Appendix B Project Concept Development Details and Basis of Cost Estimates

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Technical Memorandum 3.5 Czech Village and Rockford Road SW Watershed Drainage Studies

July 6, 2018

Appendix B Project Concept Development Details

and Basis of Cost Estimates

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Memo

Date: Friday, March 16, 2018

Project: Czech Village and Rockford Road SW Watershed Basin Study To: Dave Wallace | City of Cedar Rapids

From: John Cambridge, Steph Then, Anthony Vecchi, Mike Butterfield, Mike Schubert | HDR Subject: Appendix B: Project Concept Development and Basis of Cost Estimates

This Appendix provides the details for project concepts and their associated costs, including project descriptions and assumptions. This appendix also provides a planning-level summary of the costs, potential land acquisitions, and utility conflicts associated with each project. Cost estimates are developed using RS Means unit rates and quantities estimated from the model.

Standard percentage markups for contractor overhead, contractor fees, insurance and bonds, construction contingency, construction observation, geotechnical analysis, and engineering are included where applicable.

Because this is planning-level study, HDR did not conduct site-specific surveys to locate utilities or other potential design constraints. Planning level design was based on observations during the windshield survey and City-provided data. Utility conflicts were identified but were not included in cost estimates for each project. Property acquisition is required for the construction of several proposed projects. For this study, potentially affected properties were identified along with their current assessed value obtained from the Cedar Rapids City Assessor. For projects that require the acquisition of less than 50% of a parcel, the assessed value is reduced based on the percentage of the parcel needed. For projects that require greater than, or equal to, 50%

of a parcel, the full assessed value is used. An additional 20% was added to all property acquisition cost estimates.

Tier 1 Projects

Czech Village Watershed

6^TH ST SW & 12^TH AVE SW DETENTION BASIN – REGIONAL DETENTION ALTERNATIVE

The proposed detention basin would be an on-line facility on the two parcels currently owned by King’s Material Inc on the west side of 6^thSt SW along 12^thAve SW, shown in Figure 1 below.

Model results indicate flooding in this area during the 5-year and 100-year rainfall events caused by overtopping of the south bank of the open channel to the north. Additionally, the downstream stormsewer between 6^thSt SW and I-380 has insufficient capacity to convey the 5- year runoff hydrograph, causing flooding that exceeds 1 foot in some areas.

The proposed basin would be excavated approximately 10 feet with 4:1 ratio side slopes. The stormsewer along 14^thAve SW would be re-routed to drain into the southwestern corner of the detention basin through a new 30” RCP. The existing stormsewer running north along 6^thSt SW would also be diverted by a new structure north of 14^thAve SW. This structure would divert low

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flow into the southeastern corner of the detention basin through a 42” RCP. Excess flows in this existing stormsewer would continue north to the 72” RCP north of the Cedar Rapids City

Services Center Building.

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Figure 1: 6^th St SW & 12^th Ave SW Detention Basin

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As shown in Table 1 below, the proposed detention basin would reduce total flow to the east (pipe flow and flow on 12^th Avenue SW) by approximately 195 cfs and 620 cfs during the 5-year and 100-year rainfall events, respectively. With the detention basin, the residential area

surrounding 12^th Avenue SW would no longer flood during the 5-year rainfall event and flooding would be reduced by more than 40 acre-feet during the 100-year rainfall event, which is an 84 percent reduction in flooded volume.

Table 1: Storage Volume and Flow Rates, King’s Material Detention Basin Baseline Conditions Tier 1 Project Conditions Storage Volume (acre-feet)

N/A acre-feet available

Storage Volume (acre-feet) 78.6 acre-feet available

5-year 100-year 5-year 100-year

Used N/A N/A Used 19.5 72.6

Downstream Peak Flows (cfs) Downstream Peak Flows (cfs)

455 920 260 300

Downstream Flooded Volume (acre-feet) Downstream Peak Flows (cfs)

Downstream Flooded Volume (acre-feet)

12^th Ave Area 8.1 48 0 7.7

This project requires approximately 127,000 CY of excavation and hauling, demolition of 8 structures, and the removal of approximately 42,000 SY of pavement.

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Table 1a: 6^th St SW & 12^th Ave SW Detention Basin Concept Level Costs

Item Type Unit Quantity Cost

Earthwork Excavation CY 126,870 $ 760,000.00 Earthwork Hauling CY 126,870 $ 1,010,000.00 Demolition -- SF 35,000 $ 210,000.00

Pavement

Removal -- SY 42,120 $ 630,000.00 Pipe Installation 42" RCP LF 100 $ 20,000.00 Pipe Installation 30" RCP LF 250 $ 30,000.00 Pipe Installation 12" RCP LF 100 $ 4,000.00 Inlet -- Ea. 2 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Manhole -- Ea. 1 $ 10,000.00 Manhole

Modification -- Ea. 2 $ 4,000.00 Plug and

Abandon Pipe -- Ea. 1 $ 3,000.00

Land Acquisition -- -- -- $ 2,160,000.00

Total Cost $ 4,861,000.00 Construction Total (includes overhead) 15% $ 5,590,000.00

Contractor fee 10% $ 560,000.00

Insurance and bonds 2% $ 110,000.00

Construction Contingency 25% $ 1,400,000.00

Construction Observation 10% $ 560,000.00

Geotechnical 5% $ 280,000.00

Engineering 12% $ 670,000.00

ESTIMATED TOTAL $ 9,170,000.00

Two properties will be impacted by the construction of the project and will require City purchase.

