mill pond dam feasibility study - cms1files.revize.com

Mill Pond Dam Feasibility Study

Mill Pond Dam May 22nd 2019

Mill Pond Dam Project Highlights:

Site Map:

Labyrinth Weir

- Based on the latest dam safety inspections, the existing Mill Pond Dam is in need of repair or removal.

- Purpose of tonight’s meeting is to present the dam replacement and dam removal options being considered.

DAVISBURG

Eaton

Ro

ad

Dilley R

oad

Railroad Crossings

Railroad Crossing

Springfield Oaks Golf Course

Karl Shultz Park

Mill Pond Park

Trout Pond

Broadway

Mill Pond Dam

Rotary Park

Existing Mill Pond Dam:

Existing dam inlet

Mill Pond

Downstream dam embankment armored with grouted riprap

Upstream side of dam embankment includes sheetpile wall

In Partnership With:

Springfield Oaks Golf Course

Dam Replacement/Removal Alternatives Considered

Mill Pond Dam May 22nd 2019

How were alternatives determined?:

Alternatives Considered:

Step 1: Evaluate latest dam safety inspections, which showed the existing Mill Pond Dam is in need of replacement or removal.

- Existing dam overtops before the 100-yr flood event

- Downstream embankment has cracks in riprap armoring and signs of seepage

- Existing outlet pipe is structurally in need of replacement

- Concerns for ongoing maintenance of Mill Pond and the Dam

DAVISBURG

Eaton

Ro

ad

Dilley R

oad

Railroad Crossings

Karl Shultz Park

Mill Pond Park

Trout Pond

Broadway

Mill Pond Dam

Rotary Park

Alternatives Description

Alternative A Replace existing spillway with 36" Diameter HDPE Pipe and replace grouted riprap

Alternative B Replace existing spillway with four (4) 48" Diameter HDPE Pipes

Alternative C Replace existing spillway with a 10' by 4' Box Culvert

Alternative D Replace existing spillway with weir and new bridge

Alternative E Raise Embankment

Alternative F - (1) Remove Dam and place concrete box culvert with restored channel profile #1

Alternative F - (2) Remove Dam and place concrete box culvert with restored channel profile #2

Alternative G - (1) Remove Dam and place pre-cast open-bottom culvert with restored channel profile #1

Alternative G - (2) Remove Dam and place pre-cast open-bottom culvert with restored channel profile #2

Alternative H - (1) Remove Dam and place new bridge crossing with restored channel profile #1

Alternative H - (2) Remove Dam and place new bridge crossing with restored channel profile #2

Step 2: Provide a variety of options that meet some or all of the local partner goals

- Meet Michigan Dam Safety Requirements

- Improve habitat

- Eliminate or minimize future maintenance costs

- Provide recreational opportunities

:

Alternatives Rejected:

Alternative E was rejected from further consideration due to the fact that it increased flood stages upstream of the dam, flooding the Hart Community Center and Mill Pond Park Area.

Conceptual Level Project Costs:

Conceptual Construction Cost Estimates for All AlternativesAlternative A B C D E F G H

Channel Profile 1

Channel Profile 2

Channel Profile 1

Channel Profile 2

Channel Profile 1

Channel Profile 2

Estimated Construction Cost

$625,932.25 $672,484.73 $624,397.23 $1,226,639.67 1,058,429.12 $1,164,358.37 $997,791.62 $1,097,220.87 $1,304,758.62 $1,343,257.62

Contingency Cost (40%)

$250,372.90 $268,993.89 $249,758.89 $490,655.87 $423,371.65 $465,743.35 $399,116.65 $438,888.35 $521,903.45 $537,303.05

Engineering and Permitting (10%)

$62,593.23 $67,248.47 $62,439.72 $122,663.97 $105,842.91 $116,435.84 $99,779.16 $109,722.09 $130,475.86 $134,325.76

Construction Admin/RPR (10%)

$62,593.23 $67,248.47 $62,439.72 $122,663.97 $105,842.91 $116,435.84 $99,779.16 $109,722.09 $130,475.86 $134,325.76

Estimated Project TOTAL

$1,001,491.61 $1,075,975.57 $999,035.57 $1,962,623.47 $1,693,486.59 $1,862,973.39 $1,596,466.59 $1,755,553.39 $2,087,613.79 $2,149,212.19

