Carlon Drive Stormwater ManagementStormwater Management and Maintenance Plan
Pelops Realty Trust, Northampton, MA.
The proposed subdivision roadway will be a City-owned street. Maintenance of this street will
ultimately be the responsibility of the City. The Detention basin, drainage easements, and the
individual lots will be maintained by the individual lot owners. The following are the proposed
measures which we believe are necessary for both improved water quality, and for increased
longevity of the stormwater system. We have included several measures which will ultimately
be the responsibility of the lot owners in the course of maintaining their parking lots. By having
these parking areas regularly swept and maintained, the longevity of the detention basin is
substantially increased.
Catch Basin Sumps. The sumps within the catch basins should be cleaned a minimum of once
each year. We recommend that these shouid be evaluated at least twice each year, and they
should be cleaned if 50% of the capacity has been used. The proposed four foot sumps contain a
larger capacity than those typically used and are designed to provide for additional silt storage.
The City's street-sweeping program will help to remove particulates prior to entering the
drainage system. We recommend that the street should be vacuum swept in the early Spring to
remove the winter sand.
Parking lots. It is our recommendation that the parking lots on each lot should be vacuum swept
at least twice each year to remove accumulated sand and debris, and to reduce the sediment load
into the catch basins and the detention basin. Any catch basins located on individual lots should
be cleaned at least twice each year, or more frequently as required.
Detention Basin. The detention basin should be inspected at least twice each year to remove
any accumulated debris, and to insure that all of the outlets are clear of obstructions. The
detention basin should have a detailed inspection at least once per year. The detailed inspection
shall include an evaluation of the vegetative community within the basin, an examination of the
detention basin walls to insure that they are stable; checking of the inlet and the outlet; and an
estimation of the amount of accumulated sediment. Maintenance dredging will occur when
sediments have reduced the pool storage volume by 25%. Any sediments that are removed from
the stormwater system will be disposed of off the site in accordance wi�th all state and local
regulations.
G� �/��-!1� .S�°�c�i�l�wv�F�`:� �✓�—.�"�G��,r�-
The following set of Maintenance Requirements for Water Quality Basins is adapted from the
King County, Washington Surface Water Design Manual.
Pro�osed Maintenance Matrix for Pelo�s Realty Trust, Northam�ton, MA
Maintenance
Component
General
Side Slopes of Pond
Defect
Trash Debris
Invasive Vegetation
Pollution
Conditions When Maintenance
Is Required
Any trash and debris which exceed
1 cubic foot per 1,000 square feet
(equivalent to one office garbage
can). In general, there should be no
visual evidence of dumping/debris.
Any invasive vegetation (as listed by
the NRCS, e.g. purple loosestrife,
Phragmities, etc.)
Results expected
When Maintenance is
Conducted
Trash and debris cleared
from site.
No spread of exotic or
invasive vegetation spread
from the site to the adjacent
marsh.
Storage Area
F:\SHAREDU.ET96\ I314COM.4
Erosion
Sediment
Oil, gasoline, or other contaminants of No contaminants present
1 gallon or more or any amount found other than a surface film'.
that could: 1) cause damage to plants or
animals; 2) cause a fire hazard; or 3) be
flushed downstream into the wetlands
during rain storms.
Eroded damage over two inches deep Slopes should be stabilized by
where cause of damage is still present or using appropriate erosion
where there is potential for continued control measure(s): e.g. rock
erosion. reinforcement, erosion
fabric, planting of grass,
compaction.
Accumulated sediment that exceeds Sediment cleaned out to
25% of the designed pond capacity designed pond shape and
depth; pond replanted with
wetland plants; side slopes
reseeded to control erosion.
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King Street Brook
NoYthampton, Massachusetts
May 9, 1997
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�King Street Brook Drainage Analysis May 9,1997
I.
Introduction
This report analyzes storm water runoff for the King Street Brook watershed (see
figure 1), with the point of termination being the end of the Barrett Street culvert.
The purpose of this analysis is to determine the 10 and 100 year flood elevations
of the King Street Brook between the railroad.crossing the Barrett Street
culvert, for existing conditions and conditians after the proposed King Street fire
station has been constructed.
Calculations
The attached calculations were performed on Hydrocad version 3.20 using SCS
TR-20 methodology. The watershed area was broken into individual projects (as
required by the computer program), containiug subcatchment areas, reaches and
ponds, which were then linked toge°cher. The project flow diagrams for each
individual project, as well as a master flow diagram are attached.
Watershed subcatchment areas, their runoff coefficients, pipe slopes and pipe
diameters were provided by the City of Northampton Department of Public Works
�r: ��.typewrtten �ocument titl�d "Kyng Stree±Brook".
The subcatchment area runoff coefficients were translated into SCS Curve
Numbers. This was a�complished by correlating SCS Runoff Curve Numbers for
soil type B with runoff coefficients for areas with similar types of coverage. This
created a conversion chart t� estimate the curve number (see figure 2).
.�k:;;;�`,
t
Subcatchment area time of concentrations were deternuned as follows: areas
between 0 and 5 acres and between 5 and 10 acres were given time of
concentrations equal to 5 and 10 minutes respectively. These values are based on
an average calculated time of concentration for typical subcatchment areas in each
size group. Areas greater than 10 acres in size have calculated time of
concentrations, based on the SCS Curve Number Lag method. This was done due
to the fact that small areas were not major contributors to runoff volume in
comparison to large areas located directly adjacent to the King Street Brook. For
calculated time of concentrations, the subcatchment area slopes were taken from
the City of Northampton Topographic Maps dated April of 1965, sheet numbers
23, 24 and 31.