Table 1b: 6^th St SW & 12^th Ave SW Detention Basin Land Rights

Parcel Number Percent of Parcel

Required Assessed Value Estimated Acquisition Cost

14294-85019-00000 100% $ 1,265,700.00 $ 1,518,800.00

14294-84002-00000 100% $ 530,900.00 $ 637,100.00 ESTIMATED TOTAL $ 2,155,900.00

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12^TH AVE SW CAPACITY IMPROVEMENTS – REGIONAL DETENTION ALTERNATIVE

The proposed capacity improvement would be to add a 48” RCP alongside the existing 84” brick pipe that runs east along 12^thAve SW, south on M St SW, and crosses I-380 along the 13^thAve SW corridor. Model results indicate that the existing storm sewer in this area has insufficient capacity to convey the 5-year runoff hydrograph, leading to surcharging and inundation of the streets and yards throughout the neighborhood between 4^thSt SW and I-380, east of the CRCSC.

The proposed 48” RCP alignment is within the City’s right of way and follows the alignment of the existing brick sewer. To minimize potential utility conflicts, the new 48” RCP would be installed on the north side of the existing brick sewer. The proposed sewer would begin at the intersection of 6^thSt SW and 12^thAve SW and tie-in to the parallel 84” brick pipes on the east side of I-380, as shown in Figure 2.

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Figure 2: 12^th Ave SW Capacity Improvements

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The proposed conveyance improvements, along with the other Tier 1 projects, would reduce surface flooding on and around 12^th Avenues SW during both the 5-year and 100-year rainfall events. With the conveyance improvements, no surcharging occurs during the 5-year event.

Flood depths during the 100-year event in the 12^th Avenue SW area are reduced from 3.9 feet to 1.2 feet.

Table 2: Flow Rates, 12^th Ave SW Capacity Improvements Existing Conditions Post-project Conditions Pipe Flow (cfs)¹ Pipe Flow (cfs)¹

241 245 260 300

Overland Flow (cfs)¹ Overland Flow (cfs)¹

215 680 0 30

This project requires the removal and replacement of approximately 5,000 SY of pavement, 13 new manholes, and the installation of 2,000 LF of 48” RCP.

Table 2a: 12^th Ave SW Capacity Improvements Concept Level Costs

Pavement Removal -- SY 5,020 $ 60,000.0 Pavement Replace -- SY 5,020 $ 300,000.0 Pipe Installation 48" RCP LF 2,180 $ 500,000.00 Trenchless Pipe

Installation -- LF 300 $ 230,000.00 Manhole -- Ea. 13 $ 80,000.00 Manhole Modification -- Ea. 2 $ 4,000.00 Total Cost $ 1,174,000.00 Construction Total (includes overhead) 15% $ 1,350,000.00

Construction Contingency 25% $ 340,000.00

Engineering 12% $ 160,000.00

ESTIMATED TOTAL $ 2,230,000.00

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CHANNEL EXTENSION TO 4TH ST SW AND STORM SEWER CAPACITY IMPROVEMENTS – CONVEYANCE IMPROVEMENTS ALTERNATIVE

The proposed channel extension would be to extend the existing open channel south of CRANDIC railroad one block east, to 4^th St SW and additional 60” storm sewer from 4^th St SW to east of I-380. Model results indicate that the existing storm sewer in this area has insufficient capacity to convey the 5-year runoff hydrograph, leading to surcharging and inundation of the streets and yards throughout the neighborhood between 4th St SW and I-380, east of the CRCSC.

A new 84” RCP culvert under 6^th St SW would replace the existing 60” RCP. Additionally, a one foot diameter orifice plate was modeled on the existing 48” RCP in 6^th St SW to restrict the open channel flow from going south to the existing storm sewer. The proposed open channel is a trapezoidal channel with 3:1 side slopes and a bottom width of 10 feet. The left bank would follow the existing ground elevation next to the CRANDIC railroad; the existing minimum ground elevation along the proposed left bank is 730.4 feet. The right bank, which is on the CRCS property line, would be raised to a minimum elevation of 730 feet. The existing minimum

elevation along the CRCS property line is 728.7 feet. At the proposed channel termination on 4^th St SW, stormwater would enter a proposed 60” RCP storm sewer. The proposed 60” RCP runs along 10^th Ave SW from 4^th St SW to M St SW, south on M St SW, and crosses I-380 along the 13th Ave SW corridor and would tie-in to the parallel 84” brick pipes on the east side of I-380, as shown in Figure 3.

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Figure 3: Channel extension to 4^th Street SW and storm sewer capacity improvements.

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The proposed conveyance improvements, along with the other Tier 1 projects, would reduce surface flooding on and around 12^th Ave SW during both the 5-year and 100-year rainfall events. With the conveyance improvements, flooding during the 5-year event in post-project conditions reduced to less than 0.3 feet. Flood depths during the 100-year event in the 12^th Avenue SW area are reduced from 3.9 feet to 3.0 feet.

Table 3: Flow Rates, Channel extension to 4^th Street SW and storm sewer capacity improvements Existing Conditions Post-project Conditions

Pipe Flow (cfs)¹ Pipe Flow (cfs)¹

241 245 195 350

Overland Flow (cfs)¹ Overland Flow (cfs)¹

215 680 10 350

This project requires the excavation and hauling of 6,500 CY of material, removal and

replacement of approximately 5,000 SY of pavement, 13 new manholes, and the installation of 2,000 LF of 60” RCP.

