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4.5
Watershed Land Use and their Threats to Water Quality

Civco and others (2002) have described land use as, “the common denominator
underlying many of the issues that our communities face from nonpoint source water
pollution and open space preservation to sustainable economic development and
community character”. Changes in land use are the result of community decision-making
with regard to all of these community objectives. Development converts vegetated land
to mostly impervious surfaces. When the pattern of development emanates from urban
areas to suburban and rural areas, we call this pattern ‘urban sprawl’. Therefore, as
settlement expands into rural areas, building and road density increases in these areas
increasing the area of impervious surfaces.

The area of impervious surfaces in a watershed is essential to understanding
nonpoint source pollution potential and consequent management requirements (Schueler,
1994; Sleavin et al., 2000). Impervious surfaces include any surface that water cannot
infiltrate, such as parking lots, paved roads, sidewalks, buildings, rooftops, and highly
compacted earth. Impervious surfaces not only increase the total volume of runoff, but
also transmit pollutants readily and can even contribute to thermal pollution. Therefore,
much of the impervious surface we recognize in our community is associated with
transportation or buildings. Schueler (1994) noted that the transportation system
typically contributes the most to total impervious area in a watershed.

Impervious surfaces lead to four major impacts to a watershed. In no particular
order, these are altering the natural flow of water, aquatic habitat loss, decreasing water
quality, and loss of biological diversity. As a watershed’s imperviousness increases, the
quality of its streams decreases. Early and recent work by the Center for Watershed
Protection (CWP) in the Chesapeake Bay Watershed established a close relationship
between a watershed’s imperviousness and the state of water and habitat quality
degradation in streams (CWP, 2003). Figure 4.5-1 illustrates this relationship and
reflects the degree of stream degradation as degraded, impacted, and protected.

- 85 -

Figure 4.5-1. The Relationship between Watershed Imperviousness and Stream
Degradation

(adapted from UCONN NEMO, 2006 and Schueler, 2002)

4.5.1 Impervious Surface Build Out Analysis

UCONN CLEAR Geospatial Technology Program executed an analysis of
possible future land use conditions to estimate the increase in impervious surfaces
that could occur within the Niantic River Watershed under full buildout
conditions. A buildout is an estimate of how much development can occur on
buildable land based on current zoning densities. For this analysis, UCONN used
current state and municipal land use and zoning data to approximate what future
development might look like in the watershed. The analysis was done at the
CTDEP basin level 12, which includes all levels of natural drainage basins. The
basin delineations and their CTDEP assigned Basin Numbers are shown in Figure
4.5-2. To review the methodology and supporting material, refer to Appendix D.

12 http://dep.state.ct.us/gis/dataguides/dep/layers/basin.htm
- 86 -

Lake
Konomoc
2204-03-1
2202-05-1
2203-00-1-L2
2202-04-1-L1
2203-00-2-R1
2203-02-1
2204-00-3-R4
2202-08-2-R1
2204-00-3-R2
2202-07-1
2202-03-1
2202-02-1
2202-08-1
2202-00-1-L1
2202-00-2-R2
2202-00-3-L9
2202-06-1
2202-00-3-R2
2203-01-1
2204-01-1
2204-04-1
2202-00-1-L3
2202-11-1
2202-00-3-L8
2202-00-2-L6
2204-00-3-R3
2202-00-1*
2202-09-1
2202-12-1
2203-00-2-R2
2202-00-1-L4
2202-01-1
2202-00-2-R4
2202-00-3-R3
2202-00-2-R3
2204-04-1-L1
2202-10-1
2202-04-1
2204-02-1
2202-00-1-L2
2203-00-1-L1
2202-00-2-L7
2202-00-3-R1
2204-00-3-R1
2202-05-1-L1
2202-00-2-L5
2202-00-2-R1
2203-00-1
0
4,000
8,000
Scale In Feet
4.5-2
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
CTDEP BASIN DELINEATIONS
AND BASIN NUMBERS
AS SHOWN
1314-001
Basin Numbers.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

Impervious surface percents were calculated for current conditions and
were estimated under full-buildout conditions. These are summarized in Table
4.5-1. The results are color-coded to correspond with NEMO watershed
classifications. Basins at less than 10% impervious are shaded green, between 10
and 25% impervious are shaded yellow and above 25% impervious are shaded
red. Maps of estimated current and future percent impervious surface area for
basins follow the table (Figures 4.5-3 and 4.5-4, respectively).

Table 4.5-1. Results of Impervious Surface Estimates based on Build-out
Analysis of the Niantic River Watershed
BASIN_NO
Current IS%
IS% at Buildout
2202-00-1-L1
1.9
3.6
2202-01-1
0.4
3.9
2202-00-1-L3
0.7
3.5
2202-02-1
1.0
4.0
2202-00-1-L2
0.4
3.8
2202-00-1-L4
0.0
2.2
2202-03-1
7.5
9.5
2202-05-1-L1
3.2
3.6
2202-04-1-L1
3.6
4.4
2202-05-1
3.6
7.0
2202-00-1*
0.1
1.4
2202-00-2-L6
0.3
1.6
2202-00-2-L5
2.1
2.8
2202-00-2-R1
2.2
2.9
2202-04-1
1.0
1.3
2202-08-1
0.9
3.2
2202-00-2-R2
3.7
9.2
2202-09-1
1.0
2.7
2202-06-1
2.0
4.5
2203-00-1-L1
3.6
18.1
2203-00-1-L2
1.6
2.8
2202-00-2-R3
5.6
10.7
2202-07-1
2.3
10.0
2202-08-2-R1
1.9
3.6
2202-00-2-R4
3.4
5.6
2203-01-1
1.9
2.6
2202-00-2-L7
0.0
5.7
2203-00-2-R1
8.5
11.3
2203-00-1
6.5
6.5
2202-10-1
1.3
4.1
2202-11-1
0.0
4.2
2202-00-3-R1
0.7
3.5
2203-02-1
0.5
1.8
2202-12-1
1.8
4.5

