HomeMy WebLinkAbout20200574 Excelsior Park SUP Letter Summary for Beacon Project ISSchnabel T 518.348.8575
ENGINEERING 28 Corporate Drive,Suite 204 / Clifton Park,NY 12065 schnabel-eng.com
November 19, 2020
Mr. Paul Kruger
Development Director
Beacon Communities, LLC
54 State Street, Suite 802
Albany, NY 12207
Subject: Excelsior Park Project, Saratoga Springs, NY
(Schnabel Reference 20C25013.00)
Dear Mr. Kruger:
SCHNABEL ENGINEERING OF NEW YORK(Schnabel) is pleased to provide this summary of our prior
work performed related to Beacon Communities (Beacon) proposed Excelsior Park Project site
development at Excelsior Avenue and Ormandy Lane Saratoga Springs, New York. Since 2016, Schnabel
has been engaged by the City of Saratoga Springs (City)to perform various dam safety evaluations for the
Loughberry Lake Dam which is located approximately one half mile west of the proposed Excelsior Park
Project site. In the course of the our evaluations, Schnabel has developed a detailed hydraulic model of
the surface flows in the vicinity along the dam embankment including New York State (NYS) Route 50,
nearby properties, and properties adjacent to and including Spring Run to its crossing beneath Interstate
87. The proposed Excelsior Park Project is located just south of Route 50, west of Interstate 87 and north
of Spring Run.
This letter report puts our prior work in context, describes its intent, and provides an opinion of the
potential impact of the Loughberry Lake Dam on the proposed Excelsior Park Project development. All of
our work done to date indicates that the proposed Excelsior Park Project is well above (in elevation) and
outside of any potentially dam related inundation area or floodplain based on the 100-year design storm.
The 100-year design storm is the storm utilized by the Federal Emergency Management Agency (FEMA)
to map the regulated flood zones to inform development as administered by the local authority.
BACKGROUND
The City is the owner of Loughberry Lake Dam, located approximately one half mile west of the proposed
Excelsior Park Project site. They are responsible for maintaining a safe dam and for performing certain
activities as required by the New York Codified Rules and Regulation (NYCRR), Part 673 and enforced by
the New York State Department of Environmental Conservation (NYS DEC). Loughberry Lake Dam is
classified as a Class C, high hazard dam and is therefore held to the state's highest standard in regards to
dam safety.
Schnabel was initially engaged to perform the necessary activities to bring the dam into compliance with
the regulatory requirements. Three of our major activities included: developing an Emergency Action Plan
Beacon Communities, LLC
Excelsior Park Project
(EAP), performing a hazard classification study, and completing a comprehensive Engineering
Assessment (EA). The EAP and the hazard class study required developing and utilizing a detailed
hydraulic model to map the potential downstream inundation area (including Spring Run to Interstate 87)
assuming the dam were to fail at its maximum section. This dam failure assumption is required to identify
potentially inundated areas to evacuate (for the EAP) and to assess the potential impacts of a dam failure
on downstream lives, transportation networks, and utilities (for the hazard class study). It is important to
note that this inundation mapping is required for these analyses and is independent of the condition of the
dam or its likelihood of failure. Similar mapping would be required if the dam were new or old, concrete or
earthen, maintained or in disrepair. The presence of the inundation mapping developed for the dam is not
an indicator of the risk or likelihood of its failure.
The third activity we completed was the EA. The work was performed in accordance with the NYS DEC
Guidance Document TOGS 3.1.4 which generally requires that the dam be evaluated for embankment
stability and spillway capacity. Because the dam is regulated at New York's highest standard, it is required
to store or safely pass the runoff from a storm significantly exceeding the 100-year event. The EA
concluded that the dam needed spillway capacity improvements, a new low level outlet, and upstream
slope stability improvements.
The City subsequently retained Schnabel to design the necessary improvements to bring the dam into
regulatory compliance. One of the advancements made during the detailed design was the refinement
and expansion of the HEC-RAS (Version 5.0.7) 2-Dimensional (2D) hydraulic model which confirmed that
the dam would not overtop even under the extreme spillway design flood. Rather, flow would overtop
Route 50 at a sag point located approximately 1000 feet (ft) east of the dam near the intersection with
Veterans Way. This low point in Route 50 would effectively serve as a second armored auxiliary spillway,
safely discharging most flow from this extreme storm event away from the primary dam embankment. For
context, Route 50 was constructed to its current configuration in 1967 and has never overtopped due to
Loughberry Lake flooding. The refined modeling and the concepts for the proposed improvements have
been discussed with the NYS DEC and detailed design drawings for all project element will be submitted in
the fall of 2020 for their approval to construct. It is anticipated the construction will occur in 2022 after
which the dam will be in full compliance with the state's highest dam safety standards.
