Lake Evaluation and Enhancement Plan
Lake Truesdale
Lewisboro, New York
Prepared For:
Land-Tech Consultants, Inc. has been retained by the
Truesdale Lake Association to prepare a limnological evaluation of the 83± acre
Truesdale Lake located in Lewisboro, New York and provide lake management
recommendations.
As
part of the evaluation, Land-Tech Consultants, Inc. conducted a bathymetric
survey of the lake and collected sediment samples during a site visit on May
31, 2001. The findings presented in
this report were prepared using the physical, chemical, and biological data
collected by Allied Biological Inc., The Citizens Statewide Lake Assessment
Program (CSLAP) and Land-Tech Consultants, Inc. This report also presents a series of
recommendations, which are designed to enhance the aesthetics, recreational,
function and wildlife habitat of the lake and the associated shoreline.
The
83-acre lake is located within a residential area. The manmade lake was created in
1927. Lake Truesdale receives
surface runoff from residentially developed and undeveloped portions of the
watershed. A perennial watercourse
discharges into the northeastern portion of the lake from Pumping Station Swamp,
a drinking water wellfield located on the border of Fairfield County,
Connecticut and Westchester County, New York. The watercourse is approximately 25 feet
wide at the mouth of the lake. The
substrate of the watercourse consists of silt and sand with some gravel. Boulders and deadfall are common. A smaller intermittent watercourse
discharges into a cove located in the northeastern portion of the lake.
The lake discharges via a 200-foot wide concrete dam that is located at the northern tip of the lake. The dam was built in the early 1920s and contains an 18-foot spillway with removable springboards allowing the lake levels to be seasonally managed. A spillway height of 14 inches is maintained during the summer months. The lake water level has been raised and lowered seasonally to minimize damage from ice and to minimize encroachment of aquatic plants. The dam is listed by the New York State Department of Environmental Conservation as a low hazard, class ÒAÓ dam and is built to handle the 100-year storm event.
Eleven transects
accompanied by random spot checks in the lake identified a maximum depth to
soft sediment of approximately eleven feet. This maximum depth occurs in the middle
of the northern end of the lake.
The shoreline of the lake is vegetated with deciduous hardwoods and pines interrupted
by maintained lawns.
A watershed is a drainage
area in which all land and water areas drain or flow toward a central
collector, such as the lake.
Precipitation falling on the watershed that does not infiltrate into the ground will flow
over land to the central collector.
The size of the contributing watershed largely determines the amount of
water that enters the central collector, in this case, the lake.
This lake lies within the Waccabuc River Drainage
Basin, which is a sub-basin of the Croton Regional Basin and the Hudson Major
Basin.
The portion of this watershed contributing surface
runoff to the lake is large (2,380± acres, 963 ha), relative to the size of the
lake (83 acres, 33.6 ha) (Figure 1).
The majority of this watershed is located to the east of the lake and
contains the Pumping Station Swamp.
The size of the watershed creates a watershed to lake ratio of
28.7:1. The amount of rainfall
draining to the lake was calculated using a runoff value of approximately 55
percent of precipitation (CT DEP 1982), an annual precipitation value of 47.5
inches per year (Soil Survey of Putnam and Westchester Counties, New York,
1994), and 68.6 cm (27 inches) per year of surface lake evaporation. Therefore, the net amount of rainfall
that drains to the lake is large, (1.6 billion gallons) annually or an average
daily flow of 4 million gallons per day.
Thus, on an annual basis, the lake, with a volume of approximately
99,150,000 gallons, shows a moderate turnover rate (hydraulic residence time)
of 16.2 times per year or every 22 days.
However, since the perennial watercourse is in the
northeast portion of the lake and the discharge is at the northern tip of the
lake, it is reasonable to assume that much of the water entering the lake from
the perennial watercourse exits the system with little mixing of water in the
southern lake basin. Therefore, the
actual hydraulic residence time in the southern portion of the lake is expected
to be longer than that stated above.
The predominant composition
of the Waccabuc River Drainage Basin surrounding the lake is a mixture of
maintained lawn and small woodlots consistent with residential land uses. The dominant soil surrounding the lake
is the well drained
Paxton fine sandy loam. Other soils
include the poorly drained and somewhat poorly drained Ridgebury loam, which is
located in the northeast portion of the lake, and the moderately well drained
Woodbridge loam, which is located along the southeastern shoreline. Sun loam soils are located adjacent to
the perennial inlet and discharge stream.