- 88 -

BASIN_NO
Current IS%
IS% at Buildout
2202-00-3-R2
6.0
11.9
2202-00-3-L8
0.5
23.5
2204-03-1
7.9
21.1
2204-01-1
1.0
6.6
2202-00-3-L9
16.9
20.0
2203-00-2-R2
5.1
10.7
2204-02-1
6.6
32.8
2204-00-3-R1
10.7
16.5
2202-00-3-R3
11.5
20.7
2204-00-3-R2
5.1
6.7
2204-04-1-L1
0.0
0.1
2204-00-3-R3
5.9
6.0
2204-00-3-R4
14.9
23.2
2204-04-1
16.5
21.0

- 89 -

4.5-3
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
ESTIMATED CURRENT
PERCENT IMPERVIOUS AREA
AS SHOWN
1314-001
Estimated_imp_area.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui t e 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i ns ch mi dt U SA.c o m

4.5-4
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
ESTIMATED PERCENT IMPERVIOUS
AREA PER BASIN AT BUILDOUT
AS SHOWN
1314-001
Estimated_imp_area
_at_buildlout.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui t e 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i ns ch mi dt U SA.c o m

The results of this analysis must be viewed as one of many possible
impervious surface buildouts that could occur with the Niantic River Watershed.
By their nature, buildout analyses are best estimates of future conditions based on
current land use plans, current subdivision and building practices and various
assumptions. Buildout is not an exact science and there is no one correct
“answer”. Therefore, these results should be interpreted as possible, but not
necessarily likely. For example, towns can increase and/or decrease permitted
densities in residential zones and can change zone designations. Road frontage
requirements could be relaxed or the number of interior lots served by a common
driveway could be increased or decreased.

The analysis indicates that at buildout, impervious surface increases would
cause eight basins to change from less than 10% impervious to greater than 10%
impervious and one basin would change from less than 10% impervious to greater
than 25% impervious. In the remaining basins, impervious area would increase
but would likely stay below 10%. Basins where impervious surface increases are
significant or where basins transition from under 10% to greater than 10%
impervious surface area might be good candidates for mitigation plans to reduce
future impervious surface increases.

4.5.2 Watershed Vulnerability Assessment

A “tabletop” assessment of the watershed was completed to determine the
areas of the watershed that demand the most priority for management. A GIS-
based model considered various watershed characteristics (e.g., soil, land cover,
depth to water table) to assign priority for conservation, restoration, and
stormwater management. Areas ideal for protection against future water quality
degradation scored high for the Conservation Priority Index (CPI), which
generally highlights areas such as riparian corridors and forests. Areas prone to
erosion or increased agricultural impacts score high for the Restoration Priority

- 92 -

Index (RPI). Urbanized areas, including transportation corridors, are typically
included in the Stormwater Management Priority Index (SMPI).

This GIS-based assessment model was developed by Kleinschmidt using a
guidance document produced by the University of Massachusetts and the U.S.
Forest Service Watershed Exchange and Technology Partnership (de la Crétaz et
al., 2003). In the vulnerability assessment model, various attributes of data
inputs, which are described in Appendix E, are assigned priority ranking for each
of the three priority indices with high rankings being important for further study
and possible mitigative actions, while the lower rankings play a less significant
role in the corresponding index.

4.5.2.1 Vulnerability Assessment Results

The results of the model are presented as a map of the watershed
(Figure 4.5-5) to display the three priority indices. The three indices (CPI,
RPI, SMPI) can be shown on the same map because there are no
overlapping values (scores) between them. Each index relies on a unique
set of land cover types thereby allowing this discrete analysis. Figure 4.5-
5 displays the 80th percentile rankings for each priority index. This
percentile was calculated by determining the cumulative distribution
frequency for each of the indices and modifying the display to show only
those rankings that contained the 80th percentile and higher. By selecting
the areas (“cells”) with the highest ranking, the map indicates priorities for
each of management approach. According to Barten et al (2002), the 90th
percentile rankings “can be used to focus land conservation, pollution
prevention, and pollution mitigation efforts on areas that should generate
the greatest return on investment”.

- 93 -

95
395
New London Rd
Chesterfield Rd
Chesterfield Rd
Hartford - New London Tpke
Butlertown Rd
Turner Rd
Boston Post Rd
Salem
Lake
Konomoc
Bogue Brook
Reservoir
Barnes
Reservoir
Fairy
Lake
Darrow
Pond
Niantic
Bay
Montville
Waterford
East Lyme
Percentile
Percentile
Percentile
CPI
80th
100th
RPI
80th
100th
SMPI
80th
100th
DEP & Municipal Lands
Towns
Roads
Lakes & Reservoirs
Swamps & Marshes
0
4,000
8,000
Scale In Feet
4.5-5
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
WATERSHED VULNERABILITY
ASSESSMENT 80th PERCENTILE
AS SHOWN
1314-001
WVA results.mxd
SEK
09-06-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

Table 4.5-2 displays the area summaries of the priority indices by
jurisdiction. The areas are displayed both for the entire index range and
also for the 80th percentile. For comparison, the acreage of the entire
watershed is approximately 20,000 acres, or 31 square miles.

