Attachment 7 Hydraulic_Design_Report_09-19-2023.pdf

ASSUNPINK CREEK WATERSHED

FLOODWATER RETARDING STRUCTURE NO. 8

HYDRAULIC DESIGN REPORT

Hamilton Township, Mercer County, New Jersey

Contract # 12SPEC18D0023

Task Order # 12FPC322F0072

September 19, 2023

Joseph V. Bellini, PE, PH, D.WRE, CFM NJ Professional Engineer No. 24GE04805500

USDA-NRCS

Assunpink Creek Watershed Dam No. 8 Rehabilitation – Hydraulic Design Report

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ASSUNPINK CREEK WATERSHED DAM NO. 8 REHABILITATION

HYDRAULIC DESIGN REPORT

MERCER COUNTY, NEW JERSEY

TABLE OF CONTENTS

1.0 BACKGROUND

2.0 TERMINOLOGY

3.0 DATA REVIEW

3.1 Vertical Datum

3.2 Topographic and Structure Data

3.3 Auxiliary Spillway Profile and Soil Properties

4.0 HYDROLOGY

5.0 HYDRAULIC ANALYSIS OF EXISTING DAM AND SPILLWAYS

5.1 Hydraulic Model

5.1.1 Overview

5.1.2 Manning’s n-values

5.1.3 Internal Connections/Structures

5.2 Principal Spillway

5.2.1 Rating Curve

5.2.2 Impact Basin Analysis

5.3 Auxiliary Spillway

5.3.1 Capacity Analysis

5.3.2 Stability and Integrity Analysis

6.0 REHABILITATION DESIGN

6.1 Overview

6.2 Embankment Upgrades

6.2.1 Wave Protection

6.2.2 Wave Runup and Frost Height Assessment

6.2.3 Final Top Elevation of Dam

6.3 Auxiliary Spillway Upgrades

6.3.1 Control Section and Profile

6.3.2 Integrity (Cutoff Wall Design)

7.0 CONCLUSIONS AND RECOMMENDATIONS

8.0 REFERENCES

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LIST OF FIGURES

Figure 1. Site Vicinity Map Figure 2. Design Stage-Storage Curve Figure 3. Existing ASW Profile Plot Figure 4. HEC-RAS 2D Model Mesh at Assunpink Dam No. 8 Figure 5. Principal Spillway Rating Curve Figure 6. Section where outflow hydrograph was extracted from HEC-RAS Figure 7. 12-hour FBH Hydrographs Figure 8. Froude Number at Peak of the controlling 12-hr (Local) FBH Figure 9. 12-hr FBH Stage-Time Plot in Reservoir for Existing Conditions Figure 10. Maximum Velocities during the controlling 12-hr FBH (local) Figure 11. Maximum Velocities along the Existing ASW Centerline during the controlling 12-hr FBH (local)

LIST OF TABLES

Table 1. Existing Project Information Table 2. Existing Project Elevations and Reservoir Storage Table 3. Key Elevations and Reservoir Storage Table 4. Existing ASW Surface Profile, Station-Elevation Points Table 5. Auxiliary Spillway Soil Depths and Properties (Centerline) Table 6. Hydrologic Data Summary Table 7. Precipitation Data Table 8. Manning’s n-Values by Land Use Table 9. Results Summary for Existing Dam

APPENDICES

Appendix A: Hydraulic Design Calculations (Existing ASW Stability, Wave Runup, Wave Protection, Impact Basin Sizing, Impact Basin Riprap, and Turf Reinforcement Mat)

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LIST OF ACRONYMS AND ABBREVIATIONS

1D One-Dimensional 2D Two-Dimensional ac-ft acre-foot (acre-feet) ASW Auxiliary Spillway ARC Antecedent Runoff Condition cfs Cubic Feet per Second CN Curve Number

DEM Digital Elevation Model

EE Environmental Evaluation EGL Energy Grade Line EL Elevation

FBH Freeboard Hydrograph FHWA Federal Highway Administration FOSC Calculated Factor of Safety FOSP Project Factor of Safety fps Feet per Second ft Foot/Feet in Inch

LiDAR Light Detection and Radar

HEC-RAS Hydrologic Engineering Center – River Analysis System

JV Joint Venture

NAVD88 North American Vertical Datum of 1988 NED National Elevation Dataset NEH National Engineering Handbook NOAA National Oceanic and Atmospheric Administration NRCS Natural Resources Conservation Service

PMF Probable Maximum Flood PMP Probable Maximum Precipitation PSW Principal Spillway PSH Principal Spillway Hydrograph

RCC Roller Compacted Concrete

SCS Soil Conservation Service SDH Stability Design Hydrograph

USACE United States Army Corps of Engineers USDA United States Department of Agriculture USGS United States Geological Survey

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1.0 BACKGROUND

Under Contract No. 12SPEC18D0023, Order No. 12FPC322F0072, Aterra-Schnabel Joint Venture (ASJV) entered into a contract with Natural Resources Conservation Service (NRCS) to develop the rehabilitation design of Assunpink Creek Watershed Dam No. 8, located in Hamilton Township, Mercer County, New Jersey. The structure consists of an earthen embankment with an upstream slope of 3H:1V and a downstream slope of 2.5H:1V. The principal spillway (PSW) consists of a two-stage drop inlet concrete riser serving as an inlet to a 36-in inside-diameter reinforced concrete pipe (RCP) conduit, which outlets to an impact basin. The dam’s auxiliary spillway (ASW) consists of a 200-ft wide vegetated channel excavated into the left abutment. A site vicinity map is provided in Figure 1.

Figure 1. Site Vicinity Map

Assunpink Creek Watershed Dam No. 8 is classified as a high hazard potential (Class I) structure under Title 210, National Engineering Manual, Part 520, Subpart C, “Dams” (210-NEM-520-C) and as a Class I

– High Hazard Potential structure under the New Jersey Department of Environmental Protection (NJDEP) Dam Safety Standards (N.J.A.C. 7:20). The hazard classification is based on the potential for loss of life and property damage due to the prevalence of bridges, roads, and buildings existing in the downstream dam breach inundation zone. The objectives of this project are to rehabilitate the dam to meet or exceed both state and federal dam safety criteria and to maintain the current level of flood protection.