Estimated Project TOTAL without Upper Pond Restoration $1,571,070.40 $1,740,557.20 $1,474,050.40 $1,633,137.20 $1,965,197.60 $2,026,796.00

Maintenance Cost Estimates for 100yr Time Frame for All AlternativesAlternative A B C D E F G H

Channel Profile 1

Channel Profile 2

Channel Profile 1

Channel Profile 2

Channel Profile 1

Channel Profile 2

Estimated Maintenance Cost

$321,738.99 $288,840.70 $284,410.56 $315,599.20 $125,072.12 $125,072.12 $125,072.12 $125,072.12 $127,911.15 $127,911.15

Estimated Maintenance Costs over a 100-yr Timeframe:

Photos presented on the detailed Alternatives boards are for demonstration / example purposes of what these alternatives could look like. It is expected that as the chosen Alternative progresses the specifics of the inlet and outlet configurations will be further defined.

Replacement Alternatives A and B

Mill Pond DamMay 22nd 2019

Alternative A – Replace Existing Spillway with new 36” HDPE Pipe:

Labyrinth Weir

Alternative B – Replace Existing Spillway with four (4) 48” Diameter HDPE Pipe:

• Description - Existing corrugated metal pipe (CMP) outlet pipe will be removed and replaced with a new outlet pipe. The existing inlet structure will be used. A new outlet energy dissipation structure will be constructed . Replacement of downstream embankment armoring on Davisburg Road.

• Benefits – can utilize existing inlet structure

• Constraints - Will not increase hydraulic capacity of the dam so Davisburg Road will still overtop under high flow events; Require temporary closure of Davisburg Road. (1-2 months)

• Costs –

Utilize Existing dam inlet structure

Construction of new inlet pipe under Davisburg Road New outlet energy dissipation

Replacement of armoring on downstream embankment of Davisburg Road

Estimate Project Total Cost = $1,001,491.61

100-yr Maintenance Life-Cycle Cost = $321,738.99

• Description - Existing corrugated metal pipe (CMP) outlet pipe will be removed and replaced with four 48-inch outlet pipes. A new inlet structure and new outlet energy dissipation will be constructed

New dam inlet structure Construction of new inlet pipes under Davisburg Road

New outlet energy dissipation

• Benefits – Increases hydraulic capacity of the dam so Davisburg Road will not overtop during high flood events

• Constraints – Requires temporary closure of Davisburg Road (1-2 months).

• Costs – Estimate Project Total Cost = $1,075,975.57


Replacement Alternatives C and D


Alternative C – Replace Existing Spillway with 10-ft x 4-ft Box Culvert:

Alternative D – Replace Existing Spillway with weir and new Bridge:

• Description - Existing corrugated metal pipe (CMP) outlet pipe will be removed and replaced with a 10-ft x 4-ft box culvert. A new inlet structure and outlet structure will be constructed.

• Benefits – increases the hydraulic capacity of the dam such that Davisburg Road will no longer overtop under high flow events (reduces probability to less than 1% chance per year).

• Constraints - Require temporary closure of Davisburg Road.

• Costs – Estimate Project Total Cost = $999,035.57


• Description - Existing corrugated metal pipe (CMP) outlet pipe will be removed and replaced with a new overflow structure. A new inlet structure and outlet energy dissipation will be constructed. Davisburg Road will be reconstructed over the overflow structure with a single span bridge.

• Benefits – Increases the hydraulic capacity of the dam such that Davisburg Road will not overtop under high flow events. Road Commission would assume maintenance and operation of the new bridge.

• Constraints - Will require lengthy (months long) closure of Davisburg Road and may require vertical and horizontal changes to alignment to accommodate bridge.

