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SOUTHERN PLATTE VALLEY DENVER, COLORADO
SECTION 1135 STUDY
FEASIBILITY REPORT
APPENDIX C
HYDRAULIC ENGINEERING & STABILITY ANALYSIS
SEPTEMBER 2018 TABLE OF CONTENTS
1. INTRODUCTION ...... 1
1.1 BACKGROUND ...... ! 1.2 FEASIBILITY STIJDY AND ALIBRNATIVES ...... 2 1.2.1 Continuous emergent bank or low-/yingjloodplain bench ...... 3 1.2.2 Large wetland and riparian habitat patch ...... 3 1.2.3 In-stream, aquatic habitatrestoration ...... 4 1.2.4 Final List ofAlternatives ...... 4 1.3 STIJDY PURPoSE ...... 5 1.4 PREVIOUS REPoRTS ...... 5 2. HYDRAULIC DESIGN DATA & ASSUMPTIONS ...... 5
2.1 HYDROWGY ...... 5 2.1.1 Study Flows...... 5 2.1.2 Qualitative Climate Change Assessment ...... 7 2.2 HYDRAULIC MODEL ...... 10 2.3 STREAMBED, BANKS, AND OVERBANKS ...... 12 2.4 MANN!NG'SNVALUES ...... 15 2.5 RISKANDUNCERTAINTY ASSESSMENT ...... 17 3. STABILITY ANALYSIS ...... 17
3.1 HYDRAULIC GEOMETRY METHOD ...... 17 3.1.1 Width-Discharge Relationships ...... 18 3.1.2 Depth-Discharge Relationships ...... 19 3.1.3 Slope-Discharge Relationships ...... 21 3.1.4 Planform Geometry (Meander Wavelength) ...... 23 3.2 REFERENCE REACH ...... 24 3.3 SHEAR STRESS METHOD ...... 25 3.3.1 Shear Stress Definition ...... 25 3.3.2 Permissible Shear Stress ...... 25 3.3.3 Computed Shear Stress ...... 27 4. STREAM RESTORATION ALTERNATIVES ...... 28
4.1 IN STREAM HABITAT STRUCTURES ...... 28 4.1.1 Boulder Clusters ...... 28 4.1.2 Vanes/Vanes with J-hooks ...... 29 4.1.3 Newbury Rock Riffles/Drop Structure Modifications ...... 31 4.1.4 Floodplain Impact ofIn-Stream Structures ...... 32 4.1.5 Conceptual Structure Layout ...... 33 4.2 RIPARIAN RESTORATION AREAs ...... 35 5. HYDRAULIC IMPACTS ...... 36 6. FUTURE EFFORTS IN SUPPORT OF FINAL DESIGN ...... 40
6.1 REFINEMENT AND CALIBRATION OF THE HYDRUALIC MODELING...... 40 6.2 COLLECTION OF SEDIMENT SAMPLES TO VERIFY STABILITY ANALYSIS ...... 40 6.3 REFINEMENT OF VANE SPACING AND PLACEMENT OF BOULDER STRUCTURES ...... 40 7. REFERENCES ...... 40 LIST OF FIGURES
Figure 1 - Project Location Map ...... 2
Figure 2 - Duration Analysis Plot for USGS 06711565 SOUTH PLATTE RIVER AT ENGLEWOOD, co ...... 6
Figure 3 -Annual Peak Instantaneous Streamflow, South Platte River at Englewood, CO ...... 8
Figure 4 - Range of 93 Climate-Changed Hydrology Models of HUC 1019-South Platte ...... 9
Figure 5 -Trends in Mean of93 Climate-Changed Hydrology Models ofHUC 1019- South Platte .. 9
Figure 6 - Plan View ofHEC-RAS Sections thru Study Reach ...... 11
Figure 7 - Downstream Bed Sample Location Map ...... 14
Figure 8 - 2013 Grab Samples in Reach 2 Location Map ...... 15
Figure 9 - Typical RAS Cross-Section ...... 16
Figure 10 - RAS Cross Section in Restoration Area ...... 17
Figure 11 - Tentative Guide to Width-Discharge Relationships for Erodible Channels (EM 1110-2- 1418, p 5-8) ...... 18
Figure 12 -Top Widths of the Project Area forthe 2-10 Year Events ...... 19
Figure 13 - Mean Bankfull Depth vs Discharge and Median Grain Size (EM 1110-2-1418, page 5-9)20
Figure 14 -Hydraulic Depths in Project Area ...... 21
Figure 15 - Slope vs Discharge and Median Grain Size (EM 1110-2-1418, page 5-10) ...... 22
Figure 16 - Energy Grade Through Study Reach ...... 23
Figure 17-Bankfull Width vs Meander Wavelength (ERDC/CHL CR-01-1, pg 305) ...... 24
Figure 18 -Allowable Velocity-Depth Grain Chart (NEH Part 654 Chapter 8) ...... 27
Figure 19- Shear Stress Results - Existing Condition ...... 27
Figure 20 - Boulder Clusters (NCHRP, 2005) ...... 29
Figure 21-Vanes (NCHRP, 2005) ...... 30
Figure 22 - Vanes with J-Hooks (NCHRP, 2005) ...... 30
Figure 23 - Vane and J-Hook Typical Details (NCHRP, 2005) ...... 30 Figure 24 - Example ofRiffie Structure Constructed in Reach 2 ...... 31
Figure 25 - Newbury Riffie (NCHRP, 2005) ...... 32
Figure 26 - Reach I In Stream Habitat Structures Concept Plan View (Alt K) ...... 34
Figure 27 - Reach 3 In Stream Habitat Structures Concept Plan View (Alt M) ...... 35
Figure 28- 100 Year Water Surface Profiles for Grant Frontier Alternatives G and H ...... 37
LIST OF TABLES
Table I -Discharge Values used in Feasibility (cfs) ...... 6
Table 2 - Comparison of Discharges in Hydrology CLOMR ...... 6
Table 3 - Annual Duration Analysis for USGS 06711565 South Platte River at Englewood, CO ...... 7
Table 4 - Monthly Duration analysis for USGS 06711565 South Platte River at Englewood, Colorado ...... 7
Table 5 - Sediment Sizes (South Platte River upstream of Confluence Park) ...... 13
Table 6- South Platte River Manning's n Values ...... 16
Table 7 - Permissible Shear and Velocity for Selected Lining Materials (Fischenich, 2001) ...... 26
Table 9 - Arapahoe Riffie Quantities (Alt P) ...... 32
Table 10 - Overland Riffie Quantities (Alt Q) ...... 32
Table 11 - In Stream Habitat Structures Inventory (Alt K-Reach l:Alt M-Reach 3) ...... 33
Table 12 - Hydraulic Impacts of the Proposed Alternative ...... 37 1. Introduction 1.lBackground This report addresses the hydraulic and stability analysis for the existing condition of the Southern Platte Valley Project authorized by Section 1135 of the Water Resources Development Act of 1986 (P .L. 99- 662).
The Southern Platte Valley Project is located in the City and County of Denver, Colorado in the north central portion of the state. The proposed project area includes approximately 1.8 miles of the South Platte River from West Harvard Avenue downstream (north) to West Mississippi Avenue (Figure 1). This portion of the South Platte River is located downstream from two existing U.S. Army Corps of Engineers' multi-purpose flood control dams and reservoirs (Bear Creek and Chatfield).
The study area is divided into three reaches:
1. W. Mississippi Avenue to W. Florida Avenue Reach This reach begins at W. Mississippi Avenue and ends upstream at W. Florida Avenue and includes the main river channel and both the east and west banks, as well as the Overland Pond Park. In this reach the channel banks are unimproved and present opportunities. There is a large drop structure within the channel at Overland Pond which may present an opportunity to redesign and redistribute the riverbed gradient along the stream to improve sediment transport, riffie pool habitat, and restore connectivity of in-stream habitats.
2. W. Florida Avenue to W. Evans Avenue Reach This reach extends from upstream of W. Florida Avenue to W. Evans Avenue and encompasses primarily the east and west banks along the Overland Golf Course and Pasquinel' s Landing park. The sponsor has recently performed some restoration within the channel and along the east bank by removing and redistributing drop structures and creating a floodplain bench and side channel.
3. W. Evans Avenue to W. Harvard Avenue Reach This reach spans from W. Evans Avenue to the upstream limits of Grant Frontier Park at W. Harvard Avenue including the main channel and both banks. Existing park land along both the east and west bank presents an opportunity to relocate an existing trail allowing for restoring habitat in the floodplain.
The segment of the South Platte River within the study area has been modified and engineered by flood control infrastructure and urbanization in the City and County of Denver. Primary activities include artificially managing hydrology through the existing flood control projects, armoring the banks and realigning the river. These impacts have altered the physical structure of the system and removed the natural features of a riparian system characteristic of a stream transitioning away from a mountain front. Environmental problems in the study area are listed below.
• Channelization activities and urban development have severely altered channel dimensions, which lack natural form and function • Loss and disruption of natural substrate due to upstream dams has degraded physical and biological processes • Loss of overall stream length and sinuosity has impacted aquatic, wetland, and riparian habitat • Loss of streamside vegetation has impacted wetland and riparian habitat
1 • Loss of in-stream vegetation impacts aquatic habitat, vegetation diversity and density, and nutrient cycling • Water quality in the South Platte River watershed is degraded • Fishery habitat is degraded and populations are disconnected • Loss of stream flow due to withdrawals from the system upstream of the project area
Douglas County
Denver County, Colorado
Section 1135
US Army Corps 0.125 0.25 0.5 Miles of Engineers®
Figure l - Project Location Map
1.2 Feasibility Study and Alternatives The FID for the South Platte River Section 1135 Ecosystem Restoration Project (USACE, 2016) describes the project goals and their relationship to federal interest. This study is currently in the feasibility phase. Plan formulation is a dynamic process with various steps that should be iterated one or
2 more times. This iteration process, which may occur at any step, may sharpen the planning focus or change its emphasis as new data are obtained or as the specification of problems or opportunities changes or becomes more clearly defined. The planning process consists of the following major steps:
(a) Specification of the water and related land resources problems and opportunities (relevant to the planning setting) associated with the Federal objective and specific State and local concerns. (b) Inventory, forecast, and analysis of water and related land resource conditions within the planning area relevant to the identified problems and opportunities. ( c) Formulation of alternative plans. (d) Evaluation of the effects of the alternative plans. ( e) Comparison of alternative plans. (f) Selection of a recommended plan based upon the comparison of alternative plans.