These are poorly drained or very poorly drained soils.
The nature of the lake
subjects it to natural and man-influenced sediment loads from the contributing watershed
including adjacent roadways. As
such, the lake receives suspended particles (sand and road salt) from
upgradient sources. These particles
settle out in the lake due to the lower velocity flows of the lake in
comparison to the inlet stream.
Natural erosion from
undisturbed watersheds equals approximately 4.1 metric tons (4 tons) per acre
per year. Winter road sanding
activities will contribute coarse to fine grained sediments annually. The volume of sand is dependent upon the
severity of the
winter and municipal and state sand application practices within the watershed.
At least two previous studies have measured sediment
depths in the lake. The first
survey was conducted in 1956. A
second undated map was prepared by Allied Biological. Land-Tech Consultants, Inc. conducted a
survey on May 31, 2001.
To obtain sediment depths during the May 2001
survey, water depth to soft sediment was measured throughout the lake using a
10 foot graduated rod. The depth of
soft sediment was obtained by pushing the rod into the soft sediment and
recording the depth to refusal.
According to the data collected in 2001, the maximum
depth of the lake is over 11 feet.
This depth was located in the northern portion of the lake (See Figure 2,
Truesdale Lake Bathymetry Map).
Zero to one and a half feet of soft sediment were recorded throughout
the lake. Sediment depths appear to
be uniformly distributed throughout the lake.
The bathymetry data collected in 2001 is consistent
with data collected by Allied Biological.
The bathymetry study conducted in 1956 indicated that seven inches of
board were used in the spillway.
The 2001 study was conducted using 12 inches of board in the
spillway. Adjusting for this
difference, since 1956 the southern tip of the lake shows a one-half foot to
one foot increase in sediment, the center of the lake basin from the beach to
the inlet stream has received approximately one foot of sediment while the
northern basin appears to have received a half to one foot of sediment. Overall this equates to a range of
approximately 0.1 – 0.3 inches per year (0.3 – 0.7 cm/year) of
sediment accretion.
A
composite sediment sample was obtained from the lake near the mouth of the
perennial watercourse and sent to a laboratory to determine the grain size
distribution. The results of this
analysis are presented in Table 1 below.
The copy of the laboratory sieve analysis report is presented in the
Appendix of this report.
Table 1 Sieve Analysis
|
Sieve Size |
Percent
Passing |
Percent Composition |
Soil
Classification |
|
1½ |
100.0 |
0 |
Coarse Gravel |
|
¾Ó |
97.7 |
2.8 |
Fine Gravel |
|
¼Ó |
97.2 |
||
|
#4 |
96.8 |
2.1 |
Coarse Sand |
|
#10 |
95.1 |
||
|
#40 |
73.3 |
65.8 |
Fine Sand |
|
#100 |
29.3 |
||
|
#200 |
14.6 |
29.3 |
Silt/Clay |
Source – Special
Testing Laboratories, Inc.
Sediments entering
the lake basin from the primary inlet are characterized as gray sand (67.9%)
and silt (29.3%) with a trace of gravel (2.8%). The high percentage of fine sand is
consistent with deposition from fast to moderate flowing streams. The likely source of this sediment is primarily
road sand along with particles from upgradient stream banks dislodged during
storm events.
According to the New York
State Water Quality 2000 Report prepared by the New York State Department of
Environmental Conservation, Truesdale Lake is classified as a Class B fresh surface water
body. The recommended uses for
Class B water bodies are primary and secondary contact recreation and fishing. Waterbodies within this classification
are suitable for fish propagation and survival.
The Citizens Statewide Lake
Assessment Program (CSLAP) has been monitoring the water quality of the Lake
since 1999. Data collected
includes: temperature (oC), pH,
conductivity corrected to 25 oC (µmho/cm),
nitrate (mg/l), total phosphorous (mg/l), chlorophyll A (µg/l), true color (platinum color
units), and Secchi disk transparency (m).
In addition, three survey questions were asked of local residents.
CSLAP
reported total phosphorous ranges of 0.018 to 0.084 mg/l between 1999 and
2000. Chlorophyll A ranged from
2.37 to 116 µg/l while Secchi Disk ranged from 0.55 to 2.35m in clarity. The CSLAP data has determined that Lake
Truesdale is a clearwater and eutrophic lake (Table 2). CSLAP found that in general, Lake
Truesdale was more productive (eutrophic) than other similar lakes in the
drainage basin. The CSLAP
assessment on water clarity determined that clarity is more influenced by algae
than by depth, color or inorganic material.