Table 3a: Channel extension to 4^th Street SW and storm sewer capacity improvements Concept Level Costs

Earthwork Excavation CY 6,520 $ 40,000.0 Earthwork Hauling CY 6,520 $ 50,000.0 Railroad Flagging -- Days 15 $ 10,000.00 Pavement Removal -- SY 4,770 $ 60,000.0 Pavement Replace -- SY 4,770 $ 290,000.0 Pipe Installation 84" RCP LF 140 $ 90,000.00 Pipe Installation 60" RCP LF 1,950 $ 640,000.00 Trenchless Pipe

Installation

-- LF

300 $ 230,000.00 Manhole -- Ea. 13 $ 80,000.00 Manhole Modification -- Ea. 2 $ 4,000.00 Headwall -- Ea. 2 $ 50,000.00 Total Cost $ 1,544,000.00 Construction Total (includes overhead) 15% $ 1,780,000.00

Engineering 12% $ 210,000.00

ESTIMATED TOTAL $ 2,930,000.00

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RAILROAD OPEN CHANNEL IMPROVEMENTS

The proposed improvements to the open channel that runs along the south side of the

CRANDIC railroad line from 12^thSt SW to 6^thSt SW include widening the southern bank of the channel, clearing debris and excess vegetation from the channel, and increasing the capacity of the culverts under a railroad crossing, 10^thSt SW and 9^thSt SW. This channel currently does not have the capacity to convey the 5-year runoff hydrograph. During this event, flow breaks out of the channel to the south near each of the three culverts, inundating the surrounding businesses.

The proposed capacity improvement would replace each existing culvert with an 8’x5’ RC box culvert and would widen the channel by excavating along the southern bank until reaching a 3:1 ratio side slope. Some portions of the southern bank already have at least this steep of a side slope and would remain unchanged. Similarly, no changes would be made to the north bank of the channel that directly borders the CRANDIC railroad line. The project area is shown in Figure 4 below.

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Figure 4: Railroad Open Channel Improvements

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The proposed channel and culvert improvements, along with the other Tier 1 projects, would reduce surface flooding to the surrounding industrial area by 95 percent and 70 percent for the 5-year and 100-year rainfall events, respectively. As shown in Table 4, the flow to the 6^th Street SW culvert is increased by 40 cfs and the flow from the channel into the proposed King’s Material detention basin is increased by 170 cfs during the 100-year event.

Table 4: Flow Rates, Railroad Open Channel Improvements Existing Conditions Post-project Conditions Channel Flow (cfs)¹ Channel Flow (cfs)¹

U/S 10^th St 265 395 U/S 10^th St 295 540 U/S 9^th St 215 265 U/S 9^th St 295 540 U/S 6^th St 145 195 U/S 6^th St 255 235 Out-of-Bank Flow (cfs)¹ Out-of-Bank Flow (cfs)¹

U/S 10^th St 150 410 U/S 10^th St 0 260

U/S 9^th St 54 165 U/S 9^th St 0 120

U/S 6^th St 70 80 U/S 6^th St 30 250

This project requires the excavation and hauling of 500 CY of material, clearing and grubbing, Railroad flaggers during all work, 270 LF RC box culvert, and the removal and replacement of a railroad spur line.

Table 4a: Railroad Open Channel Improvements Concept Level Costs

Earthwork Excavation CY 450 $ 3,000.00 Earthwork Hauling CY 450 $ 4,000.00 Clearing & Grubbing -- LS 1 $ 10,000.00 Railroad Flagging -- Days 20 $ 10,000.00

Pipe Installation 8' x 5' RC

Box LF 270 $ 160,000.00 Pipe Removal 60" CMP LF 170 $ 20,000.00 Pipe Removal 36" RCP LF 100 $ 10,000.00 Pipe Removal 48" RCP LF 100 $ 10,000.00 Pavement Removal -- SY 530 $ 10,000.00 Pavement Replace -- SY 530 $ 30,000.00 Railroad Crossing LS 1 $ 20,000.00 Headwall -- Ea. 3 $ 80,000.00 Total Cost $ 367,000.00 Construction Total (includes overhead) 15% $ 420,000.00

Engineering 12% $ 50,000.00

ESTIMATED TOTAL $ 690,000.00

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12^TH ST SW & 14^TH AVE SW DETENTION BASIN

The proposed detention basin would be an on-line facility on an empty lot near 12^thSt SW and 14^thAve SW at the upstream end of the open channel running along the CRANDIC Railroad, shown in Figure 5. As outlined in the description above, model results indicate insufficient capacity in the downstream open channel, causing flooding of the surrounding area during the 5-year rainfall event.

This detention basin would be excavated approximately 6 feet and have 4:1 ratio side slopes.

Excess flow in the existing storm sewer running north along 12^thSt SW would be diverted into the southwestern corner of the detention area by a weir structure. The detention area would drain through a 12” RCP into the open channel to the north.

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Figure 5: 12^th St SW & 14^th Ave SW Detention Basin

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As shown in Table 5 below, the proposed detention basin would reduce flow into the CRANDIC Railroad open channel during the 5-year rainfall event by approximately 65 cfs. There are no significant benefits during the 100-year rainfall event.

Table 5: Storage Volume and Flow Rates, 12^th St SW & 14^th Ave SW Detention Basin Baseline Conditions Tier 1 Project Conditions

Storage Volume (acre-feet) N/A acre-feet available

Used N/A N/A Used 5 5

360 550 295 680

This project requires approximately 6,000 CY of excavation and hauling and 80 LF of 12” RCP.

Table 5a: 12^th St SW & 14^th Ave SW Detention Basin Concept Level Costs

Earthwork Excavation CY 6,100 $ 40,000.00 Earthwork Hauling CY 6,100 $ 50,000.00 Pipe Installation 12" RCP LF 80 $ 3,000.00 Inlet -- Ea. 1 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Manhole -- Ea. 1 $ 10,000.00 Land Acquisition -- -- - $ 10,000.00 Total Cost $ 133,000.00 Construction Total (includes overhead) 15% $ 150,000.00

ESTIMATED TOTAL $ 260,000.00

One property will be impacted by the construction of the project and will require City purchase.