• Costs – Estimate Project Total Cost = $1,962,623.47


New Dam inlet structure Construction of new box culvert under Davisburg Road

New outlet energy dissipation(example shown is larger scale than what this project would

require, but general concept would be similar)

Weir overflow with stepped spillway for energy dissipation

Single span bridge on Davisburg Road over stepped spillway

-20

-15

-10

-5

0

5

-200 300 800 1300 1800 2300 2800 3300 3800

Dep

th B

elo

w W

ater

Su

rfac

e (

ft)

Distance Upstream of Dam (ft)

Hard Sediment Soft Sediment Proposed Channel 2 Proposed Channel 1 Existing Outlet

Dam Removal – Proposed Restored River Channel


Stream ChannelBankfull Width

Floodplain/Riparian Zone

Floodplain/Riparian Zone

Upland Zone Upland Zone

Grass, Brush, Conifers

Sedges Grasses, Rushes

Deciduous Trees: Cottonwood, Birch etc

Grass, Brush, Conifers

Deciduous Trees: Cottonwood, Birch etc

Sedges Grasses, Rushes

Potential Channel Cross Section

Proposed Channel Profiles:

Existing Dam Culvert

Railroad Crossing

Proposed Restored River Channel Alignment:

Davisburg Road Crossing / Top of Dam

• Description – Potential restored river channel profiles were determined by looking at bathymetric data through the Mill Pond as well as looking at channel elevation in Rotary Park and at the railroad bridge crossing through the Mill Pond. Proposed Channel Profile #1 targeted minimal excavation volumes while still meeting the channel profile slope appropriate for this reach of the river. Proposed Channel Profile #2 targeted excavating down to the hard sediments, or historic river bed material for optimum channel stability and returning this reach of the Shiawassee River channel back to its historic elevation.

• As an active restoration effort, both channel profiles would require some engineered material in the form of riffles or step pools, and bank protection to stabilize the channel and prevent unwanted channel movement post-construction. All materials placed in the river and along river banks would be natural materials (stone or wood).

Example of step-pool installationsExample of channel restoration a couple years post-

construction

Example of a bank stabilization installation

Dam Removal Alternatives F, G, and H


Alternative F – Remove Dam and Place Concrete Box Culvert:

Alternative H – Remove Dam and Place New Bridge Crossing:

Alternative G – Remove Dam and Place Pre-Cast Open-Bottom Culvert:

• Description – Dam removed and replaced with a concrete box culvert under Davisburg Road

• Benefits:• Increases the hydraulic conveyance such that Davisburg Road will not

overtop under high flow events. • Returns fish passage upstream/downstream and sediment transport to

Shiawassee River downstream. • Removes dam safety concerns, maintenance, and aquatic invasive species

control within Mill Pond.• Minimal annual maintenance . • Natural river substrate present through the crossing instead of concrete.

• Constraints - Require temporary closure of Davisburg Road; Invasive species control recommended for the near term in the former impoundment.

Estimate Project Total Cost Channel 1/ Channel 2= $1,596,466.59 / $1,755,553.39


• Benefits:• Increases the hydraulic conveyance such that Davisburg Road will not overtop under high

flow events. • Returns fish passage upstream/downstream and sediment transport to Shiawassee River

downstream. • Removes dam safety concerns, maintenance, and aquatic invasive species control within

Mill Pond. • Minimal long-term annual maintenance.

• Constraints - Requires temporary closure of Davisburg Road; Invasive species control recommended for the near term for the former impoundment

• Costs –Estimate Project Total Cost Channel 1/ Channel 2= $1,693,486.59 / $1,862,973.39


• Description – Dam removed and replaced with a pre-cast open-bottom culvert under Davisburg Road

• Benefits:• Removes dam safety concerns, maintenance, and aquatic invasive species

control in Mill Pond. • Returns fish passage upstream/downstream and sediment transport to

Shiawassee River downstream. • Minimal annual maintenance . • Natural river substrate present through the crossing instead of concrete. • Bridge spanning river and floodplain provides best case scenario for

hydraulic flow through the crossing.• Road Commission for Oakland County would assume maintenance and

operation of new bridge.

• Constraints - Require lengthy (months long) temporary closure of Davisburg Road; Invasive species control recommended for the near term in the former impoundment. Most expensive option and may require vertical and horizontal changes to alignment to accommodate bridge, increasing overall project cost.

• Costs –

Estimate Project Total Cost Channel 1/ Channel 2= $2,087,613.79 / $2,149,212.19


• Description – Dam removed and replaced with a bridge crossing over the Shiawassee River.

• Costs –

Site Overview


mill pond dam feasibility study - cms1files.revize.com

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