2022 06 01 Nashawannuck Restoration Options Model Results Memo.pdfAn Equal Opportunity Employer M/F/V/H
M E M O R A N D U M
To: Kate Bentsen (MA DER)
From: Rosalie T. Starvish, P.E. (GZA)
Rex Gamble (GZA)
Stephen Lecco (GZA)
Todd Greene (GZA)
John Field (Field Geology Services)
Nicolas Miller (Field Geology Services)
Date: June 1, 2022
File No.: 15.0167005.00
Re: Memorandum – Hydrologic and Hydraulic Models for Restoration Scenarios
Nashawannuck Brook Restoration Project
Northampton, Massachusetts
In accordance with our agreement (Commonwealth of Massachusetts Contract ID
NSHWNKXGZAXDESXF2022) dated December 8, 2021, GZA GeoEnvironmental, Inc. (GZA) is pleased
to submit this memorandum to the Massachusetts Division of Ecological Restoration (DER), summa-
rizing the development and results of the hydrologic and hydraulic modeling analysis of three (3)
scenarios for the restoration of Nashawannuck Brook. This memorandum was prepared in accord-
ance with Sub-task 2.4 of the referenced contract and is subject to the Limitations provided in
Attachment A. This memorandum was prepared in partnership with Field Geology Services, LLC, un-
der subcontract to GZA.
Elevations in the memorandum reference the vertical datum NAVD88 and the horizontal datum
NAD83 Massachusetts Mainland State Plan Projection, unless otherwise specified. Vertical and hori-
zontal units are in feet, unless otherwise specified.
INTRODUCTION
GZA calibrated the hydrologic and hydraulic model that had been previously prepared by GZA in sup-
port of the Nashawannuck Brook Assessment and Master Plan of Resiliency Improvements (see
Appendix 1) based on flow data for Nashawannuck Brook provided by DER. Using the calibrated
model, GZA evaluated three (3) scenarios for the restoration of Nashawannuck Brook, based on three
(3) combinations of restoration options that were selected by DER and the project partners, the City
of Northampton and Mass Audubon. Appendix 2 presents a summary of the restoration scenarios that
were developed by DER and project partners.
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Proactive by DesignMETHODOLOGY
Model Calibration
The existing conditions model was calibrated to the measured stage elevations of three gages over two flood events on
Nashawannuck Brook. The gages used to measure discharge were installed and managed by the DER, and are located at
the upstream of the project site, in the outlet structure of the lower dam, and at the downstream end of the site as shown
by the red squares in Figure 1. The upstream and downstream gages were installed on November 2, 2020 while the dam
gage was installed on August 11, 2021. The flow data recorded by the gages and provided to GZA by DER is included in
Appendix 3.
Figure 1. Gage Locations in Project Site
GZA identified two flood events which occurred on July 17, 2021 and September 1, 2021 as usable data for calibration of
the existing conditions model. GZA applied rainfall depths and distributions recorded at Chicopee Falls / Westover Air
Force Base and reported by NOAA to the model. The July 17, 2021 storm had a cumulative rainfall depth of 3.0 inches over
16 hours and the September 1, 2021 storm had a cumulative depth of 4.3 inches over 39 hours. Note that the DER recorded
a flood event at Nashawannuck Brook on November 12, 2021, but the Chicopee Falls / Westover Air Force Base rain gage
did not record corresponding precipitation to apply to the model; therefore, GZA could not calibrate this event in the
model.
GZA performed the calibration by modifying terrain, curve number (CN) values, and Manning’s n roughness coefficients
to best fit model results to measured gage elevations. Comparisons between model outputs and gage readings were per-
formed visually.
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Proactive by DesignModeling of Restoration Scenarios
GZA modeled three (3) combinations of restoration options that were presented by DER. DER restoration practices for
Scenarios 1, 2, and 3 are shown in Appendix 2 while GZA model changes to reflect each restoration scenario are shown in
Appendix 4, slides 9 to 11. Restoration actions are identified by reach due to varying morphology and resulting restoration
practices.
To implement the restoration actions in the model, GZA modified the model terrain, structure geometry, and/or Man-
ning’s n roughness coefficient. GZA performed terrain modifications using tools built into HEC-RAS 6.2. A side-by-side
comparison of modifications to the terrain between existing and the three proposed restoration conditions in Reaches 3,
2, and 1, are shown in Appendix 4, slides 13 to 15, slides 18 to 20, and slides 21 to 23, respectively. Note that log jams
shown in these slides were modeled with changes to the Manning’s n roughness, not terrain modifications. The Manning’s
roughness was also altered with any wetland or channel creation, as well as to represent riparian planting. Note that both
existing and proposed models do not take into account the concrete blocks that currently act as channel constrictions
throughout the project area and the bank and channel cobble/boulder armoring that is present in Reach 1.
Structures were either modified in geometry or removed altogether. Both the upper and lower dams in the project site
were removed from all restoration scenarios, and terrain modified accordingly, assuming the entire dam embankment
was removed. For Scenarios 1 and 2, the Old Wilson Road culvert was enlarged to an opening geometry that meets the
requirements of the Massachusetts Stream Crossing Standards, while it was removed entirely in Scenario 3. Based on an
assumed bankfull width of 26 feet, the culvert was enlarged to a width of 32 feet (1.2 x 26) with a height of 2 feet (see
Appendix 5). For Scenarios 1, 2, and 3, the North Culvert was replaced with a bridge over a trapezoidal channel sized to
blend with the upstream and downstream conditions. Geometry alterations to Old Wilson Road for scenarios 1 and 2 are
shown in Appendix 4 slide 16, and alterations to the North Culvert for all scenarios is shown in Appendix 4 slide 17.
To demonstrate the variation in terrain modifications associated with the three restoration scenarios, GZA estimated the
net sediment movement in cubic yards for each restoration scenario. GZA exported the terrains from HEC-RAS to ArcMap
10.7.1 as 1 ft by 1 ft digital elevation models (DEMs) where the raster calculator tool was used to subtract the proposed
DEM from the existing DEM for each elevation cell and multiply each cell by the cell area, 1 square-foot. The resulting
raster was then summed to find the net sediment movement in cubic feet, which was then converted to cubic yards.
Results are shown on slide 24 of Appendix 4.
RESULTS & DISCUSSION
Model Calibration
As previously stated, the model calibration was undertaken by modifying terrain, curve number (CN) values, and Man-
ning’s n roughness coefficients. Terrain was modified intermittently within the existing stream channel such that the
channel thalweg in the model matched the longitudinal survey performed by GZA. Following this, the best fit occurred
when the CN was decreased for the entire watershed to 62 regardless of land use. Manning’s n were increased throughout
the watershed to better simulate higher roughness during shallow flows (i.e. sheet flow and shallow concentrated flows).
The resulting flow hydrographs output by the model, and plot with recorded DER data, for each event are included in
Appendix 6.
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Proactive by DesignComparing the model to the measured stage, the downstream gage appeared to be the worst fit with the existing condi-
tions model continuously showing higher baseflow and peaks than the gage. GZA believes this may be the result of a
beaver dam directly downstream of the gage, or a datum conversion error.
The existing conditions model appeared to fit the September 1, 2021 event better than the July 17, 2021 event in terms
of hydrograph shape, magnitude, and timing. This is displayed best in the upstream gage which shows the July event
having higher stage values than the model. GZA believes this is due to antecedent conditions. The July storm was preceded
by approximately 1.6 inches of rain while the September storm had no precipitation proceeding it. This effects antecedent
soil moisture conditions with the precipitation preceding the July event creating higher soil moistures resulting in less
infiltration and more runoff when the July storm hit. The worse model fit in July can also be attributed to the scale and
distribution of the July storm; the rain is less intense and peaks three times over its duration, unlike the September event
where the storm is more intense and peaks once over its duration. GZA determined this calibration appropriate to proceed
to modeling proposed restoration scenarios.
