Loading...
HomeMy WebLinkAbout2021CV30425 - Save The Poudre And No Pipe Dream Coporation V. Northern Colorado Water Conservancy District, Northern Integrated Supply Project Water Activity Enterprise, The City Of Fort Collins - 016G - Exhibit 7 Appendix C Poudre River Intake Structure Alternatives Analysis DATE FILED: August 31, 2021 10:40 AM FILING ID: 631C0FDA58B55 CASE NUMBER: 2021CV30425 POUDRE RIVER INTAKE STRUCTURE Alternatives Analysis B&V PROJECT NO. 407416 PREPARED FOR Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) 22 APRIL 2021 ©Black & Veatch Holding Company 2019. All rights reserved. Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) | POUDRE RIVER INTAKE STRUCTURE BLACK & VEATCH | Table of Contents i Table of Contents 1.0 Purpose and Background ...................................................................................................... 3 1.1 Background ............................................................................................................................................ 3 2.0 Existing Conditions .................................................................................................................. 5 3.0 Alternatives ................................................................................................................................ 6 3.1 Riffle-Crest Weir .................................................................................................................................. 6 3.2 Concrete Ogee Weir ............................................................................................................................ 7 3.3 Adjustable-Crest Weir ....................................................................................................................... 7 4.0 Intake Structure ........................................................................................................................ 9 5.0 Hydraulic Control Structure ................................................................................................. 9 References .............................................................................................................................................. 10 LIST OF FIGURES Figure 1 - Conveyance Refinement and Poudre River Intake ................................................ 4 Figure 2 - Riffle-Crest Weir Example ................................................................................................ 6 Figure 3 - Ogee Weir Example ............................................................................................................. 7 Figure 4 - Adjustable Crest Weir Example ..................................................................................... 8 Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) | POUDRE RIVER INTAKE STRUCTURE BLACK & VEATCH | Purpose and Background 3 1.0 Purpose and Background This memo provides an alternative analysis for the proposed Poudre River Intake Diversion Structure (Poudre River Intake) detailing how the preferred alternative, and proposed design, maximizes project goals of minimizing impacts to the: ◼ Site’s naturalistic character ◼ Cache La Poudre River (Poudre River) channel ◼ Poudre River riparian zone The Poudre River Intake is located on the Poudre River just upstream of E. Mulberry Street and S. Lemay Avenue in Fort Collins, Larimer County, Colorado and is part of the Northern Integrated Supply Project (NISP). The services of the Black and Veatch & AECOM team were retained to design and support the development of the Poudre River Intake diversion system. 1.1 BACKGROUND In operation of the Poudre River Intake, Northern Water would release water associated with its Grey Mountain water right (Grey Mountain water) to the Poudre River or allow Grey Mountain water to remain in the Poudre River for subsequent diversion and conveyance to the NISP Participants to improve Poudre River low flows and eliminate dry up points. This flow would also avoid and minimize water quality impacts and enhance water quality and the aquatic and riparian environment. Through operation of the Poudre River Intake, water would be released from Glade Reservoir to the Poudre River near the existing Colorado - Big Thompson (C-BT) Hansen Supply Canal delivery structure near the mouth of the Poudre Canyon. Releases would range from 18 cubic feet per second (cfs) during the winter months to 25 cfs during the summer months, or 14,350 acre- feet annually. That water would be left in the Poudre River for 12 miles as shown in Figure 1 below. The Poudre River Intake would be constructed, as described below, to divert the water released from Glade Reservoir for delivery to the NISP Participants. POUDRE RIVER INTAKE STRUCTURE | Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) 4 APRIL 2021 Figure 1 - Conveyance Refinement and Poudre River Intake Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) | POUDRE RIVER INTAKE STRUCTURE BLACK & VEATCH | Existing Conditions 5 2.0 Existing Conditions The proposed diversion location for the Poudre River Intake is driven by the legal description for this point of diversion in the associated water rights filings. The point of diversion is also upstream of the Mulberry Water Reclamation Facility. Pathogens and emerging contaminants can be a concern with effluent water. The current takeout location is just upstream of the Mulberry Water Reclamation Facility outfall to maintain water quality standards. There are several existing geographic constraints and considerations that are being considered for the proposed Poudre River Intake. The proposed project encompasses an area in the active river channel and the associated riparian zone on the Poudre River in the Homestead Natural Area. This area is a successful restoration area wherein the natural function of riparian and upland areas has been restored and enhanced. It is recognized that this area is sensitive to disturbance and is an important public use area with established access paths. As such, the project is being designed to minimize the temporary and long-term footprint of the diversion structure. Additionally, the total disturbance caused by the project to existing native plant communities and animal species due to habitat disturbance, noise, light and temporary river flow disruption will be minimized and comprehensive post construction restoration will be included to reestablish and enhance the natural function of any disturbed areas. Care will also be taken to limit temporary disruption to public use of the Homestead Natural Area. POUDRE RIVER INTAKE STRUCTURE | Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) 6 APRIL 2021 3.0 Alternatives An analysis of project alternatives and their ability to meet the goals of minimizing impacts to the site’s naturalistic character, river channel, and riparian zone is included below. 