This property is owned by CRANDIC and does not have an assessed value. A placeholder land acquisition cost of $10,000 was used for cost estimation.

Table 5b: 12^th St SW & 14^th Ave SW Detention Basin Land Rights

Required Assessed Value Estimated Acquisition Cost 14294-62004-00000 100% $ - $ 10,000.00

ESTIMATED TOTAL $ 10,000.00

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Rockford Road SW Watershed

BERM AND INLET AT ALLEY WEST OF 10^TH STREET

Runoff from the watershed is conveyed under the Union Pacific railroad tracks in four 60-inch culverts into a 140-foot long open channel section on the west side of a Cargill Plant. Open channel flow is conveyed under Cargill by a single 60-inch culvert before re-entering a channel to the north. It appears that this 60-inch conduit was installed to replace 800 feet of open channel that existed prior to the construction of the Cargill Plant.

Hydrology model results show that runoff from the 5-year storm backs up in the channel west of Cargill and overtops the right bank. Flow backing up in this channel causes flooding in the commercial development on the upstream side and leads to overland flow on the downstream side crossing over the Cargill Plant. Storm sewer intake and pipe capacity in this neighborhood is inadequate to capture the overland flow, so it is conveyed as overland flow through the Taylor neighborhood causing shallow flooding throughout the neighborhood. Model results show that if the overland flow from the 5-year storm could be returned to the open channel north of 8^th Avenue, the downstream system has sufficient capacity to convey the 5-year storm.

Approximately 240 cfs of supplemental pipe capacity would be required for a conduit parallel to the single 60-inch conduit under Cargill. Given the proximity of silo foundations and active railroad tracks, a geotechnical investigation would be required to determine the feasibility of open-cut construction of additional conduits along the existing 60-inch pipe. This supplemental pipe capacity could also be installed in the following locations.

 From the open channel to 10^th Street along 12^th Avenue

 From the open channel to the culvert at 8^th Avenue, following 12^th Ave and the alley west of 10^th Street

 West of the Union Pacific railroad line along Rockford Road to the culvert at 8^th Avenue Alternatively, the supplemental capacity could be constructed along the alley west of 10^th Street (Alley) east of the Cargill Plant site. Multiple inlets and a low berm would likely be required to intercept overland flow. Intercepting this surface flow would eliminate this source of flooding and greatly reduce flooding during the 5-year storm in the Taylor neighborhood to the east. It would also reduce the shallow flooding during the 100-year storm.

The berm would either be designed to follow the alley west of 10^th Street from 12^th Avenue to 8^th Avenue or to make a 90⁰ bend to the west at 10^th Avenue and tie in to the elevation of the nearby rail lines, as shown in Figure 6. A 66” RCP would be required to convey this surface flow along the alignment of the existing 18” sewer along 10^th Street to 5^th Avenue. Alternatively, this 66” RCP could follow the alley west of 10^th Street and discharge back into the open channel north of 8^th Avenue.

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Figure 6: Proposed Cargill Berm

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As shown in Table 6 below, this berm significantly reduces the shallow flooding in the Taylor neighborhood for the 5- and 100-year storms. For the 5-year storm, the berm prevents flooding caused by breakout flows at Cargill to homes along 10^th and 9^th Street to the north and 10^th and 9^th Avenue to the east. This project will result in an increase to the flooded area at Cargill during the 5-year event, additional flooding downstream along 5^th, 4^th, and 3^rd Avenues, and a 5%

increase to peak flow in the pipe along 5^th Avenue SW. These increases are due to the fact that overland flows are being added back into the storm sewer network at the berm where they are moving overland through the Taylor neighborhood during baseline and Tier 1 project conditions.

This proposed project has such a small effect on downstream storm sewer performance because it is reasonable to expect the storm sewer system was originally designed convey the entire 5-year storm.

For the 100-year storm, the berm reduces flooding to homes along 10^th Street and 9^th Street to the north and 10^th Avenue and 9^th Avenue to the east. However, this project would increase the amount of flooding to homes and businesses north of 5^th Avenue SW unless offset by storm sewer conveyance improvements. As with the 5-year event, the peak flow in the pipe along 5^th Avenue SW would be increased by approximately 5%.

Due to the nature of the berm’s design, the project will not be effective for small rainfall events that do not result in flow breaking out of the channel near Cargill.

Table 6: Storage Volume and Flow Rates, Veterans Memorial Detention Basin Tier 1 Project Conditions Tier 1 with Berm Conditions

Downstream Ponding (acre-feet) Taylor Neighborhood

7.1 14.2 2.8 6.4

Downstream Peak Flows (cfs) Downstream Peak Flows (cfs) 5-year 100-year 5-year 100-year

340 340 360 360

This project requires approximately 850 CY of fill and hauling and 1750 LF of 66” RCP.

