Conceptual Design
7.1 Plan Development Overview
The Selected Plan letter from the project sponsors was issued on April 29, 2015, and can be found in APPENDIX A - Project Correspondence (PDF version only). The Selected plan identifies the alternatives selected by the project sponsors to proceed into the Conceptual Design phase of the project. The Selected Plan generally followed the recommended plan alternatives, with the modification of choosing the 100-year Conveyance Alternative for Reach 1, between West 72nd Avenue and Simms Street. Incorporation of pedestrian trails were evaluated at Quaker Street and West 72nd Avenue in the conceptual design phase.
The master plan improvements are intended to mitigate flooding, and prevent erosion along Leyden Creek. Roadway crossings and the crossing with the Croke Canal are intended to convey the 100-year future conditions discharges. An exception is at West 75th Place, which will convey the 10-year discharge in accordance with Jefferson County Criteria. Future erosion potential will be managed implementing check structures. Mitigation of the 100-year floodplain within the Woodland Valley No. 7 subdivision is proposed through the implementation of adjacent channel improvements. Finally, the master plan improvements incorporate trail connections to the regional trail networks, where applicable.
7.1.1 General Recommendations
Land-use changes to contributing watersheds affect the flood hazard nature (i.e., runoff rates, volumes and depths), the transport of sediment, and the water quality of the receiving natural waterways. To encourage the implementation of this master plan, it is recommended:
- That the controlling jurisdictions take steps to stabilize all major waterways when their watershed urbanizes, rehabilitate existing degraded reaches of the waterways and their tributaries, and aggressively control erosion and sediment transport during construction activities.
- That Sponsors and any other jurisdiction having land use control powers in this watershed require new land development and significant redevelopment and publicly funded projects to provide to the maximum extent practicable runoff volume control practices (i.e., minimize directly connected impervious areas and employ infiltrating BMPs) whenever site conditions permit.
- That the controlling jurisdictions take steps to require that all BMPs for all new development, redevelopment, and publicly funded projects provide to the maximum extent practicable a Water Quality Capture Volume (WQCV) as recommended in the Urban Storm Drainage Criteria Manual - Volume 3, after accounting for volume reductions achieved using volume control practices as recommended under item b above.
- That all jurisdiction having land use control powers in this watershed continue to implement their floodplain management regulations, including regulation of the 100-year floodway and floodplain.
- If not already done so, all jurisdictions should adopt a policy of preserving the defined floodplains as open spaces to the maximum extent possible and that at least 1-foot freeboard be provided for the lowest floor above the 100-year flood elevation shown on the latest flood hazard area delineation of FIRM maps for all human occupied structures built adjacent to, or within, the defined 100-year floodplains.
- That all jurisdiction having land use control powers in this watershed continue to participate in FEMA’s flood insurance Community Rating System and public education programs.
7.1.2 Conceptual Design Cost Estimates
Cost estimates for the conceptual design were developed using UDFCD’s master planning cost estimating spreadsheet UD-MP COST, version 2.2. The Colorado Construction Index was updated to the First Quarter 2015 value of 1.0703. Utility relocation estimates were determined from information provided by the City of Arvada, Century Link, and XCEL Energy. The City of Arvada provided sanitary sewer information with approximate depths and the location and sizing of the water mains. Century Link and XCEL Energy provided approximate utility locates at each street crossing.
Easement costs were calculated from the easement area required for each of the property and the actual land value provided by Jefferson County.
7.2 Master Plan Description
The Conceptual Design is described on a reach by reach basis in Sections 7.2.1 through 7.2.4. Cost Estimates for the Selected Plan can be found in Table 7-5: Cost Estimate Summary by Reach. Schematics for the Selected Plan can be found in Figure 7-1. Master Plan maps and profiles can be found in APPENDIX H.
Downstream of Leyden Lake a design slope of 0.45% was selected for stabilization of the main channel. Upstream of the Leyden Lake, a design slope of 0.60% was selected. These values were chosen to in accordance of UDFCD criteria, previous master plans, and discussion with the project sponsors.
In general, toe protection along Leyden Creek is proposed to allow for a free meander of the low flow channel bottom, except in areas in close proximity to existing or proposed infrastructure. Bio-engineered methods and riparian vegetation is encouraged to be used as an alternate to riprap.
Two feet of cover above new storm sewers was assumed for all roadway crossings. Whenever possible, two feet of clearance between the top of sanitary sewers and the bottom of culverts was proposed. When this clearance was not feasible due to the size of the required crossing structure, one foot of clearance was provided along with a concrete encasement for the sanitary sewer. All other utilities were assumed to be relocated, if required.
Grade control was established through a combination of sloping drop structure, check structures and riffle drop structures. Check structures were used in areas which may experience future channel degradation. Drop structures were selected along proposed channels alignments and areas with significant grade changes between existing and proposed channel configurations. When the grade changes were less than 2-feet in height, riffle type drop structures were recommended.
7.2.1 Reach 1 - Confluence with Ralston Creek to Leyden Creek Park Selected Plan
The selected plan for Reach 1 recommends improving the bridge at West 72nd Avenue and increasing the conveyance capacity of the channel downstream. A 10 foot concrete pedestrian trail was also included from Simms Street through West 72nd Avenue along with a proposed pedestrian underpass with eight feet of clearance. This underpass will connect to the existing trail at Leyden Creek Park. Two sloping boulder drop structures upstream of West 72nd Avenue lower the channel invert to allow adequate clearance for the trail underpass. A 110 ft. span bridge at West 72nd Avenue has been proposed to convey the 100-year discharge of 2,083 cfs. Double stacked boulder walls have been proposed on both sides of the channel to minimize the required easements on private property. The boulder wall transitions to standard side slopes before tying into existing channel just upstream of Simms Street. The existing drop structure just upstream of Simms Street is proposed to be removed to accommodate the improvements.