Table 4.5-2. Priority Index Acreages
Municipality
------- CPI Acreage -------
RPI
Acreage
SMPI
Acreage

All Values
All Currently
Protected
Areas
Removed
All Publicly
Owned
Currently
Protected
Areas
Removed
All Values
All Values

All Priority Index Values
East Lyme
3,725
3,221 a
3,591 d
337
1,488
Montville
3,187
2,983 b
3,187
169
714
Salem
1,999
1,957 c
1,957 e
26
367
Waterford
4,169
4,169
4,169
167
1,355

Total
13,080
12,330
12,904
699
3,925

80th Percentile Priority Index Values
East Lyme
1,376
885 a
1,246 d
135
427
Montville
916
723 b
916
99
196
Salem
476
449 c
449 e
10
72
Waterford
819
819
819
54
378

Total
3,588
2,876
3,430
298
1,073

a Nehantic State Forest, The Sheffield Scientific School and the Chesterfield Road and Irvingdell Place Town
Open Spaces Removed
b Morgan R. Chaney Sanctuary Removed

c Nehantic State Forest Removed

d The Sheffield Scientific School Removed

e Nehantic State Forest Removed

- 95 -

East Lyme

The town of East Lyme shows that the greatest concentration of
conservation priority areas near the shorelines of Darrow and Clark Ponds
(Figure 4.5-6). Additional areas for conservation surround wetlands and
would form riparian buffers along Latimer and Cranberry Meadow Brooks
and the tributaries to the larger water bodies. The following areas appear
as CPI areas that may already have municipal or state protection measures
enacted by the nature of their ownership:

•
Chesterfield Road Town Open Space
•
Irvingdell Place
•
Nehantic State Forest
•
Ponderosa Park
•
The forested areas of Camp Pattagansett
•
The Sheffield Scientific School (Yale University) Open
Space

Camp Pattagansett, Ponderosa Park and the Sheffield Scientific
School are privately owned, but listed as either existing preserved open
space or recreation. Additional protection would likely only be achieved
by purchasing these properties by state or municipal organizations. The
Cavasin Dr. Town Open Space did not trigger a conservation priority
ranking recommendation, which due to the it being located primarily in a
residential area as classified in the 2004 land cover data set developed by
UCONN (Appendix D.1). Refer to Appendix E for the details on land
cover classifications included in each of the priority indices.

While the greater benefit for restoration probably lie in the larger
areas, the plan acknowledges there are several small RPI areas that exist in
East Lyme. The three primary RPI areas in East Lyme are croplands and
other agricultural lands on Quailcrest, Chesterfield and Grassy Hill Roads.
Each of these areas display priority ranking ranges from the 80th to the
99.7th or 99.9th percentile.

- 96 -

95
Chesterfield Rd
Chesterfield Rd
Hartford - New London Tpke
Butlertown Rd
Turner Rd
Boston Post Rd
Lake
Konomoc
Bogue Brook
Reservoir
Darrow
Pond
Niantic
Bay
Clark
Pond
Latimer
Brook
Cranberry
Meadow
Brook
Quailcrest Rd
Grassy
Hill Rd
Powerline ROW
Mayfield Rd
Walnut Hill Rd
395
Waterford
East Lyme
0
3,000
6,000
Scale In Feet
DEP & Municipal Lands
Towns
Roads
Lakes & Reservoirs
Swamps & Marshes
Percentile
Percentile
Percentile
CPI
RPI
SMPI
80th
80th
80th
100th
100th
100th
Chesterfield Rd.
Town Open Space
Ponderosa
Park
Niantic State
Forest
Sheffield Scientific
School
Camp
Pattagansett
Irvingdell
Place
Cavasin Dr.
Town Open Space
4.5-6
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
WATERSHED VULNERABILITY
ASSESSMENT- EAST LYME
AS SHOWN
1314-001
VAMR- East Lyme.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

The power line right of way running in an east-west direction
through East Lyme and Montville is the probably the most conspicuous
SMPI target area. This area, which is most likely vegetated, is of concern
because of the use of herbicides and frequent mowing. Each of the towns
exhibit small pockets of SMPI areas throughout the towns. Though these
show evidence of characteristics that would potentially degrade water
quality, efforts should be focused on the larger tracts, or clusters, of SMPI
areas for the greatest advantage in protecting water quality. In East Lyme
along Chesterfield Road from the town boundary to approximately
Mayfield Road exists the largest concentration of SMPI area. This locale
has priority rankings ranging up to the 99.98th percentile. Other notable
areas are a residential development along Walnut Hill Road, the area
adjacent to Interstates 95 and 395 and the residential and commercial areas
on the western shore of Niantic Bay.

Montville

The majority of the CPI areas are adjacent to water bodies and
wetland in Montville (Figure 4.5-7). The larger water bodies include the
Bogue Brook Reservoir and the northern end of Lake Konomoc. The
Morgan R. Chaney Sanctuary is an approximately 200-acre sanctuary
owned by the Connecticut Audubon Society, is designated as a
Conservation Priority Index target area. Though this is privately owned it
is unlikely that it would be sold and developed, therefore efforts in
Montville should be focused on protecting riparian areas for future
conservation.

Three RPI areas are prominent in Montville: harvested cropland on
Day Road and Grassy Hill Road and pastureland off Beckwith Road. All
areas have priority rankings ranging from the 80th to the 99.9th, 99.7th and
100th percentile for the Day Road cropland, Grassy Hill Road cropland
and the pastureland, respectively.