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Table 6a: Veterans Memorial Detention Basin Concept Level Costs

Earthwork Fill CY 850 $ 20,000

Earthwork Hauling CY 850 $ 10,000 Pipe Installation 66" RCP LF 1,750 $ 690,000 Pipe Removal 18" RCP LF 1,750 $ 70,000

Pavement Removal

-- SY 4,450

$ 50,000 Pavement

Replace

-- SY 4,450

$ 270,000

Surface Inlet -- Ea. 1 $ 10,000

Total Cost $ 1,120,000 Construction Total (includes overhead) 15% $ 1,290,000

Contractor fee 10% $ 130,000

Insurance and bonds 2% $ 30,000

Construction Contingency 25% $ 320,000

Construction Observation 10% $ 130,000

Geotechnical 5% $ 60,000

Engineering 12% $ 150,000

ESTIMATED TOTAL $ 2,110,000

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VETERANS MEMORIAL PARK DETENTION BASIN

The proposed detention basin would be an off-line facility at the southeastern corner of

Veterans Memorial Park, as shown in Figure 7. Model results indicate flooding along Rockford Road SW near Veterans Memorial Park during the 5-year and 100-year rainfall events that impacts the businesses between Rockford Road SW and the railroad. This flooding extends east into the Taylor neighborhood, caused by an open channel near Cargill overtopping.

The detention area would be excavated approximately 8 feet with 4:1 ratio side slopes and a minimum slope of 2% down its centerline. A cut in the curb on the west side of Rockford Road SW would route flow off of the street and into the detention area. A 12” RCP would drain the detention basin and connect into the existing Rockford Road SW stormsewer.

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Figure 7: Veterans Memorial Detention Basin

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As shown in t

able 7 below, adding a detention basin at Veterans Memorial Park primarily reduces flooding in the downstream Taylor neighborhood to the east. By removing water from Rockford Road SW and releasing it slowly, the peak water surface elevation upstream of the railroad culverts is reduced. This results in less flow breaking out of the channel between the railroad and Cargill and eventually flowing through the Taylor neighborhood. The results tabulated below

demonstrate the effectiveness of Tier 1 projects in reducing the ponded volume in the Taylor neighborhood by 3.5 ac-ft during the 5-year storm and 15 ac-ft during the 100-year storm. No change in peak flow within the stormsewer results from this project as it is focused primarily on surface flooding and reducing the amount of flow that arrives to the railroad culvert via the surface.

Due to the nature of the detention basin’s design, the project will not be effect for small rainfall events that do not result in excess runoff being conveyed downstream on the surface of Rockford Road SW.

Table 7: Storage Volume and Flow Rates, Veterans Memorial Detention Basin Baseline Conditions Tier 1 Project Conditions

10.6 29.2 7.1 14.2

230 240 230 240

This project requires approximately 6,000 CY of excavation and hauling and 200 LF of 12” RCP.

Table 7a: Veterans Memorial Detention Basin Concept Level Costs

Earthwork Excavation CY 6,430 $ 40,000.00 Earthwork Hauling CY 6,430 $ 50,000.00 Pipe Installation 12" RCP LF 200 $ 10,000.00 Inlet -- Ea. 1 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Connect to

Existing Manhole -- Ea. 1 $ 2,000.00 Total Cost $ 122,000.00 Construction Total (includes overhead) 15% $ 140,000.00

ESTIMATED TOTAL $ 230,000.00

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ROCKFORD ROAD SW DETENTION BASIN

The proposed detention basin would be an off-line facility at the empty lot south of AutoZone on the west side of Rockford Road SW, as shown in Figure 8. Model results indicate flooding along Rockford Road SW near Veterans Memorial Park during the 5-year and 100-year rainfall events that impacts the businesses between Rockford Road SW and the railroad. This flooding extends east into the Taylor neighborhood, caused by an open channel near Cargill overtopping.

The detention area would be excavated approximately 9 feet with 4:1 ratio side slopes and a minimum slope of 2% down its centerline. A cut in the curb on the west side of Rockford Road SW would route flow off of the street and into the detention area. Additionally, a new 18” RCP would route flow from the detention area east of AutoZone into the proposed detention area.

The removal of a 15” RCP flowing to the north under 16^th Ave SW to a drainage ditch would result in all of the runoff generated along 16^th Ave SW between Rockford Road SW and Williams Blvd SW being routed to this detention basin. A 15” RCP would drain the detention basin and connect into the existing Rockford Road SW stormsewer.

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Figure 8: Rockford Road SW Detention Basin

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As shown in Table 8 below, adding a detention basin at this location primarily reduces flooding in the downstream Taylor neighborhood to the east. By removing water from Rockford Road SW and releasing it slowly, the peak water surface elevation upstream of the railroad culverts is reduced. This results in less flow breaking out of the channel between the railroad and Cargill and eventually flowing through the Taylor neighborhood. Diverting flow from 16^th Ave SW into this detention area and away from the drainage ditch on the north side of 16^th Ave SW also results in less flow breaking out of this ditch and flooding Rockford Rd SW.

The results tabulated below demonstrate the effectiveness of Tier 1 projects in reducing the ponded volume in the Taylor neighborhood by 3.5 ac-ft during the 5-year storm and 15 ac-ft during the 100-year storm. No change in peak flow within the stormsewer results from this project as it is focused primarily on surface flooding and reducing the amount of flow that arrives to the railroad culvert via the surface.

Table 8: Storage Volume and Flow Rates, Rockford Road SW Detention Basin Baseline Conditions Tier 1 Project Conditions

10.6 29.2 7.1 14.2

230 240 230 240

This project requires approximately 13,000 CY of excavation and hauling, 80 LF of 15” RCP, and 110 LF of 18” RCP.