3.1 RIFFLE-CREST WEIR This alternative involves the installation of a channel spanning Riffle-Crest Weir structure protruding approximately one foot above the existing bed grade to create necessary headwater conditions for the diversion intake. It would convey up to 25 cfs through the intake structure at all river flows. This structure would be comprised of a boulder grade control at the headward end with a sheet pile and concrete cap hydraulic cutoff placed within the structure to be blended with the natural visual aesthetics of the riverbed. The crest of the boulder grade control structure would have varied elevations of up to approximately 0.75-feet to create hydraulic diversity and shadows for fish passage and to present visually as a natural riffle head. Additionally, the structure would ramp up slightly towards the banks to guide flows toward the center preventing bank erosion and confining flows for low flow fish passage and boater safety. Downstream of the grade control would be an alluvial riffle to tie the grade control structure invert to existing grade at approximately the same bed slope as the existing downstream riffle. The geometry, gradation and material type would be designed to increase fish passage and boater passage stability metrics. The intent of the in-channel structure would be to integrate into the natural hydraulics and aesthetics of the reach while providing the needed hydraulic head for the diversion structure. This alternative would include the diversion intake structure detailed in Section 4. Figure 2 - Riffle-Crest Weir Example Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) | POUDRE RIVER INTAKE STRUCTURE BLACK & VEATCH | Alternatives 7 3.2 CONCRETE OGEE WEIR This alternative involves the installation of a fixed concrete Ogee Weir at an approximate crest elevation of 4330.0’ which would span the main existing river channel. The concrete weir would protrude approximately 1.25 feet from the existing riverbed and extend into the bed approximately 6 – 8 feet. Course alluvial material would be installed downstream of the weir to mitigate potential scour. This alternative would also include the diversion intake structure detailed in Section 4. This alternative would convey up to 25 cfs to the proposed downstream pipe system at all river flows. The weir in this Alternative would establish a fish passage barrier. The hydraulic jump created by the weir may present a boater passage barrier or hazard. The exposed concrete weir would also create a less aesthetically pleasing character to the diversion reach compared to the Riffle-Crest Weir. Figure 3 - Ogee Weir Example 3.3 ADJUSTABLE-CREST WEIR This alternative involves the installation of a channel spanning Adjustable-Crest Weir, Obermeyer or similar, to divert flows into the intake structure. The structure would include a concrete sill and footers extending approximately 6 – 8 feet below grade, adjustable crest elevation gates, control lines (hydrualic and other), and a control house concealing a compressor and other operating system controls. This alternative would also include the diversion structure detailed in Section 4. It would convey up to 25 cfs through the intake structure at all river flows. This alternative would allow for maximized adjustability of sediment transport through the project as the crest could be lowered when possible to pass or flush sediment. This Alternative would create a barrier to both fish and boat passage when the gates were up, which would consistently be the case. This alternative would create a less aesthetically pleasing character to the diversion compared to the Riffle-Crest Weir as the non-natural structure would be visible especially when the gates are up. POUDRE RIVER INTAKE STRUCTURE | Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) 8 APRIL 2021 Visual impacts, mechanical room location, and noise may inhibit the ability to minimize the impacts to the surrounding area with this alternative Figure 4 – Adjustable-Crest Weir Example As discussed above, the Riffle-Crest Weir best meets the goals of minimizing impacts to the site’s naturalistic character, river channel, and riparian zone and is the recommended alternative and proposed design for the diversion structure. Design information for this structure is presented in the plan set. Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) | POUDRE RIVER INTAKE STRUCTURE BLACK & VEATCH | Intake Structure 9 4.0 Intake Structure All three of the proposed Alternatives include an off-channel concrete intake structure comprised of a concrete sill and guide walls, hinge crest gate, and sluice return flow gate to divert flows from the newly established pool upstream of the diversion structure and allow flow control into a vault and a buried pipe downstream of the intake structure (see Plan Set). The intent of the sluice gate would be to clear deposited sediment from in front of the intake structure. By utilizing a hinge crest gate to divert flow into the intake structure, bedload will be maintained in the river. Locked maintenance access grates, exclusion fencing, and other measures could be designed to protect the public from hazards associated with this structure. This structure would be designed to be laterally distant enough from the river to maintain the natural aesthetic of the reach. Natural alluvial materials and vegetation would be used to obscure the structure while not interfering with its efficiency. 5.0 Hydraulic Control Structure A structure is being evaluated so that the diversion and intake would be more resilient to higher flows. A boulder grade control structure would be installed at the headward end of the river right side channel of the island to amor and reduce the risk of the river altering its current main flow path. This can be seen just downstream of station 1+00 of the side channel on drawing C-04 of the Plan Set labeled “Grade Control Structure”. The intent of this structure would be to maintain existing bed grade in the river right channel. The invert of this structure would be at approximately the existing average bed elevation at this location of 4,931.0’. This sub-grade weir structure would be composed of boulder and course alluvial material and would extend down approximately 4 - 6 feet below existing grade. POUDRE RIVER INTAKE STRUCTURE | Northern Integrated Supply Project Water Activity Enterprise (NISP WAE) 10 APRIL 2021 References AECOM. 2020. ADDENDUM to the Detailed Hydraulic Evaluation and Floodplain Mapping for Cache la Poudre River, Boxelder Creek and Indian Creek - As part of the FEMA Risk MAP Cache la Poudre River Watershed Study Larimer and Weld Counties, Colorado. Prepared for Colorado Water Conservation Board. January. AECOM. 2017. Hydraulic Analysis and Floodplain Mapping Technical Support Data Notebook Ft. Collins – Cache La Poudre River Natural Valley Analysis. Prepared for Colorado Water Conservation Board. December. Anderson Consulting Engineers, Inc. 2014. Cache la Poudre River Watershed RiskMAP Flood Study Larimer and Weld Counties, Colorado Hydrologic Modeling Report. Prepared for Colorado Water Conservation Board. January 28. Anderson Consulting Engineers, Inc. 2017. Detailed Hydraulic Evaluation and Floodplain Mapping for Cache la Poudre River, Boxelder Creek and Indian Creek. Prepared for Colorado Water Conservation Board. August. Federal Emergency Management Agency (FEMA). 2013. Flood Insurance Study #08069C, Larimer County, Colorado and Incorporated Areas. Effective December 19, 2006 and Revised February 6, 2013.