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As part of the rehabilitation design, a SITES model was developed to estimate runoff to the dam and to evaluate whether the dam meets TR-210-60 criteria for spillway stability, integrity, and freeboard. The SITES model was built on the previously completed analyses performed as part of the Supplemental Watershed Plan – Environmental Evaluation (Plan-EE) (USDA-NRCS, 2021) and included updated rainfall input from the recently completed Probable Participation Study for New Jersey (Applied Weather Associates, 2022). Additional details of the hydrologic (SITES) analyses are contained in the Final Hydrology Report (Aterra-Schnabel JV, 2022). This report describes the hydraulic analysis and design of the existing and rehabilitated ASW. To meet the current state and federal dam safety and performance standards and to extend the design life of the dam, the rehabilitation measures below are recommended:

• Raise the existing top of dam to EL 80.5 to meet the NJDEP 1-ft freeboard criterion.

• Set the crest of the ASW to EL 73.3 to maintain the hydraulic efficiency of the existing spillway without increasing maximum pool elevation.

• Relocate the ASW control section downstream to optimize hydraulic capacity of the ASW and to reduce construction costs.

• Regrade the ASW inlet and exit channels to accommodate raising of the ASW and the embankment.

• Construct a roller compacted concrete (RCC) cutoff wall at the ASW control section to meet the TR-210-60 integrity criteria.

• Install rock wave protection along the upstream embankment face to prevent erosion due to wave action and due to frequent variation in pool levels.

2.0 TERMINOLOGY

Descriptive nomenclature for dams is based upon one looking downstream. The terms “right” and “left” are referenced in this manner. The reservoir side is known as “upstream” with the opposite side of the dam referred to as “downstream.”

3.0 DATA REVIEW

3.1 Vertical Datum

The vertical datum used for the topographic survey was the North American Vertical Datum (NAVD 88).

All elevations presented in this report reference the NAVD 88 datum. The datum referenced for elevations shown on the as-built drawings is not clearly noted. However, based on a comparison of as-built and topographic survey elevations of the top of the riser structure, the datum shift is -1.29 ft (i.e., as-built datum – NAVD 88 = 1.29 ft).

3.2 Topographic and Structure Data

Critical dimensions of the existing dam and spillways were obtained from the Plan-EE (USDA-NRCS, 2021), as-built drawings (USDA-SCS, 1966), and recent survey (Continental Mapping Consultants, LLC, 2022). A summary of key project dimensions is provided in Table 1 and Table 2. Table 3 provides a summary of key elevations and associated storage values. The stage-storage curve (Figure 2) is based on the sediment survey and LiDAR data presented in the Plan-EE document (USDA-NRCS, 2021). See the Final Hydrology Report (Aterra-Schnabel JV, 2022) for additional details regarding the stage-storage curve development.

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Table 1. Existing Project Information

Description Parameter Drainage Area 2.76 sq mi

Embankment Length 1400 ft Maximum Embankment Height 19 ft

Inside Dimensions of Riser 3.0 ft x 9.0 ft Low Stage Orifice 0.75 ft x 2.25 ft High Stage Orifice (2) 1.5 ft x 9.0 ft

Size of Conduit 36 in Length of Conduit 99 ft

ASW Width 200 ft ASW Length 375 ft

ASW Side Slope 2.5H:1V ASW Channel Exit Slope 3%

Table 2. Existing Project Elevations and Reservoir Storage

Feature Elevation (NAVD88) PSW Conduit, Upstream Invert1 60.21

PSW Conduit, Downstream Invert 59.12 Normal Pool1 64.67

Low Stage Crest1 64.67 High Stage Crest1 71.21

ASW Crest2 73.30 Settled Top of Dam3 79.50

1 Based on surveyed elevation of riser and as-built dimensions of riser structure.

2 Mean value, surveyed elevations in ASW control section varied.

3 Minimum value, surveyed elevations along top of dam varied.

Table 3. Key Elevations and Reservoir Storage

Feature Design Existing

Elevation

(NAVD88)

Storage (ac-ft)

Elevation

(NAVD88)

Storage (ac-ft)

Top of Dam 80.5 2054.6 79.5 1776.9

ASW Crest1 73.3 501.5 73.3 501.5 PSW High-Stage Riser

Crest 71.2 288.7 71.2 288.7

PSW Low-Stage Orifice Crest 64.7 17.1 64.7 17.1

1 Existing ASW control section is non-uniform and mean crest elevation is listed.

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Figure 2. Design Stage-Storage Curve

3.3 Auxiliary Spillway Profile and Soil Properties

Table 4 contains the station-elevation data (i.e., surface profile) that follows the ASW centerline shown in the survey drawings (Continental Mapping Consultants, LLC, 2022). The stationing and centerline alignment from the survey drawings approximately follow the ASW centerline shown in the as-built drawings. ASW soil material properties and strata described in the Final Hydrology Report (Aterra- Schnabel JV, 2022) are summarized in Table 5 and illustrated in Figure 3.

Table 4. Existing ASW Surface Profile, Station-Elevation Points

Station (ft) Elevation

(NAVD88)

Station (ft) Elevation

(NAVD88)

117.00 69.01 524.78 71.90

117.50 70.83 576.62 70.15

220.89 72.22 635.04 68.44

270.10 72.65 682.24 67.59

324.78 72.81 730.38 66.97

379.43 72.98 775.97 66.70

423.20 73.55 819.09 65.54

472.41 72.70

0 250 500 750 1,000 1,250 1,500 1,750 2,000 2,250 2,500 2,750 3,000

El ev at io n (N

AV

D

Storage (ac-ft)

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Table 5. Auxiliary Spillway Soil Depths and Properties (Centerline)

Strata

Description Headcut Index Plasticity Index

Clay

Dry Density (lb/ft3)

Representative Diameter (in)

Topsoil - 0.03 4 10 80 0.0762 Coastal SP-SM 0.04 0 0 100 0.0210

Alluvial 3 SM 0.03 0 0 100 0.0087 Alluvial 4 SC-SM, ML 0.06 5 17 90 0.0067

Alluvial (2) SM 0.03 0 0 100 0.0087

Figure 3. Existing ASW Profile Plot

4.0 HYDROLOGY

The hydrologic parameters were developed as part of the Plan-EE (USDA-NRCS, 2021) with rainfall updates performed as part of the rehabilitation. Rainfall updates were documented in the Assunpink Final Hydrology Report (Aterra-Schnabel JV, 2022). Table 6 provides a summary of hydrologic parameters for the watershed upstream of the dam.

Table 6. Hydrologic Data Summary

Parameter Value Drainage Area 2.76 mi2

Curve Number (Existing) 78 Curve Number (Developed)1 79

Time of Concentration 2.68 hr 1 Used for design.