This project would remove the only structure in the 100-yr floodplain downstream of West 72nd Avenue, the First Church of Arvada. All residential structures in the Woodland Valley No. 3 subdivision would also be removed from the Zone X Shallow Flooding Hazard Area.
Upstream of West 72nd Avenue, in Leyden Creek Park, the channel is proposed to be lowered to remove the regulatory floodplain from the homes in the Woodland Valley No. 7 subdivision. A riffle drop structure is proposed to transition the channel back to existing grades at the upstream end of improvements. Approximately 530 feet of pedestrian path will need to be relocated with the proposed channel project.
The eight homes currently within the 100-year floodplain would all be removed by this project.
There are several known utilities in this project reach. These utilities will need to be protected, or relocated.
-
WATER
-
6 inch AC crossing proposed channel upstream of Simms Street
-
12 inch STL at West 72nd Avenue
-
8 inch CI at West 72nd Avenue
-
10 inch AC upstream of West 72nd Avenue
-
-
SEWER
-
8 inch VCP near pedestrian bridge upstream of Simms Street
-
8 inch VCP near pedestrian bridge upstream of West 72nd Avenue
-
-
XCEL Gas
-
XCEL Electric
-
Century Link
Table 7-1 : Reach 1 Cost Estimate Summary
| Description | Quantity | Unit | Unit Cost | Total Cost | ||
|---|---|---|---|---|---|---|
| Hydraulic Structures | ||||||
| Sloping Drop Structures | ||||||
| Height (ft) | Bottom Width (ft) | Yn (ft) | ||||
| 4 | 54 | 5 | 1 | EA | $136,617.72 | $136,618.00 |
| 2.5 | 54 | 5 | 1 | EA | $123,143.67 | $123,144.00 |
| Channel Improvements | ||||||
| Soil Riprap, Type M | 1000 | C.Y. | $75.00 | $75,000.00 | ||
| Grouted Boulders, 48" | 1422 | S.Y. | $214.00 | $304,356.00 | ||
| Excavation, Mid Range | 12066 | C.Y. | $26.00 | $313,716.00 | ||
| Excavation, Low Range | 233 | C.Y. | $12.00 | $2,796.00 | ||
| Excavation, Low Range | 661 | C.Y. | $12.00 | $7,932.00 | ||
| Excavation, Mid Range | 708 | C.Y. | $26.00 | $18,408.00 | ||
| Landscaping and Maintenance Improvements | ||||||
| Trail/Path, Concrete (10' Width) | 2030 | L.F. | $47.00 | $95,410.00 | ||
| Special Items (User Defined) | ||||||
| Removal of existing bridge | 2000 | S.F. | $50.00 | $100,000.00 | ||
| 110 ft span bridge | 4400 | S.F. | $250.00 | $1,100,000.00 | ||
| 2 ft Riffle Drop | 160 | C.Y. | $150.00 | $24,000.00 | ||
| Removal of existing pedestrian bridge | 300 | S.F. | $50.00 | $15,000.00 | ||
| New pedetrian bridge | 300 | S.F. | $300.00 | $90,000.00 | ||
| Removal of drop structure U/S Simms |
833 | C.Y. | $50.00 | $41,650.00 | ||
| Land Acquisition | ||||||
| Easement/ROW Acquisition | 1.02 | ACRE | $162,316.67 | $165,563.00 | ||
| Master Plan Capital Improvement Cost Summary | ||||||
| Capital Improvement Costs | ||||||
| Pipe Culverts and Storm Drains | $0.00 | |||||
| Concrete Box Culverts | $0.00 | |||||
| Hydraulic Structures | $259,762.00 | |||||
| Channel Improvements | $749,958.00 | |||||
| Detention/Water Quality Facilities | $0.00 | |||||
| Removals | $0.00 | |||||
| Landscaping and Maintenance Improvements | $95,410.00 | |||||
| Special Items (User Defined) | $1,370,650.00 | |||||
| Subtotal Capital Improvement Costs | $2,475,780.00 | |||||
| Additional Capital Improvement Costs | ||||||
| Dewatering | $24,757.80 | L.S. | $24,758.00 | |||
| Mobilization | 5% | $123,789.00 | ||||
| Traffic Control | $15,000.00 | L.S. | $15,000.00 | |||
| Utility Coordination/Relocation | $30,000.00 | L.S. | $30,000.00 | |||
| Stormwater Management/Erosion Control | 5% | $123,789.00 | ||||
| Subtotal Additional Capital Improvement Costs | $317,336.00 | |||||
| Land Acquisition Costs | ||||||
| ROW/Easements | $165,563.00 | |||||
| Subtotal Land Acquisition Costs | $165,563.00 | |||||
| Other Costs (percentage of Capital Improvement Costs) | ||||||
| Engineering | 15% | $418,967.00 | ||||
| Legal/Administrative | 5% | $139,656.00 | ||||
| Contract Admin/Construction Management |
10% | $279,312.00 | ||||
| Contingency | 25% | $698,279.00 | ||||
| Subtotal Other Costs | $1,536,214.00 | |||||
| Total Capital Improvement Costs | $4,494,893.00 | |||||
| Master Plan Operation and Maintenance Cost Summary | ||||||
| Description | Quantity | Unit | Unit Cost | Total Annual Cost | ||
| Hydraulic Structure Maintenance (e.g. debris removal, erosion, structural repairs, etc.) | 2 | EA | $535.00 | $214.00 | ||
| Channel Maintenance (e.g. sediment & debris removal, erosion, tree & weed removal, etc.) | 1850 | L.F. | $2.00 | $740.00 | ||
| Trail Maintenance (e.g. structural repairs, crusher fines, etc.) | 2030 | L.F. | $5.00 | $2,030.00 | ||
| Total Annual Operation and Maintenance Cost | $2,984.00 | |||||
| Effective Interest Rate | 1.50% | |||||
| Total Operation and Maintenance Costs Over 50 Years | $104,439.00 | |||||
7.2.2 Reach 2 - Leyden Creek Park to Upstream of Alkire Street Selected Plan
An extension of Ward Road from West 72nd Avenue north to the existing alignment was in development at the time of this master plan. 30% conceptual design plans were provided by the City of Arvada for incorporation into this report. The roadway expansion will include a stream crossing downstream of West 75th Place as well as two pedestrian trail underpasses.