Eutrophication is an aging process where water
quality and biological productivity go through stages of succession. A pond or lake naturally ÒevolvesÓ from
one trophic state to another. This
is a natural process involving the addition of nutrients, including nitrogen
and phosphate. However, it is very
common for this process to be accelerated (cultural eutrophication) by
introducing higher concentrations of nutrients to the pond through erosion,
agricultural runoff, residential fertilizer use and inefficient septic systems.
Plants, both
phytoplankton (algae) and vascular plants, require nutrients such as metals, nitrogen and phosphorous to grow. Growth of plants is typically limited by
the growth factor, which is present in the least quantity relative to the
growth demands of the plant. The
limiting factors of interest are generally plant nutrients, usually nitrogen and/or
phosphorus. These two elements are
usually the least available. If the
limiting nutrient becomes depleted, growth stops despite the fact that other
nutrients might still be available.
In most eastern
New York ponds and lakes, phosphorus is the nutrient that limits algal growth.
Typically during cultural eutrophication, these
additional sources of limiting nutrients are provided, removing the growth
limitation. This in turn allows for
algal blooms and the establishment of aquatic weeds. This process speeds up the natural
succession of the pond and can lower water quality.
The high concentration of total phosphorous
indicates that phosphorous is abundant in the lake (not limiting) allowing
algal growth to prosper. Limiting
the introduction of phosphorus in this system is very important and is a major
focus of the enhancement plan.
Table 2 New
York State Trophic Status Criteria
|
Parameter |
Oligotrophic |
Mesotrophic |
Eutrophic |
|
Transparency
(m) |
>5 |
2 - 5 |
<2 |
|
Total
Phosphorous (mg/l) |
<.010 |
0.010 – 0.020 |
>0.020 |
|
Chlorophyll
a (µg/l) |
<0.002 |
0.002 – 0.008 |
>0.008 |
Phosphorous binds to sediment allowing the sediment to act as a reservoir
for phosphorous. This storage of
phosphorous can be tapped by rooted aquatic emergents or re-suspended by storm events due to
the shallow nature of the lake. To
determine the levels of phosphorous stored in the sediment, an indication of
phosphorous loading, a composite sediment sample was obtained from the lake on
May 31, 2001. This sample was sent to a State approved
contract laboratory (Certification #PH-0574) for analysis. Total phosphorous levels for the lake
sediment were reported as 410 mg/kg.
Phosphorus is often transported in aquatic systems
by adsorbing to fine sediments. As
such, a significant fraction of the total annual phosphorous load to the lake
probably occurs during storm events.
Potential sources of phosphorus include fertilizers, inadequately
renovated septic effluent and exposed soil. The partially wooded buffer surrounding
the lake functions to filter or uptake nutrients reducing the amount of
nutrients entering the water.
Fertilizer and droppings from Canada geese and other waterfowl are also
contributors to the total phosphorous levels observed in regional lakes.
Based
on data collected in 1999 and 2000, CSLAP reported that the lake becomes more
productive during the summer months.
This was based on increasing nutrient and algae levels increasing and
water clarity decreasing. The short
monitoring period, two years, limits the ability to determine how much of this
productivity is due to nutrient loading from the watershed.
The
water quality information provided in this report is a summary of the data
reported by CSLAP. The reader will
find a detailed assessment of the water quality in Truesdale Lake presented in
the CSLAP Annual Report.
Aquatic plants are a vital part of lake
ecosystems; they provide cover for juvenile fish and essential habitat to many
groups of aquatic invertebrates that serve as food for fish. Macrophytes (aquatic plants) also
provide a direct food source for wildlife (particularly waterfowl and
muskrats). Too many macrophytes can
limit swimming, fishing, boating, and aesthetic appreciation.
Algae (phytoplankton).
Excessive algae can also alter the ecosystem. The amount of algae in small lakes and
ponds of the region tends to be highest in late summer. The seasonal increase in water
temperature and light availability (longer days) allows the algae to reproduce
faster. If nutrient levels are too high, some
algae can form dense blooms or even floating scums on the surface, reducing
water transparency to less than one foot.
Algal productivity is usually low in the winter because of low water
temperature and low light
availability.