Reaches that subcatch.ment areas flow through were either underground drainage
lines or open channels. Information for the drainage lines was obtained from the
typewritten document provided by the City of Northampton Departrnent of Public
Works. Information for open channels and culverts was obtained from the City of
Northampton Topographic Maps, site inspection and Northampton Bikeway
Storm System plans dated 1987. The more conservative pipe diameters and pipe
1.
King Street Brook Drainage Analysis May 9,1997
slopes were taken from the King Street Brook document provide by the City of
Northampton for any values in question. Manning's coefficients for the drain lines
were assumed to be 0.013 and values for the open channels were based on site
inspection and the attached table of Mauning Roughness Coefficient taken from
the Massachusetts Highway Manual.
The King Street Brook from the railroad crossing to the Barrett Street culvert was
modeled. as a pond to deternune the flood storage elevation. The pond size is
based on site inspection and on the City of Northampton Topographic Maps. The
outlet structure, the Barrett Street weir and culvert, was modeled using the as-built
information provided by the City of Northampton Department of Public Works.
The calculations assume that the King Street Brook, downstream of the Barrett
Street Culvert, has been dredged.
Calculations for the watershed area, for the 10 and 100 year storm frequencies, aze
attached for existing conditions as well as the proposed conditions after the
proposed King Street fire station has been built.
Information for the proposed King Street fire station, including hydrograph
information and areas, were provided by Almer Huntley Jr. Associates of
Northampton, Massachusetts on May 9, 1997.
.••Yy
':i
IV. Summary.
The results of the calculations are shown in the following table:
King Street Brook
(Railroad fo Barreit Sfreet)
10 Year Storm 100 Year Storm
Existing Proposed Existing Proposed
Peak Elevation (ft) 144.0 144.0 144.7 144.8
Peak Flow Rate In (cfs) 184.3 179.3 328.0 317.9
Peak Flow Rate Out (cfs) 53.3 53.4 80.3 81.4
Volume In (acre-ft) 37.9 38.2 64.2 64.6
Volume Out (acre-ft) 35.4 35.5 49.2 49.5
The values listed above are for the King Street Brook from the railroad through
the Barrett Street culverts. The stortn water runoff which enters into the center of
the Barrett Slreet culvert is not reflected in these values. It is assumed that the
peak n.uioff will enter and exit the Barrett Street culvert prior to the peak time for
the watershed area.
2
��J
I
King Street Brook Drainage Analysis May 9,1997
A.s shown in the above chart, the peak flood elevation for the area. between the
railroad and Barrett Street did not change for the 10 year storm and increased for
the 100 year storm by orie tenth of a foo� The.peak flow rates into the pond
decreased due to the proposed detention basin for the fire station which attenuated
the peak flow rate. The volume of runoff in and out of the brook have increased
slightly, due to the proposed fire sta.tion.
3
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ALMER HUNTLEY, JR. ASSOCIATES, INC.
SURVEYORS ENGINEERS LANDSCAPE ARCHITECTS
1
October 28, 1996
City of Northampton
Conservation Commission
City Hall
210 Main Street
Northampton, MA 01060
RE: Pelops Realty Trust Definitive Subdivision
(Huntley Project No. 96055D)
Dear Commissioners:
This letter is to respond to the cornments received from the review of the Notice of Intent
submitted on behalf of Pelops Realty Trust by Baystate Environmental Consultants BEC)
and the Conservation Commission. The issues addressed herein are related to hydrology
and hydraulic aspects of the project.
We have reviewed prior reports prepared for the Barrett Street marsh. The historical data
does not contain adequate hydrologic calculations regarding the storm water flow for this
watershed. The City of Northampton DPW data indicated a ten year storm peak rate of 360
cfs at the Barrett Street crossing.
The 1984 report prepared by Almer Huntley, Jr. and Associates was based upon survey data
and reconnaissance of thz watershed area and drainage structures within the area. The
report does not contain any hydrological analyses of the watershed. To date we have not
been able to locate �any hydrological studies that have been performed for the watershed.
In examining, the "1984 Report" there are several items that relate directly to the watershed
hydrology. The 24" culvert under Barrett Street was identified as being undersized. This
assumption was not based upon any hydrologic data but rather on the fact the upstream
structure is a 4' x 4' box culvert and the downstream structure is a 4' x 5' box culvert. This
configuration reslricts the flow under Barrett Street and functions similar to a dam. The
rehabilitation work being undertaken on Barreit Street is not adequate to preclude the area
from flooding. The water level is being established by a weir at elevation 140.50'. The
1984 st�idy established the hydraulic gradient at the crossing to be 139.17'.
To respond items 1, 2, 3 and 4 on page 5 of 6 from t�e BEC preliminary review dated
October 17, 1996, an abbreviated watershed analysis was performed to analyze the 10 and
100-year storm events. The analysis utilized previously developed data contained in the
(S00) 227-7723 •(413) 534-744� FAX (413) 586-9159 0 30 INDUSt7t[AL D1trvE EASr P.O. BoX 588 NoR�atvllYroN, MA 01061