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Table 8a: Rockford Road SW Detention Basin Concept Level Costs

Earthwork Excavation CY 13,160 $ 80,000.00 Earthwork Hauling CY 13,160 $ 110,000.00 Pipe Installation 15" RCP LF 80 $ 3,000.00 Pipe Installation 18" RCP LF 110 $ 10,000.00

Pavement

Removal -- SY 160 $ 2,000.00 Pavement

Replace -- SY 160 $ 10,000.00 Inlet -- Ea. 1 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Plug and

Abandon Pipe -- Ea. 2 $ 10,000.00 Land Acquistion -- -- -- $ 10,000.00 Total Cost $ 255,000.00 Construction Total (includes overhead) 15% $ 290,000.00

ESTIMATED TOTAL $ 470,000.00

Table 8b: Rockford Road SW Detention Basin Land Rights

14300-28004-00000 40% $ 10,000.00 $ 4,800.00

ESTIMATED TOTAL $ 4,800.00

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Tier 2 Projects

10TH AVE SW DETENTION BASIN – CONVEYANCE IMPROVEMENTS ALTERNATIVE

The proposed detention basin would be an off-line facility on the parcel currently owned by Alliant Energy on the north side of 10^th Ave SW, shown in Figure 9 below. Model results indicate flooding in this area during the 5-year and 100-year rainfall events caused by overtopping of the south bank of the open channel to the west. Additionally, the storm sewer between 6^thSt SW and I-380 has insufficient capacity to convey the 5-year runoff hydrograph, causing flooding that exceeds 1 foot in some areas.

The proposed basin would be excavated approximately 8 feet with 4:1 ratio side slopes. The proposed storm sewer along 10^th Ave SW would have a diversion structure that would allow flow to enter the proposed basin via 24” RCP. The proposed basin outlet, near the intersection of 10^th Ave SW and M St SW, is an 18” RCP that connect to the proposed 60” RCP storm sewer.

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Figure 9: 10^th Ave SW Detention Basin

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The proposed detention basin, along with the other Tier 1 and Tier 2 projects, would reduce surface flooding on and around 12^th Ave SW during both the 5-year and 100-year rainfall

events. With the detention basin, the flooded volume between 6^thSt SW and I-380 is reduced by approximately 1 acre-foot during the 100-year event.

Table 9: Flow Rates and Flooded Volume, 10^th Aveue SW Detention Basin Tier 1 Project Conditions Tier 2 Project Conditions Storage Volume (acre-feet)

N/A acre-feet available

Used N/A N/A Used 0.9 6.5

400 440 400 440

Downstream Flooded Volume (acre-feet) Downstream Peak Flows (cfs)

Downstream Flooded Volume (acre-feet)

12^th Ave Area 1.9 34.3 1.8 33

This project requires the excavation and hauling of 10,000 CY of material, the installation of 200 LF of RCP.

Table 9a: 10^th Ave SW Detention Basin Concept Level Costs

Earthwork Excavation CY 10,490 $ 60,000.00 Earthwork Hauling CY 10,490 $ 80,000.00 Pipe Installation 24" RCP LF 85 $ 10,000.00 Pipe Installation 18" RCP LF 70 $ 4,000.00 Inlet -- Ea. 1 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Manhole Modification -- Ea. 2 $ 4,000.00

Land Acquisition -- -- -- $ 200,000.00

Total Cost $ 378,000.00 Construction Total (includes overhead) 15% $ 430,000.00

ESTIMATED TOTAL $ 700,000.00

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Table 9b: Rockford Road SW Detention Basin Land Rights

Required Assessed Value Estimated Acquisition Cost 14283-37001-00000 50% $ 169,800.00 $ 203,800.00

ESTIMATED TOTAL $ 203,800.00

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ALANDALE PARK OPEN CHANNEL IMPROVEMENTS

The proposed improvements to the open channel that runs north from Wilson Ave SW, through Alandale Park, and ends near 12^th St SW & 19^th Ave SW include widening the channel, clearing debris and excessive vegetation, and increasing the capacity of culverts. Model results indicate that the open channel and culverts in this area do not have sufficient capacity to convey the 5- year runoff hydrograph, leading to flooding along 21^st Ave SW and downstream of the open channel along 12^th St SW.

The proposed capacity improvement would replace the existing 72” CMP under 21^st Ave SW with a 72” RCP and would widen the channel by excavating along the banks until reaching a 3:1 ratio side slope. The project area is shown in Figure 10.

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Figure 10: Alandale Park Open Channel Improvements

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As shown in Table 10, the Alandale Park open channel and culvert improvements reduce flooding on 12^th Street SW by 25 cfs and 60 cfs during the 5-year and 100-year rainfall events, respectively.

Table 10: Flow Rates, Alandale Park Open Channel Improvements Existing Conditions Post-project Conditions Pipe Flow (cfs)¹ Pipe Flow (cfs)¹

145 160 190 210

Overland Flow on 12^th St. (cfs)¹ Overland Flow on 12^th St. (cfs)¹ 5-year 100-year 5-year 100-year

60 165 35 105

This project requires approximately 3,000 CY of excavation and hauling, 30 LF of 72” RCP, and the removal and replacement of approximately 700 SY of pavement.

Table 10a: Alandale Park Open Channel Improvements Concept Level Costs

Earthwork Excavation CY 2,900 $ 20,000.00 Earthwork Fill CY 50 $ 1,000.00 Earthwork Hauling CY 2,900 $ 20,000.00 Clearing &

Grubbing -- LS 1 $ 10,000.00 Pipe Installation 72" RCP LF 30 $ 10,000.00 Pipe Removal 72" CMP LF 30 $ 10,000.00

Pavement

Removal -- SY 670 $ 10,000.00 Pavement

Replace -- SY 670 $ 40,000.00 Headwall -- Ea. 1 $ 30,000.00 Total Cost $ 151,000.00 Construction Total (includes overhead) 15% $ 170,000.00

ESTIMATED TOTAL $ 280,000.00

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MANHOLE MODIFICATIONS BEHIND EVERGREEN PACKAGING EQUIPMENT

The proposed modifications relate to four manholes along the stormsewer easement south of Evergreen Packaging Equipment and west of 6^th St SW. Model results indicate flooding west of 26^th Ave SW during the 5-year rainfall event cause by insufficient capacity in the stormsewer with manholes shown in Figure 11.