Aquatic vascular plants and
algae are a major problem in Lake Truesdale. The physical removal of weeds goes back
to 1950 using weed cutters and harvesting.
Chemical treatment was initiated in 1957 under the direction of Cornell
UniversityÕs State
School of Agriculture, Conservation Department. The weed control program has been
continued ever since under the advice of professional aquatic biologists. Allied Biological has been performing
aquatic plant surveys and conducting chemical weed control using Aquathol K since the mid 1980s.
The weed population is
treated with Aquathol K in the spring.
A program that applies algaecide (copper sulfate) to the lake is
employed during July to August.
Copper sulfate is effective
in controlling many species
of aquatic plants, however, it may cause increased copper concentrations in the
lake sediments and negatively impact the benthic invertebrates living in the
sediment. There is also the concern
that copper could affect invertebrates in the water column such as zooplankton.
The results of the 2000 Allied Biological treatment
program found that the earlier part of the season (May) was dominated by
curly-leaf pondweed (Potamogeton crispus). Other species identified were leafy
pondweed (Potamogeton foliosus) and
filamentous algae. The only plant
identified by CSLAP during the May through October 2000 field events was Najas flexilis (bushy pondweed). This plant was found in the northeast
cove in approximately 0.24 meters of water. The plants identified in these two
reports are in drastic contrast to each other. This discrepancy should be resolved.
Applications in May of both Aquathol K and copper
sulfate controlled the curly-leaf pondweed and algae allowing leafy pondweed (Potamogeton foliosus) to become dominant
by mid summer. Additional
applications of copper sulfate were used to control the leafy pondweed. Algae (Nitella sp.) was identified in the southern cove and was treated
with copper sulfate. Algal blooms
of blue-green algae and filamentous algae appeared in June and were treated in
July and August with copper sulfate.
These data collected by Allied Biological showed an
increased pondweed growth and a slight reduction in planktonic algae growth in
comparison to 1999. The weed and
algal control program employed Lake Truesdale is effective in controlling the
seasonal weed population.
Copper
binds to particulate matter in the water and sediment and as an element will
persist indefinitely in the soil.
Copper is strongly bioaccumulated and is typically stored in the liver
and brain. Fish especially trout
and carp are very susceptible in soft or acid water. This toxicity decreases as water
hardness increases (Extension Toxicology Network). Copper sulfate is toxic to aquatic
invertebrates such as worms, pond snails and clams.
Copper
sulfate is highly water soluble, but also easily binds to particulate matter
and sediment. To determine the
levels of copper in the sediment, a composite sediment sample was obtained from
the lake on May 31, 2001, and analyzed for total copper to determine the
retention of copper in the sediments introduced from the application of copper
sulfate. These samples were sent to
a State approved contract laboratory (Certification #PH-0574) for
analysis. Total copper levels in
Lake Truesdale were reported as 34 mg/kg.
The average copper levels for the region is around 20 mg/kg.
Although
the application of copper sulfate has been done by professionals under strict
guidelines, the long period of application (44 years) warrants the monitoring
of copper concentrations in the lake water. Comparing the results with known
toxicological thresholds (LD 50) will help determine if any impacts have been
caused by the long period of copper sulfate application.
Additional
Observations.
The area around the
lake has a high wildlife support capacity (songbirds, game birds,
mammals). Sources of water, food,
and cover are common. The diversity
of structural vegetative types surrounding the lake includes turf grass, mixed
deciduous hardwoods, and riparian (stream corridor) habitat.
Fisheries were not investigated,
however, several species of fish likely occupy the lake. Potential fish species populating the
lake include sunfish, perch, small mouth bass, large mouth bass, minnows and
darters. Although continuous
application of chemical treatments to a water body has the potential to harm
fish and other aquatic species, reports from local residents state that the
lake continues to support a healthy fish population. A routine fish monitoring program should
be initiated to document the health and species diversity of the fish
population in Lake Truesdale.
The lake currently has high
landscape, scenic, and recreational values. The lake receives flow from overland flow and from a
perennial watercourse discharging into the northeastern shoreline. The lake has accumulated approximately
one foot of sediment since 1965.