Twin 9 ft. x 4 ft. RCBC’s are proposed to convey the 10-year discharge of 520 cfs below West 75th Place to meet Jefferson County Criteria. Less than 1 foot of depth of overtopping occurs during the 100-year event. A concrete encasement of the sanitary sewer will also be required to accommodate the proposed culvert and allow two feet of roadway cover. A drop structure transition upstream of the road is also required. This project will not have a significant impact on the floodplain and will not remove the home downstream of West 75th Place from the floodplain.
To mitigate the roadway overtopping and shallow flooding that impacts property to the east of Alkire Street, new box culverts have been proposed. Four 12 ft. x 4 ft. RCBC’s are required to convey the 100-year discharge without overtopping the low point in Alkire Street. Headwater depth at this location is limited by the sanitary crossing located east of the stream crossing. This project will require that the existing pond features, upstream of Alkire Street, be adjusted and lowered accordingly. A 4 foot sloping drop structure is proposed to transition back into existing grades along the channel.
There are two existing structures in the floodplain downstream of the proposed project limits east of Alkire Street. Although these improvements will not remove these structures from the 100-yr floodplain, this project would alleviate the overtopping at Alkire Street, removing eleven structures including six residential homes from the shallow flooding hazard area.
Several check structures proposed within Reach 2 will stabilize the channel slope preventing future channel degradation
The only known utility at West 75th Place is the sanitary sewer at an approximate depth of 8 feet.
At Alkire Street there are several known utilities:
-
WATER
- 18” PVC at Alkire Street
-
SEWER
- 12” PVC at Alkire Street, Depth approximately 9.5 feet
-
Century Link
-
Xcel Electric
-
Xcel Gas
Table 7-2 : Reach 2 Cost Estimate Summary
| Description | Quantity | Unit | Unit Cost | Total Cost | ||
|---|---|---|---|---|---|---|
| Concrete Box Culverts | ||||||
| Box Culvert Pipe | ||||||
| Individual Box Span (ft) | Box Height (ft) | No. of Barrels | Length (ft) | |||
| 9 | 4 | 2 | 54 | L.F. | $1,524.02 | $82,297.00 |
| 12 | 4 | 4 | 50 | L.F. | $3,673.69 | $183,684.00 |
| Headwall and Toewalls | ||||||
| Individual Box Span (ft) | No. of Barrels | Total Span (ft) | ||||
| 9 | 2 | 21.00 | 2 | EA | $1,618.47 | $3,237.00 |
| 12 | 4 | 52.00 | 2 | EA | $4,272.84 | $8,546.00 |
| Wingwalls (includes wingwalls on either side of channel and concrete apron) | ||||||
| Individual Box Span (ft) | Box Rise (ft) | No. of Barrels | ||||
| 9 | 4 | 2 | 2 | EA | $9,214.00 | $18,428.00 |
| 12 | 4 | 4 | 2 | EA | $15,287.41 | $30,574.80 |
| Hydraulic Structures | ||||||
| Sloping Drop Structures | ||||||
| Height (ft) | Bottom Width (ft) | Yn (ft) | ||||
| 4 | 40 | 5 | 1 | EA | $116,149.82 | $116,150.00 |
| Check Structures | ||||||
| Check Structure, Concrete | 210 | L.F. | $289.00 | $60,690.00 | ||
| Channel Improvements | ||||||
| Soil Riprap, Type M | 395 | C.Y. | $75.00 | $29,625.00 | ||
| Excavation, Mid Range | 1432 | C.Y. | $26.00 | $37,232.00 | ||
| Excavation, Mid Range | 7000 | C.Y. | $26.00 | $182,000.00 | ||
| Soil Riprap, Type M | 580 | C.Y. | $75.00 | $43,500.00 | ||
| Removals | ||||||
| Removal of culvert pipe (D<48") | 54 | L.F. | $21.00 | $1,134.00 | ||
| Removal of culvert pipe (48"<D<84") | 50 | L.F. | $54.00 | $2,700.00 | ||
| Special Items (User Defined) | ||||||
| Asphalt Remove and Replace-Alkire | 270 | S.Y. | $60.00 | $16,200.00 | ||
| 2 ft. Riffle Drop | 104 | C.Y. | $150.00 | $15,600.00 | ||
| Asphalt Remove and Replace-W75th Pl | 140 | S.Y. | $60.00 | $8,400.00 | ||
| Concrete Encasement | 18 | C.Y. | $642.00 | $11,556.00 | ||
| Land Acquisition | ||||||
| Easement/ROW Acquisition | 1.10 | ACRE | $105,060.00 | $115,566.00 | ||
| Master Plan Capital Improvement Cost Summary | ||||||
| Capital Improvement Costs | ||||||
| Pipe Culverts and Storm Drains | $0.00 | |||||
| Concrete Box Culverts | $326,767.00 | |||||