Current NOAA precipitation-frequency data and temporal distributions from NOAA Atlas 14 (NOAA, 2019), including New Jersey Atlas 14 Update Adjustment Factors, and Probable Maximum Precipitation Study for the State of New Jersey (Applied Weather Associates, 2022) were used for rehabilitation design. In addition to temporal distributions recommended by NJDEP (NJDEP, 2022), rainfall for the

September 19, 2023 Page 10 Aterra-Schnabel Joint Venture ©2023 All Rights Reserved controlling 6-hour SDH scenario was distributed using the NRCS standard distribution (USDA-NRCS, 2019). Table 7 summarizes the precipitation data used for each controlling scenario in this analysis.

Table 7. Precipitation Data

Scenario Distribution Depth (inches) 100-Year 24-hour Rainfall NOAA Atlas 14 8.66

6-hour SDH 6-hr standard NRCS 11.61

12-hour FBH 10th Percentile Local Storm PMP 32.03

5.0 HYDRAULIC ANALYSIS OF EXISTING DAM AND SPILLWAYS

5.1 Hydraulic Model

5.1.1 Overview

The USACE HEC-RAS (version 6.3.1) computer program was used to supplement the SITES model and complete the hydraulic analysis of the dam, the spillway system, and the downstream area.

HEC-RAS utilizes 2D unsteady-state solutions (based on continuity and momentum principles) appropriate for modeling hydraulic performance of spillway systems. 2D unsteady-state solutions accurately account for spatial variability in the terrain and surface roughness, while providing improved computational stability compared to 1D solutions. Chapter 2 of the HEC-RAS Hydraulic Reference Manual (USACE Hydrologic Engineering Center, 2016) provides additional details of the 2D unsteady-state computational approach that demonstrate its suitability for this application.

The previously developed HEC-RAS model was utilized for evaluation of flood reduction benefits of the dam and the model domain extended to the confluence with Assunpink River. To maintain continuity with the previous study and to confirm that the flood reduction benefits remain unchanged, the model domain was not altered; however, the upstream stage-storage area that utilized level pool routing was converted to a 2D flow area to better represent hydraulic routing of the design events through the reservoir. The model terrain was updated with bathymetric and topographic survey data. The 2D flow area mesh consists of 50-ft by 50-ft grids with 15-ft by 15-ft refinement areas along the ASW and the downstream channel as shown in Figure 4. The inflow hydrographs from SITES were used to establish the upstream inflow boundary conditions. The downstream boundary was set by assuming “normal depth” at a slope of 0.1%. Baseflow was introduced at various points downstream of the dam.

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Figure 4. HEC-RAS 2D Model Mesh at Assunpink Dam No. 8

5.1.2 Manning’s n-values

Manning’s n-values for the 2D model were derived using guidance developed by NRCS (NRCS-Kansas, 2016) and previous experience. A high Manning’s n-value (10) was assigned to structures to represent reduced conveyance in the floodplain. The land cover data used as the basis for n-value estimation was a high resolution (combination of source data ranging from 0.3- to 1-meter resolution data) data set for the State of New Jersey within the Delaware River Basin developed by the University of Vermont Spatial Analysis Laboratory (University of Vermont Spatial Analysis Laboratory, 2014). See Table 8 for a complete list of Manning’s n-values used in the HEC-RAS model.

Table 8. Manning’s n-Values by Land Use

Land Use n- Value

Land Use n- Value

Land Use n- Value

Concrete Channel 0.017 Low Vegetation 0.04 Tree Canopy over

Structures 10

Downstream Reach 0.025 Tree Canopy over Roads 0.016 Water 0.035

Upstream Reach 0.03 Roads 0.016 Emergent Wetlands 0.07

Scrub-Shrub 0.10 Tree Canopy over Other Impervious Surfaces 0.02 Barren 0.025

Tree Canopy 0.12 Other Impervious Surfaces 0.02 Structures 10

5.1.3 Internal Connections/Structures

Internal connections were incorporated to represent the dam/spillway and downstream roadways (including eleven culvert/bridge crossings) in the HEC-RAS 2D model. The top of the embankment

Dam Embankment

ASW

PSW Riser and Conduit

Inflow

Downstream Channel

September 19, 2023 Page 12 Aterra-Schnabel Joint Venture ©2023 All Rights Reserved followed the DEM terrain. The PSW was represented as a gate with stage-discharge relationship obtained from the SITES model. The ASW crest and exit channel were incorporated into HEC-RAS within the 2D flow area mesh.

5.2 Principal Spillway

5.2.1 Rating Curve

As described in Section 5.1.3, the stage-discharge relationship for the existing PSW was developed in SITES and is shown in Figure 5.

Figure 5. Principal Spillway Rating Curve

5.2.2 Impact Basin Analysis

An existing USBR Type VI impact basin is used to dissipate energy at the PSW conduit outfall. Design parameters were calculated in accordance with USDA-SCS Technical Release No. 49 (TR-49) (USDA- SCS, 1971) for comparison with the existing impact basin to determine if replacement is warranted to bring the PSW energy dissipation system into conformance with current design standards. The results indicate minor differences in dimensions between as-built and TR-49 dimensions that are not expected to have a significant impact on the structure’s ability to dissipate energy. The most notable difference is the 0.8 to 1.0 ft higher side walls in the TR-49 calculation, compared to the corresponding as-built height dimensions. Additional riprap is proposed along the top of the side walls to protect the adjacent wall backfill from erosion due to splash during a design event. Impact basin sizing calculations are provided in Appendix A.

Calculations were also performed to evaluate existing riprap located just downstream of the PSW impact basin according to TR-49. These calculations indicate that the minimum required riprap size is 7 inches. Work associated with proposed embankment improvements will disturb the area downstream of the impact basin so riprap will need to be replaced according to the minimum riprap size and placement dimensions as specified in TR-49. Impact basin riprap calculations are provided in Appendix A.

0 20 40 60 80 100 120 140 160 180

W at er S ur fa ce E le va tio n

(N

AV

D

Flow (cfs)

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5.3 Auxiliary Spillway

5.3.1 Capacity Analysis

A capacity analysis of the existing ASW was conducted using the HEC-RAS 2D model for the FBH storm that produced the highest maximum water surface elevations in the reservoir (12-hour 10th percentile local storm), as documented in the Final Hydrology Report (Aterra-Schnabel JV, 2022). The results from HEC-RAS 2D and SITES are shown in Table 9.