This is not an excessive accretion rate. Some of this sediment is entering the lake from the
perennial watercourse, altering the bathymetry of this lake, and decreasing its
depth. The sediment load to the
lake is probably the major contributor to the high total phosphorous and nitrogen
in the system. The lake contains
high phosphorous and
chlorophyll A levels resulting in abundant aquatic plants and seasonal algal
blooms. These blooms are
effectively controlled by a continuous weed control program using Aquathol K
and copper sulfate. This program
has been in effect since 1956 and has contributed to the high concentrations of copper in the
sediment.
The lake is lacking a
diversity of habitat. The lake is
shallow with gentle slopes offering little variation in depth for fish habitat.
Limiting excessive
phosphorous and nitrogen
concentrations is essential to the balance of this system. The high nutrient content in the lake
will continue until changes in the watershed are made to reduce sediment and
nutrient loads. The following
section provides recommendations on a watershed approach to improve the conditions in the lake.
Non-point source pollutants in stormwater runoff may originate from a variety of sources (Table 3). The data collected from Lake Truesdale during this evaluation indicated that phosphorus-laden sediments are a major concern in stormwater runoff. The Best Management Practice systems proposed for the Lake Truesdale watershed were selected following a thorough review of their effectiveness at reducing non-point sources of pollution (primarily sediment and secondary phosphorus), associated costs, and site constraints.
Table 3 -
Potential Sources of Urban Runoff Pollutants
|
Source |
Pollutants of Concern |
|
Soil Erosion |
Sediment and attached soil nutrients, organic
matter, and other absorbed pollutants. |
|
Atmospheric deposition |
Hydrocarbons emitted from automobiles, dust,
aromatic hydrocarbons, metals, and other chemicals released from industrial
and commercial activities. |
|
Construction materials |
Metals from flashing and shingles, gutters and
downspouts, galvanized pipes and metal plating, paint, and wood. |
|
Manufactured products |
Heavy metals, halogenated aliphatics, phthalate
esters, PAHs, other volatiles, and pesticides and phenols from automobile
use, pesticide use, industrial use, and other uses. |
|
Plants and animals |
Plant debris and animal excrement |
|
Non-storm water connections |
Inadvertent or deliberate discharges of sanitary
sewage and industrial wastewater to storm drainage systems. |
|
Onsite disposal systems |
Nutrients and pathogens from failing and
improperly sited systems. |
From U.S. EPA Publication 840-B-92-002,
1990.
BMPs vary in their effectiveness in removing pollutants (Watershed Protection Techniques, Technical Note 95, 1997). In addition, consistency within comparative studies of the effectiveness of various BMPs is highly variable, and therefore the removal capacities provided should be considered guidelines that will most likely differ depending on the storm event, site conditions, etc.
The estimated average removal rates for total suspended solids (TSS), total phosphorus (TP), total nitrogen (TN), nitrate (N03) and other pollutants (bacteria, metals) of selected Best Management Practice systems are presented in Table 4.
Table 4 - Estimated Average Pollutant Removal Capacity of Different Stormwater Filter Systems |
|||||
|
|
Removal Efficiency (%) |
|
|||
|
Management
Practice |
TSS |
TP |
TN |
N03 |
Other pollutants |
|
Drainage Channel1 |
30 |
10 |
zero |
zero |
Bacteria - negative |
|
Grass Channel1 |
65 |
25 |
15 |
neg. |
Hydrocarbons - 65% Metals - 80-90% Bacteria - negative |
|
Dry Swale1 |
90 |
65 |
50 |
80 |
Metals - 80-90% |
|
Wet Swale1 |
80 |
20 |
40 |
50 |
Metals - 40-70% |
|
Filter Strip1 |
70 |
10 |
30 |
zero |
Metals - 40-50% |
|
Gravel Filter1 |
80 |
80 |
65 |
75 |
Hydrocarbons - 85% Metals - 50-75% |
|
Catch Basin with Sump (Water Quality Inlet) 2 |
35 |
5 |
20 |
no data |
Lead - 15% Zinc - 5% |
|
Oil/Grit Separator2 |
15 |
5 |
5 |
no data |
Lead - 15% Zinc - 5% |
1 From Claytor and Schueler 1996.
2 From Environmental Protection Agency 1990.
The following section contains a brief summary of some of the advantages and disadvantages associated with selected BMPs.