| Hydraulic Structures | $176,840.00 | |||||
| Channel Improvements | $292,357.00 | |||||
| Detention/Water Quality Facilities | $0.00 | |||||
| Removals | $3,834.00 | |||||
| Landscaping and Maintenance Improvements | $0.00 | |||||
| Special Items (User Defined) | $51,756.00 | |||||
| Subtotal Capital Improvement Costs | $851,554.00 | |||||
| Additional Capital Improvement Costs | ||||||
| Dewatering | $8,515.54 | L.S. | $8,516.00 | |||
| Mobilization | 5% | $42,578.00 | ||||
| Traffic Control | $25,000.00 | L.S. | $25,000.00 | |||
| Utility Coordination/Relocation | $30,000.00 | L.S. | $30,000.00 | |||
| Stormwater Management/Erosion Control | 5% | $42,578.00 | ||||
| Subtotal Additional Capital Improvement Costs | $148,672.00 | |||||
| Land Acquisition Costs | ||||||
| ROW/Easements | $115,566.00 | |||||
| Subtotal Land Acquisition Costs | $115,566.00 | |||||
| Other Costs (percentage of Capital Improvement Costs) | ||||||
| Engineering | 15% | $150,034.00 | ||||
| Legal/Administrative | 5% | $50,011.00 | ||||
| Contract Admin/Construction Management |
10% | $100,023.00 | ||||
| Contingency | 25% | $250,057.00 | ||||
| Subtotal Other Costs | $550,125.00 | |||||
| Total Capital Improvement Costs | $1,665,917.00 | |||||
| Master Plan Operation and Maintenance Cost Summary | ||||||
| Description | Quantity | Unit | Unit Cost | Total Annual Cost | ||
| Culvert Maintenance (e.g. sediment & debris removal, erosion at entrance/exit, structural repairs, etc.) | 308 | L.F. | $1.00 | $154.00 | ||
| Hydraulic Structure Maintenance (e.g. debris removal, erosion, structural repairs, etc.) | 1 | EA | $535.00 | $107.00 | ||
| Channel Maintenance (e.g. sediment & debris removal, erosion, tree & weed removal, etc.) | 530 | L.F. | $2.00 | $212.00 | ||
| Total Annual Operation and Maintenance Cost | $473.00 | |||||
| Effective Interest Rate | 1.50% | |||||
| Total Operation and Maintenance Costs Over 50 Years | $16,555.00 | |||||
7.2.3 Reach 3 - Upstream of Alkire Street to Leyden Lake Selected Plan
During the September 2013 event, spill flows from Leyden Creek diverted east, flooding areas within the Cameo Estates subdivision. Although the flood flows generally exceed that of the 100-year level, a project has been proposed to help mitigate future hazards. Mitigation in this area includes re-grading of the pond bank east of Cameo Estates which will help keep flows within Leyden Creek and prevent overflows from spilling towards the Cameo Estates subdivision. Costs have been included for the pond embankment, and a new pond outlet structure. An easement cost has been included since the pond is located on private property and will require coordination with the project owner.
Downstream of the Croke Canal presents an opportunity for wetland mitigation. The wetlands south of Leyden Creek should be maintained and improved during final design. A maintenance trail is included which should be incorporated into any pedestrian trail expansion in the area.
At the Croke Canal a triple cell 10 ft. x 3 ft. RCBC will convey the 100-year discharges underneath the canal eliminating the need for the existing siphon and prevent any comingling of flows between the canal and Leyden Creek. The downstream bank of the canal will also be reinforced, with a defined spillway to protect the canal in the event that overtopping occurs. The spillway was designed at the existing overtopping elevation ensuring only flows in excess of the canal capacity are discharged over the spillway. Feasibility of including a purge structure to reduce flows in the canal at this location should be investigated in the future between representatives from the Croke Canal and City of Arvada; however this purge structure has not been included in this plan, at this time.
Similarly, at Indiana Street a 10 ft. x 6 ft. RCBC is proposed to convey the 100-year discharge below the roadway. Several drop structures are needed throughout this reach to achieve the grade needed to eliminate the siphon flow under the Croke Canal. The only two structures within the 100-year floodplain would be removed by the implementation of this project.