Table 9. Results Summary for Existing Dam

Storm Scenario Maximum Water Surface Elevations (feet NAVD88)

SITES HEC-RAS 2D

12-hour Local Storm 10th percentile PMP 78.95 79.46

Hydrographs from HEC-RAS and SITES at the ASW 12-hour 10th percentile Local FBH storms are plotted in Figure 7. Note that the difference in maximum water surface elevations for the existing dam is caused by two factors: 1) the varying elevation profile along the control section of the ASW and 2) the effects of tailwater. The elevations along the existing control section vary, which is accurately modeled in the two-dimensional HEC-RAS model but not SITES. Similarly, tailwater conditions are not represented in the SITES model making the HEC-RAS model more conservative.

Figure 6. Section where outflow hydrograph was extracted from HEC-RAS

Section A (where ASW Outflow Hydrograph was Extracted)

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Figure 7. 12-hour FBH Hydrographs

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

11,000

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

Fl ow

(c fs

Time (hours)

12-hr Inflow 12-hr - Section A (RAS) 12-hr Outflow (SITES)

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The capacity analysis included evaluation of whether supercritical flow conditions occur in the exit channel, which would indicate proper performance of the control section. The existing ASW exit channel is a grass-lined open channel. The HEC-RAS 2D results indicate that supercritical flow develops at the existing ASW control section during the peak of the FBH, with Froude numbers ranging from approximately 1.0 to 2.0 (see Figure 8). These results indicate that the existing control section functions properly and initiates supercritical flow despite the influence of high tailwater. Therefore, the 2D model alone can capture the influence of both the ASW control section hydraulics and the tailwater submergence on headwater in the reservoir without independent weir calculations.

Figure 8. Froude Number at Peak of the controlling 12-hr (Local) FBH

As shown in Table 9, the maximum pool elevation during the 12-hr FB event does not exceed the top of dam elevation. Water surface elevation in the reservoir throughout the FBH simulation was extracted from the 2D model and is plotted against the existing top of dam elevation in Figure 9. Based on these results, the existing ASW has sufficient capacity to pass the FBH without overtopping the dam embankment.

Existing Control Section Location

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Figure 9. 12-hr FBH Stage-Time Plot in Reservoir for Existing Conditions

Velocities along the entire ASW were evaluated using the HEC-RAS 2D results. The results indicate that in the exit channel, just downstream of the control section, the maximum velocities approach 12.5 ft/sec.

Note that the buried RCC cutoff wall was designed with the assumption that the ASW will experience headcut to the valley floor (from the results of the SITES model) and, therefore, the maximum velocities and their potentially erosive behavior were not used to inform the design of the auxiliary spillway.

Figure 10. Maximum Velocities during the controlling 12-hr FBH (local)

12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM

W at er S ur fa ce E le va tio n

(N

AV

D

Time

Existing Top of Dam

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Figure 11. Maximum Velocities along the Existing ASW Centerline during the controlling 12-hr FBH (local)

5.3.2 Stability and Integrity Analysis

According to TR 210-60, “vegetated and earth spillways must be stable and not erode when routing the auxiliary spillway hydrograph through the dam. The design stress must not exceed the maximum stress limitations for the vegetated and earth spillways in any reach of the constructed exit channel. Base the stress limitations on uniform flow conditions in the exit channel during the maximum discharge when routing the auxiliary spillway hydrograph.”

Stability was evaluated using the SITES-generated maximum stresses during the SDH and allowable stresses derived using AH-667 (ARS, 1987). The calculations incorporated soils information from the SITES Profile and Soil Properties input. The complete stability calculations can be found in Appendix A.

The result of the calculations indicate that the soil and vegetation are predicted to erode, and the existing spillway does not meet stability criteria. Note that the proposed rehabilitation design includes structural measures to prevent headcut progression and, therefore, the stability criteria is not applicable for the proposed spillway configuration.

According to TR 210-60, the spillway should also be evaluated for headcut development to determine if a headcut will breach the ASW by advancing beyond the upstream edge of the control section (the level crest) during the FBH. According to the Final Hydrology Report (Aterra-Schnabel JV, 2022), the SITES analysis indicates that a headcut will occur along the ASW and the headcut will progress past the control section during the passage of the FBH. Therefore, the existing ASW does not meet integrity criteria and measures to prevent the headcut formation or progression should be incorporated into the rehabilitation project.

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6.0 REHABILITATION DESIGN

6.1 Overview

As discussed in Section 1.0, the rehabilitation design will incorporate measures to ensure sufficient dam height and ASW hydraulic capacity under updated hydrologic conditions, protect the ASW control section from breaching, and ensure long term embankment stability. This section addresses how the design will accomplish each of these objectives using the results of the hydraulic analysis presented herein.

6.2 Embankment Upgrades

6.2.1 Wave Protection

Recent inspections and field surveys indicate that there is no existing riprap along the upstream slope of the embankment. Site visit photographs also indicate that vegetation has not established along the upstream slope approximately at normal pool level, as well as several feet above normal pool level.

This condition appears to be caused by a constant reservoir level fluctuation, which does not allow for vegetation to establish. To evaluate the extents of the required wave protection, a calculation based on TR-69 (USDA-SCS, 1983) was developed. The results of the analysis estimate the required upper and lower limit of wave protection of EL 66.2 and 63.2, respectively, with minimum rock size of 6 inches.

Meanwhile, site observations found that vegetation had not established up to EL 69. Therefore, the upper limit of rock should be EL 69 to account for both wave action and reservoir fluctuation. The lower limit of the rock should ultimately be set at EL 65 because the upstream embankment slope flattens out at this elevation. The wave protection calculations are included in Appendix A.

6.2.2 Wave Runup and Frost Height Assessment

In addition to preventing the FBH storm from overtopping, TR 210-60 states that the “dam crest elevation must be above the higher of either auxiliary spillway hydrograph plus wave action or auxiliary spillway hydrograph plus frost conditions.”

TR-210-60 requires that the dam crest contain the SDH storm plus wind-generated wave runup. A wave runup analysis was conducted for the SDH event using the USDA-NRCS TR-56, “Guide for Design and Layout of Vegetated Wave Protection for Earthen Embankments and Shorelines” (USDA- NRCS, 2014). The analysis resulted in a significant wave height of 0.93 feet and total wave setup and runup height over vegetation of 2.33 feet above the maximum SDH water surface (EL 75.82). This equals a wave runup of EL 78.15. The wave runup calculations are included in Appendix A.