The modifications to these four manholes involve opening the manhole lids in a way that allows flow to surcharge during rainfall events. This will allow lead to incidental flood storage along the stormsewer alignment in this area that will reduce flood risk to homes on the east side of 6^th St SW.

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Figure 11: Manhole Modification Behind Evergreen Packaging Equipment

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As shown in Table 11, by allowing the pipes to surcharge out of the manholes, the flood volume upstream is reduced by 0.6 acre-feet and 2.3 acre-feet. The volume of water stored in the low- lying area is approximately 0.9 and 3.6 acre-feet during the 5-year and 100-year event, respectively.

Table 11: Storage Volume and Flow Rates, Manhole Modification Behind Evergreen Packaging Equipment Baseline Conditions Tier 1 Project Conditions

Storage Volume (acre-feet) Storage Volume (acre-feet)

Used 0 0 Used 0.9 3.6

Upstream Flooded Volume (acre-ft)

Upstream Flooded Volume (acre-feet)

1.7 9.1 1.1 6.8

This project requires approximately clearing and grubbing and modifying 4 manholes.

Table 11a: Manhole Modification Behind Evergreen Packaging Equipment Concept Level Costs

Clearing &

Grubbing -- LS 1 $ 10,000.00 Manhole

Modification -- Ea. 4 $ 4,000.00 Total Cost $ 14,000.00 Construction Total (includes overhead) 15% $ 20,000.00

Insurance and bonds 2% $ 400.00 Construction Contingency 25% $ 5,000.00 Construction Observation 10% $ 2,000.0 0

Geotechnical 0% $ -

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SWALE BETWEEN 16^TH ST SW & 15^TH ST SW

This project would involve removing an existing 60” RCP running between houses from 16^th St SW and 15^th St SW and replacing it with a swale, or drainage ditch, as shown in Figure 12.

Model results in this area that the existing stormsewer throughout this neighborhood is under- sized and unable to convey the 5-year runoff hydrograph, causing flooding of backyards throughout the block of homes between 16^th St SW and 15^th St SW. This inundation occurs because the backyards in this neighborhood are a relative low point.

The proposed swale is 10 feet deep with 1:1 ratio side slopes. Flow enters the swale at 16^th St SW and re-enters the 60” RCP at 15^th St SW. The steep side-slopes would be reinforced to ensure slope stability during high flows and fencing would be required for to ensure safety.

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Figure 12: Swale Between 16^th St SW & 15^th St SW

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The results shown in Table 12 demonstrate the effect of this project in reducing the backyards and homes between 16^th St SW and 15^th St SW flooded during the 5-year and 100-year rainfall events. While this project would increase the volume of water exposed stored on the surface in this location, it would significantly reduce the surface area flooded. This project would reduce the amount of ponding in backyards by 1.7 ac-ft during the 5-year rainfall event and 1.4 ac-ft for the 100-year event. This downstream effect of this project, however, is minimal. The

downstream peak flow is increased by 15% during the 5-year rainfall event and decreased by 11% during the 100-year rainfall event. This difference in impacts on peak flow is due to the fact that the project functions as a conveyance improvement during smaller storms and a small detention area during larger storms.

The impact of this project, primarily its inability to prevent flooding of homes and backyards, indicates a need for a more fundamental change to the stormsewer in this area. Other potential projects at this location were investigated as part of this study but not included in this report.

These projects were intended to increase conveyance capacity and were less effective at eliminating flooding and caused higher increases in peak flow downstream.

Table 12: Storage Volume and Flow Rates, Swale Between 16^th St SW & 15^th St SW Baseline Conditions Tier 2 Project Conditions

Ponding in Backyards (acre-feet)

2.1 3.7 0.4 2.3

260 740 300 660

This project requires approximately 1,000 CY of excavation and hauling, slope stabilization, and the removal of approximately 270 LF of 60” RCP.

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Table 12a: Swale Between 16^th St SW & 15^th St SW Concept Level Costs

Earthwork Excavation CY 1,170 $ 10,000.00 Earthwork Hauling CY 1,170 $ 10,000.00

Slope

Stabilization -- LS 1 $ 250,000.00 Fencing -- LS 1 $ 4,000.00 Pipe Removal 60" RCP LF 270 $ 30,000.00 Inlet -- Ea. 1 $ 10,000.00 Headwall -- Ea. 1 $ 10,000.00 Land Acquistion -- -- -- $ 40,000.00 Total Cost $ 364,000.00 Construction Total (includes overhead) 15% $ 420,000.00

ESTIMATED TOTAL $ 690,000.00

Four properties will be impacted by the construction of the project and will require City easement or purchase.

Table 12b: Swale Between 16^th St SW & 15^th St SW Basin Land Rights

14293-54008-00000 10% $ 68,800.00 $ 8,300.00

14293-54022-00000 10% $ 81,200.00 $ 9,700.00

14293-54009-00000 10% $ 74,800.00 $ 9,000.00

14293-54021-00000 10% $ 79,300.00 $ 9,500.00

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Tier 3 Projects

12^TH ST SW & WILSON AVE SW DETENTION BASIN

The proposed detention basin would be an on-line facility located at the southwest parking lot at the vacant Cryovac Building near 12^th St SW & Wilson Ave SW, shown in Figure 13. Model results indicate flooding in this location caused by insufficient capacity in the downstream stormsewer during both the 5-year and 100-year rainfall events.