- 98 -

New London Rd
Chesterfield Rd
Chesterfield Rd
Hartford - New London Tpke
Butlertown Rd
Turner Rd
Lake
Konomoc
Bogue Brook
Reservoir
Barnes
Reservoir
Fairy
Lake
Darrow
Pond
Cranberry
Brook
Hill Rd
Powerline ROW
Walnut Hill Rd
Great
Swamp
Day Rd
Grassy Hill Rd
Beckwith Rd
Montville
0
2,000
4,000
Scale In Feet
DEP & Municipal Lands
Towns
Roads
Lakes & Reservoirs
Swamps & Marshes
Percentile
Percentile
Percentile
CPI
RPI
SMPI
80th
80th
80th
100th
100th
100th
Morgan R. Chaney
Sanctuary
4.5-7
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
WATERSHED VULNERABILITY
ASSESSMENT- MONTVILLE
AS SHOWN
1314-001
VAMR-Montville.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

The power line right of way running in an east-west direction
through East Lyme and Montville is the main concern within the SMPI
target areas. As with Montville, the major concern for water quality is
from the use of herbicides and frequent mowing. Two other noticeable
areas, aside from the small pockets of SMPI areas, are the commercial
areas along Route 85 (Hartford-New London Turnpike) and the low-
medium residential development along Grassy Hill Road. The priority
rankings for each of these areas include percentiles ranging from 80 to
100. A barren plot adjacent to Lake Konomoc and Great Swamp exhibits
concern with its proximity to the Morgan R. Chaney Sanctuary, which
includes Great Swamp and Lake Konomoc. The priority rankings range
from the 80th to the 99th percentile in this 5.5 acre plot.

Salem

The town of Salem shows that the greatest concentration of
conservation priority areas are located near the shorelines of Fairy Lake,
Horse Pond and Barnes Reservoir (Figure 4.5-8). Additional areas for
conservation surround wetlands and would form a riparian buffer along
the tributaries to the larger water bodies. The Nehantic State Forest is
designated as a CPI target area, but could be excluded from any further
action because of the fact that it is a State Forest.

Salem shows a small target area of RPI along New London Road
near Skyline Drive. This area is classified as a horse farm operation in the
2004 land cover classifications. Of greater concern in Salem, is an RPI
area along Beckwith Road that is designated as Harvested Cropland in the
land cover. The priority ranking for this area received “scores” ranging up
to the 99th percentile. The proximity of this target area to wetlands should
elevate the concern with this area as it reached the 99th percentile in this
study.

- 100 -

New London Rd
Chesterfield Rd
Bogue Brook
Reservoir
Barnes
Reservoir
Fairy
Lake
Meadow
Grassy
Hill Rd
Powerline ROW
Day Rd
Grassy Hill Rd
Beckwith Rd
Horse
Pond
Skyline Dr
Corrina Ln
Salem
0
1,500
3,000
Scale In Feet
DEP & Municipal Lands
Towns
Roads
Lakes & Reservoirs
Swamps & Marshes
Percentile
Percentile
Percentile
CPI
RPI
SMPI
80th
80th
80th
100th
100th
100th
Niantic State
Forest
4.5-8
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
WATERSHED VULNERABILITY
ASSESSMENT- SALEM
AS SHOWN
1314-001
VAMR-Salem.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

The SMPI target areas in Salem are all a result of the commercial,
residential and transportation development in the watershed. Very small
tracts are shown scattered throughout the town along roadways and in
residential areas. The two focal points of SMPI in Salem are a
commercially developed area along Route 85 (New London Road) and in
a residential development at the end of Corrina Lane, adjacent to a wetted
area. Both of these priority areas have scores ranging from the 80th
percentile up to the 99.6th percentile.

Waterford

The CPI areas that have the potential for conservation surround
wetlands, the southern shoreline of Lake Konomoc and would form
riparian buffers along the smaller tributaries (Figure 4.5-9). The West
Farms Land Trust appears as a CPI area that may already have protection
measures enacted by the nature of its ownership/organization, though it is
privately owned. Kiddie Beach, which is a municipally owned area does
not appear as CPI because it is located in a residential area. Again, refer
to Appendix E for the details on land cover classifications included in each
of the priority indices.

A few very small areas are included in the RPI in Waterford.
There are only two relatively sizable RPI areas. One is a harvested
cropland near the town boundary and adjacent to Interstate 95 with a
priority ranking ranging from the 80th to the 99.7th percentile. The other
larger area is a pastureland north of the Hartford Turnpike at the
headwaters of a small tributary to Oil Mill Brook with a priority ranking
ranging from the 80th to the 96.6th percentile.

The SMPI areas in Waterford are concentrated along commercial
and residential areas along the Hartford Turnpike, Interstate 95 and the
western shore of Niantic Bay. Unlike the other towns, the SMPI has very

- 102 -

95
Chesterfield Rd
Butlertown Rd
Boston Post Rd
Lake
Konomoc
Niantic
Bay
Quailcrest Rd
395
Hartford Tpke
Oil
Mill
Brook
Waterford
0
2,500
5,000
Scale In Feet
DEP & Municipal Lands
Towns
Roads
Lakes & Reservoirs
Swamps & Marshes
Percentile
Percentile
Percentile
CPI
RPI
SMPI
80th
80th
80th
100th
100th
100th
West Farms
Land Trust
Kiddie Beach
4.5-9
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
WATERSHED VULNERABILITY
ASSESSMENT- WATERFORD
AS SHOWN
1314-001
VAMR-Waterford.mxd
SEK
09-07-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
35 Pr at t Str e e t, Sui te 201
Esse x , Co nne c ti c ut 06 426
Te l ep hone : ( 860) 767- 5 069
Fax : ( 860 ) 76 7- 509 7
www .K le i nsc h mi dt U SA.c o m

few smaller pockets of priority areas. The commercial area along the
Hartford Turnpike is the largest area of SMPI with priority ranking ranges
from the 80th percentile up to the 99.98th percentile. The residential
development adjacent to Niantic Bay is classified as being medium to high
density with priority rankings reaching up to the 99.8th percentile.