The frost condition was assessed by estimating the depth below the embankment crest that is potentially susceptible to frost heave, considering frost depths in the region and soil types. The interpretation of the TR 210-60 requirement was that the maximum reservoir level for the SDH storm should be below the embankment region susceptible to frost heave. According to the USDA-NRCS’s “Understanding Soil Risks and Hazards” (USDA-NRCS, 2004), the following conditions must exist for frost action to occur:

1. The soil must be susceptible to frost.

2. Water must be available in sufficient quantities.

3. Temperatures must be cold enough to cause soil and water to freeze.

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The NRCS’s 2004 guidance further states that “susceptibility to frost is related to the size distribution of soil particles and the size and continuity of small voids between the soil particles. In general, free draining, coarse grained soils, such as sands and gravel, are not susceptible to frost, whereas clays, silts, and very fine sands even in small proportions support the formation of ice lenses.” According to samples collected at Boring B19-601, the soil near the embankment crest is described as silty sand (SM), fine to coarse sand, few gravel, and brown, which fits the characteristics of being frost susceptible. However, the quantity of water seeping into the top portion of the embankment from precipitation is expected to be very low, given the limited surface area and low permeable soils (CL and GC). According to Cornell University’s, “Northeast Regional Climate Center, Atlas of Soil Freezing Depth Extremes for the Northeastern United States” (DeGaetano, 1996), the maximum depth of freezing under bare soil with a 100-year return period in Mercer County is approximately 100 cm, 39 inches, or 3.3 feet. Despite the low likelihood that sufficient water would be available, 3.3 feet of freeboard above the SDH was used to address frost conditions, which corresponds to a minimum embankment crest of EL 79.12.

6.2.3 Final Top Elevation of Dam

The maximum reservoir water surface elevation with the rehabilitated ASW was estimated in HEC-RAS to be EL 79.48 for the controlling FBH scenario (compared to EL 79.46 with the existing ASW configuration). As stated in Section 3.2, the existing dam crest (EL 79.5) meets TR-210-60 criteria because it is not overtopped by the FBH. However, NJDEP Dam Safety Standards require that “the minimum elevation of the top of the dam must be that necessary to pass the design storm with at least one foot of freeboard to the top of the dam” (NJDEP, 2017). Therefore, the rehabilitation design incorporates dam crest raise to EL 80.5.

6.3 Auxiliary Spillway Upgrades

6.3.1 Control Section and Profile

The geometry of the proposed control section and vertical profile were designed to both prevent a headcut progression into the embankment and to balance the overall earthwork volumes for the project.

Autodesk Civil3D software was used to approximate potential headcut progression geometry and compute earthwork volumes. The control section was moved downstream so that potential headcut erosion would occur farther away from the embankment of the dam. This also requires that the training dike be extended and raised to accommodate the 1-ft freeboard requirement. As discussed previously, the existing ASW control section is uneven with elevations ranging from 73.0 ft to 73.9 ft and a mean elevation of 73.3 ft. HEC-RAS 2D model runs indicate that a uniform crest elevation of 73.3 ft at the proposed location of the control section will provide almost identical hydraulic capacity and water surface elevations both downstream and upstream of the dam during the FBH event, as well as during the 100-year flood event. The proposed ASW crest adjustment requires additional fill that was also considered in the earthwork balance. The primary source of excavated material is the construction of the RCC cutoff wall, discussed in the following section.

6.3.2 Integrity (Cutoff Wall Design)

As indicated in Section 5.3.2, maintaining the integrity of the ASW during a high flow event requires a cutoff wall. A rock surface was not identified during the geotechnical explorations. Therefore, it is recommended that the bottom of the proposed cutoff wall extends to at least the valley floor elevation (estimated to be EL 57). The cutoff wall is comprised of a buried stepped RCC structure located below

September 19, 2023 Page 20 Aterra-Schnabel Joint Venture ©2023 All Rights Reserved the control section and extending to valley floor at a 2H:1V slope. The RCC protection extends up the side slopes for the entirety of the control section and then transitions to a single sloping plane down to the valley floor. The top of the RCC armoring will be one foot below proposed grade for the entirety of the control section.

The design of the proposed stepped RCC cutoff wall primarily involves developing the RCC layout and confirming global stability (without earth material downstream providing passive resistance). No hydraulic sizing calculations were developed to support the design since the cutoff wall does not function as a hydraulic conveyance system, such as an RCC stepped chute and stilling basin. The chute/stilling basin system’s function is to dissipate energy during the FBH storm and not allow a headcut to form (other than possibly some concentrated scour at the downstream end of the stilling basin end sill), thus requiring hydraulic sizing calculations. The RCC cutoff wall design permits a headcut to occur but restricts it from advancing to the point of breaching the dam or ASW crest.

A reinforced concrete starter wall placed at the upstream end of the control section remains exposed at the surface and is set to EL 73.3 to maintain the crest elevation in the event of headcut erosion. The ASW approach channel was evaluated for erosion potential during both the 100-year and FBH events, which could undermine the reinforced concrete starter wall. The 100-year analysis demonstrated that unreinforced vegetation would withstand the 100-year event. The FBH scenario demonstrated that the underlying substrate would erode with unreinforced vegetation in the ASW approach channel.

Therefore, it is recommended that turf reinforcement matting be installed to prevent soil loss and potential undermining of the ASW starter wall during the FBH event. Turf reinforcement mat calculations are included in Appendix A.

7.0 CONCLUSIONS AND RECOMMENDATIONS

The hydraulic analysis shows that the existing top of dam does not meet NJDEP freeboard requirements.

In addition, vegetated and earth spillway TR-210-60 criteria for ASW stability and integrity are also not met. The following upgrades are recommended to meet the current dam safety and performance standards:

• Raise the top of the dam to EL 80.5

• Move the control section of the ASW further downstream and level the ASW crest elevation to

EL 73.3

• Provide riprap wave protection on the upstream embankment slope from EL 65 to EL 69

• Construct a buried RCC cutoff wall at the control section and extend it to valley floor EL 57 at 2H:1V slope.

• Extend and raise the training dike with the raised top of dam and relocated control section.

• Regrade the ASW inlet and exit channel with relocated and leveled control section.

September 19, 2023 Page 21 Aterra-Schnabel Joint Venture ©2023 All Rights Reserved

8.0 REFERENCES

Applied Weather Associates. (2022). Probable Maximum Precipitation Study for the State of New Jersey.