Table 5a - Catch Basins with hoods and sumps |
||||
|
Advantages |
Provide high degree of removal efficiencies for larger particles and debris as pretreatment |
Require minimal land area |
Flexibility to retrofit existing small drainage areas and applicable to most urban areas |
Biannual cleaning of sumps can reduce TSS levels by 10-25% and phosphorus levels by 10-20%*. |
|
|
|
|
|
|
|
Disadvantages |
Not feasible for drainage area greater than one acre |
Marginal removal of small particles, heavy metals, and organic pollutants |
Not effective as water quality control for intense storms, require frequent sediment removal. |
Minimal nutrient removal |
|
|
|
|
|
|
|
Factors |
Maintenance |
Sedimentation storage |
|
|
|
|
|
|
|
|
|
Costs |
@ $1,500/unit |
|
|
|
* Carrying Capacity of Public Water Supply Watersheds, CT DEP Bulletin No. 11.
|
Table 5b - Stone Filters |
|||
|
Advantages |
May provide ground water recharge |
Requires minimal land area |
May helps replicate pre-development hydrology, increase dry weather base flow |
|
|
|
|
|
|
Disadvantages |
Dependent upon in-situ soils |
Requires maintenance, access is a problem. |
|
|
|
|
|
|
|
Factors |
Treatment volume |
Filtration media |
Soil percolation rates |
|
Table 5c - Vegetated Filter Strip (VFS) |
|||||
|
Advantages |
Low maintenance requirements. Can effectively reduce velocity |
Can be used as part of the runoff conveyance system to provide pretreatment |
Can effectively reduce particulate pollutant levels in areas where runoff velocity is low to moderate |
Provides excellent urban wildlife habitat. Requires minimal land area |
Economical |
|
|
|
|
|
|
|
|
Disadvantages |
Often concentrates water, which significantly reduces effectiveness |
Ability to remove soluble pollutants highly variable |
Limited feasibility in highly urbanized areas where runoff velocities are high and flow is concentrated |
Requires periodic repair, re-grading, and sediment removal to prevent channelization |
|
|
Table 5d - Stone Waterfall |
|||||
|
Advantages |
Can effectively reduce velocity |
Low maintenance requirements |
Requires minimal land area |
|
|
|
|
|
|
|
|
|
|
Disadvantages |
High Construction costs |
|
|
|
|
|
|
|
|
|
|
|
|
Factors |
Storage volume |
Detention time |
Pool shape |
Wetlands biota |
Seasonal variation |
|
|
|
|
|
|
|
|
Costs |
$3,000/unit |
|
|
|
|
|
Table 5e - Oil/Grit Separator |
|||||
|
Advantages |
Captures coarse-grained sediments and some hydrocarbons |
Requires minimal land area |
Flexibility to retrofit existing small drainage areas and applicable to most urban areas |
Shows some capacity to trap trash, debris, and other floatables |
Can be adapted to all regions of the country |
|
|
|
|
|
|
|
|
Disadvantages |
Not feasible for drainage area greater than one acre |
Minimal nutrient and organic matter removal |
Not effective as water quality control for intense storms |
Concern exists over the pollutant toxicity of trapped residuals |
Requires high maintenance |
|
|
|
|
|
|
|
|
Factors |
Sedimentation storage volume |
Outlet configurations |
|
|
|
|
|
|
|
|
|
|
|
Costs |
$8,000 - $10,000 |
|
|
|
|
MANAGEMENT RECOMMENDATIONS
Currently, Lake TruesdaleÕs
aquatic plants are heavily managed and ecologically out of balance. The management activities conducted on
Lake Truesdale have been focused on treating the effects of the unbalanced
nature of the lake and not on treating the cause. The highly eutrophic nature of the lake
is most likely caused by excess nutrients entering the lake from the watershed. Sources in the watershed include roads
(sand, salt, etc.), the use of fertilizers and herbicides on residential lawns,
inefficient septic systems and other factors that are common today.
Currently there are two main
problems with Lake Truesdale. These
two problems are sediment accretion and high nutrient content. On paper, these factors can be
separated, however, in an ecosystem they are very much related. The recommendations listed below were
established to address the watershed as a whole and not just the lake. Although in todayÕs society it is impossible
to manage the entire watershed, several actions can be taken, to significantly
reduce many of the problems addressed by this evaluation.