4.5.2.2 Discussion

In Figure 4.5-5, the Conservation Priority Index shows lands along
waterways and among the CTDEP and municipal lands, which would be
beneficial to put into conservation, if they are not already, to help protect
water quality by acting as buffers from those land uses that threaten water
quality. The Restoration Priority Index identifies lands in agricultural
areas where application of BMPs or other management activities, such as
restoration of ecological functions, may help to improve or protect against
further degradation of water quality. The Stormwater Management
Priority Index distinguishes lands where improved stormwater
management activities may protect water quality (de la Crétaz et al.,
2003).

Priority areas represented on the assessment map require added
consideration by land use decision-makers (i.e. planning and zoning
officials, developers, and resource managers). Parcels that correspond to
the priority area should raise extra concern when development or other
land use changes are proposed. These results are not intended to impose
new regulation or de facto prohibitions on proposed land uses, rather they
highlight the need for careful site plan review and field verification with
regard to valuable watershed land characteristics. Riparian corridors
provide an illustrative example of this point; streamside vegetated zones
are of the highest conservation priority in this watershed.

- 104 -

For restoration or stormwater management priorities, the
assessment results may trigger a site investigation of soils to account for
soil types and their characteristics along with slope gradient that will
determine the most appropriate management option. For example, the
USDA NRCS maintains an online soil survey generated from the National
Cooperative Soil Survey (NCSS). This tool allows landowners and land
use decision-makers to learn about the soils associated with a given
property, including the soil’s suitability for various uses. This information
is paramount to make sensible location decisions for development and
stormwater management practices. The web survey may be accessed at:
http://websoilsurvey.nrcs.usda.gov/app/. Site specific soil surveys always
provide a better estimate of appropriate BMP decisions, but the NRCS
may be used for the purposes of general planning.

The Connecticut State Office of NRCS performed an analysis of
soil suitability and common stormwater management practices in
Connecticut (USDA NRCS, 2005)13. By looking at soil suitability based
on several characteristics NRCS was able to determine the benefits and
limitations of using selected stormwater management practices. In the
case of the Niantic River, this information will be very useful in selecting
stormwater management measures.

4.5.3 Stormwater Management Modeling Results

“Estimate current and future watershed nonpoint source pollution
conditions and source loadings bases on projected land use changes”

The overall goal of assembling an analysis of current pollutant loading
estimates, versus futures loading estimates, is to determine the potential risk of
pollutant loadings in addition to localized hot-spots where more focus may be
required. Assessing these risks on a watershed scale are difficult with such a

13 ftp://ftp-fc.sc.egov.usda.gov/CT/water/CT-TP-2005-3.pdf
- 105 -

variety of land covers, land uses, point and nonpoint pollution and even
differences between the ages of certain land covers. Additionally, proximity of
pollutant sources and the respective course of transport may affect the actual
loading to certain waterbodies. In order to complete this assessment, various
generalizations and assumptions were made across the watershed using the best
available information to equally assess the current and future pollutant loadings.

The purpose of this study is not to calculate the actual pollutant loadings
from a certain subcatchment, but rather what the potential loading may be during
various scenarios to aid in the planning and development process. Calibration of
pollutant loadings to observed data were not attempted. This study is intended
solely to provide planners with information that may help in making either zoning
or water quality/treatment ordinance and decisions.

4.5.3.1 Model Description

Estimating current and future nonpoint source pollution within a
watershed is a complicated task and best accomplished with computer
software tools. A model was developed to simulate the current and the
potential future contributions of pollutants to the watershed.

Various models were assessed for their applicability to the Niantic
River Watershed, and the USEPA Stormwater Management Model
version 5.008 (SWMM5) was chosen as the most versatile model. The
SWMM model allows for easy integration of data import and exports from
GIS and simple modifications to model data for various run scenarios.
Additionally, the model has a flexible interface for land cover types,
pollutant loadings and BMP management.

Pollutant contributions were determined on a subcatchment basis
dependent on the type of land cover and soils data. The SWMM model
used the Event Mean Concentration (EMC) approach, which assumes a

- 106 -

constant concentration of a pollutant in modeled runoff, regardless of the
storm duration. Thus, the amount of pollutant concentration (in kg or lbs)
is directly associated to the volume of runoff received from the
subcatchment. The amount of runoff is determined from the soil type,
percent impervious, and the land cover within the subcatchment; i.e. the
more impervious a subcatchment, or the less infiltration within the
subcatchment because of poor soil conditions, the higher the volume of
runoff received and the greater pollutant loading.

4.5.3.2 Modeled Pollutants

The following key pollutants were studied within the SWMM
model:

•
Total Suspended Solids (TSS)
•
Total Kjeldahl Nitrogen (TKN)
•
Total Nitrogen as NO2 & NO3 (TN)
•
Total Phosphorous (TP)
•
Biological Oxygen Demand (BOD)

Total Suspended Solids (TSS) is particulate matter that is
transmitted within runoff and may be created from either picking up
particles as flow passes over the ground, or from erosion within the
subcatchment. These sediments usually stay ‘suspended’ in the flow and
do not settle out until the flow slows down, usually within a waterbody.
TSS loading can lead to excessive sedimentation, transportation and
deposition of excessive nutrients, and clouding of water reducing light
penetration. Total Kjeldahl Nitrogen (TKN) is the contribution of
organic nitrogen and ammonia in runoff. This is usually contributed by
sewage or manure discharges to water bodies. Total Nitrogen as Nitrate
(NO3) and Nitrite (NO2) (TN) is usually contributed to waterbodies from
the over application of fertilizers, atmospheric deposition, or runoff from
excessive agricultural farming practices. Excessive TN can lead to algal

- 107 -

blooms within waterbodies reducing water quality and dissolved oxygen
levels. Total Phosphorous (TP) includes both the amount in solution and
also in particulate form. It is usually obtained from agricultural drainage,
wastewater, and potentially industrial discharges. Phosphorous can
contribute to the eutrophication of surface waterbodies. Finally,
Biological Oxygen Demand (BOD) is the amount of oxygen required by
microorganisms to degrade the wastes biologically. Heavy concentrations
of BOD can lead to low dissolved oxygen levels and be harmful to aquatic
species.