Hydraulic Modeling related to the Excelsior Park Project
Schnabel was retained by Beacon to review the 2D hydraulic modeling results previously developed to
assess the potential impacts on the proposed Excelsior Park Project. The prior modeling and mapping
was developed to support design decisions for the City's dam rehabilitation project and to develop
inundation mapping for their Emergency Action Plan. The Emergency Action Plan, and the inundation
mapping, identifies potentially inundated areas in the event of a pending or ongoing dam emergency. The
hydraulic model predicts the resulting flood depths and velocities within the flood limits.
An overview of the 2D hydraulic model mesh is provided in Figure 1 below. The mesh extends from
approximately three (3) miles upstream of Lougberry Lake Dam to approximately 1.5 miles downstream
from the Dam and includes the extents of the properties comprising the Excelsior Park Project. The mesh
contains approximately 54,000 computation cells with an overall average cell size of 50 ft by 50 ft. The
model geometry also includes hydraulic structures representing road/railroad crossings as well as the
principal and auxiliary spillways at Loughberry Lake Dam.
20C25013.00/November 19, 2020 Page 2 Schnabel Engineering of New York
Beacon Communities, LLC
Excelsior Park Project
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Elevation data used in the model geometry is based on a 2-meter Digital Elevation Model (DEM) data
derived from a LiDAR bare earth point cloud. Manning's n-value roughness coefficients were set based
upon the 2011 National Land Classification Dataset (NLCD). 2D Area Manning N-Value Regions were
used to refine the n-values for major roadways, the stream channel, as well as for buildings.
The 2D hydraulic model includes, an inflow boundary condition at the northern limit of the model
geometry to represent storm induced runoff hydrographs upstream of the large railroad embankment to
the north of Loughberry Lake, a second inflow hydrograph boundary condition to Loughberry Lake
downstream of the railroad embankment, a third inflow hydrograph boundary condition for Spring Run
downstream of Loughberry Lake Dam, and a fourth inflow hydrograph boundary condition representing
local runoff between the dam and Interstate 1-87. Flow hydrographs for the boundary conditions were
extracted from an HEC-HMS hydrologic model that was developed by Schnabel for the Engineering
Assessment of Loughberry Lake Dam.
20C25013.00/November 19, 2020 Page 3 Schnabel Engineering of New York
Beacon Communities, LLC
Excelsior Park Project
The site plan for the proposed Excelsior Park Project site was provided by Beacon (as prepared by the
LA Group) and is provided as Figure 2.
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Figure 2—Proposed Excelsior Park Project Site
As referenced earlier, Schnabel's hydraulic model confirmed that under the extreme spillway design flood
event(significantly greater than the 100-year event)flow would overtop Route 50 at a sag point located
approximately 1000 ft east of the dam near the intersection with Veterans Way. This low point in Route 50
would effectively serve as a second armored auxiliary spillway, safely discharging most flow from this
extreme storm event away from the primary dam embankment. Under these circumstances, these
overtopping flows are expected to impact areas west of Veterans Way prior to returning to the main Spring
Run drainage way. Figure 3 illustrates the inundation area resulting from this event. The figure shows the
limits and depth of inundation downstream of, and adjacent to, Loughberry Lake Dam. As clearly shown,
no dam or Spring Run related flooding is predicted to occur on the proposed Excelsior Park Project site.
20C25013.00/November 19, 2020 Page 4 Schnabel Engineering of New York
Beacon Communities, LLC
Excelsior Park Project
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Closing
In closing, it is our opinion that the proposed Excelsior Park Project site development at Excelsior Avenue
and Ormandy Lane in Saratoga Springs, NY will not be subjected to flooding related to discharges from or
failure of the Loughberry Lake Dam or from related elevated levels of Spring Run.
Please do not hesitate to contact me at 518-348-8580, or via email at gdaviero@schnabel-eng.com,
should you have any questions or need additional information.
Sincerely,
SCHNABEL ENGINEERING OF NEW YORK
))///:,tizfz7
Gregory J. Daviero, PhD, PE
Principal
GJD:scc
20C25013.00/November 19, 2020 Page 5 Schnabel Engineering of New York