1. The accumulation of
sediments is primarily due to the unrestricted flow from the two largest inlet
streams discharging into the northeastern portion of the lake. Due to the size of the watershed, it
would be impossible to eliminate sedimentation and the introduction of
nutrients into the system. The
large wetland system located to the east of the lake traps sediment and removes
nutrients that enter the watershed upgradient of the wetland. However, many sources exist down
gradient. Sediment sources in close
proximity to the inlet are considered the principal sources of sediment
loading. The most practical way to
control these influences to the lake is near the stream/lake interface. Remove the sediment at the mouth of the
perennial stream and from the northeastern cove at the mouth of the
intermittent stream. Install
sediment forebays within both of the inlet streams. A sediment forebay would capture
sediment before entering the lake, reducing sediment entering the lake. Once properly designed and installed,
periodic maintenance (sediment removal) would be simple and relatively
inexpensive.
2. The southern and northeastern
coves could be dredged to provide greater depths and a more diverse habitat for
wildlife including fish and turtles.
Boulders or stumps could be placed in a limited area of the lake to
provide basking areas for turtles and frogs and escape cover for small
fish. These areas contain deep soft
sediment deposits. Therefore,
removing the sediment would remove some of the nutrients and plant seed
contained within the sediment.
Seeds and nutrients would eventually be replenished, however, with
forebays installed their accumulation would be retarded. The dredging of these areas would be
expensive, would require the development of a detailed dredging plan, and
permits from the Town, State of New York and possibly the Army Corps of
Engineers.
3. Ensure that the entire Lake
contains adequate shoreline vegetative buffers. Vegetative buffers consisting of native
shrubs and dense, tall grasses slow down overland flows allowing particulates
to settle out. These plants also
take up nutrients for their own metabolism reducing the amount of nutrients
entering the pond. The buffer
should be a minimum of 15 feet wide and preferably 25 feet wide around the lake
to allow uptake of nutrients that would enter the lake via runoff. Turf environments should grade into coarse
grass buffers and then to shrubs for maximum effectiveness. Depending on cover story vegetation,
land use and soils, the woody (shrubs) buffer or herbaceous (grass) buffer may
be used independently. For the
points of access, i.e. beach along eastern shore, the already established grass
buffer should be adequate. Grass
buffers need to be mowed twice per year to remove accumulated nutrients.
4. Application of fertilizer to
the maintained lawns adjacent to the lake should be based on the nutrient needs
of the grasses, and the results of the soil nutrient analysis. Proper selection of turf grass species
will also reduce the need for excessive nutrient application. At a minimum, insure that only enough
fertilizer is applied to meet the needs of the lawn and plantings. Typically lawn fertilizers are
water-soluble and their use should be minimized near open water. Soil samples can be analyzed to
determine if phosphorus is needed.
If not needed, no more phosphorus should be applied. Use of a mulching lawn mower to return
grass clippings to the lawn would reduce the amount of fertilizer needed. If possible, discontinue fertilizer
applications to trees, shrubs, flowerbeds, and turf grass in areas that drain
to the pond. Applications of
fertilizer should not be done immediately preceding heavy rain and only organic
slow release fertilizers should be used when available. Fertilizer should not be applied more
than once per year.
5. The recommendations outlined
in #3 and #4 above are most effective when owners of the properties that drain
to the lake follow the same recommendations around the inlet streams. The property owners who abut the streams
that drain to the lake should be informed of the potential impacts caused by
excessive fertilization and the ways to reduce impacts to the pond such as
vegetative buffers.
6. Lake residents should also
be made aware that poorly functioning septic systems can introduce additional
concentrations of phosphorous to the lake and therefore should be properly
maintained.
7. Introduce rooted emergents
along the shore of the lake. These
plants would take up nutrients (including nitrogen and phosphorous) making
lower concentrations available for algal species. The introduction of emergents would also
increase the aesthetics of the pond, create escape cover for fish and provide
attachment sites for amphibian egg masses and macroinvertebrates (aquatic
insects).
8. Since waterfowl can
contribute significant phosphorus to your pond, do everything you can to
discourage them from visiting the lake and the surrounding lawns (e.g.
vegetative buffers, nettings, or dogs).
The buffer cited in # 3 above can be effective in minimizing the
attractiveness of your pond to waterfowl.
9. During our May 15, 2001 lake
inspection with Ray Morse and Sue Innis, we were shown six locations where
stormwater entered the lake. All of
these areas have noticeable sedimentation problems and are, therefore, probable
nutrient sources. The following are
brief descriptions of the six areas and possible ways to capture sediment and
nutrients before they enter the lake.