There are several known utilities in the project reach:
-
WATER:
-
24” STL Consolidated raw water supply at Alkire Street
-
18” PVC at Alkire Street
-
-
Century Link
-
XCEL Electric
Table 7-3 : Reach 3 Cost Estimate Summary
| Description | Quantity | Unit | Unit Cost | Total Cost | ||
|---|---|---|---|---|---|---|
| Concrete Box Culverts | ||||||
| Box Culvert Pipe | ||||||
| Individual Box Span (ft) | Box Height (ft) | No. of Barrels | Length (ft) | |||
| 10 | 3 | 3 | 104 | L.F. | $2,286.03 | $237,747.00 |
| 10 | 6 | 1 | 56 | L.F. | $1,001.20 | $56,067.00 |
| Headwall and Toewalls | ||||||
| Individual Box Span (ft) | No. of Barrels | Total Span (ft) | ||||
| 10 | 3 | 33.00 | 2 | EA | $2,731.41 | $5,463.00 |
| 10 | 1 | 12.00 | 2 | EA | $993.24 | $1,986.00 |
| Wingwalls (includes wingwalls on either side of channel and concrete apron) | ||||||
| Individual Box Span (ft) | Box Rise (ft) | No. of Barrels | ||||
| 10 | 3 | 3 | 2 | EA | $10,002.98 | $20,006.00 |
| 10 | 6 | 1 | 2 | EA | $12,314.98 | $24,630.00 |
| Hydraulic Structures | ||||||
| Sloping Drop Structures | ||||||
| Height (ft) | Bottom Width (ft) | Yn (ft) | ||||
| 4 | 20 | 5 | 2 | EA | $86,913.29 | $173,827.00 |
| 2.5 | 20 | 5 | 2 | EA | $78,313.29 | $156,627.00 |
| Check Structures | ||||||
| Check Structure, Concrete | 160 | L.F. | $289.00 | $46,240.00 | ||
| Channel Improvements | ||||||
| Soil Riprap, Type M | 750 | C.Y. | $75.00 | $56,250.00 | ||
| 18-inch Riprap, Type H | 600 | C.Y. | $86.00 | $51,600.00 | ||
| Excavation, Low Range | 1090 | C.Y. | $12.00 | $13,080.00 | ||
| Excavation, Mid Range | 8387 | C.Y. | $26.00 | $218,062.00 | ||
| 18-inch Riprap, Type H | 200 | C.Y. | $86.00 | $17,200.00 | ||
| Excavation, Mid Range | 50 | C.Y. | $26.00 | $1,300.00 | ||
| Detention/Water Quality Facilities | ||||||
| Detention (User Entered Quantities) | ||||||
| Outlet Works | 1 | EA | $25,000.00 | $25,000.00 | ||
| Removals | ||||||
| Removal of culvert pipe (D<48") | 300 | L.F. | $21.00 | $6,300.00 | ||
| Landscaping and Maintenance Improvements | ||||||
| Wetlands Plantings | 1 | ACRE | $26,758.00 | $32,110.00 | ||
| Trail/Path, Concrete (10' Width) | 950 | L.F. | $47.00 | $44,650.00 | ||
| Special Items (User Defined) | ||||||
| Asphalt Remove and Replace | 180 | S.Y. | $65.00 | $11,700.00 | ||
| Concrete Cutoff Wall for Cameo Pond | 35 | C.Y. | $642.00 | $22,470.00 | ||
| Land Acquisition | ||||||
| Easement/ROW Acquisition | 180 | S.Y. | $65.00 | $11,700.00 | ||
| Master Plan Capital Improvement Cost Summary | ||||||
| Capital Improvement Costs | ||||||
| Pipe Culverts and Storm Drains | $0.00 | |||||
| Concrete Box Culverts | $345,899.00 | |||||
| Hydraulic Structures | $376,694.00 | |||||
| Channel Improvements | $357,492.00 | |||||
| Detention/Water Quality Facilities | $25,000.00 | |||||
| Removals | $6,300.00 | |||||
| Landscaping and Maintenance Improvements | $76,760.00 | |||||
| Special Items (User Defined) | $34,170.00 | |||||
| Subtotal Capital Improvement Costs | $1,222,315.00 | |||||
| Additional Capital Improvement Costs | ||||||
| Dewatering | $12,223.15 | L.S. | $12,223.00 | |||
| Mobilization | 5% | $61,116.00 | ||||
| Traffic Control | $15,000.00 | L.S. | $15,000.00 | |||
| Utility Coordination/Relocation | $18,400.00 | L.S. | $18,400.00 | |||
| Stormwater Management/Erosion Control | 5% | $61,116.00 | ||||
| Subtotal Additional Capital Improvement Costs | $167,855.00 | |||||
| Land Acquisition Costs | ||||||
| ROW/Easements | $86,609.00 | |||||
| Subtotal Land Acquisition Costs | $86,609.00 | |||||
| Other Costs (percentage of Capital Improvement Costs) | ||||||
| Engineering | 15% | $208,526.00 | ||||
| Legal/Administrative | 5% | $69,509.00 | ||||
| Contract Admin/Construction Management |
10% | $139,017.00 | ||||
| Contingency | 25% | $347,543.00 | ||||
| Subtotal Other Costs | $764,595.00 | |||||
| Total Capital Improvement Costs | $2,241,374.00 | |||||
| Master Plan Operation and Maintenance Cost Summary | ||||||
| Description | Quantity | Unit | Unit Cost | Total Annual Cost | ||
| Culvert Maintenance (e.g. sediment & debris removal, erosion at entrance/exit, structural repairs, etc.) | 368 | L.F. | $1.00 | $184.00 | ||
| Hydraulic Structure Maintenance (e.g. debris removal, erosion, structural repairs, etc.) | 4 | EA | $535.00 | $428.00 | ||
| Channel Maintenance (e.g. sediment & debris removal, erosion, tree & weed removal, etc.) | 1010 | L.F. | $2.00 | $404.00 | ||
| Detention/WQ Maintenance (e.g. sediment & debris removal, mucking out, tree & weed removal, structural repairs, etc.) | 0.5 | ACRE | $1,605.00 | $401.00 | ||
| Trail Maintenance (e.g. structural repairs, crusher fines, etc.) | 950 | L.F. | $5.00 | $950.00 | ||
| Total Annual Operation and Maintenance Cost | $2,367.00 | |||||
| Effective Interest Rate | 1.50% | |||||
| Total Operation and Maintenance Costs Over 50 Years | $82,844.00 | |||||
7.2.4 Reach 4 - Upstream of Leyden Lake
To incorporate the future pedestrian trail, a 180 ft. span bridge is proposed at Quaker Street. A 10 foot concrete pedestrian trail with 10 feet of clearance will provide access to the south along Quaker Street for future trailhead and pedestrian bridge east of Quaker Street. Two sloping drop structures are proposed upstream of Quaker Street to allow adequate roadway cover. This plan follows the current alignment of Quaker Street. Future changes to Quaker Street should be considered with final design of the improvements. There are four structures in the 100-year floodplain. The new channel and bridge will remove two of the structures from the floodplain, while the other two structures area located upstream of the proposed project and would remain in the 100-yr floodplain.