Modeling of Restoration Scenarios
The resulting inundation area extents and water depth associated with the 10-year return frequency flood event for each
proposed restoration scenario are presented by reach in Appendix 4 slides 26 through 34. The results demonstrate that
the establishment of connected floodplain and wetlands widens the inundation area, but also reduces the overall depth
of water within the channel and increases flood storage within the reach. These effects occur primarily in reaches 3 and
1, and are more dramatic in Scenario 3 which included the largest expanse of proposed floodplain and wetland creation.
Slides 35 through 50 of Appendix 4 present profiles of the maximum velocity along Nashawannuck Brook for each reach
and for each scenario for the 2-, 10-, and 100-year return frequency flood events. Each chart is also marked with the
median maximum velocity for comparative purposes. Based on the modeling results, the median maximum velocity along
Nashawannuck Brook does not change significantly in reaches 3 and 2, but does decrease in reach 1 with each restoration
scenario, with the most dramatic reduction observed from Scenario 3. The velocity profiles show spikes in maximum ve-
locity downstream of existing structures (Old Wilson Road, culverts and dams) in existing conditions which are largely
reduced or completely eliminated in the proposed restoration scenarios, suggesting that removal of the hydraulic con-
strictions caused by these structures will reduce the potential for associated scour.
The impacts on peak discharges as a result of the restoration scenarios are presented in Appendix 4 slides 52 through 56.
Overall, peak discharges increase with each restoration scenario, most likely due to the reduction in hydraulic constrictions
including the enlargement or removal of the Old Wilson Road culvert and other crossings, removal of the upper dam in
reach 3, and removal of the lower pond dam in reach 2. These increases in peak discharge are tempered by channel-
spanning log jams, floodplain lowering, wetland creation, and increased sinuosity – all of which increase roughness or
reduce slope. However, for larger flow events, these treatments are less effective at mitigating the increases in peak flows
as a result of infrastructure changes (removal of hydraulic constrictions).
CONCLUSIONS
The hydrologic and hydraulic modeling of three (3) proposed scenarios for the restoration of Nashawannuck Brook pro-
vides insight into the potential outcomes of each restoration scenario. The three proposed restoration scenarios include
the removal or modification of most of the infrastructure that currently creates hydraulic restrictions, such as the dams
and culvert crossings, which results in an overall increase in peak discharges downstream. However, the other restoration
elements, including channel-spanning log jams, floodplain lowering, wetland creation, stream channel reconstruction with
increases in sinuosity and decreases in slope, contribute to reductions in maximum channel velocities and increases in
flood storage, which is especially evident by the model results for scenario 3.
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Proactive by DesignThe model outputs contribute to an understanding of the potential hydraulic changes to the Nashawannuck Brook system
as a result of the restoration scenarios during a snapshot in time and must be considered in the context of overarching
restoration goals. The potential habitat and ecosystem benefits of restoration are not quantified by the hydrologic and
hydraulic modeling results.
It is GZA’s understanding that DER has installed an additional stream monitoring gage and will continue to collect stage
data from the new gage and the previously installed gages. In the future, additional data collected can be used to refine
the model, also taking into consideration any restoration elements that are implemented.
CLOSING
We trust that the information contained in this memorandum meets your needs at this time. Please feel free to contact
us if you have any questions or comments.
Attachments:
Attachment A - Limitations
Appendices:
Appendix 1 – Nashawannuck Brook HEC-RAS Model Report from Nashawannuck Brook Assessment and Master Plan of
Resiliency Improvements, June 30, 2020
Appendix 2 – Nashawannuck Brook restoration project: H&H modeling and restoration scenarios (City of Northampton,
Mass Audubon, MA Division of Ecological Restoration)
Appendix 3 – Nashawannuck Brook Flow Data
Appendix 4 – Nashawannuck Brook Proposed Restoration Scenarios Hydrologic and Hydraulic Analysis Powerpoint
Slides from May 17, 2022
Appendix 5 – Stream Segment Data and Culvert Sizing Calculations
Appendix 6 – Model Calibration Results
ATTACHMENT A
LIMITATIONS
USE OF REPORT
1.GeoEnvironmental, Inc. (GZA) prepared this Report on behalf of, and for the exclusive use of the Client for the stated
purpose(s) and location(s) identified in the Report. Use of this Report, in whole or in part, at other locations, or for
other purposes, may lead to inappropriate conclusions and we do not accept any responsibility for the consequences
of such use(s). Further, reliance by any party not identified in the agreement, for any use, without our prior written
permission, shall be at that party’s sole risk, and without any liability to GZA.
STANDARD OF CARE
2.Our findings and conclusions are based on the work conducted as part of the Scope of Services set forth in the Report
and/or proposal, and reflect our professional judgment. These findings and conclusions must be considered not as
scientific or engineering certainties, but rather as our professional opinions concerning the limited data gathered and
reviewed during the course of our work. Conditions other than described in this Report may be found at the subject
location(s).
3.The interpretations and conclusions presented in the Report were based solely upon the services described therein,
and not on scientific tasks or procedures beyond the scope of the described services. The work described in this Report
was carried out in accordance with the agreed upon Terms and Conditions of Engagement.
4.GZA's evaluation was performed in accordance with generally accepted practices of qualified professionals performing
the same type of services at the same time, under similar conditions, at the same or a similar property. No warranty,
expressed or implied, is made. The findings are dependent on numerous assumptions and uncertainties inherent in
the review process. The findings are not an absolute characterization of operations and maintenance preparedness,
but rather serve to evaluate minimum standards of performance provided by the documentation reviewed.
RELIANCE ON INFORMATION FROM OTHERS
5.In conducting our work, GZA has relied upon certain information made available by public agencies, Client, and/or
others. GZA did not attempt to independently verify the accuracy or completeness of that information. Any inconsist-
encies in this information which we have noted are discussed in the Report.
COMPLIANCE WITH CODES AND REGULATIONS
6.We used reasonable care in identifying and interpreting applicable codes and regulations necessary to execute our
scope of work. These codes and regulations are subject to various, and possibly contradictory, interpretations. Inter-
pretations with codes and regulations by other parties are beyond our control.
ADDITIONAL INFORMATION
7.In the event that the Client or others authorized to use this Report obtain information on conditions at the site(s) not
contained in this Report, such information shall be brought to GZA's attention forthwith. GZA will evaluate such infor-
mation and, on the basis of this evaluation, may modify the opinions stated in this Report.
ADDITIONAL SERVICES
8.GZA recommends that we be retained to provide services during any future investigations, design, implementation
activities, construction, and/or property development/ redevelopment at the Site(s). This will allow us the opportunity
to: i) observe conditions and compliance with our design concepts and opinions; ii) allow for changes in the event that
conditions are other than anticipated; iii) provide modifications to our design; and iv) assess the consequences of
changes in technologies and/or regulations.
APPENDIX 1
NASHAWANNUCK BROOK HEC-RAS MODEL REPORT FROM NASHAWANNUCK BROOK ASSESS-
MENT AND MASTER PLAN OF RESILIENCY IMPROVEMENTS, JUNE 30, 2020
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1.0 DATUMS
Elevations in this appendix reference the vertical datum NAVD88. Locations in this appendix reference horizontal
datum NAD83 Massachusetts Mainland State Plane Projection. Vertical and horizontal units are in feet, unless
otherwise specified.
2.0 OBJECTIVE
The objective of the hydrologic and hydraulic analysis was to evaluate flow paths, flow depths, flow velocities, and flow
rates at the former Pine Grove Golf Course located at Old Wilson Road in Northampton, Massachusetts (Site) for
existing and proposed conditions. GZA used the USACE’s HEC-RAS version 5.0.7 software to construct a hydraulic
numerical model of the Site’s contributing watershed, which includes Nashawannuck Brook.