ARS. (1987, September). Stability Design of Grass-Lined Open Channels. Agriculture Handbook No. 667.

U.S. Department of Agriculture, Agricultural Research Service.

Aterra-Schnabel JV. (2022, December 9). Assunpink Creek Watershed Floodwater Retarding Structure No. 8 Existing Structure Hydrology Report, Hamilton Township, Mercer County, New Jersey.

Continental Mapping Consultants, LLC. (2022, 06 13). Assunpink Creek Watershed DAM 8 Block 2169 Lot 2, Hamilton Township, Mercer County, New Jersey.

DeGaetano, A. W. (1996, March). Atlas of Soil Freezing Depth Extremes for the Northeastern United States. Research Series, Publication No. RR 96-1. Cornell University, Northeast Regional Climate Center.

NJDEP. (2017). Dam Safety Standards. Trenton: New Jersey Administrative Code.

NJDEP. (2022). Additional Storm Analysis / Temporal Distribution Memo (Conclusions and Recommendations section).

NOAA. (2019, March 26). Hydrometeorological Design Studies Center. Retrieved from Precipitation Frequency Data Server: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=wv

NRCS-Kansas. (2016, July 12). Manning's n Values for Various Land Covers.

University of Vermont Spatial Analysis Laboratory. (2014, 01 14). High-Resolution Land Cover, State of New Jersey, Delaware River Basin, 2013. www.pasda.psu.edu.

USACE Hydrologic Engineering Center. (2016, February). HEC-RAS Hydraulic Reference Manual.

USDA-NRCS. (2004). Understanding Soil Risks and Hazards, Using Soil Survey to Identify Areas with Risks and Hazards to Human Life and Property.

USDA-NRCS. (2014, April). A Guide for Design and Layout of Vegetated Wave Projection for Earthen Embankments and Shorelines. Technical Release 56.

USDA-NRCS. (2019, March). Earth Dams and Reservoirs. Technical Release 210-60. U.S. Department of Agriculture, Natural Resources Conservation Service.

USDA-NRCS. (2021). Supplemental Watershed Plan No. 6 & Environmental Evaluation for the Rehabilitation of Floodwater Retarding Structure No. 8 of the Assunpink Creek Watershed.

Hamilton Township, Mercer County, New Jersey.

USDA-SCS. (1966). Assunpink Creek Watershed Project Floodwater Retarding Dam No. 8. Mercer County, New Jersey. As-Built Drawings.

USDA-SCS. (1971). Criteria for the Hydraulic Design of Impact Basins associated with Full Flow in Pipe Conduits. Technical Release No. 49.

USDA-SCS. (1983, May 24). Riprap for Slope Protection against Wave Action. Techncial Release (TR) No. 69. U.S. Department of Agriculture, Soil Conservation Service.

September 19, 2023 Aterra-Schnabel Joint Venture

APPENDIX A

HYDRAULIC DESIGN CALCULATIONS (EXISTING

ASW STABILITY, WAVE RUNUP, WAVE PROTECTION,

IMPACT BASIN SIZING, IMPACT BASIN RIPRAP, AND

TURF REINFORCEMENT MAT)

CALCULATION COVER SHEET

Project

Assunpink Creek Watershed Dam No. 8 Rehabilitation

Project No.

22pr1205.06

Title

Existing Auxiliary Spillway Stability Calculation

Computer Program Used

Microsoft Excel (Version 2205, Build 15225.20204)

Purpose and Objectives

1. Calculate the soil and vegetal shar stress in the existing auxiliary spillway for the spillway design hydrograph

(SDH) using AH667 and TR-60 guidance.

2. Determine if the soil and/or vegetation of the existing auxiliary spillway will erode during the SDH.

Summary of Conclusions

The SDH produced an effective soil stress of 1.46 psf and a vegetal stress of 0.65 psf. The existing spillway primarily consist of type SM soil, which has an allowable stress of 0.01 psf. The vegetation has an allowable stress of 2.16 psf.

Therefore, the soil is predicted to erode and the existing ASW does not meet stability criteria.

Originator

Petr Masopust 1/16/2023

Print Signature Date

Checker

Tom Saldutti 1/16/2023

TomSaldutti Image https://aterrasolutions-my.sharepoint.com/personal/joe_bellini_aterrasolutions_com/Documents/5_Projects/NRCS_IDIQ_2018/NE_Project/Assunpink_Rehab_Design/

10_Supporting_Calculations/Stability_results - Analysis

Date:

Designer: Petr Masopust Checked By:

Project: ACW8

County: Mercer Check Date:

State: NJ

SITES file name: ExSDHFBH6hrBuiltout.d2c

AS Width: 200 ft wide

SM

10 Plasticity Index of Aux Spwy Topsoil (for CH, CL, GC, GM, MH, ML, OH, OL, SC, SM)

0.200 in Topsoil D75 diameter (for GP, GW, SP, SW)

80 pcf

2.70

2.88

4.0% see Erosionally Effective Stress For Stability Analysis of Aux Exit Channel tbl

2.11 psf Total Stress, from SITES 6-hr SDH (psf)

1.456 psf Soil Effective Stress, from SITES 6-hr SDH (psf)

Soil Stress Analysis

Soil

Plasticity Index

PI

or

D75

Allowable

Effective

Stress τab

Void

Ratio e

Void Ratio

Correction

Ce

= τab *

(Ce)^2 τa

TR-60

AS Use

Freq

Multiplier

AH 667

Adjusted

Allowable

Stress τa

SITES

6-hr SDH

Soil Effective

Stress

SM PI=10 0.019 psf 1.11 0.745 0.011 psf 1 0.011 psf 1.456 psf

Vegetal Stress Analysis

Overall Stability

Version: 2.8 4/21/2011

Notes:

AH667/TR-60 Auxiliary Spillway 6-hr SDH Stability Analysis from SITES

SITES 6-hr SDH Vegetal Stress τveg = τtot - τeff

0.65 psf

CI - Retardance curve index

AH 667 Table 3.2

AH 667 Allowable vegetal stress

(AH 667 Eqn 1.17) τva = CI * 0.75

2.88 2.16 psf

Aux Spwy Retardance Class (A-E) or Retardance Curve Index (2.88-10)

Auxiliary spillway anticipated average use (see TR-60 2nd ed., pg 7-3)

Project

Data

Jan 16, 2023

This spreadsheet facilitates the USDA-NRCS TR-60 2nd edition stability analysis for earthen/vegetated auxiliary spillways with

SITES software output.