The City and County of Denver and their many partners have invested approximately $35.0M along the South Platte River in the last 7 years on projects to improve riparian and wetland habitats, in-channel aquatics, and recreation/educational opportunities along the river. The City and County of Denver have produced two master plans, the River North Greenway Master Plan (2009) and the River South Greenway Master Plan (2009). The two master plans were the basis for the overall River Vision Implementation Plan (2010). The purpose of these plans was to collaborate with citizens, property owners and stakeholders to introduce and develop opportunities for improving the river's ecological, infrastructure and recreation systems. The master plans characterize existing conditions and offer recommendations on how to move forward and serve as an overarching framework to guide potential ecosystem restoration and other improvements. Some of the projects from the master plans have been completed using a variety of non-federal funds including: rehabilitation of Johnson Habitat Park and Pasquinel's Landing park, Weir Gulch, as well as constructing a series of in-stream rifiles to replace a large drop structure at Overland Golf Course.
During the February 4, 2016 site visit, the PDT and sponsor discussed several potential ecosystem restoration measures, summarized below, but this list would be subject to refmement during the feasibility phase.
1.2.1 Continuous emergent bank or low-lying floodplain bench
This measure could be applied on either or both banks throughout the entire study area to restore the river's access to its adjacent floodplain (Figure 8). Re-vegetation with native wetland and riparian plants would restore a more productive riparian zone and improve biodiversity. Lowering the banks and benching the adjacent floodplain while flattening the bank slopes may increase the flood carrying capacity of the channel with a goal of offsetting any roughness added through the additional vegetation. This may also present an opportunity to potentially contribute to reducing flood risks as an incidental benefit. Restoration of a riparian buffer comprised of native trees, shrubs and herbaceous plants extending along the bank line through the study reach would not only produce habitat benefits in the vicinity of the restoration but provide much needed connectivity between larger habitat patches, contributing to restoration at a system scale.
1.2.2 Large wetland and riparian habitat patch
In less confined reaches (Grant Frontier Park, Overland Pond Park, West Arizona to West Louisiana and South Santa Fe), the availability of larger patches of land may offer slightly different ecosystem restoration opportunities. Existing pedestrian trails can be relocated to upland areas, allowing conversion
3 of lands adjacent to the river to wetland and riparian habitats. Excavation and lowering of the floodplain could open up larger acreages to wetland and possibly side-channel restoration (as was recently completed at Pasquinel's Landing park). Additional fringe wetlands could be established and combined with the re-connection of the floodplain.
1.2.3 In-stream, aquatic habitat restoration
Potential in-channel restoration opportunities exist in the form of providing low-flow channel features that would concentrate flows throughout this portion of the river during low-flow periods. These aquatic improvements would restore natural aquatic habitat ensuring minimum depth and velocities suitable to fish passage, reducing temperatures, improving sediment transport, and decreasing stagnation and algal blooms, all of which would contribute to restoring habitat diversity and function. Replacement or relocation of existing drop structures, like the one at the Overland Pond Park, would redistribute the hydraulic drop over a greater distance and restore fish passage and improve sediment transport processes ( eg. Restoration of riffle pool complexes. In-stream snags and woody debris may be integrated to increase fish and macroinvertebrate habitat. Some stream meandering may also be incorporated to increase sinuosity and channel complexity. 1.2.4 Final List of Alternatives
A full discussion of the alternatives is presented in the main feasibility report. Below is a full listing with a brief description of the alternatives considered:
• Alternative A- In-Fill Aqua Golf to Create Wetland Habiat • Alternative B - Relocate Greenway Trail and Create Riparian Wetland Habitat on Left Bank • Alternative C - Create Riparian/Wetland Habitat in Upstream Portion of Reach 2 • Alternative D - Low Flow Channel Through Overland Golf Course • Alternative E - Relocate Pedestrian Trail Through "South" Grant Frontier Park and Create Riparian/Wetland Habitat • Alternative F - Modify the Harvard Gulch Outfall and Redirect the Flow to Create a "Parallel" Channel • Alternatve G - Relocate the Greenway Trail and Create Riparian/Wetland Habitat Within the Left Bank Portion of Grant Frontier Park • Alternative H-North Low-Flow Channel Through Modified Grant Frontier Park • Alternative I- South Low-Flow Channel Through Modified Grant Frontier Park • Alternative J - Both Low-Flow Channels Through Modified Grant Frontier Park • Alternative K - In-Stream Measures Within Reach 1 • Alternative L - Modify the Existing Drop Structure in Reach 1 With the Addition of an Additional Drop Structure. • Alternative M - In-Stream Measures Within Reach 3 • Alternative N - Modify the Existing Drop Structure In Reach 3 With the Installation of an Additional Drop Structure • Alternative 0 - Revegetate Both Banks Throughout Reach 2 • Alternative P - Modify the Existing Drop Structure in Reach 1 With the Installation of a Riffle Structure • Alternative Q - Modify the Exiting Drop Structure in Reach 3 With the Installation of a Riffle Structure
4 • Alternative R - Modfiy the Harvard Gulch Outfall and Redirect the Flow to Create a "Parallel" Channel and Construct the South Low-Flow Channel Through Modified Grant Frontier Park. • Alternative S - Revegetate Right Bank in Downstream Portion of Reach 2 • Alternative T -Revegetate West Bank in Reach 1 1.3Study Purpose The purpose of the current study is to complete a hydraulic and stability analysis of the identified alternatives and the existing condition. The main study components are summarized below:
• Review relevant studies performed and other available data and information • Perform a stability analysis of existing conditions and the alternative alignments • Develop one-dimensional hydraulic models for existing conditions and the alternatives using the HEC-RAS (River Analysis System) computer program • Describe potential in-stream habitat structures for the study area • Create typical cross sections, plan & profile figures • Summarize and compare the restoration alternatives
1.4 Previous Reports Previous engineering reports were obtained and reviewed as well as other pertinent studies and publications from local, state, and Federal agencies, including:
• Project Management Plan, South Platte River Section 1135 Ecosystem Restoration Project, USACE Omaha District, Sepetember 2014.
• Geomorphic Assessment at Survey Cross-Sections, South Platte River, Urban Drainage and Flood Control District, June 1996.
• Phase 1andPhase11 Summary Report South Platte River Multi-Objective River Improvements, Urban Drainage and Flood Control District (Prepared by Merrick & Company), September 2016.
• CLOMR Request for South Platte River, Chatfield to Fort Lupton, Colorado Urban Drainage and Flood Control District (Prepared by Wright Water Engineers), November 2015.
2. Hydraulic Design Data & Assumptions The general data and assumptions used for the hydraulic design and stability analysis are described in this section, including South Platte River hydrology, bed and bank material, and Manning's n values. All elevations cited in this study are based on the NAVD88 vertical datum. 2.1 Hydrology 2.1.1 Study Flows Studies of the hydrology of the South Platte River by the U.S. Army Corps of Engineers (USACE) date back to the 1970's. The earliest documented study of the entirety of the reach within UDFCD's jurisdiction was conducted by Merrick in 1983. This subsequently led to a 1984 Phase A report (master plan) prepared by Wright Water Engineers, Inc. (WWE). The peak discharge profile in the Phase A report was determined from a modeling effort, based on the earlier model by the USACE. This included design
5 storm assumptions (southeast and east storm centers) and yielded discharge profiles that have been in effect in the metropolitan Denver area for many years.
In 2015, UDFCD undertook an update of the South Platte River Hydrology to take advantage of the additional 3 0 years of record in support of a CLO MR request. Upon the initiation of this feasibility study, the flows were still under review. The hydrology CLOMR was finalized and approved in June of2016. Final values differed slightly from those utilized in this feasibility study. The hydrology CLOMR resulted in a significant reduction in peak flow values across the range of events from the previously recognized hydrology.