3.0 METHODOLOGY
To evaluate the hydraulics of the site, GZA performed hydraulic simulations of various 24-hour storms. This analysis
was performed using the two-dimensional, unsteady, mixed flow regimes within HEC-RAS.
The HEC-RAS model was developed following these steps:
1.GZA identified the watershed extents using the USGS online software called StreamStats.
2.GZA imported digital terrain data and land cover data for the watershed extents.
3.GZA utilized field data and observations to edit the terrain data to create an “existing conditions” terrain.
4.GZA defined the model extents, called the 2D Flow Area, within HEC-RAS.
5.GZA assigned a grid size resolution and HEC-RAS generated a grid within the model extents.
6.GZA modified the grid using breaklines, which are used to align grid cells with significant topographic features,
such as high points (i.e. ridges) and refinement regions, which are used to create different grid resolutions to
better represent microtopography.
7.GZA added dams and culverts within the model extents.
8.GZA added boundary conditions. Boundary conditions can be locations of incoming or outgoing flow. Incoming
flow was modeled as rainfall over the entire model extents. Outgoing flow was modeled using Manning’s
equation at the downstream edge of the model extent.
HEC-RAS uses the terrain data, land cover data, and grid to generate cross sections at each grid face and storage-
elevation curves for each grid cell. Once the boundary conditions and grid are complete, GZA was able to route flow
through the model extents.
GZA simulated the 24-hour storms by adding a precipitation boundary condition to the model. HEC-RAS computes the
volume of water added to each grid cell and routes the water through the cells. The routing depends on variations in
channel valley geometry/storage, roughness, lateral inflows/outflows, acceleration effects, and hydraulic structures
such as dams and culverts.
Inundation mapping was then developed from the results from the HEC-RAS simulation. The inundation area is
calculated by HEC-RAS and can be exported to ArcMap (GIS). The inundation areas are calculated by comparing the
ground elevation to the maximum water surface elevations. Water surface elevations are linearly interpolated
between grid faces. In those areas where the water surface elevation is greater than the ground elevation, the area is
considered inundated.
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The timing and extent of flooding at various locations can be extracted from HEC-RAS. Information such as peak flows,
maximum water surface elevations (i.e., stage), and flow paths are useful outputs extracted from the model.
4.0 WATERSHED MODEL DESCRIPTION
The watershed for the Pine Grove Golf Course was delineated along the Nashawannuck Brook, slightly downstream of
the golf course limits. Nashawannuck Brook is a small tributary to the Manhan River, with headwaters north of Rocky
Hill Road (State Route 66) between Florence Road and the Ice Pond Drive in Northampton, Massachusetts.
Nashawannuck Brook flows through Pine Grove Golf Course discharging to the Manhan River about 2.0 miles
downstream of Old Wilson Road. The watershed is approximately 0.5 square miles. The area upstream of State Route
66 is mostly forested and residential. The area between State Route 66 and Old Wilson Road is a forested wetland
which has been impacted by development and transmission lines. The area downstream of Old Wilson Road includes
forest and the golf course.
4.1 2D FLOW AREA
The perimeter of the 2D Flow Area is the watershed boundary, as computed with USGS StreamStats v4.3.11. The 2D
flow area consists of a grid of 15,620 cells with an average cell size of about 40 feet by 40 feet (see Figures 1 and 2).
Breaklines were used to align grid cell edges with high ground, such as roadways and ridges.
The 2D flow area was linked with a terrain. The terrain was created from LiDAR data captured in 20151 with 1-meter
spacing. GZA downloaded the LiDAR data from NOAA Data Access Viewer website which mosaiced, reprojected, and
clipped the data. GZA compared the LiDAR data with cross section data from GZA’s field survey. The LiDAR data did
not capture the minimum streambed elevations at all locations, however, the elevations were close enough for the
purposes of this analysis, in GZA’s opinion. The LiDAR data included some stream crossings that have been removed
from the Site. GZA removed the stream crossings from the terrain model.
The 2D flow area was also linked with spatial land use data (see Figure 3). The land use data is a statewide dataset
based on imagery captured in 20162. The land use dataset was downloaded from MassGIS and imported to HEC-RAS.
GZA assigned a Manning’s n value to each land use type3. The Manning’s n values ranged from .025 to 0.16 and are
summarized in the table below:
Table 1: Manning’s n Values for Different Land Uses
Land Use Manning’s n Land Use Manning’s n
Bare Land 0.025 Palustrine Emergent Wetland 0.07
Deciduous Forest 0.16 Palustrine Forested Wetland 0.16
Developed Open Space 0.025 Palustrine Scrub/Shrub Wetland 0.16
Evergreen Forest 0.16 Pasture/Hay 0.03
Grassland 0.035 Scrub/Shrub 0.1
Impervious 0.025 Water 0.04
1 Maine and Massachusetts 2015 Q1 and Q2 LiDAR project, acquired April 9, 2020.
2 2016 Land Cover/Land Use data layer, published by MassGIS and NOAA OCM, acquired April 9, 2020.
3 Manning’s n Values for Various Land Covers to Use for Dam Breach Analyses, NRCS Kansas, July 12, 2017.
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4.2 POND
Within GZA’s model extents is one existing pond (“Lower Pond”), which was constructed to provide irrigation.
Lower Pond was modeled as a hydraulic structure within the 2D grid. The embankment geometry and elevation were
extracted from the LiDAR data. GZA modeled the weir, drop inlet structure, and outlet pipe from the plans titled “Pine
Grove Golf Course Phase I Restoration”, dated February 26, 2020, and from data collected in the field.
4.3 BRIDGES/CULVERTS
GZA identified four (4) culverts and one (1) bridge crossing along the Nashawannuck Brook through the Pine Grove
Golf Course. GZA modeled the culverts as hydraulic structures within the 2D grid. The flow through the culverts was
calculated using culvert flow equations. Culverts or the storm drains at State Route 66 were not investigated as part of
this model.
The most upstream culvert modeled passes water under Old Wilson Road. The concrete circular culvert has an inside
diameter of 30 inches. Old Wilson Road was incorporated into the 2D area as the top of the structure, with elevations
of the roadway extracted from the terrain data. GZA estimated the culvert dimensions from field collected data.
Downstream of Old Wilson Road there is circular corrugated metal culvert which pass under a gravel access road on
the golf course property. Based on the field data, the culvert has an inside diameter of 27.5-inches. Field observations
indicate that the culvert invert at the outlet is submerged by approximately 1 foot of water. The invert and access road
elevations, estimated from LiDAR, were 220.0 and 222.4 feet, respectively.
Further downstream an additional gravel access road spans Nashawannuck Brook with two culverts installed. The main
pipe, 18-inch steel, was significantly blocked with debris at the time of the site visit. A secondary 31-inch corrugated
plastic culvert is set at a higher elevation. This pipe appeared to discharge beneath the access road to a 42-inch
concrete pipe, which then discharges downstream. The LiDAR shows the roadway top at elevation at 220.6 feet. GZA
estimated the culvert inverts to be 215.5 and 216.3 feet, respectively.
The last structure was a bridge built onto concrete waste blocks embedded in the channel bank. This bridge is also
maintained for property access and maintenance. GZA estimated the bridge deck elevation to be 162.5 feet and
modeled the stream channel as a concrete box culvert structure. The inverts were estimated from LiDAR to be 161.0
feet.