Pollutant loading was analyzed using a comparative process of
percent change of a certain pollutant contribution for the same storm
event. Viewing it from this perspective allows a ‘risk’ based assessment
of which pollutants possess the highest potential for pollutant loading in a
given subcatchment. Should an area be designated as high risk to a certain
pollutant, then development within the subcatchment may be assessed to
determine if there currently is excessive loading, or with development, if
loading may become an issue.

4.5.3.3 Model Scenarios

In order to assess the potential risk from various pollutants, the
baseline existing conditions must be established. The existing land covers,
soil types and pollutant loadings were modeled within SWMM using a
hypothetical storm event.

For the proposed conditions, areas that are currently considered
‘developable’ had to be determined. Any land areas considered
developable were then changed from the existing land cover type to a
general composite ‘developable’ cover. Further discussion of how this
was developed may be seen in the methodology section in Appendix F.
Summary statistics for each of the subcatchments were calculated within
the GIS, which then were used to determine the loading EMC for each

- 108 -

subcatchment. Additionally, a composite curve number for each
subcatchment was determined and used in the routing of the storm event.

After the developed conditions were determined assuming
maximum buildout of all lands, certain BMPs were applied to the land
covers in areas considered developed. For detailed information on how
the developable lands were determined refer to Appendix F.3. There may
be existing loadings that will remain unchanged even with further
development, so the BMPs are only applied to future development. This
allows an analysis of the efficiency of general BMP implementation
throughout the watershed.

The following results discuss these various analyses and the results
with respect to specific pollutants and BMP implementation.

4.5.3.4 Results

Maps outlining the potential pollutant loading have been prepared
and can be found in Appendix F.5. There are five figures for each of the
targeted pollutants previously described. Different figures outlining the
potential pollutant loading have also been prepared. For each of the
targeted pollutants there are four figures that follow the format below:

•
Existing Conditions
•
Proposed Fully Developed Conditions
•
Proposed Fully Developed w/ BMP Implementation
•
Percent Change Pollutant Loading

This results in a total of sixteen figures (Figures F-1 to F-16). An
additional figure (F-17) has been prepared to show the percent of land area
that is considered developable by subcatchment. This figure is important
to show how the watershed could potentially change, and why some

- 109 -

pollutant levels may be increasing while others may decrease. The
following pages discuss some of the results which may be seen on the
respective figures.

Total Suspended Solids (TSS) - Total suspended solids is usually
a contribution of sediment through activities that disturb the ground
surface or result in bare earth subject to potential erosion. There are two
areas that are specifically highlighted, especially in the existing
conditions, that are worth noting.

The first is a large residential construction project just east of
Darrow Pond in the Town of East Lyme. For land covers such as a
construction project, the area receives a relatively high EMC value for
TSS contribution.

Similarly, the Town of Montville has a fairly large quarry and
extractive mining facility northwest of Bogue Brook Reservoir. Mining
activities by nature have exposed and unstabilized material potentially
subject to erosion. These areas, because of their land covers, have the
potential for high TSS loading.

Of important note is the fact that an area may have potentially high
EMC contributions, but may not actually contribute the whole portion to a
receiving waterbody. For example, a quarry is subject to excessive
erosion, but is inherently an inwardly draining feature and should retain
most of the TSS contribution within stormwater runoff. Similarly, areas
that are under construction or barren unstabilized lands should have
construction BMPs in-place reducing the actual contribution of TSS to
receiving waterbodies.

On a broad scale, the development of the watershed over-
abundantly shows an increase in TSS loading from subcatchments when

- 110 -

comparing existing conditions (F-9) to potential full development
conditions (F-10). Areas that become developed and move from stabilized
fields or woodlands towards urban developments will generally contribute
more TSS to receiving waterbodies. Considering the various
developments and the applications of BMPs, there is a chance to reduce
the loading of TSS on a watershed scale, but is still considered a
significant increase over existing conditions. Not all new developments
will have BMPs in place, such as low to medium density residential
developments, or even most common roadways.

Comparing the percent developable land to percent change in TSS
loading shows that areas currently developed have the lowest increase in
TSS loading. In some cases, the relative loading even in the fully
developed scenario is low. For example, the military installation is mostly
fields and grass areas with a low average TSS contribution. Should the
land use change from its currently designated use, then the area may
experience a significant increase.

Suspended solids from runoff do not maintain their suspension
continuously towards the outfall of a subcatchment. Values shown for
TSS concentrations are quite high for general water quality standards, as
they do not account for natural processes that may help to eliminate some
of the concentration. As runoff passes through a large wetland expanse,
and velocities are reduced, and there may be a significant reduction in TSS
through filtration and settling action. The values shown on the TSS
figures show a decent representation of potential areas of risk through
existing and potential development.

Biological Oxygen Demand (BOD) - Biological Oxygen Demand
represents the amount of oxygen required by microorganisms to
biodegrade wastes. When human or animal activities replace woodlands
or fields, which do contain a background BOD, the level of BOD increases

- 111 -

substantially. Some of the BOD may come from failing septic systems,
lawns and gardens, commercial landscaping and even animal wastes.

Figures F-1 through F-3, shows BOD contribution as mg/L from
each subcatchment. The ranges displayed represent normal water quality
standard ranges according to Table 4.5-3.