Table I -Discharge Values used in Feasibility (cfs)
River RS 2-yr 5-yr 10-yr 25-yr 50-yr 100- 200- 500- {cfs) {cfs) {cfs) {cfs) {cfs) yr yr yr {cfs) (cfs) (cfs) South Platte 259315 2600 4300 5600 7400 11400 13800 15100 19100
Table 2 - Comparison of Discharges in Hydrology CLO MR
Peak Discharge (cfs) Location 10%Annual Chance 2 % Annual Olance 1 % Annual Olance 0.2%Annual Olance Existing I Proposed!% Diff Existing I Proposed I% Diff Existing IProposedl% Diff Existing IProposedl% Diff West Dartmouth 6400 I 5000 1-22% 12100 I 10700 1-16% 16soo I 13100 1-21% 31500 I 18400 1-42%
Additional low flow analysis was performed in support of identifying flow needs for fish and water quality. Duration flow values near the project area are plotted in Figure 2. The values were developed utilizing HEC-SSP and the period of record of daily flow values for USGS 06711565 SOUTH PLATTE RIVER AT ENGLEWOOD, CO
Diratiai AnalJlil PICll 1\:r SPR1136_Diratiai 4,500
4,000
3,500
3,000 + +
~ 2500 >-- U'
~ 2,000 -- LL 1,500
1,000 -
500 I ______T I -- l 10 20 30 40 50 ea 70 80 90 100 Percanl ol Time ElC88dad - lnterpolatad Cirw ------C~Cirw Figure 2 - Duration Analysis Plot for USGS 06711565 SOUTH PLATTE RIVER AT ENGLEWOOD, co
6 Table 3 -Annual Duration Analysis for USGS 06711565 South Platte River at Englewood, CO
%ofTime Exceeded Q (cfs) 99 20 95 33 90 41 80 54 50 114 25 278 15 428 10 630 5 1150 2 2130 1 2666.1 0.1 3698.1
Table 4 - Monthly Duration analysis for USGS 06711565 South Platte River at Englewood, Colorado
%ofTime JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Exceeded Q (cfs) 99 16 18 21 30 29 24 21 15 16 30 19 18 95 30 30 33 47 54 50 45 36 31 36 27 25 90 37 37 40 59 94 101 67 64 41 41 33 34 80 42 45 59 81 169 179 125 101 51 47 43 43 50 61 75 91 220 357 382 301 226 92 77 77 60 25 97 112 145 405 999 942 563 398 152 124 128 96 15 114 126 193 555 1798 1289 742 563 217 166 163 122 10 125 139 238 762 2180 1758 963 700 269 203 200 139 5 148 165 301 1289 2733 2460 1890 956 379 382 312 200 2 184 202 436 1883 3189 3385 2560 1278 622 959 565 278 1 248 221 740 2212 3439 3610 2935 2369 895 1099 1052 319 0.1 404 300 1306 2520 3903 4128 3806 3139 1759 1985 1230 570
2.1.2 Qualitative Climate Change Assessment This qualitative analysis followed guidelines set out in ECB 2016-25 Guidance for Incorporating Climate Change Impacts to Inland Hydrology in Civil Works Studies, Designs, and Projects, Appendix C.
7 The goal of a qualitative analysis of potential climate threats and impacts to USACE hydrology - related projects and operations is to describe the observed present and possible future climate threats, vulnerabilities, and impacts relevant to the study goals or engineering designs. The qualitative approach on its own will not produce binding numerical outputs, but may identify the direction of change in climate variables relevant to elements of the hydrology study. In some cases, the qualitative approach may be useful in characterizing future conditions that can be considered in the context of project goals or design vulnerabilities and impacts. This, in turn, can be used to describe future without project conditions or inform decisions during the alternative formulation and selection phase, when one project alternative can be judged to reduce vulnerabilities or enhance resilience more than the others, as well as during the design phase. At the time of this publication, the methods for incorporating climate change into the planning process are still developing. The best available science and the use of professional judgement are needed to address the risks associated with climate change.
The USACE Climate Hydrology Assessment Tool was used to identify historic trends in instantaneous peak flows at USGS gage 06711565 as a proxy for understanding how flows iin the water shed have changed over the period ofrecord. Results from that analysis are presented in the figures below. 10K •
BK
iii £ 6K • ~ • ~ ~ 4K • • • • • • • • • • 2K • • • • • • • • • • • • • • • • • OK 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 201 4 2016 Water Year Figure 3 - Annual Peak Instantaneous Streamflow, South Platte River at Englewood, CO
8 45K Projected Routed Runoff not bia~d corrected. Not for use in quantitative assessments.
40K
35K
12 !:!. 30K £• ~ c;;~ ~ 25K ~-g ::; E ~ ·~ 20K
Ij"' ~ ~ 15K ·~ a.
10K
SK
OK .
CMIP-5 Data Downscaled to HUC-4 level via BCSD MeU10d, Based on 93 comb1m1t1ons of GC/IAIRCP model prcyect1ons Figure 4-Range of 93 Climate-Changed Hydrology Models ofHUC 1019-South Platte
10K Projected Routed Runoff not biased corrected. Not for use In quantitative as!>eSsments.
12 !:!. .g• 7K J ~ 1' 6K ~ E ii! ·~ 5K ::; Ij
~ 4K ~ £ 0 3K
::;~
2K
1K
OK : Year :::2000 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 Water Year
CMIP-5 Data, Downscaled to HUC-4 level via BCSD Method, Based on 93 combmatlons of GClvl/RCP model prOJectJons Figure 5 - Trends in Mean of 93 Climate-Changed Hydrology Models of HUC 1019 - South Platte
9 Results of the literature review indicate an increase in extreme precipitation intensity, a decline in snowpack and streamflow, shift in the timing of runoff to earlier in the year, an increase in average monthly temperature for both summer and winter, and a decrease in snow water equivalent (SWE).
The USACE Climate Change Hydrology Assessment Tool did not find statistically strong results for the South Platte River HUC and the stream gauge at the site. Analysis of historical trends as they relate to annual peak instantaneous streamflows indicate a slight decreasing trend in streamflow. Analysis of 93 Climate-Changed hydrology models ofHUC 1019 South Platte indicate a mean result of little to no change in annual maximum monthly streamflows. Considering the full range ofhydrologic models, there is a chance of significant increases in runoff volume at the site. Considering the mean of the projected annual maximum monthly streamflow projections from the 93 climate changed hydrology models, the analysis shows a slight upward trend in the values projecting into the future.
The USACE Watershed Vulnerability Assessment Tool does not indicate the project area to be at risk.
While literature review and results indicate increases in extreme precipitation and annual peak flows, this qualitative analysis concludes, based on mean projections, that climate change impacts in the project area will not be significant over the life of the project. It should be acknowledged that ifthe maximum projections in the climate simulations for annual peak flows prove accurate, the design assumptions that have gone into the measures proposed in this feasibility study would likely no longer prove accurate. Assumptions on size of riprap, habitat elevations relative to flow frequency, scour assumptions, and other various items would need to be revisited. Direct consequences would include the likelihood of increased O&M costs, reduced performance in terms of successful restoration of the habitats, and perhaps reconfiguration of the project's construction.
2.2Hydraulic Model The model used for the existing conditions was provided by the sponsor. The model utilizes HEC-RAS and was updated in May 2016 by Olsson and Associates. Olsson, on behalf ofUDFCD, combined data from various models developed since 1979 and formed them into one continuous geometry representing the best available data. The extent of the model covers from Chatfield Dam downstream to Baseline Road. Much of the model in the project study area has been updated with recent topographic data in connection with the in stream improvements in reach 2. The model provided contained no XS data downstream of the drop structure in reach 1. Additional sections were incorporated into the model to represent reach I. The additional sections do not contain detailed bathymetry. Development of the model for existing conditions is ongoing. Modifications to the model, such as adjustment of bank stations and roughness values, have already occurred concurrent to this feasibility study. It is important to note that as the project proceeds into the design phase that the latest version of the existing condition be incorporated into the design.
Simulations were run using Version 4.1.0