See below of a summary of structures modeled:
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Table 1: Nashawannuck Brook at Pine Grove Culverts
Culvert Shape Chart # Length
(ft)
Span
(ft)1
Rise/Diameter
(ft) 1
Inlet Elevation
(ft-NGVD29) 2
Outlet
Elevation
(ft-NGVD29) 2
Description
Culvert #1 Circular 1 – Concrete
Pipe Culvert 66.1 NA 2.5 223.2 221.0
At Old Wilson Road, Inlet
side not observed; outlet
side flush with field
stone headwall.
Culvert #2 Circular
2 – Corrugated
Metal Pipe
Culvert
36 NA 2.29 220.0 219.5 Gravel access near Old
Wilson Road
Culvert #3 Circular 2 – Corrugated
Metal Pipe 49.8 NA 1.5 215.5 214.1 Gravel access below
“Upper Pond”
Culvert #4 Circular 1 – Concrete
Pipe Culvert 35 NA 2.58 216.3 214.4 Gravel access below
“Upper Pond”
Pond
Structure Circular 2 – Corrugated
Metal Pipe 75 NA 2.58 180.0 174.0 Lower Pond
Bridge Access Box 8 – Flared
Wingwalls 13.9 5 1 161.0 160.8 Bridge
1. Inside diameters measured by GZA field personnel.
2. Inlet and outlet elevations were estimated using terrain created from LiDAR.
5.0 DOWNSTREAM BOUNDARY CONDITION
The model ends approximately 4,000 feet downstream of the Old Wilson Road culvert. The streambed slope at the
downstream limit is approximately 0.7%. GZA assigned a normal depth boundary condition (i.e. Manning’s equation)
with the measured slope.
6.0 PRECIPITATION BOUNDARY CONDITION
The inflow boundary condition for the 2D Flow Area is precipitation, which was adjusted for each storm event.
Precipitation depths were obtained from NOAA Atlas 14 Precipitation-Frequency Atlas of the United States Volume 10
Version 3, dated 2015 and revised 2019 (see Table 2). The depths were processed in the software WinTR-20 V3.2 to
develop storm hyetographs that nest smaller duration storms within larger duration storms.
GZA used the Curve Number Method to compute soil infiltration. The watershed’s hydrologic soil groups were acquired
from the NRCS Web Soil Survey. The soil groups and land use data were used to determine an area weighted curve
number for the watershed4. The computed curve number, 62, assumes good hydrologic condition for the soils. GZA
used the curve number to calculate initial abstraction (i.e. losses before runoff begins). GZA used the HEC-HMS
software to compute the infiltration losses for each storm hyetograph. Precipitation data in increments of 6 minutes
were extracted from HEC-HMS and input to HEC-RAS as a boundary condition.
4 Table 2-2 in “Urban Hydrology for Small Watersheds”, Technical Release 55, Natural Resources Conservation Service, June 1986.
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Table 2: HEC-RAS Precipitation Inputs
Recurrence
Interval
24-hour Precipitation Depth (inches)24-hour Precipitation Excess (inches)
2-Year 3.11 0.56
10-Year 4.99 1.65
50-Year 7.02 3.12
100-Year 7.97 3.87
7.0 CALIBRATION
Two benchmarks were established for calibrating the model: 1) the peak flow just upstream of Old Wilson Road, and
2) the peak flow at the model’s downstream limit. Peak flows were computed with USGS StreamStats, which uses
regression equations and the parameters of drainage area, mean basin elevation, and percent storage to estimate peak
flows for a watershed. GZA compared the StreamStats peak flows with stream gage data from “Magnitude of Flood
Flows at Selected Annual Exceedance Probabilities for Streams in Massachusetts”5 and with the Flood Insurance Study
from Hampshire County. The comparison confirmed that the peak flows from StreamStats were reasonable and would
be used for model calibration.
Table 3: Peak Flow Comparison
Watershed
StreamStats for
Nashawannuck
Brook
Gage
1100800
Gage
1100900
Gage
1123160
Gage
01124750
Gage
1187850
Gage
1196990
DRNAREA (SQ. MI.) 0.5 0.74 0.70 0.72 0.49 0.56 0.30
SLOPE (%) 8.069 4.42 3.20 8.91 4.54 9.28 4.16
FOREST (%) 42.06 0.98 4.84 24.27 2.60 6.38 29.13
ELEV (FT) 243 203 97 936 778 715 1,903
LC06STOR (%) 5.95 2.01 22.12 4.09 8.64 0.31 0.00
LC11IMP (%) 4.61 1.17 8.12 0.13 2.06 0.29 1.04
WETLAND (%) 4.32 1.73 20.00 4.09 8.64 0.31 0.00
2-Year Flow (CFS)
23.2
(11.7 – 45.9)* 58 18 27 15 0 25
10-year Flow (CFS)
52.1
(25.3 – 107)* 97 35 40 34 0 36
100-year Flow (CFS)
104
(45.6 – 236)* 156 121 87 168 0 79
* Flows in parenthesis are the upper and lower range provided by StreamStats.
GZA simulated the 2-year, 10-year, and 100-year storms in HEC-HMS and extracted the peak flow at each benchmark
location. The simulations resulted in larger peak flows than those presented in StreamStats. GZA calibrated the
Manning’s n values and the Curve Number to match the modeled peak flows to the peak flows from StreamStats.
5 “Magnitude of Flood Flows at Selected Annual Exceedance Probabilities for Streams in Massachusetts”, Scientific Investigations Report 2016-
5156, U.S. Geological Survey, Philip J. Zarriello, 2017.
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A curve number of 65 was chosen, which corresponds with an initial abstraction of 1.077 inches. The calibrated
Manning’s N values are presented below in Table 4. The peak flows from the calibrated model are presented in Table
6. GZA also blocked the Old Wilson Road culvert by 1 foot to account for blocking by sediment.
Table 4: Calibrated Manning’s n Values
Land Use Calibrated Manning’s n Land Use Calibrated Manning’s n
Bare Land 0.025 Palustrine Emergent Wetland 0.21
Deciduous Forest 0.48 Palustrine Forested Wetland 0.3
Developed Open Space 0.25 Palustrine Scrub/Shrub Wetland 0.3
Evergreen Forest 0.48 Pasture/Hay 0.09
Grassland 0.105 Scrub/Shrub 0.3
Impervious 0.075 Water 0.12
8.0 PROPOSED CONDITIONS
GZA simulated 6 proposed conditions, which are summarized in Table 5. Stream crossings, including culverts and dams,
were either left unchanged, replaced with a 14-foot span bridge, or removed. GZA also performed two simulations
with wetlands added by creating depressions in the terrain to simulate the addition of wetlands within the Site. GZA
added a total of 20 depressions, each 3 feet deep, with a total area of 23 acres. In addition, GZA performed two
simulations with revised Manning’s n values and revised Curve Number to reflect the grassy golf course being replaced
by forest and the addition of a meadow. A curve number of 63.8 was calculated based on the change in area from golf
course to meadow and forest. The hyetograph for the adjusted curve number was calculated using previously methods
described in Section 6.0.
Table 5: Summary of Proposed Conditions Inputs
Simulation Name
Old
Wilson
Road
Culvert
#2
Culverts
# 3 and #4
(Dual Culverts)
Lower
Pond
Dam
Bridge Wetlands
Manning’s n
and Curve
Number
Scenario A -Replace Replace Replace ---
Scenario A Wetlands -Replace Replace Replace -Added -
Scenario A Land Use -Replace Replace Replace --Revised
Scenario B Replace Remove Remove Remove Remove --
Scenario B Wetlands Replace Remove Remove Remove Remove Added -
Scenario B Land Use Replace Remove Remove Remove Remove -Revised
* Replacements are with 14-foot span bridge.