Throughout Pattridge Open Space, check structures have been proposed to stabilize the channel slope and prevent future degradation and erosion.
At West 82nd Avenue a five cell 10 ft. x 5 ft. RCBC crossing structure has been proposed to convey the 100-year discharge below the roadway. Sloping drop structures are required for roadway cover to transition between the existing and proposed channel elevations and to provide cover at the roadway. During final design spreading out the culverts along West 82nd Avenue should be investigated to minimize grade change in the Pattridge Open Space area.
Upstream, at Blue Mountain Road, the existing crossing structure is proposed to be replaced with an 8 ft. x 6 ft. RCBC. Approximately 1300 feet of Blue Mountain Road is also proposed to also be reconstructed to gain adequate roadway cover over the proposed culverts and to prevent overtopping back into the Leyden Creek Watershed. A double stacked 48” grouted boulder wall will prevent flows overtopping the railroad from contributing to the Leyden Creek watershed. These flows will be conveyed under Blue Mountain Road through a second 8 ft. x 6 ft. RCBC east of the stream crossing. The final design of elevating Blue Mountain Road should investigate any impacts to the homes and property downstream of Blue Mountain Road.
The known utilities in Reach 4 include:
Quaker Street:
-
WATER:
-
12” AC transitioning to a 24” PVC at Quaker Street
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6” AC Leyden Townsite private system
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14” PVC in Pattridge Open Space
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XCEL Electric Line at Quaker Street, Pattridge Open Space, and West 82nd Avenue.
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XCEL High Pressure Gas
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CenturyLink
Table 7-4 : Reach 4 Cost Estimate Summary
| Description | Quantity | Unit | Unit Cost | Total Cost | ||
|---|---|---|---|---|---|---|
| Concrete Box Culverts | ||||||
| Box Culvert Pipe | ||||||
| Individual Box Span (ft) | Box Height (ft) | No. of Barrels | Length (ft) | |||
| 10 | 5 | 5 | 44 | L.F. | $4,537.54 | $199,652.00 |
| 8 | 6 | 2 | 35 | L.F. | $1,590.37 | $55,663.00 |
| Headwall and Toewalls | ||||||
| Individual Box Span (ft) | No. of Barrels | Total Span (ft) | ||||
| 10 | 5 | 55.00 | 2 | EA | $4,552.35 | $9,105.00 |
| 8 | 2 | 19.00 | 2 | EA | $1,464.33 | $2,929.00 |
| Wingwalls (includes wingwalls on either side of channel and concrete apron) | ||||||
| Individual Box Span (ft) | Box Rise (ft) | No. of Barrels | ||||
| 10 | 5 | 5 | 2 | EA | $18,869.74 | $37,739.50 |
| 8 | 6 | 2 | 2 | EA | $13,953.41 | $27,906.80 |
| Hydraulic Structures | ||||||
| Sloping Drop Structures | ||||||
| Height (ft) | Bottom Width (ft) | Yn (ft) | ||||
| 4 | 75 | 5 | 1 | EA | $167,316.61 | $167,317.00 |
| 2.5 | 75 | 5 | 1 | EA | $150,834.71 | $150,835.00 |
| 4 | 49 | 5 | 1 | EA | $129,307.14 | $129,307.00 |
| 2.5 | 49 | 5 | 1 | EA | $116,551.19 | $116,551.00 |
| 4 | 30 | 5 | 1 | EA | $101,530.48 | $101,530.00 |
| Check Structures | ||||||
| Check Structure, Concrete | 2170 | L.F. | $289.00 | $627,130.00 | ||
| Channel Improvements | ||||||
| Soil Riprap, Type M | 375 | C.Y. | $75.00 | $28,125.00 | ||
| Excavation, Low Range | 3422 | C.Y. | $12.00 | $41,064.00 | ||
| Excavation, Mid Range | 4158 | C.Y. | $26.00 | $108,108.00 | ||
| Excavation, Low Range | 240 | C.Y. | $12.00 | $2,880.00 | ||
| Excavation, Mid Range | 4967 | C.Y. | $26.00 | $129,142.00 | ||
| Soil Riprap, Type M | 400 | C.Y. | $75.00 | $30,000.00 | ||
| Excavation, Mid Range | 23071 | C.Y. | $26.00 | $599,846.00 | ||
| Grouted Boulders, 36" | 100 | S.Y. | $203.00 | $20,300.00 | ||
| Removals | ||||||
| Removal of culvert pipe (48"D<84") | 163 | L.F. | $54.00 | $8,802.00 | ||
| Landscaping and Maintenance Improvements | ||||||
| Trail/Path, Concrete (10' Width) | 820 | L.F. | $47.00 | $38,540.00 | ||
| Special Items (User Defined) | ||||||
| Asphalt Remove and Replace - W 82nd | 300 | S.Y. | $65.00 | $19,500.00 | ||
| Asphalt Remove and Replace - BMRoad | 5600 | S.Y. | $65.00 | $364,000.00 | ||
| 180 ft. span bridge - Quaker Street | 5400 | S.F. | $250.00 | $1,350,000.00 | ||
| Pedestrian Trail Bridge D/S of Quaker | 1400 | S.F. | $350.00 | $490,000.00 | ||
| Land Acquisition | ||||||
| Easement/ROW Acquisition | 1.77 | ACRE | $202,258.76 | $357,998.00 | ||
| Master Plan Capital Improvement Cost Summary | ||||||
| Capital Improvement Costs | ||||||
| Pipe Culverts and Storm Drains | $0.00 | |||||
| Concrete Box Culverts | $332,995.00 | |||||
| Hydraulic Structures | $1,292,670.00 | |||||
| Channel Improvements | $959,465.00 | |||||
| Detention/Water Quality Facilities | $0.00 | |||||
| Removals | $8,802.00 | |||||
| Landscaping and Maintenance Improvements | $38,540.00 | |||||