10 .1?1:~/'Net>UC • "~ ~. -- :§ ~ol " ~bv Wdl Adr nrk lltlt(' 11 SOWi! Plllltt 2 ---I South Platll 1 L191nd 5280 WS 500-yr (er.) ws 200-yr (er.) WS 100-yr (er.) 5260 WS 50-yr (cfo) WS 25-yr(cfo) we 1o-yr (cfo) we 5-yr (cfo) 5240 ws 2-yr (cfo) g Lit S1ruct c .S! Gro'"1d l 5220 .. 11 RightLlvH 1!l <;' ... ! iii ~ 0 .. t1: ~ .. :Ii ; .. Cl l 'ti ~ " Li ! ~ ~ 5200 ; I I... I... ILL :! ... ti 1!l I! i! i .!i .!i i ~ c 10 .!i Cl 1! ~ ... zt zt ~ Ii Ii e- 2' 'ii l ij ~ ~ ~ 11. 11. 11. :s: 1! 8 5180 l 1~ .,t ~ i·c a: ., ~ Ill i i .!! :I! !I J ~ :I! ... o( L~ ~ ... 1"' ~ LL LL LL ~ '!§ .. I ~ '"i 'E 'E 'E ::J :::J 'l I! 'Ii I! I! I! E! 11. ii: If. Cl Cl Cl ~ ~ 11. 5160 i I 252000 254000 256000 258000 260000 262000 264000 266000 Main Channel Distance (ft) 2.3Streambed, Banks, and Overbanks UDCFD performed a geomorphic assessment of the South Platte River in 1996. The study utilized surveyed cross sections and on site observations to summarize the conditions of various reaches of the South Platte River. General description of the study site was characterized as such within the report: • The river has been straightened and realigned. Sinuosity is 1.09. • The river's flood channel is narrow and relatively deep compared to the Rural river. •Except during periods of very low flow, there are hardly any exposed bars. • There is much less riparian vegetation. • The river is bounded by very high-valued lands. • Human works are everywhere. • Most ofthe reach is completely protected by riprap or rubble. In general, the River was observed to be in a degradational state. The rate of degradation in recent history has slowed. Specific to the study reach, the presence of control structures serves to halt localized degradation effects. Banks within the study reach are largely stabilized with riprap/rubble and are able to withstand flows with minimal damage. A lot ofthis aged protection is no longer visible, having been covered up by soil and vegetation. Monitoring suggests only small portions are subject to lateral erosion. Sediment samples ofthe South Platte River were collected by UDFCD in 2013 and 2015 as part of a study of River Improvements on the South Platte River downstream of 6th Avenue. The study is approximately 5 miles downstream of this study area, but the results are likely relevant due to similar hydrology and stream dimensions. The surface bed layer consists predominantly of sand and gravel. The median diameter (d50) ranges from 1 to 5 mm and averages 2.66 mm, which is classified as very fine gravel. Other key gradation parameters d16 ranges from .29 to 1 mm and averages 0.52 mm (coarse sand), and d84 ranges from 5 to 32 mm and 12 averages 14.7 mm (medium gravel). There does not appear to be any significant trends or differences between the sand bar or river samples. In addition, as part of the recent restoration efforts done in Reach 2 of the study area, the City and County of Denver collected grab samples in October of2013 for the purposes of identifying potential contaminants. While gradation testing wasn't performed, lithologic descriptions of the materials stated that sands intermixed with cobbles and pea gravel were encountered and classified under the USCS system as "SP" or poorly graded sands. It is strongly recommended that these values be confrrmed to be indicative of on site conditions, through the acquisition of bed samples at proposed work areas, before designs proceed to the final phase. Table 5 - Sediment Sizes (South Platte River upstream of Confluence Park) Sample Location d16 d50 d84 dmax (mm) TH-1 Sand 0.35 2.1 10 25 TH-2 River 0.45 2.2 32 75 TH-3 Sand 0.42 5 18 75 TH-4 River 1 2.1 6 25 TH-5 Sand 0.5 1.9 5 20 TH-6 Sand 0.29 1 15 35 TH-7 River 0.7 2.2 15 75 TH-8 Sand 0.4 2.1 9 25 TH-9 River 0.4 3 17 35 TH-10 Sand 0.7 5 20 75 Average (mm) 0.52 2.66 14.70 46.50 Standard Deviation (mm) 0.22 1.32 7.94 24.95 Coeffecient of Variation 0.42 0.50 0.54 0.54 13 14 Legend :oo N e Sediment Locations ~Sea~le: iiiiiiiiii1 .= 500'iiiiiiiil •~ ! SITE PLAN 0 Test Pil River Vision Project Wesr Florida Avenue at S.outh P!:;rte River CJ Suspected Landfill Area City ancf County of Denver, Colorado Figure 8 - 2013 Grab Samples in Reach 2 Location Map 2AManning'1 n Valua This study adopts manning's n values utili7.ed in the existing conditions model provided by UDFCD. Roughness values in the model are horimntally varied and change from section to section. Jn general, roughness was set to the values in Table 6. Deviations occur in areas where modifications to the channel have occurred. These deviations generally indicate changes in roughness from restoration actions. It should be noted that the base model is being actively developed by UDFCD. This study has made an assumption ofthe model being properly calibrated. A component of the design phase should be incorporating the proposed alternative into the final version ofthe UDFCD model and independent confirmation ofits calibration through the collection ofwater surface profiles. 15 Table 6 - South Platte River Manning's n Values Manning's n River In-Channel Overbanks .03 .045 Range: Range: South Platte (.02 - .06) (.03 - .07) .048 .048 Overland Range: Range: Park (.015 - .055) (.048 - .055) ... ,.. Arw•adl'IR!lb "'-ch•1 RI•~ 31S;lll:i'*'d~U:t.ib"-•d'llllnfbGlallil .03 .045 5275 Legend 5270 ws 100-yr (ds) ws 50-yr (cfs) 5265 ws 10-yr (cfs) @: c 5260 WS 2-yr (cfs) 0 Ground l 5255 . iii Bank Sta 5250 5245 5240 2100 2200 2300 2400 2500 2600 2700 Station (ft) Figure 9 - Typical RAS Cross-Section 16 Legend 5270 ws 100-yr (cfs) ws 50-yr {cfs) ws 10-yr {cfs) §: 5260 c WS 2-yr {cfs) 0 .. Ground ~ . w 5250 Bank Sta 5240 1900 2000 2100 2200 2300 2400 2500 Station {ft) Figure 10 - RAS Cross Section in Restoration Area 2.5 Risk and Uncertainty Assessment The with and without project conditions rely on forecasts of future conditions and events that cannot be know with complete certainty. Sources of uncertainty include: • Future hydrologic events: Stream.flow and rainfall events will impact the performance of environmental restoration. Extended drought following construction of the project would impact the performance of planting measures. Extreme events could cause geotechnical failures or exceed the design capacity of structures. • Hydraulic parameters: Major sources of uncertainty in the modeling and calculation of stage are the error in the selection of Manning's n, modeling of bridges and other flow obstructions, calibration to observed high water marks, modeling of channel cross sections, expansion/contraction factors for changes in channel width, and starting water surface profiles. The state ofthe art ofhydraulic analysis is not yet able to handle all ofthe natural sources ofuncertainty. • Channel stability: Sedimentation processes could lead to excess scour or deposition within the proposed side channels at Grant Frontier Park. Excess scour around proposed structures could increase the frequency of maintenance assumed in this study. 3. Stability Analysis A stability analysis was performed to evaluate the existing channel. Streams and rivers adjust their channel shapes and particle sizes in response to the supply of water and sediments from their drainage areas, and this in turn can affect streambed stability. In order to define a stable channel configuration for each alternative, the following three methods were applied: (1) hydraulic geometry relationships, (2) analogy or ''reference reach" method, (3) shear stress method, and (4) planform geometry comparison. The hydraulic geometry and shear stress methods are quantitative methods used to evaluate channel stability while the analogy (reference reach) method was used in a primarily qualitative manner. 3.lHydraulic Geometry Method The hydraulic geometry method is an empirical design approach, based on the premise that natural streams and rivers tend to "develop in a predictable way, producing an approximate equilibrium between the channel and the inflowing water and sediment" (Leopold and Maddock, 1953 in Copeland et al., 2001, 17 page 55). Hydraulic geometry relationships relate bankfull channel dimensions such as width, depth, and slope to discharge or watershed drainage area, and serve as useful tools for the preliminary selection of stable channel dimensions and plan.form parameters. Described in this section are width-discharge, depth-discharge, slope-discharge, and planform parameter relationships. 3 .1.1 Width-Discharge Relationships Hydraulic geometry relationships that express average bankfull width as a function of bankfull discharge are typically used to determine channel width in restoration design. EM 1110-2-1418, Channel Stability Assessment for Flood Control Projects, presents guidance for defining this relationship. Top widths of the existing stream were taken from the existing conditions HEC-RAS model. curve no. 1000 .... 3 700 ... a ,,,r "' ~00 :,...-"' / ...... ,,,,,,.....- ~ ;:: ...... / v ..... ~ :mo ,..V / ::i::: .,, ... / v I- :,...- .... ,,, V"'" 0 200 / ?; ,,,,...... / w v <.:> ~ ./ J...... 1.1.. 100 v a:"" J' :::> - ,.., "' ~ (/) 70 ... _, ...... l..' _, ...... ,,,,, :::> 50 ... " u. __,,,,- .,,...... ::!: z ..,/ ,,,,,.,...... , oc( 30 .,,., / ID / V"' 20 .,,,,,...... - - I Q 100 2 5 IOOO 2 5 IOOOO 2 5 100 000 CHANNEL-FORMING OR BANK-FULL DISCHARGE, cfs TENTATIVE GUIDANCE: CURVE 1: STIFF COHESIVE OR VERY COARSE GRANULAR BANKS. CURVE 2: AVERAGE COHESIVE OR COARSE GRANULAR SANKS. CURVE 3: SANDY ALLUVIAL BANKS. Figure 11 -Tentative Guide to Width-Discharge Relationships for Erodible Channels (EM 1110-2-1418, p 5-8) 18 260 Top Width 10-yr (dlJ) 240 Top Width 2-yr (dlJ) 220 200 180 180 140 120 100 254000 258000 258000 280000 282000 Main Channa Distanoe (ft) Figure 12-Top Widths of the Project Area for the 2-10 Year Events According to the relationships outlined in EM 1110-2-1418, assuming channel forming flows fall within the 2-10 year events (2700-5700 cfs), the South Platte River is in a stable configuration in tenns of channel width. There are several areas at the upstream and downstream of the project where access to the overbanks exceeds the expected values shown in Figure 11. It's notable that these correspond to the recent restorations ofPasquinel's landing and Grant Frontier Park North. 