9.0 SIMULATION PARAMETERS
GZA ran the simulations with a 10 second time step. HEC-RAS can perform two-dimensional unsteady flow routing with
either the Full Saint Venant equations of the Diffusion Wave equations. GZA used the Diffusion Wave equations. The
HEC-RAS User’s Manual provides guidance on which equations to use.
10.0 RESULTS
The results of the analysis are shown in Table 6.
June 5, 2020
GZA File No. 15.0166826.00
Nashawannuck Brook HEC-RAS Model Report
Page | 7
Table 6: Comparison of Peak Flows (cfs) at Downstream Limit
Simulation 2-Year 10-Year 50-Year 100-Year
HEC-RAS Existing Condition 12 50 126 177
HEC-RAS Scenario A 13 52 164 221
HEC-RAS Scenario A Wetlands 6 39 120 167
HEC-RAS Scenario A Land Use 9 48 134 187
HEC-RAS Scenario B 13 60 169 224
HEC-RAS Scenario B Wetlands 6 42 121 169
HEC-RAS Scenario B Land Use 9 52 134 183
The results show that both Scenario A and Scenario B, with structure changes only, result in larger peak flows at the
downstream limit. The addition of wetlands mitigates the increase in peak flow significantly, to the point of reducing
peak flows below Existing Conditions. The results suggest that less depressions or shallower depressions may be
sufficient. The change in land use (i.e. Manning’s n and infiltration) also mitigates some of the increase in peak flow,
however, the peak flows remain higher than Existing Conditions. Additional results showing changes in maximum
depths for selected scenarios are presented in Figures 4-7.
The modeling shows that some combination of increased wetlands storage, increased Manning’ n, and increased
infiltration, can result in reduced peak flow from the Site, despite the loss of attenuation from the stream crossings
and dam.
Figures
Note: Basemap depicts terrain in feet, NAVD88.
Figure 1: Watershed Model with Terrain Data
Note: Basemap aerial photography is Bing Satellite generated from within HEC-RAS Mapper.
Figure 2: Watershed Model with Aerial Imagery
Figure 3: Watershed Model with Existing Conditions Land Use Data
Existing Conditions – Maximum Flow Depth (3.8ft) Scenario A: Forest – Maximum Flow Depth (4.6)
Note: Basemap aerial photography is Bing Satellite.
Figure 4: Comparison of Existing Conditions and Scenario A: Revert to Forest for Two Year Storm
Existing Conditions – Maximum Flow Depth (5.8ft) Scenario A: Forest – Maximum Flow Depth (5.7ft)
Note: Basemap aerial photography is Bing Satellite.
Figure 5: Comparison of Existing Conditions and Scenario A: Revert to Forest for Ten Year Storm
Existing Conditions – Maximum Flow Depth (7.0ft) Scenario A: Forest – Maximum Flow Depth (7.1ft)
Note: Basemap aerial photography is Bing Satellite.
Figure 6: Comparison of Existing Conditions and Scenario A: Revert to Forest for Fifty Year Storm
Existing Conditions – Maximum Flow Depth (7.4ft) Scenario A: Forest – Maximum Flow Depth (7.5ft)
Note: Basemap aerial photography is Bing Satellite.
Figure 7: Comparison of Existing Conditions and Scenario A: Revert to Forest for One Hundred Year Storm
June 1, 2022
File No. 15.0167005.00
Hydrologic and Hydraulic Models for Restoration Scenarios Memorandum
Page | 9
Proactive by Design
APPENDIX 2
NASHAWANNUCK BROOK RESTORATION PROJECT: H&H MODELING AND RESTORATION SCE-
NARIOS (CITY OF NORTHAMPTON, MASS AUDUBON, MA DIVISION OF ECOLOGICAL
RESTORATION)
Nashawannuck Brook
restoration project:
H&H modeling and restoration scenarios
City of Northampton
Mass Audubon
MA Division of Ecological Restoration
Objectives of H&H modeling
•Evaluate changes in hydrology from inflow to outflow
•Evaluate downstream impacts (e.g., floodwaters leaving site)
•Evaluate changes to water surface elevations across site
•Determine changes from different interventions
Key decision points
•Infrastructure (dams, weirs, culverts, concrete blocks, tile drains)
•How much to remove? All or subset?
•Old Wilson Road culvert: replace or remove?
•Stream corridor
•Modify existing channel or construct new channel?
•Lower floodplain? Where and by how much?
•Wetland resources
•Where most beneficial?
•What spatial extent?
Questions to answer with H&H modeling
•How much flood storage needs to be added to compensate for
removal of dams and other structures?
•How much additional flood storage can be added to reduce
flashiness?
•How much does the floodplain need to be lowered to not raise Base
Flood Elevations?
•Where would wetland creation provide most benefit?
•How large do wetlands need to be to create necessary storage?
H&H modeling scenarios from Master Plan
Notes:
•Wetland condition represented by 20 depressions, each 3 feet deep, totaling 23 acres
•Manning’s n and curve number represent land use change from golf course to forest and meadow
H&H modeling results from Master Plan
•Existing conditions:
•Structures impound water during 10-year storm and larger
•All structures (except upper dam) overtopped during 50-year storm
•Scenario B:
•Increase in peak flows downstream
•Upper dam and lower dam attenuate peak flows
•Wetland scenarios:
•Addition of wetland storage mitigates and reduces peak flows despite increase in flows from removing structures
•Note: Master Plan does not specify where the wetland storage would occur (implies that depressional areas are distributed throughout)
Scenario 1: Limited Interventions
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Replace Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Modify existing channel:
add channel-spanning
log jams
•Limited riparian
plantings
•Add small wetlands along
stream corridor
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Modify existing channel:
add channel-spanning
log jams
•Limited riparian
plantings
•Add small wetlands along
stream
•Add small wetlands away
from stream
Note: Bold indicates differences between scenarios
Scenario 2: Intermediate Interventions
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Replace Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Lower floodplain,
reconstruct natural
channel
•More extensive riparian
plantings
•Add medium-size wetlands
along stream corridor
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Remove bank armoring,
reconstruct natural
channel
•More extensive riparian
plantings
•Add medium-size wetlands
along stream
•Add medium-size wetlands
away from stream
Note: Bold indicates differences between scenarios
Scenario 3: Full-Scale Interventions
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Remove Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Lower floodplain,
reconstruct natural
channel
•More extensive riparian
plantings, extending into
upland
•Add large-size wetlands
along stream corridor and
along intermittent channels
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Create new channel, fill
old channel
•More extensive riparian
plantings, extending into
upland