Users enter project data, auxiliary spillway width, topsoil data, vegetation, auxiliary spillway flow frequency, and SITES 6-hr

SDH stress values. Depending on the soil, either PI or D75 input is needed.

The allowable vegetal and effective soil stresses are computed using USDA-ARS Ag Handbook 667 "Stability Design of Grass-

Lined Open Channels". The design SITES stresses are compared to the AH 667 stresses (as modified by TR-60). An appropriate design has equal or lower design stresses than allowable stresses.

Based on input auxiliary spillway width and ratio of allowable effective stress:design effective stress the minimum auxiliary spillway width for stability is computed. Integrity analysis may require a wider auxiliary spillway.

Topsoil

Properties

Specific Gravity of Topsoil, Gs

Soil erodes--effective soil stress exceeds adjusted allowable soil stress!! Consider widening to

27531 ft, raising the auxiliary spillway or selecting a higher plasticity topsoil.

Vegetation

Unacceptable design. Soil and/or vegetation predicted to erode.

AS Flow Frequency

SITES

6-hr SDH values

Vegetation is stable. SITES 6-hr SDH actual vegetal stress less than allowable AH 667 vegetal stress.

Dry Density of Topsoil (lbs/ft

Dominant Textural Soil Class of Aux Spwy Topsoil

TomSaldutti Typewritten Text Tom Saldutti

TomSaldutti Typewritten Text 1/16/2023

Wave Runup

1. Calculate the maximum height of wave runup using guidance from TR-56.

2. Determine if the top of dam elevation is sufficient to contain wave runup.

The maximum elevation of wave setup and runup in the reservoir was predicted to be 78.15 NAVD88. The existing top of dam is at elevation 79.5 and will sufficiently contain wave runup.

Tom Saldutti 12/5/2022

Madhat Fares 1/5/2023

MadhatFares Pen Madht Jane

Project/Location: Assunpink Watershed Dam No 8 (NJ)

Calculation: Wave Runup Calculation - Fetch

By: Tom Saldutti Date: 12/5/2022

Checked: Madhat Fares Date: 1/5/2023

Radial Length Bearing cos cos_length

-42 404.88 71 0.7431 300.88

-36 473.98 77 0.8090 383.46

-30 546.69 83 0.8660 473.45

-24 572.10 89 0.9135 522.64

-18 606.45 95 0.9511 576.77

-12 1163.36 101 0.9781 1137.94

-6 1299.32 107 0.9945 1292.20

0 1323.14 113 1.0000 1323.14

6 1123.79 119 0.9945 1117.63

12 1116.26 125 0.9781 1091.87

18 761.15 131 0.9511 723.90

24 682.99 137 0.9135 623.94

30 601.88 143 0.8660 521.24

36 568.14 149 0.8090 459.63

42 342.12 155 0.7431 254.24

13.5109 10802.94

Effective Fetch (feet) 800

Effective Fetch (miles) 0.151

Calculation: Wave Runup over Vegetation

By: Tom Saldutti Date: 12/5/2022

Checked: Madhat Fares Date: 1/5/2023

Overland Wind Vel (mph) (Fig 4) 73.50

Wind Ratio (Fig 5) 1.025

Overwater velocity (mph) 75.34

Effective Fetch, Fe (feet) 800

Effective Fetch, Fe (miles) 0.151

Maximum Fetch, F (feet) 1323

Maximum Fetch, F (miles) 0.251

Average Water Depth along Fetch Line (ft), Avg depth from

ASJV Sediment Storage Survey Table 1 + SDH depth 13.10

Sig Wave Height, Hs (ft) (Eq. 3) 0.93

Angle of Embankment Slope, θ (_H:1V) 3.00

Angle of Embankment Slope, θ (rad) 0.32

Angle of Embankment Slope, θ (deg) 18.43

Deepwater Wave Length, L (ft) (Eq. 10) 19.32

Surf Parameter, δ (Eq. 9) 1.52

Wave Setup Ht., S (ft) (Eq. 6) 0.08

Wave Runup Ht., R (ft) (Eq. 8) 2.25

Total Wave Setup+Runup Ht. (ft) 2.33

SDH Maximum Stillwater Elev (ft NAVD88) 75.82

Maximum Elev. Wave Setup+Runup (ft NAVD88) 78.15

Note - Equations and figures referenced from:

TR-56 A Guide for Design and Layout of Vegetated Wave

Protection for Earthen Embankments and Shorelines

Wave Protection

1. Calculate the upper and lower limits of protection as well as the minimum rock size for riprap wave protection of the upstream embankment face using guidance from TR-69.

Using wave information from the wave runup calculation, it was determined that riprap protection is required from elevation

63.2 to 66.2. The minimum rock size for the wave protection is six inches.

Madhat Fares 1/5/2023

Tom Saldutti 1/5/2023

MadhatFares

Calculation: Riprap Wave Protection Calculation

By: Madhat Fares Date: 1/5/2023

Checked: Tom Saldutti Date: 1/5/2023

Normal Pool Elevation (ft NAVD88) 64.67

Overland Wind Vel (mph) (Fig 4) 73.50

Wind Ratio (Fig 7) 1.025

Overwater Velocity (mph) 75.34

Effective Fetch (feet) 800

Effective Fetch (miles) 0.151

Sig Wave Ht., Hs (ft) (Eq. A17) 0.93

Sig Wave Period, T (sec) (Eq. A18) 1.64

Min Rock Weight, W50 (#) (Fig 8) 14.0

Min Rock Size, D (ft) (Fig 9) 0.5

Min Rock Size, D (inches) 6.00

Min Rock Mattress Thickness, 1.5*D (ft) 0.75

Wave Setup, S (ft) (0.1*Hs or 0.5' max) 0.09

Wave Length, L (ft) (Fig 11) 21.0

Hs/L 0.044

Relative Wave Runup, R/Hs (ft) (Fig 12) 1.55

Wave Runup, R (ft) 1.45

Upper Limit, S+R (ft) 1.54

Lower Limit, 1.5*Hs (ft) 1.40

Upper Limit Proection Elev (ft NAVD88) 66.2

Lower Limit Protection Elev (ft NAVD88) 63.3

Note - Equations and figures referenced from:

TR-69, Riprap for Slope Protection Against Wave Action

Assunpink Watershed Dam No.8 Rehabilitation

Project No.