The proposed basin would be excavated approximately 6 feet with 4:1 ratio side slopes. Excess flow would be diverted to this detention basin via a weir at the downstream end of the open channel nearby. An outlet structure would connect to the existing stormsewer along 12^th St SW and limit outflow from the detention area to reduce downstream peak flows.

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Figure 13: 12^th St SW & Wilson Ave SW Detention Basin

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As shown in Table 13 below, the proposed detention basin would reduce total flooded volume downstream (Alandale Park and open channel area) by approximately 0.1 acre-feet and 1.5 acre-feet during the 5-year and 100-year rainfall events, respectively. With the detention basin, flow from the open channel no longer contributes to flooding on Wilson Avenue SW near 12^th Street SW. There are minimal stormwater flooding benefits from this project, but the detention basin could be utilized for a water quality improvement initiative.

Table 13: Storage Volume and Flow Rates, 12^th St SW & Wilson Ave SW Detention Basin Baseline Conditions Tier 1 Project Conditions

Storage Volume (acre-feet) N/A acre-feet available

Storage Volume (acre-feet) 4.4 acre-feet available 5-year 100-year 5-year 100-year

Used Used 2.2 4.4

Downstream Flooded Volume (acre-feet)

Downstream Flooded Volume (acre-fet)

1.3 3.0 1.2 1.5

This project requires approximately 7,000 CY of excavation and hauling, re-routing of existing sanitary sewer, and the removal of approximately 5,000 SY of pavement.

Table 13a: 12^th St SW & Wilson Ave SW Detention Basin Concept Level Costs

Earthwork Excavation CY 7,100 $ 40,000.00 Earthwork Hauling CY 7,100 $ 60,000.00 Pavement Removal -- SY 4,510 $ 50,000.00

Fence

Removal/Replacement -- LS 1 $ 4,000.00 Pipe Removal 15" RCP LF 300 $ 10,000.00 Manhole Removal -- Ea. 3 $ 4,000.00 Re-Route Sanitary

Sewer -- LS 1 $ 40,000.00 Pipe Installation 12" RCP LF 20 $ 1,000.00 Inlet -- Ea. 1 $ 10,000.00 Outlet -- Ea. 1 $ 10,000.00 Manhole -- Ea. 1 $ 10,000.00 Manhole Modification -- Ea. 1 $ 2,000.00

ESTIMATED TOTAL $ 970,000.00

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One property will be impacted by the construction of the project and will require City easement or purchase.

Table 13b: 12^th St SW & Wilson Ave SW Detention Basin Land Rights

14324-26001-00000 10% $ 2,227,000.00 $ 267,200.00

ESTIMATED TOTAL $ 267,200.00

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PERFECT GAME DETENTION BASIN

The proposed detention basin would be an off-line facility located on the Perfect Game lot as shown in Figure 14. Model results, and anecdotal information, indicate that this area

experiences up to flooding during the 5-year rainfall event and as much as 5 feet of inundation during the 100-year rainfall event. This parcel is situated at a relative low point where flow backs up due to insufficient capacity in the culverts crossing the railroad to the east.

The proposed detention basin would be excavated approximately 10 feet with 4:1 side slopes and a minimum slope of 2% down its centerline. This excavation will tie in to the existing drainage ditch at the western edge of the property toward the railroad culverts. A curb cut on Rockford Road SW would be used to route flow from the street into the detention area, reducing flood risk to neighboring businesses.

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Figure 14: Perfect Game Detention Basin

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Model results shown in Table 14 demonstrate the fact that the Perfect Game detention area does not significantly reduce downstream flooding or peak flows during the 5-year and 100-year rainfall events. However, this project has value and in other ways. The Perfect Game building is known to have experienced flooding several times in the recent past and model results indicate it could experience flood depths greater than 5 feet during a 100-year rainfall event. With this in mind, there is an opportunity for the City to pursue a buyout and replace the building with this project, reducing flood risk to neighboring businesses during smaller rainfall events.

Table 14: Storage Volume and Flow Rates, Perfect Game Detention Basin Tier 1 Project Conditions Tier 3 Project Conditions

7.1 14.2 6.8 13.2

Downstream Peak Flows (cfs)

230 240 230 240

This project requires approximately 2,000 CY of excavation and hauling, demolition of 1 structures, and the removal of approximately 4,000 SY of pavement.

Table 14a: Perfect Game Detention Basin Concept Level Costs

Earthwork Excavation CY 1,620 $ 10,000.00 Earthwork Hauling CY 1,620 $ 10,000.00 Demolition -- SF 12,540 $ 80,000.00 Pavement Removal -- SY 4,300 $ 60,000.00 Inlet -- Ea. 1 $ 10,000.00

Engineering 12% $ 120,000.00

ESTIMATED TOTAL $ 1,630,000.00

Table 14b: Perfect Game Detention Basin Land Rights

14293-77002-00000 100% $ 573,800.00 $ 688,600.00

ESTIMATED TOTAL $ 688,600.00

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NEWPORT’S DETENTION BASIN

The proposed detention basin would be an on-line facility on the north side of the Newport’s Flowers lot adjacent to Wilson Ave SW, shown in Figure 15. Model results indicate flooding in this area for both the 5-year and 100-year rainfall events. Further downstream in the watershed, runoff from this area contributes to the flooding problems experienced along Rockford Road SW.

The detention basin would be excavated approximately 7 feet with 4:1 ratio side slopes and a minimum 2% slope along the centerline. The existing stormsewer in this area would be removed and the detention basin would be tied in to existing sewer upstream and downstream. An outlet structure would limit flow leaving the detention area to maximize the reduction in peak flow downstream.

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Figure 15: Newport’s Detention Basin