| Special Items (User Defined) | $2,223,500.00 | |||||
| Subtotal Capital Improvement Costs | $4,855,972.00 | |||||
| Additional Capital Improvement Costs | ||||||
| Dewatering | $48,559.72 | L.S. | $48,560.00 | |||
| Mobilization | 5% | $242,799.00 | ||||
| Traffic Control | $25,000.00 | L.S. | $25,000.00 | |||
| Utility Coordination/Relocation | $115,000.00 | L.S. | $115,000.00 | |||
| Stormwater Management/Erosion Control | 5% | $242,799.00 | ||||
| Subtotal Additional Capital Improvement Costs | $674,158.00 | |||||
| Land Acquisition Costs | ||||||
| ROW/Easements | $357,998.00 | |||||
| Subtotal Land Acquisition Costs | $357,998.00 | |||||
| Other Costs (percentage of Capital Improvement Costs) | ||||||
| Engineering | 15% | $829,520.00 | ||||
| Legal/Administrative | 5% | $276,507.00 | ||||
| Contract Admin/Construction Management |
10% | $553,013.00 | ||||
| Contingency | 25% | $1,382,533.00 | ||||
| Subtotal Other Costs | $3,041,573.00 | |||||
| Total Capital Improvement Costs | $8,929,701.00 | |||||
| Master Plan Operation and Maintenance Cost Summary | ||||||
| Description | Quantity | Unit | Unit Cost | Total Annual Cost | ||
| Culvert Maintenance (e.g. sediment & debris removal, erosion at entrance/exit, structural repairs, etc.) | 335 | L.F. | $1.00 | $168.00 | ||
| Hydraulic Structure Maintenance (e.g. debris removal, erosion, structural repairs, etc.) | 5 | EA | $535.00 | $535.00 | ||
| Channel Maintenance (e.g. sediment & debris removal, erosion, tree & weed removal, etc.) | 1045 | L.F. | $2.00 | $418.00 | ||
| Trail Maintenance (e.g. structural repairs, crusher fines, etc.) | 820 | L.F. | $5.00 | $820.00 | ||
| Total Annual Operation and Maintenance Cost | $1,941.00 | |||||
| Effective Interest Rate | 1.50% | |||||
| Total Operation and Maintenance Costs Over 50 Years | $67,934.00 | |||||
Table 7-5 : Cost Estimate Summary by Reach
| Reach | Project | Jurisdiction | Reach Length (mi.) | Capital | Easement/ROW | Eng/Admin/Legal | Contingency | Total Capital Cost | 50-year O&M Cost |
|---|---|---|---|---|---|---|---|---|---|
| Reach 1 | W 72nd Avenue | City of Arvada | 0.25 | $2,673,786 | $141,346 | $802,136 | $668,447 | $4,285,715 | $78,889 |
| Woodland Valley | City of Arvada | 0.05 | $119,330 | $24,217 | $35,800 | $29,833 | $209,180 | $25,550 | |
| Reach 1 | 0.83 | $2,793,116 | $165,563 | $837,936 | $698,280 | $4,494,895 | $104,439 | ||
| Reach 2 | W. 75th Place | Jefferson County | 0.10 | $240,334 | $67,013 | $72,100 | $60,084 | $439,531 | $9,310 |
| Alkire Street | City of Arvada | 0.15 | $692,525 | $48,553 | $207,758 | $173,131 | $1,121,967 | $7,245 | |
| Check Structures (3) | Jefferson County | -- | $67,367 | $0 | $20,210 | $16,842 | $104,419 | $0 | |
| Reach 2 | 1.20 | $1,000,226 | $115,566 | $300,068 | $250,057 | $1,665,917 | $16,555 | ||
| Reach 3 | West of Cameo Estates | Jefferson County | -- | $73,228 | $29,284 | $21,968 | $18,307 | $142,787 | $14,035 |
| Indiana Street / Croke Canal | Jefferson County | 0.27 | $1,265,616 | $57,325 | $379,685 | $316,404 | $2,019,030 | $35,560 | |
| Check Structures (3) | City of Arvada | -- | $51,326 | $0 | $15,398 | $12,832 | $79,556 | $0 | |
| Reach 3 | 1.43 | $1,390,170 | $86,609 | $417,051 | $347,543 | $2,241,373 | $49,595 | ||
| Reach 4 | Quaker Street | City of Arvada | 0.13 | $2,747,524 | $336,778 | $824,257 | $686,881 | $4,595,440 | $43,960 |
| Pattridge Open Space | City of Arvada | 2.08 | $701,115 | $0 | $210,335 | $175,279 | $1,086,729 | $0 | |
| W. 82nd Avenue | City of Arvada | 0.15 | $768,277 | $774 | $230,484 | $192,069 | $1,191,604 | $19,005 | |
| Blue Mountain Estates | City of Arvada | -- | $1,313,212 | $20,446 | $393,964 | $328,303 | $2,055,925 | $4,970 | |
| Reach 4 | 6.46 | $5,530,128 | $357,998 | $1,659,040 | $1,382,532 | $8,929,698 | $67,935 | ||
| Master Plan Total Cost | 9.92 | $10,713,640 | $725,736 | $3,214,095 | $2,678,412 | $17,331,883 | $238,524 |
Table 7-6 : Cost Estimate Summary by Jurisdiction
| Jurisdiction | Capital | Easement / ROW | Engineering | Legal/Administrative | Contract Admin/CM | Contingency | Total Capital Cost | Annual O&M Cost | 50-Year O&M Cost |
|---|---|---|---|---|---|---|---|---|---|
| City of Arvada | $9,083,136 | $572,114 | $1,362,472 | $454,157 | $908,315 | $2,270,785 | $14,650,979 | $5,132 | $179,619 |
| Jefferson County | $1,630,504 | $153,622 | $244,575 | $81,525 | $163,051 | $407,627 | $2,680,904 | $1,683 | $58,905 |
Figure 7-1 : Master Plan Schematic
7.3 Prioritization and Phasing
In general, drainage improvements should be constructed from downstream to upstream to avoid any adverse impacts. Due to the isolated nature of each alternative in the master plan, no adverse impacts would be expected from implementing the proposed projects separately. A discussion on prioritization from an engineering perspective is presented below.