Table 4.5-3. BOD Loading Quality Ranges
BOD (mg/L)
Water Quality
<2.0
Very Good
3.0 - 9.0
Somewhat Polluted
>10
Polluted

Following these ranges of subcatchment contributions, there are
currently areas that are considered high contributors of BOD to receiving
waterbodies, most notably a subcatchment at the southern most end of the
watershed. There are several other locations that show increased levels
BOD contribution and are mostly associated to currently developed
residential areas. The residential BOD contribution, whether it is low or
high density residential, is the highest EMC contributor of all land covers.
Seeing that developed land is proposed to be majority residential and
associated facilities, there would be a significant increase in BOD
loadings. The proposed development condition (F-2) shows a tremendous
increase in BOD loading with continued development at the prescribed
residential densities. From the numerical modeling standpoint, the only
factors limiting this increase in loadings are restricted residential
development from buffers around riparian zones and waterbodies. These
are not acting so much as a ‘filter’ within the model, but rather a limiting
factor to percent land available for development. In all actuality, these
buffers reduce loading to receiving bodies, but that reduction is not
directly accounted for in the model.

- 112 -

Through the implementation of BMPs (Figure F-3), there is a
potentially large reduction in BOD loading. Since the highest contributor
of BOD is from residential land covers, and the most likely use of
stormwater management may be through detention and retention basins,
there is a potential 50% reduction in BOD loadings with these BMPs. The
choice of BMP is fairly important with respect to BOD loading and
without any treatment, could lead to severe degradation of stream and lake
water quality.

Forested lands have a relatively low BOD loading, thus, with such
a dramatic change in land cover to residential, there is an associated severe
increase in BOD loading as shown in Figure F-4.

Total Phosphorus (TP) - Phosphorus is one of the key pollutants
of concern with respect to urban stormwater runoff quality. Phosphorus
can be found in animal wastes, detergents and fertilizers, automobile
exhaust, atmospheric deposition or erosion. Phosphorus is usually
associated directly with the amount of suspended solids; a reduction of
TSS can indirectly result in a reduction of TP. Total phosphorus consists
of both the organic and inorganic forms. Phosphorous is usually
considered the limiting nutrient in freshwater tributaries and lakes, as
such, and its contribution can become more important than nitrogen
loading.

The existing conditions model shows areas of elevated TP
contribution, typically in subcatchments with more pastureland or
horsefarms. There is a significantly higher level of phosphorus
contribution from these lands than compared to other land cover types.

With respect to determining what lands are developable,
pasturelands and horse farms are considered developable lands, and since
they have such an increased loadings, there is a potential reduction in TP

- 113 -

loading through the development of the land in certain subcatchments.
This can actually be seen in a subcatchment directly southwest of Lake
Konomoc at its outlet (F-6).

Through the use of BMPs, reductions of TP may be possible. In
general, as land is developed into commercial and residential uses, the
amount of TP phosphorus increases, thus requiring BMPs to reduce
overall system loading. The most efficient BMP is through a retention
basin with efficiencies around 60%, followed by dry detention and
extended detention basins with 30 and 15% respectively. The highest
increases in BMP loading are in subcatchments with the most new
potential development.

Total Nitrogen (TN) - Nitrogen is the other major pollutant of
concern in urban stormwater runoff, in addition to phosphorus. Excessive
nitrogen is a nutrient that can lead to algal blooms and eutrophication of
waterbodies. Sources of nitrogen include failed septic systems, excessive
fertilization of lawns or crops, atmospheric deposition, plant debris and
animal wastes. Residential areas have a relatively high nitrogen loading
with respect to other land uses; an exceptionally high nitrogen loading
may be seen from golf courses, but would have a lower density than other
more common land covers.

Total nitrogen encompasses the sum of the Nitrate and Nitrite
(NO3 and NO2) in addition to the Total Kjeldahl Nitrogen (TKN) as
ammonia and organic nitrogen. These values were modeled separately,
but summed for analysis as total nitrogen. Atmospheric deposition of
nitrogen was not directly accounted for within the model.

The existing conditions model shows elevated levels of nitrogen
loading (Figure F-13) across the watershed with an excessive loading
around an existing construction development east of Darrow Pond. Levels

- 114 -

of nitrogen appear directly correlated to the amount of development in a
certain subcatchment. In areas adjacent to the lower Niantic River, which
are already developed, there is a limited increase in nitrogen loading.
Additionally, these areas appear to be sewered for the most part reducing
the chances of direct waste discharge to the bay, which could be seen with
a failing septic system.

Proposed conditions show a marked increase in potential nitrogen
loading with areas of >50% increase (Figures F-14 and F-16). Methods of
reducing nitrogen loading are limited and efficiencies are relatively low.
The highest reported efficiency of nitrogen removal is from retention basin
facilities with approximately a 70% efficiency rate, although more
common and practical are either dry detention with a 30% efficiency or
wet retention with a 15% efficiency.

It appears that with the proposed conditions of significant
residential development, there may be excessive nitrogen loading to
receiving waterbodies. More stringent BMPs operating in series may be
required to limit nitrogen loading helping to prevent the eutrophication of
receiving waterbodies.

4.5.3.5 Pollutant Loadings by Receiving Waterbodies

Within the Niantic River Watershed, there are several waterbodies
that may currently be considered sensitive and require protection from
further pollution. Major waterbodies have been outlined and the total
pollutant loadings have been evaluated. This may be useful for
determining, with respect to other receiving waterbodies in the watershed,
which may be receiving excessive pollutants currently and which may be
more susceptible to further changes from development.