•Add large-size wetland
complex encompassing
southern extent of historic
wetland area
Note: Bold indicates differences between scenarios
Infrastructure
•All scenarios:
•Replace cart-path culvert with bridge
•Remove concrete blocks
•Remove upper dam/culvert structure
•Remove weir
•Remove lower/irrigation dam
•Old Wilson Road culvert:
•Scenario 1 & 2: replace
•Scenario 3: remove
Stream corridor
Scenario 1: Limited Scenario 2: Intermediate Scenario 3: Full Scale
Log jams
Channel reconstruction
Riparian plantings
Floodplain lowering/fill removal
Wetland resources
Scenario 1: Limited Scenario 2: Intermediate Scenario 3: Full Scale
Example extents shown in orange
June 1, 2022
File No. 15.0167005.00
Hydrologic and Hydraulic Models for Restoration Scenarios Memorandum
Page | 10
Proactive by Design
APPENDIX 3
NASHAWANNUCK BROOK GAGE DATA
Appendix 3
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
11/2/202012/2/20201/2/20212/2/20213/2/20214/2/20215/2/20216/2/20217/2/20218/2/20219/2/202110/2/202111/2/202112/2/2021Stage, ftDate
Nashawannuck Brook -Gage Stages
US Stage, ft
DS Stage, ft
Pond Stage, ft
Appendix 3
219.00
219.50
220.00
220.50
221.00
221.50
222.00
222.50
223.00
223.50
11/2/202012/2/20201/2/20212/2/20213/2/20214/2/20215/2/20216/2/20217/2/20218/2/20219/2/202110/2/202111/2/202112/2/2021Elevation, ft NAVD88Date
Nashawannuck Brook -U/S Gage Elevations
Appendix 3
177.5
178
178.5
179
179.5
180
180.5
181
181.5
182
8/2/20219/2/202110/2/202111/2/202112/2/2021Elevation, ft NAVD88Date
Nashawannuck Brook -Pond Gage Elevations
Appendix 3
154.50
155.00
155.50
156.00
156.50
157.00
157.50
158.00
11/2/202012/2/20201/2/20212/2/20213/2/20214/2/20215/2/20216/2/20217/2/20218/2/20219/2/202110/2/202111/2/202112/2/2021Elevation, ft NAVD88Date
Nashawannuck Brook -D/S Gage Elevations
June 1, 2022
File No. 15.0167005.00
Hydrologic and Hydraulic Models for Restoration Scenarios Memorandum
Page | 11
Proactive by Design
APPENDIX 4
NASHAWANNUCK BROOK PROPOSED RESTORATION SCENARIOS HYDROLOGIC AND HYDRAU-
LIC ANALYSIS POWERPOINT SLIDES FROM MAY 17, 2022
Nashawannuck Brook
Proposed Restoration Scenarios
Hydrologic & Hydraulic Analysis
May 17, 2022
Revised May 25, 2022
1
AGENDA
•Overview of Restoration
Scenarios
•Model Development
•Model Results
•Next Steps
2
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Replace Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Modify existing channel:
add channel-spanning
log jams
•Limited riparian
plantings
•Add small wetlands along
stream corridor
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Modify existing channel:
add channel-spanning
log jams
•Limited riparian
plantings
•Add small wetlands along
stream
•Add small wetlands away
from stream
Note: Bold indicates differences between scenarios
Scenario 1
3
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Replace Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Lower floodplain,
reconstruct natural
channel
•More extensive riparian
plantings
•Add medium-size wetlands
along stream corridor
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Remove bank armoring,
reconstruct natural
channel
•More extensive riparian
plantings
•Add medium-size wetlands
along stream
•Add medium-size wetlands
away from stream
Note: Bold indicates differences between scenarios
Scenario 2
4
Infrastructure Stream Corridor Wetland Resources
Reach 3
(Upstream)
•Remove Old Wilson Road
culvert
•Replace cart-path culvert
with bridge
•Remove concrete blocks
•Remove upper
dam/culvert structure
•Lower floodplain,
reconstruct natural
channel
•More extensive riparian
plantings, extending into
upland
•Add large-size wetlands
along stream corridor and
along intermittent channels
•Expand wetland area
adjacent to upper/former
irrigation impoundment
Reach 2
(Middle)
•Remove weir
•Remove irrigation dam
•Construct new channel
through former
impoundment
•Create wetland along
channel of irrigation
impoundment
Reach 1
(Downstream)
•Remove concrete blocks •Create new channel, fill
old channel
•More extensive riparian
plantings, extending into
upland
•Add large-size wetland
complex encompassing
southern extent of historic
wetland area
Note: Bold indicates differences between scenarios
Scenario 3
5
Infrastructure
•All scenarios:
•Replace cart-path culvert with bridge
•Remove concrete blocks
•Remove upper dam/culvert structure
•Remove weir
•Remove lower/irrigation dam
•Old Wilson Road culvert:
•Scenario 1 & 2: replace
•Scenario 3: remove
6
Stream corridor
Scenario 1: Limited Scenario 2: Intermediate Scenario 3: Full Scale
Log jams
Channel reconstruction
Riparian plantings
Floodplain lowering/fill removal
7
Wetland resources
Scenario 1: Limited Scenario 2: Intermediate Scenario 3: Full Scale
Example extents shown in orange
8
Building the Hydraulic Model –Reach 3
9
Building the Hydraulic Model –Reach 2
10
Building the Hydraulic Model –Reach 1
11
Hydraulic Model Terrain –Existing Conditions
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and
Control Structure
Bridge South/
Cart path crossing
Lower Pond Dam
Artificially
straight channel
Artificially
straight channel
12
Hydraulic Model Terrain –Scenario 1 –Reach 3
Existing Proposed
Replace culverts
Small wetlands
along corridor
Log jams
Remove dam13
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Hydraulic Model Terrain –Scenario 2 –Reach 3
Existing Proposed
Replace culverts
Lower floodplain and
connect medium-size
wetlands
Remove dam
Construct sinuous channel
14
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Hydraulic Model Terrain –Scenario 3 –Reach 3
Existing Proposed
Replace culvert Lower floodplain and
connect large-size
wetlands
Remove dam
Construct sinuous channel
Remove Old Wilson Rd crossing
Larger wetland at old
impoundment
Wetland along
intermittent channel
15
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Hydraulic Model Structures –Old Wilson Road
Existing:
Proposed:
(Scenario 1 & 2)
16
Hydraulic Model Structures –North Culvert
Existing:
Proposed:
(All Scenarios)
17
Hydraulic Model Terrain –Scenario 1 –Reach 2
Existing Proposed
Remove weir
Remove dam
Construct channel
Create wetland
18
Upper Pond and
Control Structure
Lower Pond Dam
Hydraulic Model Terrain –Scenario 2 –Reach 2
Existing Proposed
Remove weir
Remove dam
Construct channel
Create wetland
19
Upper Pond and
Control Structure
Lower Pond Dam
Hydraulic Model Terrain –Scenario 3 –Reach 2
Existing Proposed
Remove weir
Remove dam
Construct channel
Create wetland
Construct channel
20
Upper Pond and
Control Structure
Lower Pond Dam
Hydraulic Model Terrain –Scenario 1 –Reach 1
Existing Proposed
Small wetlands
along corridor
Log jams
21
Bridge South/ Cart
path crossing
Hydraulic Model Terrain –Scenario 2 –Reach 1
Existing Proposed
Lower floodplain and
connect medium-size
wetlands
22
Bridge South/ Cart
path crossing