Priority 1 - Public Safety:
From a public health and safety
standpoint the alternative with the highest priority of implementation
would be at Indiana Street and the Croke Canal crossing. This area was
severely impacted during the September 2013 event and required breaching
of the Croke Canal to prevent further damages downstream. An
uncontrolled breach of the canal could result in flood damages through
the Cameo Estates, and nearby neighborhoods. The implementation of this
project separates Leyden Creek 100-year discharges from the canal,
further protecting the Canal’s integrity during flood events. A
formalized spill location has also been proposed to manage spill flows
in excess of the canal capacity.
Priority 2 - Emergency Access:
Improvements at West 82nd Avenue are
recommended next to improve localized access during storm events. During
the September 2013 flood this roadway was severely overtopping,
eliminating the possibility of vehicular use. Blue Mountain Road
presents similar access concerns as West 82nd Avenue as it serves as
the primary access for residents in the area. By implementing roadway
and culvert improvements, residents will have improved access during
major storm events. Improvements at Blue Mountain Road will also reduce
trans basin inflows to the Leyden Creek watershed.
Priority 3 - Floodplain Reduction:
Several structures are located
within a shallow, 100-year, flood hazard area east of Alkire Street.
Improvements at Alkire would convey flow underneath the roadway and
reduce flood risk within these shallow flooding zones. Similarly,
improving the channel near Woodland Valley No. 7, upstream of West
72nd Avenue would also remove the eight homes from the 100-year
floodplain. This improvement requires a minimal level of easement
acquisition to implement the improvements.
Priority 4 - Minimum Flood Improvements:
While the West 75th Place
project would not have significant impact on reducing 100-year
floodplain limits, this project would reduce the frequent flooding of
the roadway crossing. The project would convey all discharges up to the
10-year event, whereas the existing crossing structure does not have the
capacity to convey the 2-year event.
Priority 5 - Future Roadway and Trail Needs:
Although projects at
West 72nd Avenue to Simms Street and at Quaker Street will remove
several properties from the floodplain, each of these projects will
require significant easements from private properties to implement the
improvements. For these reasons, is it recommended that these two
projects be implemented alongside, or ahead of, other City needs
including roadway expansion projects or extensions of the regional trail
network.
7.4 Water Quality Impacts
No regional water quality improvements are proposed for the Leyden Creek watershed. New developments, such as Leyden Rock, and Leyden Ranch West, will manage water quality on a site specific basis.
Eroding channel banks also can lead to degradation in water quality throughout a watershed. By implementing the proposed stable channel slopes and stabilization structures, erosion will be less prominent, improving overall water quality along Leyden Creek.
7.5 Operations and Maintenance
Culvert maintenance for all proposed improvements was assumed to occur once every two years. Channel and all proposed hydraulic structures maintenance was assumed to be performed once every five years. Maintenance would include routine mowing of grass lined channels, debris removal, and sediment removal
7.6 Environmental and Safety Assessment
Implementation of the recommended plan will reduce flood hazards at selected roadway crossings. These changes will also improve emergency access during flood events. With exception to at 75th Place, culvert capacity up to the 100-year event has been provided.
ERO assessed the study area for potential wetlands and waters of the U.S., threatened and endangered species, and general wildlife use. Below is a summary of the resources found at the study area and recommendations or future actions necessary based on the current site conditions and federal, state, and local regulations. ERO’s entire assessment can be found in APPENDIX E - Wetland and Riparian Inventory (PDF version only).
7.6.1 General
Although there are some regulated resources in the study area, none of them are unique or regionally important. Aside from potential depletions associated with new water bodies, ERO has not identified any significant regulatory constraints on the proposed projects. Because of their dynamic natures, site conditions and regulations should be reconfirmed by a qualified consultant prior to conducting construction activities within the watershed.
7.6.2 Wetlands and Other Waters of the U.S.
Leyden Creek, most of its tributaries, and abutting wetlands are likely waters of the U.S. Any activity in the proposed alternatives that would require placing dredged or fill material into Leyden Creek, tributaries, or wetlands must comply with Section 404 of the Clean Water Act. Many of the activities in the proposed alternatives would provide a net benefit to the stream, particularly reestablishing open reaches and grading the channel.
7.6.3 Threatened and Endangered Species
There is no suitable habitat present for any listed threatened or endangered species, but depletions associated with new water bodies would likely require consultation on potential depletions associated with the water bodies and their potential effects on downstream threatened and endangered species on the Platte River in Nebraska. If construction activities are likely to take place outside of the Preble’s Denver metro block clearance zone, it is recommended that a threatened and endangered species letter to the U.S. Fish and Wildlife Service be submitted.
7.6.4 Migratory Birds and Other Wildlife
If any active nests are found in the study area, any work that would destroy the nests should not be conducted until the birds have abandoned the nests. If possible, ground-clearing activities should occur outside of the April 1 through August 31 migratory bird breeding season. If construction activities would occur during the migratory bird breeding season, a nest survey should be conducted immediately prior to construction.