- 115 -

Table 4.5-4 is a list of receiving waterbodies separated by major
catchments (Figure 4.5-10). Each location defines the total pollutant load
received from the synthetic storm event from all contributing
subcatchments without BMPs implemented. In ‘real-life’ conditions, the
pollutant load may be lower because of natural treatments upstream, or it
may be higher from local erosion within a stream or an unknown point
source. The summary does provide a reference for which each
subcatchment can be compared.

- 116 -

Table 4.5-4 – Summary of Total Pollutant Loadings by Major Receiving Waterbody
Oil Mill
Brook
Oil Mill
Lower Latimer Brook
Silver Falls
Barnes Reservoir
Cranberry Meadow Brook
Bogue Brook Reservoir
Niantic River
Stony Brook
Upper Niantic
Existing (lbs)
3,475
4,750
4,231
1,455
1,968
983
5,464
1,638
486
Developed (lbs)
4,596
5,984
5,274
2,237
2,258
1,394
6,325
2,118
715
Difference (lbs)
1,121
1,234
1,043
782
290
411
861
480
229
Drainage Area (ac)
3,692.5
3,128.3
3,639.6
1,848.8
1,667.7
1,080.5
3,014.4
1,273.0
412.4
Developed
(lbs/ac)
1.2
1.9
1.4
1.2
1.4
1.3
2.1
1.7
1.7
Existing Normalized
(lbs/acre)
0.9
1.5
1.2
0.8
1.2
0.9
1.8
1.3
1.2
Increase Normalized
(lbs/acre)
0.30
0.39
0.29
0.42
0.17
0.38
0.29
0.38
0.56
Existing (lbs)
646
676
855
249
392
169
739
283
79
Developed (lbs)
696
818
823
337
351
206
834
315
105
Difference (lbs)
50
142
-32
88
-41
37
95
32
26
Drainage Area (ac)
3,692.5
3,128.3
3,639.6
1,848.8
1,667.7
1,080.5
3,014.4
1,273.0
412.4
Developed
(lbs/ac)
0.19
0.26
0.23
0.18
0.21
0.19
0.28
0.25
0.25
Existing Normalized
(lbs/acre)
0.17
0.22
0.23
0.13
0.24
0.16
0.25
0.22
0.19
Increase Normalized
(lbs/acre)
0.014
0.045
-0.009
0.048
-0.025
0.034
0.032
0.025
0.063
Existing (lbs)
6,627
11,765
9,737
1,779
3,978
1,942
19,677
4,195
1,006
Developed (lbs)
31,206
34,403
37,050
16,202
14,222
9,533
35,159
14,193
5,037
Difference (lbs)
24,579
22,638
27,313
14,423
10,244
7,591
15,482
9,998
4,031
Drainage Area (ac)
3,692.5
3,128.3
3,639.6
1,848.8
1,667.7
1,080.5
3,014.4
1,273.0
412.4
Developed
(lbs/ac)
8.5
11.0
10.2
8.8
8.5
8.8
11.7
11.1
12.2
Existing Normalized
(lbs/acre)
1.8
3.8
2.7
1.0
2.4
1.8
6.5
3.3
2.4
Increase Normalized
(lbs/acre)
6.66
7.24
7.50
7.80
6.14
7.03
5.14
7.85
9.77
Existing (lbs)
225,986
325,441
1,210,247
62,724
78,932
37,878
144,304
92,383
18,762
Developed (lbs)
286,621
457,166
441,335
150,401
137,614
21,591
250,744
151,109
43,902
Difference (lbs)
60,635
131,725
-768,912
87,677
58,682
-16,287
106,440
58,726
25,140
Drainage Area (ac)
3,692.5
3,128.3
3,639.6
1,848.8
1,667.7
1,080.5
3,014.4
1,273.0
412.4
Developed
(lbs/ac)
77.6
146.1
121.3
81.4
82.5
20.0
83.2
118.7
106.5
Existing Normalized
(lbs/acre)
61.2
104.0
332.5
33.9
47.3
35.1
47.9
72.6
45.5
Increase Normalized
(lbs/acre)
16.4
42.1
-211.3
47.4
35.2
-15.1
35.3
46.1
61.0
Receiving
Waterbody
Pollutant
Latimer Brook
Niantic River
*Top two values for current loading per acre, and loading increase per acre, have been highlighted in each row
TP Load
BOD Load
TSS Load
TN Load

- 117 -

Salem
Montville
Waterford
East Lyme
Oil Mill
Silver Falls
Niantic River
Latimer Brook
Barnes Reservoir
Stony Brook
Cranberry Meadow Brook
Bogue Brook Reservoir
Upper Niantic
0
7,000
14,000
Scale In Feet
Legend
Towns
Waterbodies
Lakes & Reservoirs
Swamps & Marshes
Streams
Major Basins
Barnes Reservoir
Bogue Brook Reservoir
Cranberry Meadow Brook
Latimer Brook
Niantic River
Oil Mill
Silver Falls
Stony Brook
Upper Niantic
4.5-10
DEPT OF ENVIRONMENTAL PROTECTION
HARTFORD, CONNECTICUT
NIANTIC RIVER WATERSHED
MANAGEMENT PLAN
MAJOR DRAINAGE BASINS
LOCUS MAP
AS SHOWN
1314-001
SWMM_MajorBasins.mxd
SEK
9-12-2006
Scale:
Project No:
Filename:
Drawn By:
Date Drawn:
75 M ai n St. , P O Box 5 76
Pit ts fi e ld , M ai ne 0496 7
Te l ep hone : ( 207) 487- 3 328
Fax : ( 207 ) 48 7- 312 4
www .K le i nsc h mi dt U SA.c o m

4.5.3.6 Discussion

The results appear to provide a decent approximation o