3 .1.2 Depth - Discharge Relationships 19 100 ,,,,., . ·-· -·- ---- . >-- .... ~ - L-- ...... :;: ... ,..... ~ ...... - ..... - ---i.- ...... ,---- -~ ,,.... ,,...... _. _...... 1---"' -~ ..-· ~ """ I ~ -- -· ...,, .. - - _, ..,,., - .- -- - ""' ~ _-.. ... - ... .. - --v ~--- ~ __ ...... ---.- .... -_....., .... / 1--- ,_- - ~ I_,...... -- ,,.. .- -- i.--· ,,.... -1--"' i,...- v ...... - ~ -""' ,...... ,,.... - v - -_. ~ .- 7 v ,,...... ""' ./ __.. v . 200 500 1000 2 5 10000 2 5 100000 CHANNEL-FORMING OR BANK-FULL DISCHARGE, cfs Figure 13 -Mam Bankfull.Dcp1h VI Discharp and Median Grain Sm (EM 1110-2-1418, page S-9) 20 SPR1136 Plan: FHAD South Platte River 5/18/2016 South Platte 1 10 Legend Hydr Depth 10-yr {cfs) Hydr Depth 2-yr (cfs) B 6 4 2 o-+-~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 250000 280000 270000 280000 290000 300000 310000 320000 Main Channel Distance (ft) Figure 14 -Hydraulic Depths in Project Area The EM over predicts the mean bankfull depth compared to the results of the HEC-RAS modeling. Given the incised nature ofthe project area, it is reasonable to assume that events in excess ofthe 2-year control the channel forming characteristics. Considering that the EM is intended only to provide approximate estimates, the differences in depth are not necessarily an indicator of channel instability. Further characterization in the design phase of this effort of sediment composition ofthe study area should be undertaken to better defme this relationship. 3 .1.3 Slope-Dis«:harge Relatiomihips 21 I I ' r-...... r--. '-- - I'--.~ 'f~diurn nn -t- -I'--. ~ I l t-- ..._r-...... O 0.0001 100 2 5 1000 2 5 10000 2 5 100000 CHANNEL-FORMING OR BANK-FULL DISCHARGE. cts Figin IS - Slope vs Dillclmge md Median Gmin Size (EM 1110-2-1418, page S-10) Aanm.ing 11DSO1epru •llKI by C011ne to m.edimn l8llds, the s1opo predieton in EM 1418 do not petfunn well. The plot predicta a DSO of30..SO mm when pluggillg in the llC1ual &lope ofthe ll1rcaml. However, 1lope1 compullld Dling hydnm.lil: geometry ~llliOlllbips are cons:idend the leut well-diweloped ofth.I three vmiablN (widib/dep1h/11lope). Channell with und beds where mudi of the flow occars at fluh floods tlelld to hive these value• mider imclk*d by he ~. Overall slope 1hrough the project area ii approximately .OOIS ftlfl. lllggCltiDg a higb1y unmblc clliimel confi&l"ltion. However, 1his is highly vviablo and altered &om tb.l lllllurll <:Olldition duo Ui gndo control pr-1throughout1he proj!Kll The prmence ofgtado emdn>l and llln!mnbmlk ll1Jlbiliation upllrelm. at: wilhin. md downslle.lm ofthe project reach serve to mitipte the rilk ofllopc inl1llbilitie1 being Clllled by the proposed almmlivM. 22 ,.______South Plott.1 ------>< Lltgtlnd E.G. Slope 10-yr (els) 0.006 E.G. Slope 2-yr (cfs) 0.005 0.004 ~ !. 0 ii.i cj 0.003 ui 0.002 0.001 254000 256000 258000 260000 262000 264000 266000 268000 Main Channel Dietance (fl) Figure 16 - Energy Grade Through Study Reach 3.1.4 Planform Geometry (Meander Wavelength) Empirical relationships that correlate meander wavelength with bankfull channel width were developed by Hey and Thorne (2001 ). Once meander wavelength has been estimated and sinuosity calculated following the determination of channel slope, the ideal reach-average planform configuration can be specified. 23 ,..,.,.. ., . 10000 ~------+------!---- ,. ..· .·· ..., ... 10 100 1000 Bankfull Width, W (m) Figure 17-Bankfull Width vs Meander Wavelmgdl {ERDC/CHL CR.-01-1, pg 30S) RofermwiDg Figure 12. top widths for South Platte River for the 2 to 10 year evcmt in tho projoct area mo approximat.cly 3Sm to 43m, respectivoly. Conespondjq m.emdor wavehmgths for 1his nngo ofbankfull widths are 300 to 700 me•rs. Tho project reach fil1ls well short ofthese melriu with a meander wavekmgth ofapproximately 2SOO meters. The cbmmcl for 1hc project resch is highly engineered in planfmm. The meander wavelength values represent an estimation ofwhat would be c:cmsidercd a reuonable approxjmation of a Dll1ural alignment for the channel Aa can be seen fi:om the confidence intervall in Figure 17, the range ofmeander wavekng1h values span nearly an order ofmagnitude.The highly engineered, straightaed llllture ofthe project reaches of stream are incomistcnt wiil the pndil:tions. 3.2Reference Reach This medmcl is buecl on 1ho theory that stream restoration design variabla, (width, depth, and slope), can be estimated using a refermce reach as a pattern. The refeJence reWi must be stable and alluvial 811.d have a similar channel-forming discharge 811.d boundary conditions as 1be project reach. In addition. the reach should be cboaen from either 1ho samo channel and watcmbccl or an area wilh similar dwact.cristi" to the ~ect area. Watershed and ~I similarities include, but are not limited to, hydrology, hydraulic geomcntry, sediment load, and bed and bankmatmal. Given the higbly urbanized and engineered nature ofthe reWi cum:nt1y and CODStrainta placecl due to adj scent propertiea, altered hydrology, and floodplain conc:ems. n:stcration to a fully natuml condition will not be adili:vable at die site. However, there are oppommities to provide incremental improvemmts to the habitat functionality at die 11ite. The City and County ofDenver hu developed a master plan for this stretch ofriver and has already implemented improvemeD.1111 to olher reaches ofthe South Platte River. 24 A realistic goal for this project would be to achieve some of the objectives laid out in the Master Plan and improve habitat connectivity between the various reaches. Thus, there will be some limitations placed on selection of a reference reach for purposes of practicality. In order to find a section of the River truly "natural" in its planform , one would have to look well upstream or downstream of the site. Natural stream characteristics of the South Platte River rapidly change as you exitthe foothills of the Rocky Mountains and enterthe plains to the east of the City. Further discussion of reference reach selection will be performed with the sponsor as feasibility goes forward and project goals are further defmed. Desirable features will be informed by past successes and failures encountered during restoration of other portions of the South Platte River adjacent to the study area. 3.3Shear Stress Method The shear stress method was used to check the stability of the existing channel. In this section, shear stress terms are defmed, approach is discussed, shear stress equations are given, and the results are presented. 3 .3 .1 Shear Stress Definition The shear stress terms used in this section are defmed below: • Computed shear stress - Shear stress calculated based on the hydraulic characteristics of the stream for a particular peak discharge (e.g., the bankfull discharge). Types of computed shear stress include average boundary shear stress, maximum bed shear stress, average bank shear stress, and the maximum shear stress in a bend. • Permissible shear stress - Average shear stress that the bed or bank can withstand before a significant amount of material begins to move or erode. Permissible shear stress is a function of the bed/bank material size, the presence of cohesive soils, and bank slope and vegetation. 3 .3 .2 Permissible Shear Stress Table 7 lists recommended values of permissible shear stress and velocity over a wide array of bed material types (Fischenich, 2001). The values presented in Table 7 relate to average values of shear stress or velocity. Velocity and shear stress are neither uniform nor steady in natural channels. Short term pulses in the flow can give rise to instantaneous velocities or stresses of two to three times the average; thus, erosion may occur at stresses much lower than predicted. Because limits presented were developed empirically, they implicitly include some off this variability. However, natural channels typically exhibit much more variability than the flumes from which these data were developed. Maintaining the assumption of graded silts and cobbles representing the bed of the streams within the project boundary, movement of bed material may be expected to occur at shear stress values of .43 lb/sq ft or velocities in the range of 4 fps. The table also provides insights into the sorts of stabilization measures which may be appropriate should they be integrated into any of the alternatives. 