22pr1205.06

Title

Principal Spillway Conduit Outfall – Energy Dissipation Design Calculations

Computer Program Used

N/A

Purpose and Objectives

• Calculate USBR Type VI impact basin design parameters for comparison with the existing impact basin on-site to determine if replacement is required.

• The Type VI impact basin design calculations were completed in accordance with the USDA-SCS “Criteria for the

Hydraulic Design of Impact Basins associated with Full Flow in Pipe Conduits”, Technical Release No. 49 (TR-49), dated March 29, 1971.

Summary of Conclusions

• Using a flow of 130.95 cfs (based on a headwater at the ASW crest), the design calculations showed that the impact basin would have key dimensions and elevations as listed in the table below. As-Built dimensions and elevations are included for comparison.

Parameter Description Calculated Values As-Built Values

Bottom Elevation 57.20 57.27

End Sill Elevation 59.10 59.10

Depth of Basin (feet) 8.55 7.75

Length (feet) 15.20 14.67

Width (feet) 11.40 11.00

Height of Sidewall at

Wingwall Junction (feet)

5.70 4.67

Height of Baffle Wall (feet) 4.28 4.83

Height of End Sill/Pipe Invert above Apron Slab (feet)

1.83 1.90

• Although the recommended depth, length, and width of the basin are greater than the As-Built dimensions, the minor difference is not expected to have a significant impact on the structure’s ability to dissipate energy for the principal spillway.

• The height of the sidewall at the wingwall junction is also undersized but observed conditions immediately downstream of the impact basin show no signs of excessive splash or erosion. Riprap will be placed up to the height of the sidewall to mitigate erosion from future high flow events.

• The height of the baffle wall and height of end sill/pipe invert above the apron slab in As-Built condition are greater than the recommended values, which both indicate increased potential for energy dissipation.

Madhat Fares 02/23/2023

Print Sign Date

Checker

Tom Saldutti 02/27/2023

Print Sign Date

MadhatFares

Project: Assunpink Watershed Dam No.8 Rehabilitation Design PAGE 1

Calculation: NRCS TR-49/USBR Type VI Impact Basin Design

By: Madhat Fares Date: 2/23/2023

Checked: Tom Saldutti Date: 2/23/2023

VARIABLE PARAMETER DESCRIPTION UNIT VALUE

Q Design Discharge cfs 130.95

D Conduit Diameter feet 3.00

S Conduit Slope ft/ft 0.0111 ELo Conduit Outlet Invert Elev feet 59.10 g Acceleration due to Gravity ft/s

32.16

W Basin Width feet 11.40

L Length of Basin feet 15.20

H Depth of Basin feet 8.55 d Height of End Sill and Pipe Invert above Apron Slab feet 1.90 f Height of Baffle Wall feet 4.28 a Distance to Upstream Face of Baffle Wall feet 5.70 c Height of Sidewall and Wingwall of Junction feet 5.70 e Width of Splash Brim feet 0.95 z1 Basin Bottom Elev feet 57.20 z2 Top of End Sill Elev feet 59.10

Nominal (average) gravitational acceleration

= (3/8)*W [see calc page 2 for TR-49 equations]

= (1/6)*W [see calc page 2 for TR-49 equations]

= (3/4)*W [see calc page 2 for TR-49 equations]

= (4/3)*W [see calc page 2 for TR-49 equations]

See TR-49, nomograph ES-188 below

= z1 + d

= ELo - d

= (1/12)*W [see calc page 2 for TR-49 equations]

= (1/2)*W [see calc page 2 for TR-49 equations]

= (1/2)*W [see calc page 2 for TR-49 equations]

As-Builts (C3D Pipe drawn in ASNPK-3D-TD)

SOURCE/REMARKS

As-Builts (C3D Pipe drawn in ASNPK-3D-TD)

36-inch RCP, obtained from as-built drawings

Design discharge with reservoir at ASW crest, from PSW rating curve

W=11.4 feet

Q = 131 cfs

D = 3.00 ft

Assunpink Watershed Dam No.8 Rehabilitation

Project No.

22pr1205.06

Title

Impact Basin Riprap Design Calculation

Computer Program Used

N/A

Purpose and Objectives

• Calculate the size, dimensions, length, and elevations for the riprap located just downstream of the principal spillway impact basin.

• Used guidance contained in SCS/NRCS Technical Release No. 49, “Criteria for the Hydraulic Design of Impact

Basins associated with Full Flow in Pipe Conduits”.

The calculation was developed for the riprap protection downstream of the impact basin per TR-49, which indicates that the riprap should cover a minimum of 1 basin width downstream of the end sill, with the top along the side slopes corresponding to the top of the impact basin walls at the end sill. The minimum thickness is 1/6 of the basin width.

Drawing No. ES-189 of TR-49 is used for the riprap size.

Inputs: Q=130.95 cfs (at WSEL=ASW crest), D (pipe diameter) = 3 feet, y (vertical distance from top of end sill to top of riprap in the channel) = 0.0 feet

Q/D5/2 = 130.95/3(5/2) = 8.4 y/D = 0.0

C = 3.0 (see Figure 1 from TR-49, ES-189, Sheet 1 of 1)

Min Riprap Size = 7 inches (see Figure 2 from TR-49, ES-189, Sheet 1 of 1), Use D50 = 7 inches

Madhat Fares 2/23/2022

Print Sign Date

Checker

Tom Saldutti 02/27/2023

Print Sign Date

MadhatFares

Figure 1 from TR-49, ES-189, Sheet 1 of 1

Figure 2 from TR-49, ES-189, Sheet 1 of 1

Assunpink Creek Watershed Dam No. 8 Rehabilitation

Project No.

22pr1205.06

Title Turf Reinforcement Mat at Auxiliary Spillway Approach

Computer Program Used Erosion Control Materials Design Software (ECMDS Version 7.0) Developed by North American Green

Purpose and Objectives

• Select an appropriate liner material to prevent erosion from high velocity flows upstream of the ASW level section

• The input parameters for discharge and channel slope (energy gradient) were obtained from the HEC-RAS 2D results. The input parameters for channel bottom width and side slopes were set according to the proposed approach channel geometry. Vegetation parameters were assumed based on visual observations and soil type was obtained from the geotechnical investigation.

• The Channel Analysis Design Module contained within ECMDS Version 7.0 provides recommendations for effective temporary and/or permanent erosion protection of swales and channels conveying intermittent concentrated uniform water flows.