one of the primary design goals was to increase the dam's hydraulic capacity compared to both the original and current conditions - thereby decreasing the stage at the control structure for any given flow rate. And when stage at the control structure is reduced, the upriver stage will also be reduced. Therefore, the addition of the proposed Tilting Weir WLCS will not cause a harmful interference with the Shiawassee River's existing discharge and/ or stage characteristics.

During flood conditions the stage of the Bad River is typically elevated similar to the Shiawassee River, and flood flows will pass into the Bad River primarily dependent on the stage condition of the Bad River (i.e.

outlet or tailwater control). Further, at Shiawassee River stages lower than the Emergency Spillway (586.35), the addition of the Tilting Weir WLCS will improve the MDNR's ability to control and manage Shiawassee River flow into the Bad River, thus providing an additional tool for Bad River flood control.

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7. Temporary Cofferdam Hydraulic Impact

A temporary cofferdam is proposed in order to isolate the WLCS and outlet channel construction activities from the Bad River flow (i.e. work in the dry). The contractor will pump out and dredge the outlet channel, dewater the dredged spoils, regrade and recompact the dredged spoils to the new outlet channel shape, and will then install riprap armor on geotextile where specified. The cofferdam will lie across the mouth of the outlet channel aligned between the existing banks of the Bad River. The proposed top of cofferdam elevation is just 580.5±, or 2.5 ft. above the existing river bottom at that location. The entire cofferdam will be about 1.75 ft. below the river's OHWM of 582.25, such that it will be submerged by any medium stage event in the Bad River. In that instance the construction work will be stopped until the outlet channel is re-drained. The cofferdam is proposed to remain in place for not more than 2 months during the later summer (mid-July thru mid-September) low water construction period. Since the cofferdam joins the Bad River's existing banks and parallels the direction of flow, its temporary existence during the late summer low water construction period will not cause a harmful interference with the river's existing discharge and/ or stage characteristics.

The base width of the cofferdam is proposed to be approximately 12.5 ft. wide to allow for 1V:2.5H side slopes. This bottom width will allow a small excavator to perch on the cofferdam for ease of construction and removal. The dam will be constructed of soils dredged from the outlet channel bottom immediately adjacent to the cofferdam alignment. The net change in soil volume below OHWM related to the cofferdam construction will be zero cubic yards. Upon completion of the outlet channel regrading, the temporary cofferdam area will be excavated/dredged down to the proposed bottom elevation of 576.5. The spoils will be drained and trucked to one of the proposed permitted stockpile locations. The net change in soil volume after cofferdam removal is included in the dredging volumes identified in the permit application package.

The soil erosion and sedimentation control plans call for a turbidity curtain on the Bad river side of the cofferdam during its construction and removal. Dewatering pumps will utilize outlet filter bags to limit sediment discharge.

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8. Temporary Spoils Stockpile Hydraulic Impact

MDNR is requesting authorization to temporarily stockpile up to 125 CY of the dredging spoils at Location 'B'. See the attached revised Site Maps in Appendix 2, and Project Plans in Appendix 4. The spoils will be used by Wildlife Management Division to improve wetlands surface water management and soil moisture retention in the Managed Waterfowl Hunting Zone cells 49-52 in 2014. The proposed stockpile location is on the east berm/ embankment of cells 49-52, approximately 2,000 feet east of the nearest Shiawassee River channel. The USGS Map elevation on top of the berm is approximately 587 ft., ensuring that the stockpile will be above the primary impoundment level of the Shiawassee Flats Dam, 586.35. The top of berm is 12 to 15 ft wide, and the base of the stockpile will therefore be limited to12 to 15 ft wide. The existing berm and proposed temporary stockpile are also oriented north/south such that flood waters can easily pass alongside them during high stage flood events. The temporary existence of this minor stockpile will not cause a harmful interference with the river's existing discharge and/or stage characteristics.

The soil erosion and sedimentation control plans call for silt fence surrounding this temporary stockpile until the stockpile is depleted.

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APPENDIX!

EXISTING CONDITIONS PHOTOGRAPHS

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50015 Seven Tubes Outlet Channel, View to North

12/05/2012 - Photo 50028 Seven Tubes Outlet Channel, View of Existing Culverts

Appendix 1.1 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

February 21, 2013

MDTMB 751.08274.BDW, Index 86930

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50017 Seven Tubes Outlet Channel, Upper View to Northwest

12/05/2012 - Photo 50032 Seven Tubes Outlet Channel, Lower View to West

Appendix 1.2 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50016 Seven Tubes Outlet Channel, Upper View to Northeast

12/05/2012 - Photo 50033 Seven Tubes Outlet Channel, Lower View to East

Appendix 1.3 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50019 Seven Tubes Inlet Channel, Upper View to West

12/05/2012 - Photo 50025 Seven Tubes Inlet Channel, Lower View to West

Appendix 1.4 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50022 Seven Tubes Inlet Channel, Upper View to East

12/05/2012 - Photo 50026 Seven Tubes Inlet Channel, Lower View to East

Appendix 1.5 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

8/21/2008 - Photo 4229 Radial Gates WLCS Inlet, View to North

9/05/2011 - Photo 0008 Radial Gates WLCS Outlet, View to South

Appendix 1.6 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

CR Response - April 25, 2013 ii ! I

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50015 Seven Tubes Outlet Channel, View to North

12/05/2012 - Photo 50028 Seven Tubes Outlet Channel, View of Existing Culverts

Appendix 1.1 MDNR - WIidiife Management Div .