25 Table 7 - Permissible ShNr and Velooity for Selected Lining Mataials (Fi1ehenich, 2001). Pennissible Permrss1ble Citatiort(s) Boundaly Categ01}' Bo..,dary Type Shear Stress Velocity lbl ft sec Soils Fine colloidal sand 0.02 -0.03 1.5 A Sandy loom (noncolloidal) 0.03 - 0.04 1.75 A Allu\ial Silt (noncolloidal) 0.045-0.05 2 A Silty loam (noncolloidall 0.045-0.05 1.75 - 2.25 A Fi rm loam 0.075 2.5 A fine gravels O.Q75 2.5 A Stiff clay 0.26 3 - 4.5 A, F Alluvial silt (colloidal) 0.26 3.75 A Graded loam to Cobbles 0.38 3.75 A Graded silts to cobbles 0.43 4 A Shales and hardpan 0.67 6 A GroveVCobble 1-in. 0.33 2.5-5 A 2-in. 0 .67 3-6 A 6-in. 2.0 4 - 7.5 A 12~n. 4.0 5.5 - 12 A Veaetation Class A turf 3.7 6 - 8 E, N Class B turf 2.1 4.7 E, N Class c turf 1.0 3.5 E, N long native ~sses 1.2-1 .7 4 - 6 G, H, L, N Short 11alive Md bunch gmss 0.7 -0.95 3 -4 G, H, L, N Reed plantings 0.1-0.6 NIA E, N Hardwood tree plantings 0.41-2.5 NIA E, N Tem12Q.mct. D~radabJe RECPs Jute net 0.45 1 - 2.5 E, H, M Straw with net 1.5-1.65 1 -3 E,H, M Cooonut fiber wilh net 2.25 3 -4 E, M Fiberglass rov'ing 2.00 2.5- 7 E, H, M Non-Oeg_radoble RECPs Urwegelated 3 .00 5 -7 E, GrM Partially eslablished 4.0-6.0 7.5- 15 E,G, M Fully vegelated S-.00 8- 21 F, L, M ~ 6 - in. doa 2.5 5-10 H 9 - in. ct., 3.8 7- 11 H 12 - in. d., 5.1 10 -13 H 18 - i ru !., 7.6 12 -16 H 24 - in. d., 10.1 14 -18 E Soil Bioe!]g,ineeli!]g, Wattles 0.2-1.0 3 C, l, J, N Reed fascine 0 .6-1.25 5 E Ccir roU 3-5 8 . E,M,N Vegetated coir mat 4-8 9.5 E,M,N Live .brush n1attress (initial) 0.4-4.1 4 B. E,I Live brush mattress (grown) 3.90-8.2 12 8 , C, E, I, N Brush layering (initiaVgrown) 0.4-6.25 12 E, 11 N live fascine 1.25-3.1.0 6 - 8 C, E, l, J Live willow stakes 2.10-3.10 3 - 10 E,N, O Hord St•dncing Gabjons 10 14 -19 D Concrete 12.5 >18 H ' Ranges of values generalty reflect mult1pJe sources of data or dlffe~nt tesbng condtt1ons. A Ch.>119, H.H. (1988}. F. Julien, P.Y. (1995). K. Sprague., C.J. (1999). 8. Florineth. (1982) G. Kouw.en. N.: Li. R. M.: and Simons . D.B .. {1980). L. Temple. D.M. (1980). C. G~g.ras.er, C. (1998). H. NonT13n, J. N. {1Q7 5}. M. TXDOT (1"99) D. Goff. K ( 1999 ~ L Schtechtl. H, M . and R. Stem. ( fgge). N. Data from A1J1hot (2001 ) E Gray. D.H .. and So£r. R.B. (1996). J. Sclloklitisch, A {1Q37}. 0 . USACE ( 11Xl7). Chapter 8, Part 654 S1mlm RoslDlation Design of1ho Natianal Bngineming Handbook provides aimilar guid111Ce. Figure 18 prcsema a relatioDBhip bctw=l lllowabk velocity, depdi.11111 grain IDllerill siz.e. Tho reJatimship 11118Psls a amble DSO bed matorial aim of25to40mm.for1be 500/o and 10% ACE events respectively. the values are presented with blue dots on 1llc plot. This plot also supports the com:lusion t1ult, abeom 1be grado COldrol p.'Osait in 1ho ~ 1ho project 1'Cll.lh is in a dogradational stldo. 26 100 - t-H+ ·-- t· - + 7() ' - ' ' 60 t- 40 ·- I :JO - 0.,1(11 ,., I of Bow I . 2 Q.01 0Jl2 0.(lli 0.10 0.20 2 n Figure 11 -Allowable Voloc:ity-Depth Grain Chait (NEH Put 654 Chapter I) ,,______...,,.,., ______.....,, •.---==---, 4 I!' f I I ------ 27 Values taken from the HEC-RAS simulation are largely in excess of the values recommended in Table 7. This suggests a degradational environment for the existing stream or possibly incorrect assumption of bed material type. The presence of grade control within the project area serves to offset this effect. The large spikes are due to the change in slopes at the grade control structures. 4. Stream Restoration Alternatives 4.lln Stream Habitat Structures In stream habitat structures are designed to provide shelter and habitat for fish and other aquatic organisms as well as help to establish channel bed and bank stability. The City and County of Denver has installed in stream habitat structures, primarily vanes, boulder clusters, and modifications to existing drop structures in areas adjacent to the study area and elsewhere on the South Platte River. For the purpose of alternative formulation, a suite of structures were considered for application throughout the project reach. 4.1.1 Boulder Clusters Natural streams with beds coarser than gravel often feature large roughness elements like boulders that provide hiding cover and velocity shelters for fish and other aquatic organisms. If a constructed or modified channel lacks such features, adding boulder clusters are an effective and simple way to improve aquatic habitat. Recently completed efforts in Reach 2 of the project area utilized boulder clusters as a aquatic restoration component. Boulder clusters provide hiding cover and velocity shelters for fish through the turbulence found in their wakes. They also provide stony substrate for attachment-type macroinvertebrates. If bed material is fme enough for scour to occur, boulders also develop stable pool habitat and physical diversity associated with a range of depths, velocities, and bed material sizes. Boulder clusters can make a relocated or reconstructed channel look more natural and add visual interest to an otherwise uniform view. If desirable, boulder clusters may be configured to trap woody debris and provide additional cover benefits. Boulder clusters provide fish rearing habitat, and areas for adult fish. Boulder clusters are simple, natural-looking features that add visual diversity and habitat to degraded, uniform reaches. Consequences of failure are generally slight (NCHRP, 2005). 28 Figule 20 - Boulds Clustm (NCHRP, 2005) 4.1.2 VUCllV81lCS wttJi J'-lloob V111e11 ue ~ dQQQnlimiOWI, tnlDlwnc lllnll:b.nll IDflcd into die tlow in order to n:cb:e lollal hllDk aoaion by nxliic:..1ins flaw fiom du: nev bmik to 1he mllcr ofdie di911nel .. ~ illlllllellm tip1 ofthe ltnduM -typioally low enouah to be ~mbipptd by Ill :11.owa and cftllU llope upwsd to re&Oh bankfull stago elovation at the bant. Vws with J-Hoob are reclirec:tM, di!eolllilluous 'UpotiWW110in•ing llmlsver.tO stone mueturos wilh tile tips pJaeod iD a ~poimng •r ccmfigumimL Tips are~ embedded iD. tile strelmbed '° 1hll ~ 1R llUlnncrgcd &mD durinaJ low tlowt. Tis mucluiw mtim:t Bows away fiom Ullllable dmlmbanka, while enlumcins llqWllic luihimt llDd pleyaical divmity dimugh cn:mion ofm poola. v-and v-with J-Hoob decreue ...elooily, ahec llNu and m-n power adj-m to the bank, and increaao hm in tllO CC1lter oftio d!annel Sec!imMt tnmlpart C... ij#H!!llO and capacity-majntained 8S a NIUlt oftile ---lhou llNls llDd .a-power in tho ceumthird oftho chmmel, when tho J-Hook. i.a locaied. Backwater OllC:lllll &4jaect to 1flo bank,~ MCli-t depollilioa in tho m11r-bellk --. llldRdueiqaelivo bak.cnem EnYDilili!h 11faJ ha- 611 orv-wifh J-ffoob inclwlc improvi:d 1-thit: bbit.t, c:n:idian O!'nudn.taumce ofpool llllcl rime habilat. impmwd fiah rearillg habilat, and holding - :IVr aduh fillh (NCHRP, 2005). Tho mo and shape oftho bouldma are critical to SUCCCISS. Very largo NCtmguJar boalden are best fi>r eomtruc:timi. It is iwpccativo dl8t tho rocb fit tQbtly toptlm liom top to bottom without fi>rming gaps. (hp1 Mwwww tile Jlds aeae a flow c:cmvagouco. iDmuiDg )oqljncf veloeitiel llld a helillll tlow pauan dian nipidly ~sediments dnough die lllnlQu!e. nu. i8 cBpCdally impodllDt for die 1-ldma Dell' dic bak. beA!1se YllllCll in dcai111"'41D pRWDOll.l depotilion along the 1oc ofthe llmmlballk.. v-GU mbjeotto unclinnlnlng and faihmi du to 11Co11t. All iDstallatlou will inolwle excavation to iDslall foam l!OnK to miti&a!D this pcaiblo f.ailllle. 29 Figure 21-Vanes (NCHRP, 2005) Figure 22- Vanes with J-Hooks (NCHRP, 2005) NO!£S.· N()T{S: I (1tf}#rimlflll $ MW""°"'" 1. C11J)df>m~1s11e,_. sho"'" (.JoltnsrJn t1I cl., 200f) /fief vo~ (.IOl>tt!POll ,,, of., 2001) ll>ol - lorc11 flo,., o "'O.t' from In. ""Ol>l"#I lorr11 /Jo.., 0"'0)" from 1m. t:h 2, fypicoVy. a -M'- .Jtr 4, fl'Mt $>J99.,$fMdiSfQnetf •. fll'QfWfl) 1$ t•~# "ndcf.ln//Of/,JIYl)is 1.. ic11111 11 IMt:llofVl#l.,,;ql" choflMI ..idf/1 (d ,. 2W). (d " 2W). li'mti,,.ty ""9r. f101 l 30 4.1.3 Newbury Rock Rimes/Drop Structure Modifications Newbury rock riflles are ramps or low weirs with long aprons made from riprap or small boulders. Typically they are spaced in intervals of 5 to 7 channel widths, but in this application they are proposed to be placed immediately below existing grade control structures to lessen the drops currently present. The two locations identified include the structures at Overland Park (RAS STA 253779) and the Arapahoe Intake (RAS STA 263934). The structures are built by placing rock fill within an existing channel. The upstream slope of the rock fill is typically much steeper than the downstream slope, which creates a longitudinal profile quite similar to natural riffies. These structures provide limited grade control, pool and riffle habitat, and visual diversity in otherwise uniform channels (NCHRP, 2005). Similar structures have been recently installed in reach 2 of the area. For purposes of aesthetics, function, and continuity the proposed riffies will be designed similarly. - + - z P 9 o 40 ih SClrrUINfECT ( , •• .-rl ) C!JM lAllE BfOC NQ? ~US AA<: LCNCTH Cl M .7.1 7~.l 127.Df> " - '·'48.5.) CJ" 174.71 ..,, ' ~ H .18 ,,.. L2 - . L.1 - , .. : ~ ""'o.t.44 8 1.4'1 5235 ~230 SCAI.£: 1-0RZ.l"• JO' 'it:AJ..E' HORZ !"• JO' 'wt:RT. 1·.. 10' VERT.1"• 10' ~ ~ N ~ 0 N ' I I Sheet Revisions Project Number UREIAH DIWtla Al() FlOOO C0NTR0.. mum '°" CO!lsnu:notl CRAN'T-~""W"J~K~AUJ,tEOA ':"~ ~ lillKE ~ ~ U M WO~~~ !3d-fl o..:;u HO. 2 MATERIAL~t LAYOUT Pl.AN 7 ~h ~ C> A{:- (!:~~= ~: Sl>ff"'""""'" C-84 ~~~--'--'-~~-'-~~~-'-=-'=...... ::O___JL.=.=.=c ~---1..,;.;.:____;c_.:....::.