Hydraulic Model Terrain –Scenario 3 –Reach 1
Existing Proposed
Construct sinuous channel
Lower floodplain and
connect large-size
wetlands
Fill in old channel
23
Bridge South/ Cart
path crossing
Hydraulic Model Terrain –Sediment Movement
Proposed Restoration Net Sediment Movement
(cubic-yard)
Scenario 1 11,000 (removal)
Scenario 2 31,000 (removal)
Scenario 3 50,000 (removal)
24
Hydraulic Model –Restoration Scenario Results
25
Existing Proposed
Scenario 1 -Reach 3 –Inundation Area
10-Year Flow Event
26
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Existing Proposed
Scenario 2 -Reach 3 –Inundation Area
10-Year Flow Event
27
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Existing Proposed
Scenario 3 -Reach 3 –Inundation Area
10-Year Flow Event
28
Old Wilson Road
(undersized culvert)
Culvert North
(undersized)
Upper Pond and Control
Structure
Existing Proposed
Scenario 1 -Reach 2 –Inundation Area
10-Year Flow Event
29
Upper Pond and
Control Structure
Lower Pond Dam
Existing Proposed
Scenario 2 -Reach 2 –Inundation Area
10-Year Flow Event
30
Upper Pond and
Control Structure
Lower Pond Dam
Existing Proposed
Scenario 3 -Reach 2 –Inundation Area
10-Year Flow Event
31
Upper Pond and
Control Structure
Lower Pond Dam
Existing Proposed
Scenario 1 -Reach 1 –Inundation Area
10-Year Flow Event
32
Bridge South/ Cart
path crossing
Existing Proposed
Scenario 2 -Reach 1 –Inundation Area
10-Year Flow Event
33
Bridge South/ Cart
path crossing
Existing Proposed
Scenario 3 -Reach 1 –Inundation Area
10-Year Flow Event
34
Bridge South/ Cart
path crossing
Reach 3 –Maximum Velocity
2-Year Flow Event
Scenario 1 = 0.6 ft/s
Existing=0.8 ft/s
Old Wilson Rd
Culvert North Upper Dam
Log jams = velocity decrease
35
Reach 3 –Maximum Velocity
2-Year Flow Event
Scenario 3 = 0.6 ft/s
Scenario 2=0.6 ft/s
Old Wilson Rd
Culvert North Upper Dam
36
Reach 3 –Maximum Velocity
10-Year Flow Event
Scenario 1 = 1.1 ft/s
Existing=1.2 ft/s
Old Wilson Rd
Culvert North Upper Dam
Log jams = velocity decrease
37
Reach 3 –Maximum Velocity
10-Year Flow Event
Scenario 3 = 1.2 ft/s
Scenario 2=1.3 ft/s
Old Wilson Rd
Culvert North Upper Dam
38
Reach 3 –Maximum Velocity
100-Year Flow Event
Scenario 1 = 1.9 ft/s
Existing=1.9 ft/s
Old Wilson Rd
Culvert North Upper Dam
Log jams = velocity decrease
39
Reach 3 –Maximum Velocity
100-Year Flow Event
Scenario 2 = 2.2 ft/s
Scenario 3=2.1 ft/s
Old Wilson Rd
Culvert North Upper Dam
40
Reach 3 -Water Surface Elevation (XS 4)
10-Year Flow Event
Existing Condition Scenario 1
Scenario 2 Scenario 3
41
Reach 2 –Maximum Velocity
2-Year Flow Event
Scenario 1 = 2.4 ft/s
Existing=2.6 ft/s
Scenario 2 = 2.2 ft/s
Scenario 3 =2.4 ft/s
Start of Lower Dam Pond
42
Reach 2 –Maximum Velocity
10-Year Flow Event
Existing = 4.1 ft/s
Scenario 1 =4.2 ft/s
Scenario 2 = 3.9 ft/s
Scenario 3 =4.1 ft/s
Start of Lower Dam Pond
43
Reach 2 –Maximum Velocity
100-Year Flow Event
Scenario 1 = 6.6 ft/s
Existing=6.6 ft/s
Scenario 2 = 6.2 ft/s
Scenario 3 =6.4 ft/s
Start of Lower Dam Pond
44
Reach 1 –Maximum Velocity
2-Year Flow Event
Cart path bridge
Scenario 2 = 1.1 ft/s
Scenario 1 = 0.7 ft/s
Existing = 1.3 ft/s
Median maximum velocity for reach Log jams = velocity decrease
45
Reach 1 –Maximum Velocity
2-Year Flow Event
Scenario 3 = 0.3 ft/s
Median maximum velocity for reach46
Reach 1 –Maximum Velocity
10-Year Flow Event
Cart path bridge
Scenario 1 = 1.5 ft/s
Scenario 2 = 2.2 ft/s
Existing=2.5 ft/s
Median maximum velocity for reach Log jams = velocity decrease
47
Reach 1 –Maximum Velocity
10-Year Flow Event
Scenario 3 = 0.7 ft/s
Median maximum velocity for reach48
Reach 1 –Maximum Velocity
100-Year Flow Event
Cart path bridge
Existing = 4.8 ft/s
Scenario 2 = 4.0 ft/s
Scenario 1 = 3.3 ft/s
Median maximum velocity for reach Log jams = velocity decrease
49
Reach 1 –Maximum Velocity
100-Year Flow Event
Scenario 3 = 1.6 ft/s
Median maximum velocity for reach50
Reach 1 -Water Surface Elevation (XS 8)
10-Year Flow Event
Existing Condition Scenario 1
Scenario 2 Scenario 3
51
Hydraulic Model –Peak Discharge Results
Peak Discharges (cfs)
Scenario Recurrence
Interval (yr)
Location in Project Site
Reach 3 Reach 2 Reach 1 Downstream
ExtentStartMiddleEndStartMiddleEndStartMiddleEnd
Existing
Conditions
1 1.5 2.4 3.1 3.1 3.5 3.6 3.0 3.2 3.7 4.1
2 4.3 6.6 8.2 8.3 9.5 10 10 11 13 14
10 27 38 40 40 47 51 51 54 61 66
50 103 131 119 120 140 142 152 161 178 193
100 151 187 188 190 219 223 237 254 278 303
Proposed
Conditions
Scenario 1
1 1.4 2.1 2.6 2.6 2.9 3.0 3.3 3.7 4.1 4.6
2 4.6 6.9 8.3 8.4 9.4 10 11 11 13 14
10 33 49 58 59 64 67 71 76 84 92
50 103 154 178 179 196 204 216 224 243 267
100 155 212 249 251 277 288 304 325 356 394
Proposed
Conditions
Scenario 2
1.0 1.4 2.2 2.7 2.7 3.0 3.2 3.4 3.7 4.2 4.7
2.0 4.6 7.0 8.4 8.4 9.4 10 11 11 13 14
10 34 49 59 59 64 67 72 76 84 91
50 103 155 181 182 200 207 220 231 248 273
100 156 213 250 251 274 288 315 326 358 394
Proposed
Conditions
Scenario 3
1 1.3 2.2 2.6 2.6 2.9 3.0 3.3 3.4 3.9 4.2
2 4.8 7.1 8.3 8.3 9.3 10 10 11 13 14
10 34 49 58 58 63 66 70 75 82 89
50 105 154 176 177 193 202 213 221 245 265
100 157 209 246 248 273 285 299 315 338 368
52
Hydraulic Model –Peak Discharge % Change
% Difference from Existing Conditions
Scenario Recurrence
Interval (yr)
Location in Project Site
Reach 3 Reach 2 Reach 1 Downstream
ExtentStartMiddleEndStartMiddleEndStartMiddleEnd
Proposed
Conditions
Scenario 1
1 -9 -12 -16 -16 -17 -14 12 14 11 11
2 6 5 2 1 -1 1 4 1 -1 -1
10 25 28 48 48 37 32 41 39 38 39
50 0 18 50 49 40 44 43 38 36 38
100 3 13 32 32 26 29 28 28 28 30
Proposed
Conditions
Scenario 2
1 -8 -8 -12 -13 -13 -11 16 15 14 13
2 6 7 2 2 -1 1 3 3 2 2
10 25 29 48 48 38 32 43 40 38 39
50 0 18 52 52 43 46 45 43 39 41
100 4 14 32 32 25 29 33 29 29 30
Proposed
Conditions
Scenario 3
1 -12 -10 -16 -16 -16 -15 11 6 3 1
2 10 8 1 1 -2 0 3 2 -2 -3
10 25 28 46 46 35 30 39 37 36 35
50 1 18 48 47 38 42 40 37 38 37
100 4 12 30 31 24 28 26 24 21 21
53
Hydraulic Model –Peak Discharge Results
2-Year Flow Event
54
Hydraulic Model –Peak Discharge Results
10-Year Flow Event
55
Hydraulic Model –Peak Discharge Results
100-Year Flow Event
56
Results –Summary -General
•Inundation
•Connected floodplains improves storage (Scenario 3 –Reaches 1 and 3)
•Median Maximum Velocity –changes with restoration
•Reach 3 –velocities maintained (some slight increase)
•Reach 2 –slight reduction in velocities
•Reach 1 –marked reduction in velocities, especially Scenario 3
•Peak Flows
•Larger events (10-yr, 100-yr) –peak flows increase with restoration,
increase is less with Scenario 3
•Smaller events (2-yr) –at downstream limit, decrease with scenarios 1
& 3
57
Results –Summary -General
•Eliminating hydraulic constrictions by removing dams and upsizing
crossings affects the most significant changes in the model, leading to
increased peak velocities and discharges.