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50017 Seven Tubes Outlet Channel, Upper View to Northwest

12/05/2012 - Photo 50032 Seven Tubes Outlet Channel, Lower View to West

Appendix 1.2 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MD'IMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50016 Seven Tubes Outlet Channel, Upper View to Northeast

12/05/2012 - Photo 50033 Seven Tubes Outlet Channel, Lower View to East

Appendix 1.3 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50019 Seven Tubes Inlet Channel, Upper View to West

12/05/2012 - Photo 50025 Seven Tubes Inlet Channel, Lower View to West

Appendix 1.4 MDNR - WIidiife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

12/05/2012 - Photo 50022 Seven Tubes Inlet Channel, Upper View to East

12/05/2012 - Photo 50026 Seven Tubes Inlet Channel, Lower View to East

Appendix 1.5 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

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MDTMB/MDNR Shiawassee River State Game Area - 208180.01

8/21/2008 - Photo 4229 Radial Gates WLCS Inlet, View to North

9/05/2011 - Photo 0008 Radial Gates WLCS Outlet, View to South

Appendix 1.6 MDNR - Wildlife Management Div.

Shiawassee River State Game Area

James Twp., Saginaw Co.

CR Response - April 25, 2013

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11 APPENDIX2

11 SITE MAPS

Locations and Modeling Limits

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)5E'1ElT PD.

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1' ----- •"' To SWiJn ,<' Creek Road_'

MICHIGAN

DEPARTMENT OF NATURAL RESOURCES

SHIAWASSEE RIVER

STATE GAME AREA

Great Lakes, Great Times, Great Outdoors www.michigan.gov/dnr

SAGINAW COUNTY, MICHIGAN

Scale 1:55000

0 0-25 0_5 0,75 1 Miles ( l To r.Amer ~~ad -I - ◊ : Pa'rking Lot & ..... ~ : Bo~t Access o .__,~---~-------~~~~---- '..... ' .. , l ~ I ::• :::·::- ::•:

A 14

! I i--1---1--l), ~ i/f< '?

' I ' ' ' ••••'"••••I.,.,., ..... ., •

' SEE :

NA IONAL .. :

WILD~IF1f20

::R-f=FQGE _ l

General Area - Open to Hunting permit required, contact office

Wildlife Refuge - DO NOT ENTER

[."':j Closed to Waterfowl Hunting

2'.zi Managed Waterfowl Hunting Zone - Hunting by permit only, 2-4 hunters per party, Party Permits areas 6-48 , 55-90

~ Managed Waterfowl Hunting Zone -

• Hunting by permit only, Individual Permits areas 1-5, 49-52, 61-117, 137-150

• Area Headquarters (in St Charles)

■ Parking Area

A Boat Access/Launch A Pull-Over

~ Foot Access or Field Entrance ~ Blind - Wheelchair Accessible D contact area office for details llll ® Pumping Station ~ Dike & Ditch Areas

CAUTION - Deep Water! Always use care when near all water areas, /'../ State/Federal Highway ~ County Road /'v Street /Local Road /'/ Railroads ,,• •• ,,Two-Track/ Trail [ =-_i City Limits

/'--./ Township-Range-Section Lines - Sections numbered (1-36) near center t,:/-:/1 Lakes / Ponds / Water /'--./ Perennial Stream/ Waterways ,,- '- ' Intermittent Stream/ Drainage m Portions of this area designated Watchable Wildlife viewing areas, For more information on this and other areas, contact DNR offices or visit on the internet at: http://www.michigan.gov/dnr

Hunter Monies Made This Area Possible DNR-Wildlife Map - area 730101 (was 0813, Rev, 8/2006 -MLS) n r I

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APPENDIX3

RIVER FLOW DATA

Monthly Flows & Annual Flood Frequency

- ---, - - ____,I ___.

Shiawassee River@ Fergus Rd Gauging Station - Monthly Flow Stats 1940 to 2010, CFS Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Monthly Averages 473 575 1010 925 625 365 223 153 179 244 327 423 Monthly Std Deviatiom: 381 410 466 474 448 256 204 123 204 294 246 286 Monthly Maximums 1358 1843 2047 2564 2532 1212 1135 668.5 1271 1921 1286 1274 Monthly Minimums 80.5 76.4 140 253.4 155.3 86.1 42.1 42.2 42.1 40.6 58.9 62.9 10% Trim Mean 455 553 1001 895 587 346 197 141 153 209 305 409 20% Trim Mean 427 535 985 879 557 326 188 130 138 186 286 393 f l r 1

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Powell, Jerry

From:

Sent:

To:

Cc:

Subject:

DEQ-LWM-QREQ DEQ-LWM-QREQ [DEQ-LWM-QREQ@michigan.gov) Monday, December 08, 2008 5:07 PM VanderHeide, Dan Joy Brooks; Jim Pawloski Re: flood or low flow discharge request (ContentlD - 168812)

This reply is being sent -via email only.

We have estimated the flood frequency discharges requested in your email of December 1, 2008 (Process No. 20080459), as follows:

Shiawassee River at Shiawassee Flats Dam, Dam ID 1819, Section 34, TllN, R03E, Swan Creek Township, Saginaw County, has a…