___J Figure 24 - Example of Riffie Structure Constructed in Reach 2 31 Figure 2S - Nnbmy BilBo (NCHRP, 2005) Tablo 8 -Arapahoe Riftlo Quautitios (Alt P) lntllcl - Rllll• Stnlei1119 Wldlhfftl HI! SI-•.., .. Volume ICYI I Dimension1 1,i 3.5 _g .,. C&4.I Tons Rl""'n Excwatlan ltYI Grout ISFI No12s Header Boulden 198 13 3' Bo11lden1. panlally em Footer Boulders 1!lll 40 3' Boulde!S. la~ly em bedded In the creek Rltrle Ponlon 8Sll Q lZ' DlOOex>bl>les Beddia. 169 103 4" D100• ovel fa'foundallon LB i!O' Refutal 1!11 211 RB30' Refusal .... :m Groutlns '""'tlon811 MM! Table 9 - Overblnd Riffle Quanlilie1 (Ah Q) Dwarland ,... Rlffllt !lllnl- . Wldth(ftl HI!" s1-.1~1 •• VolumelCYI _g .., Dimensions "' z ~ Ton1Rf""'n ExaMlllan ltYI Grout ISFI No12s Header Boulden 1!lll 13 3' Boulde!S. panlally em bedded Footer 8oulders 191 40 3' 8ouldel'S,, la~ly em bedded In the creek Rlffle Ponlon Z!l'J :1211 D100ciobl>les Beddin. '.11 511 4" D1DO• ..,,.I fol'foundation L8 311' Refusal .... :m RB30' RefllSll all 211 Grautlns lnntlonall ..!!!d ln-etnam habitat lllrWlmnll Ulld to illl:rocluce mughneu 111> the channel In the cuo of'Vlllle1 and bolllder llndunD, it c:an bo arguod tbat ICOllr llO tho d!anneJ illducod by tho lllacturos would oft"sot 111)' impac:t of tho llrU.cturel OD -water sur&eo elowtion. Pngirwncl riftlm niao tho bed ofthe ch•nno! awl thus impaet Wits smticel iD 1boir nnmMirto viclDity and for somo di,dan... lijldUwww. Tho iu-O-ltlzuaww Dllllt bo lllll1ymd to qmmdfy tho :Ooodplain implcir, e.spoeially c:om!eriDg dun ii littlo 10110 ehamml 32 freeboard at some locations and the potential consequences to the adjacent built environment. It is possible, upon further design of the alternatives, that implementation of the riffie structures will have to be abandoned or scaled back due to floodplain impacts. However, given the low profile of the structures proposed and their proximity to the upstream larger drops, it is expected that their effect will be negligible under flood level flows. 4.1.5 Conceptual Structure Layout Two of the three project reaches were defined where in-stream structural measures were deemed to be potentially advantageous. Reach two was excluded due to recent work of similar nature that had been completed in 2015 to restore the aquatic habitat in the reach. Within the identified reaches, different structure types were conceptually applied. A listing of those structures and associated quantities is listed below. Sizing of rock for the structures exceeds recommendations of the Isbash criteria. Spacing of the structures was determined using guidance available in (CHRP, 2005). Plan views of the structures are shown below as well. Table 10 - In Stream Habitat Structures Inventory (Alt K-Reach !:Alt M-Reach 3) Reach 1 (Florida-> Mississiooi) Structure #of Stone Qty I Excavation Excavation Stone Total Notes Type Structures Structure I Structure Total (Tons) (CY) (Tons) (CY) Vanes 12 135 50 1620 600 D100=30" Boulders 18 3 0 54 0 Assume 3-5' Boulders to be Utilized Reach 3 (Evans->Xcel) Structure #of Stone Qty I Excavation Excavation Stone Total Type Structures Structure I Structure Total (Tons) (CY) (Tons) (CY) Vanes 9 135 so 1215 450 D100=30" Boulders 36 3 0 108 0 Assume 3-5' Boulders to be Utilized 33 Figure 26 - Reach 1 Jn Streem Habitat Struotures Ccnwept Plan View (Alt K) 34 Figure 27 -Reach 3 In S1ream Habitat Struciures Concept Plan View (AltM) 4.2 Riparian Restoration Area The most beneficial ecosystem restoration alternatives :from the Feasibility Study (G and H) would involve grading along the right bank ofthe river through the southern portion of Grant Frontier Park. 3S Alternative H would relocate the pedestrian trail at Grant Frontier Park in Reach 3 and re-grade the right bank to create wetland habitat as well as riparian habitat. A low-flow side channel would be constructed in areas of Grant Frontier Park. This created wetland would receive hydrology at the 2-year WSE. Preliminary grading plans and countours are presented in Appendix E. Alternative G includes re-grading the existing bank in the downstream portion of Reach 3 on the left bank across Grant Frontier Park and creating a riparian and wetland habitat complex. All of this area was already existing low quality habitat, however, the area would improve in quality and functional output following construction. The created wetland would be designed to receive hydrology at the 2-year WSE. Preliminary grading plans are presented in Appendix E. 5. Hydraulic Impacts Evaluating the hydraulic effects of the project alternatives that could impact the South Platte River floodplain has been a focus of this feasibility study. The most up-to-date HBC-RAS hydraulic model for the study area has been provided by the Urban Drainage and Flood Control District (UDFCD) from their on-going Flood Hazard Area Delineation (FHAD) study. The FHAD study utilizes updated channel geometry and revised peak flows for the South Platte River that were approved in a 2016 Conditional Letter of Map Revision (CLOMR) from the Federal Emergency Management Agency (FEMA). The CLOMR flows are significantly lower than those used for the current effective regulatory floodplain mapping, primarily due to the addition of 30 years of record to the analysis. The base (I-percent annual chance exceedance) flood profiles computed using the FHAD model and the 2016 CLOMR flows were lower than the current effective Flood Insurance Study (FIS) base flood profiles through the SPV study area. The selected ecosystem restoration alternatives from the Feasibility Study (G and H) would involve grading along the right bank of the river through the southern portion of Grant Frontier Park. The hydraulic analyses with the FHAD model and the 2016 CLOMR flows found that the grading for ecosystem restoration alternatives would result in both increases and decreases to the I-percent annual chance (base) flood water surface profiles at and upstream of the locations of the modifications. The maximum increase in the base flood profile for with-project was about 0.5 foot above pre-project conditions. The increased water surface profile would be contained within the Grant Frontier Park property and would not impact any National Flood Insurance Program (NFIP) insurable structures. 36 SPR1135 Plan: l)Exisl_FISQs 1211412017 2)Prop_FISQs 1211412017 Legend 5265 EG FIS_ 100yr-Exist_FISQs +t-+--1!-lfr--t--t-+----+--+-+--+-+--r--+-+--+--t-t--+-+--+-+--r--+-+--+-f-t--+-+--+-+--+----1>-"'/--+ ---EG-FlS-_ 1-0oYr-- P-rop~-FIS-Q;- __., / +t--H----+ll-t--t--t--++-+-1-+-++-t--+--t-+-H-++-t-1-+-+-t--+-+--l-:::t---F+-+-hf' ------ _i-- - i--_.., ~ EG Dralt_FHAD_100yr- Exist_FISQs :=:~~~~:~=:==~=:=~~=:=~:=:~===~~=:=~~=:=~~::--==~=~~--::i--:=~=~i--~=_.,=~/=: EG-D-ratt=F_HA_D~-100-yr-P-rop-_Fisas 5260 1---i-- -~ -~ ~v ::::=:::: -- ~~~ -~~ WS FIS_100yr - Exist_FISQs ~v _i--....-__ , _,-i _,.,.. WS FIS_100yr - Prop_FISQs ': .~.,... -~~~e_w~le - - L--:i..-=-~ ~~ ~~~--~c-Et=~A'h~-n•,~- ~;m~..-~~~~ -+--~-~-='~-~~t"'tF::H-~"""~=~~4+~~=+=+++=H=+++==+ WS Drafl_FHAD_100yr -Exisl_FISQs itlT-f-£~.-~~~!~~r;;'*-~-· 4°=\=Ffyi---H-++++-H-+-+-H-++++-H-+ ws orai1_FHA0_10oir- Prop_F1sas TL... - -- _, --' 1 Ground 5255 r-.- .c-i-- 'K I 5257' Low Point in Left OVerbank at which spill initiates I I 0 ~ ··~ .:: 5250 I I 5245 --..__... 5240 . t -+- t- 1 - ~ "' "'" M ~ M "'"' - N M MM""" N N NN "' "' "'"'-,--,-- ~ 261000 262000 263000 264000 Main Channel Distaoce (ft) Figure 28 - 100 Year Water Surface Profiles for Grant Frontier Alternatives G and H Table 11 - Hydraulic Impacts ofthe Proposed Alternative Hydraulic Impacts of Proposed Project (All elevations are feet to NAVD88) With-Project. 50% 20% With-Project. Cross SO% minus 20% With- With- Section Existing Existing min• Project Existin~ Project Existing (feet) 260559 5246.31 5246.31 0.00 5248.11 5248.11 0.00 260673 5246.47 5246.42 -0.05 5248.19 5248.l -0.09 260787 5246.85 5246.93 0.08 5248.46 5248.63 0.17 261126 5241.53 5241.51 -0.02 5249.03 5249.06 0.03 261366 5248-12 5248_00 -0.12 5249-43 5249.31 -0.12 261466 5248.94 5249.04 0.10 5250.12 5250.18 0.06 261800 5249.54 5249.52 -0.02 5250.15 5250.65 -0.10 261849 5249.51 5249.53 -0.04 5250.11 5250.63 -0.14 261927 5249.84 5249.76 -0.08 5251.08 5250.92 -0.16 262779 5250.95 5250.81 -0.14 5252.43 5252.21 -0.22 263316 5251.66 5251.51 -0.09 5253-36 5253.22 -0.14 263855 5252.45 5252.40 -0.05 5254.25 5254.16 -0.09 263904 5253.59 5253.60 0.01 5254.43 5254.43 0.00 37 264495 5256.77 5256.77 0.00 5258.23 525823 0.00 264923 5257.56 5257.56 0.00 5259.19 5259.19 0.00 10% With-Project 4% W-Project Cross 10% 4% With- minus With- minus Section Eiistin& E:s:istin& Proiect E:s:istintz Proiect Eiistintz 260559 5249.26 5249.26 0.00 5250.68 5250.68 0.00 260673 5249.33 5249.21 -0.12 5250.74 5250.61 -0.13 260787 5249.56 5249.8 0.24 5250.93 5251.27 0.34 261126 5250.1 5250.17 0.07 5251.47 5251.6 0.13 261366 5250.44 5250.37 -0.07 5251.74 5251.75 O.oI 261466 5251.02 5251.05 0.03 5252.24 5252.29 0.05 261800 5251.65 5251.48 -0.17 5252.81 5252.63 -0.18 261849 5251.67 5251.43 -0.24 5252.84 5252.56 -0.28 261927 5252.02 5251.76 -0.26 5253.16 5252.89 -0.27 262779 5253.44 5253.15 -0.29 5254.64 5254.36 -0.28 263316 5254.52 5254.34 -0.18 5255.91 5255.74 -0.17 263855 5255.45 5255.33 -0.12 5256.88 5256.77 -0.11 263904 5255.01 5255.01 0.00 5256.28 5256.09 -0.19 264495 5259.17 5259.17 0.00 5259.17 5259.17 0.00 264923 5260.19 5260.19 0.00 5260.19 5260.19 0.00 Hydraulic Impacts of Proposed Project 2% With-Project. 