•These increases are tempered by channel-spanning log jams, floodplain
lowering, wetland creation, and increased sinuosity –all of which
increase roughness or reduce slope.
•These treatments are less effective at mitigating the effects of
infrastructure changes at higher flows.
•Model outputs such as peak velocity (in the channel) and peak flow
may not be capturing the whole story. There are many habitat and
ecosystem benefits that are not easily quantified by these model runs.
•Restoration actions will depend on restoration goals.
58
Next Steps
•Select preferred restoration scenario for conceptual design
•Submit Draft Memorandum –Hydrologic and Hydraulic Models for
Restoration Scenarios: 5/27/22
•Submit Final Memorandum –Hydrologic and Hydraulic Models for
Restoration Scenarios: 6/30/22
•Submit Draft Conceptual Design Plans, Basis of Design memo, including
cost opinions for review: 6/8/22
•Submit Final Conceptual Design Plans, Basis of Design memo, including
cost opinions: 6/30/22
•Submit Geomorphic Assessment Report, Ecological Conditions Update
Report: 6/8/22
•Submit Final Memorandum and Restoration Options List: 6/30/2259
June 1, 2022
File No. 15.0167005.00
Hydrologic and Hydraulic Models for Restoration Scenarios Memorandum
Page | 12
Proactive by Design
APPENDIX 5
CULVERT SIZING CALCULATIONS
Order Reach Segment Length Stream Dominant Morphology Channel BF elev XS Area Channel Mean Max Width/ Floodprone Entrenchment(feet) type Sed Size (dominant) slope (ft) (sq.ft) width (BF) depth (ft) depth (ft) depth Width (ft)1 NAW‐3 3D 210 C 4 Riffle‐Pool 0.74% 221.6 18.5 25.6 0.7 1.8 35.5 114 4.52 NAW‐3 3C 390 C 4 Riffle‐Pool 0.79% 219.4 16.3 16.3 1.0 2.5 16.3 200 12.33 NAW‐3 3B 218 C 4 Riffle‐Pool 0.53% 217.9 9.1 10.6 0.9 1.6 12.4 90 8.54 NAW‐3 3A 324 B 5 Impounded 0.11% 217.0 26.5 40.8 0.7 1.6 62.9 80 2.05 NAW‐2 2D 246 B 4 Step‐Pool 5.08% 203.3 11.4 16.1 0.7 1.4 22.6 33 2.16 NAW‐2 2C 356 B 4 Step‐Pool 4.60% 195.5 16.8 16.7 1.0 2.0 16.5 40 2.47 NAW‐2 2B 137 C 4 Step‐Pool 5.87% 185.0 14.5 20.1 0.7 1.4 27.8 74 3.78 NAW‐2 2A 183 N/A 5 Impounded 0.18% 180.1 N/A N/A N/A N/A N/A N/A N/A9 NAW‐1 1D 336 C 4 Riffle‐Pool 4.28% 166.8 14.6 14.7 1.0 2.0 14.8 46 3.110 NAW‐1 1C 453 C 4 Riffle‐Pool 0.80% 163.1 15.5 16.0 1.0 2.2 16.5 160 10.011 NAW‐1 1B 491 C 4 Riffle‐Pool 0.57% 161.2 15.5 13.8 1.1 2.4 12.3 180 13.112 NAW‐1 1A 336 B 5 Impounded 1.03% 156.3 39.9 16.9 2.4 3.0 7.1 28 1.7
MA Stream Crossing Standards - Culvert Sizing Calculations - Old Wilson Road over Nashawannuck Brook
ASSUME BANKFULL WIDTH OF 26'
span length = 1.2 x bankfull width =31.2 feet
=9.5 meters
OPTIMUM STANDARDS (bridge)BRIDGE SPAN =9.5 meters 31.2 FEET
BRIDGE height =6 feet (minimum opening height of 6 ft required)
=1.8 meters
culvert crossing length =8 meters (measured from Google Earth)
2.20 > 0.5 meters
Will an opening height of 6 ft fit at the site?NO, 2.5 ft max
CROSSING SPAN =9.5 meters 31.2 FEET
CROSSING height =2 feet (no minimum required)
=0.6 meters
culvert crossing length =8 meters (measured from Google Earth)26 FEET
0.73 > 0.250 METERS
2.4 > 0.82 FEET
openness ratio (rectangular) =
GENERAL STANDARDS (bridge, 3-sided box,
open bottom arch)
openness ratio (rectangular) =
June 1, 2022
File No. 15.0167005.00
Hydrologic and Hydraulic Models for Restoration Scenarios Memorandum
Page | 13
Proactive by Design
APPENDIX 6
MODEL CALIBRATION RESULTS
Appendix 6
7-17-2021
220.50
221.00
221.50
222.00
222.50
223.00
223.50
7/16/2021 12:00 7/17/2021 0:00 7/17/2021 12:00 7/18/2021 0:00 7/18/2021 12:00 7/19/2021 0:00 7/19/2021 12:00 7/20/2021 0:00 7/20/2021 12:00WSEL FT NAVD88Date & Time
7-17-2021 U/S Gage
Recorded Upstream Gage Elev.Model Calibrated Results
177.5
178
178.5
179
179.5
180
180.5
181
181.5
182
7/16/2021 12:00 7/17/2021 0:00 7/17/2021 12:00 7/18/2021 0:00 7/18/2021 12:00 7/19/2021 0:00 7/19/2021 12:00 7/20/2021 0:00 7/20/2021 12:00WSEL FT NAVD88Date & Time
7-17-2021 Pond Gage
Model Calibrated Results
NO RECORDED RESULTS
Appendix 6
156.00
156.50
157.00
157.50
158.00
158.50
159.00
159.50
160.00
160.50
7/16/2021 12:00 7/17/2021 0:00 7/17/2021 12:00 7/18/2021 0:00 7/18/2021 12:00 7/19/2021 0:00 7/19/2021 12:00 7/20/2021 0:00 7/20/2021 12:00WSEL FT NAVD88Date & Time
7-17-2021 D/S Gage
Recorded Downstream Gage Elev.Model Calibrated Results
Appendix 6
9-1-2021
220.5
221
221.5
222
222.5
223
223.5
8/30/2021 12:00 8/31/2021 0:00 8/31/2021 12:00 9/1/2021 0:00 9/1/2021 12:00 9/2/2021 0:00 9/2/2021 12:00 9/3/2021 0:00 9/3/2021 12:00WSEL FT NAVD88Date & Time
9-1-2021 U/S Gage
Recorded Upstream Gage Elev.Model Calibrated Results
177.5
178
178.5
179
179.5
180
180.5
181
181.5
182
8/30/2021 12:00 8/31/2021 0:00 8/31/2021 12:00 9/1/2021 0:00 9/1/2021 12:00 9/2/2021 0:00 9/2/2021 12:00 9/3/2021 0:00 9/3/2021 12:00WSEL FT NAVD88Date and Time
9-1-2021 Pond Gage
Recorded Pond Gage Elev.Model Calibrated Results
Appendix 6
156.5
157
157.5
158
158.5
159
8/30/2021 12:00 8/31/2021 0:00 8/31/2021 12:00 9/1/2021 0:00 9/1/2021 12:00 9/2/2021 0:00 9/2/2021 12:00 9/3/2021 0:00 9/3/2021 12:00WSEL FT NAVD88Date & Time
9-1-2021 D/S Gage
Recorded Downstream Gage Elev.Model Calibrated Results