1% With-Project. Cross 2% 1% With- minus With- minus Section Eiistin& E:s:istin& Proiect E:s:istintz Proiect Eiistintz 260559 5253.30 5253.30 0.00 5254.85 5254.85 0.00 260673 5253.35 5253.19 -0.16 5254.89 5254.72 -0.16 260787 5253.54 5254.00 0.46 5255.08 5255.58 0.50 261126 5254.08 5254.28 0.20 5255.60 5255.82 0.20 261366 5254.29 5254.39 0.10 5255.80 5255.95 0.10 261466 5254.72 5254.84 0.12 5256.16 5256.33 0.12 261800 5255.21 5255.06 -0.15 5256.60 5256.49 -0.15 261849 5255.24 5254.93 -0.31 5256.62 5256.31 -0.31 261927 5255.51 5255.3 -0.21 5256.87 5256.7 -0.21 262779 5256.99 5256.8 -0.19 5258.25 5258.08 -0.19 263316 5258.49 5258.39 -0.10 5259.78 5259.69 -0.10 263855 5259.59 5259.52 -0.07 5260.92 5260.86 -0.07 263904 5259.21 5259.12 -0.09 5260.58 5260.51 -0.09 264495 5262.63 5262.62 -0.01 5263.86 5263.85 -0.01 264923 5263.92 5263.91 -0.01 5265.23 526522 -0.01 0.5% With-Project 0.2% W-Project Cross O.!% 0.2% WHb- minus With- minus Section Eiistin& E:s:istine Project E:s:i1tin2 Project E:s:istin2 260559 5255.69 5255.69 0.00 5258.13 5258.13 0.00 260673 5255.71 5255.55 -0.16 5258.14 5257.97 -0.17 260787 5255.9 5256.41 0.51 5258.36 5258.88 0.52 261126 5256.41 5256.64 0.23 5258.84 5259.06 0.22 261366 5256.59 5256.76 0.17 5258.97 5259.18 0.21 261466 5256.93 5257.12 0.19 5259.24 5259.48 0.24 261800 5257.33 5257.24 -0.09 5259.59 5259.59 0.00 261849 5257.34 5257.04 -0.30 5259.55 5259.27 -0.28 261927 5257.59 5257.46 -0.13 5259.75 5259.74 -0.01 38 262779 5258.93 5258.82 -0.11 5260.94 5260.93 -0.01 263316 5260.48 5260.42 -0.06 5262.49 5262.48 -0.01 263855 5261.66 5261.61 -0.05 5263.68 5263.68 0.00 263904 5261.33 5261.28 -0.05 5263.41 5263.4 -0.01 264495 5264.53 5264.52 -0.01 5264.53 5264.52 -0.01 264923 5265.95 5265.94 -0.01 5265.95 5265.94 -0.01 Discussions regarding the floodplain permitting for the SPV Section 1135 project and the increases to the base flood profile were conducted during teleconferences with The City and County of Denver and the UDFCD on December 13 and 20, 2017. The following are some determinations made through those discussions: • Due to the effective floodway designation, a CLOMR from FEMA is required with the floodplain permit application for any increase in the base flood profile when comparing existing (without project) conditions to proposed(with-project) conditions .. • An increase in base flood profile is allowed with a CLOMR if no NFIP insurable structures are adversely impacted. Adverse impacts to insurable structures are not allowed under the NFIP. • It was suggested that the hydraulic impacts of the favored ecosystem restorations alternatives be evaluated with a hydraulic model utilizing the FHAD geometry with the current-effective (higher) FIS peak flows to mimic a standard CLOMR. This scenario was computed by the USACE. The results indicated that for without project conditions, the base flood profile would not impact insurable structures but that the higher profile for the with-project condition profiles would likely result in overtopping the left (west) bank which would impact insurable structures, which is not allowed. • Based on the hydraulic analyses that had been conducted, it was determined that there were two scenarios that would apply for the CLOMR analysis that would allow a floodplain permit to be issued for the preferred alternative to be constructed: • If the FHAD hydraulic modeling has been adopted in the current effective FIS at the time the CLOMR application is being prepared, the hydraulic analyses would use the FHAD hydraulic model geometry and 2016 hydrology by default. This should result in the with-project conditions base flood profile not impacting any insurable structures. • If the FHAD has not been adopted at the time the CLOMR for the floodplain permit application prepared, the FHAD model geometry and the 2016 peak flows would need to be used for the hydraulic analysis. The CLOMR application and hydraulic modeling would have to extend upstream and downstream from the SPV project area to tie in both without project and with-project base flood profiles into the effective base flood profile within 0.5 foot, per NFIP criteria. • While the effective model may need to be used for the CLOMR, the FHAD model with updated geometry and 2016 hydrology is considered best available information and should be used for design. The discussions between the City and County of Denver, UDFCD and the USACE have developed two acceptable methods for obtaining the :floodplain permit for the project. During the project design phase, 39 modifications to the feasibility study project configuration may be identified that would reduce or eliminate any increase in the base flood profile. 6. Future Efforts in Support of Final Design Components of this study have been evaluated to various levels of design. This section summarizes recommendations of future efforts to be included in final design of the selected alternative as this project moves beyond the feasibility stage into implementation. 6.1 Refinement and Calibration of the Hydrualic Modeling. The model used for this study is currently being further developed by the project sponsor. In addition to incorporating updates made through the sponsor's efforts, the model should be independently verified for calibration through the use collection of water surface profiles, verification of existing bathymetry through surveys, and surveys to define the existing drop structures to which modifications are proposed. Utilizing the collected data, detailed modeling of proposed in stream modifications should be performed. 6.2 Collection of Sediment Samples to Verify Stability Analysis This study relied on sediment samples collected several miles downstream and generally classified soil grab samples in reach 2 as being representative of the project condition. The assumption is reasonable given similar hydrology, stream dimensions, and the absence of major sediment loads being introduced between the sites. However, collection of on site samples to verify this assumption would mitigate risk of relying on off-site data to inform the design. Utilizing the on-site data, Part 654, Stream Restoration Design, of the National Engineering Handbook should be used to evaluate the stability of the final design. 6.3 Refinement of Vane Spacing and Placement of Boulder Structures. This study operated on a base assumption that vane spacing would be done on a distance of two times the average top width of the project reach. More detailed methods are available which may improve project performance and biologic outputs. Spacing, angling, and elevations of individual structures is required. In addition, coordination with biologist should be performed to maximize the value offered by the boulder placements. 7. References USACE, 1994. Hydraulic Design of Flood Control Channels, EM 1110-2-1601, Change 1, Department of the Army, U.S. Army Corps of Engineers, Washington, D.C. USACE, October 1994, EM 1110-2-1418, Channel Stability Assessment For Flood Control Projects, Department of the Army, U.S. Army Corps of Engineers, Washington, D.C. USACE, September 2001, ERDC/CHL TR-01-28, Hydraulic Design ofStream Restoration Projects, U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS. USACE, February 2016, HEC-RAS, River Analysis System, User's Manual, Version 5. 0, U.S. Army Corps of Engineers, Hydrologic Engineering Center, Davis, California. USACE, September 2016, ECB 2016-25, Guidance for lncorpating Climate Change Impacts to Inland Hydrology in Civil Works Studies, Designs, and Projects. Department ofthe Army, U.S. Army Corps of Engineers, Washington, D.C. Fischenich, C. (2001). Stability Thresholds for Stream Restoration Materials, ERDC lN-EMRRP-SR-29 USACE, Vicksburg, MS. May 2001. 40 Soar, P.J. and C.R. Thorne. (2001). Channel Restoration Design for Meandering Rivers. US Anny Corps of Engineers, Engineer Research and Development Center, Washington, DC. ERDC/CHL CR- 01-1. 273 Pp. Transportation Research Board (2005). Environmentally Sensitive Channel and Bank Protection Measures. NCHRP. Project Management Plan, South Platte River Section 1135 Ecosystem Restoration Project, USACE Omaha District, Sepetember 2014. Geomorphic Assessment at Survey Cross-Sections, South Platte River, Urban Drainage and Flood Control District, June 1996. Phase I and Phase II Summary Report South Platte River Multi-Objective River Improvements, Urban Drainage and Flood Control District (Prepared by Merrick & Company), September 2016. CLOMR Request for South Platte River, Chatfield to Fort Lupton, Colorado Urban Drainage and Flood Control District (Prepared by Wright Water Engineers), November 2015. FEMA. (2016). South Platte River Hydrology CLOMR Case No 16-08-0330R. Federal Emergency ManagementAgency. June, 1,2016. NRCS (2006). Part 654 Stream Restoration Design National Engineering Handbook. Natural Resource Conservation Service. August 2006. 41