The locations of the six areas appear on Figure 2 (Truesdale Lake
Bathymetry).
q Remove a section of the
pipe, so its end is farther from the edge of the water.
q Enlarge the outlet area
between the end of the pipe and the edge of the water.
q Create a plunge pool within
the outlet area.
q Create a semi-circular
forebay in the water.
q Plant the surrounding
shallow water area with aquatic vegetation selected to compete with algae for
nutrients.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for the sediment basin and as-needed
maintenance for the forebay.
q Remove a section of the pipe
running north from the catch basin, and replace the pipe section with a
vegetated channel. In a location
where access for maintenance equipment is available, construct a small sediment
basin. Extend the channel to the
lake. Use rip rap to armor channel
sections that are steep enough to be susceptible to erosion.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for the channel and sediment basin.
q Clean out and re-vegetate
the channel at the south end of the beach.
Near the waterÕs edge, build a small settling basin, then a forebay in
the water.
q Plant the surrounding
shallow water area with aquatic vegetation selected to compete with algae for
nutrients.
q Sort out the drainage pipes
associated with the two catch basins in Truesdale Lake Drive south of the driveway. Identify one outlet pipe and confirm
that it leads to the catch basin north of the driveway. Block and remove all other pipes from
this catch basin. Remove the 12Ó
concrete pipe running north-south.
q Construct one or more
channels lined with rip rap leading from the area north of the driveway to the
lake. Ensure that all pipes north
of the driveway discharge to this channel.
Construct a forebay in the water at the end of the channel.
q Plant the surrounding
shallow water area with aquatic vegetation selected to compete with algae for
nutrients.
q Repair eroded areas on the
property.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for the channels and as-needed
maintenance for the forebays.
q The channel has a flat slope
and wide bed, both conducive to sedimentation. Restore the sediment-trapping
capabilities of the channel by removing the large silt and sand deposits that
exist between the road culvert and the manmade pond.
q Construct one or more
sediment basins within the channel at location(s) where access for maintenance
would be available.
q Reconstruct the channel to
improve its aesthetics, increase its resistance to erosion and improve its
sediment removal characteristics.
This may involve creation of a series of riffles and pools, where the
pools would provide a series of small sediment traps.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for the channel and sediment basin(s).
q Open up the area where the
watercourse enters the lake.
Construct a crescent-shaped forebay in the water. Deepen the forebay area and a short area
of watercourse immediately upstream from the waterÕs edge to provide for
sediment storage.
q Plant the surrounding
shallow water area with aquatic vegetation selected to compete with algae for
nutrients.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for sediment storage area and
as-needed maintenance for the forebay.
q Construct a rip rap channel
from the road drainage pipe outlet for the length of the slope that is steep.
q Where the slope flattens
approaching the water, excavate a sediment basin.
q Construct a forebay within
the lake.
q Plant the surrounding
shallow water area with aquatic vegetation selected to compete with algae for
nutrients.
q Provide annual maintenance
(sediment removal, erosion repair, etc.) for the sediment basin and as-needed
maintenance for the forebay.
We believe the recommendations presented above adequately address the issues
identified by this evaluation while enhancing the functions and aesthetics of
the lake. If there are any
questions concerning the evaluation of the existing conditions or regarding the
proposed activities, please contact us to discuss them.
Sincerely,
LAND-TECH CONSULTANTS, INC.
Thomas Ryder Michael Bartos, P.E.
Environmental Analyst Senior Associate
Robert, Jontos
Partner
Allied Biological, 2000. Letter from Glenn P. Sullivan , CLM to Ray Morse dated November 21, 2000.
Claytor, R. A. and T. S. Schueler. 1996. Design of stormwater filtering systems. The Center for Watershed Protection, Silver Springs, MD.
Comparative Pollutant Removal Capability of Urban BMPs: a Reanalysis. 1997. Watershed Protection Techniques 2-4:515-520.
Connecticut Department of Environmental Protection, Bureau of Water Management. 1996. Caring for our lakes. Watershed and in-lake management for Connecticut lakes.
Kishbaugh S.A. and B. R. Hohenstein 2001. 2000 Interpretive Summary New York Citizens Statewide Lake Assessment Program (CSLAP) Lake Truesdale. NYS Department of Environmental Conservation Division of Water, Lake Services Section.
Doenges, J. M., C. P. Allan, R.J. Jontos and C. A. Liebler. 1990. Carrying capacity of public water supply watersheds: A literature review of impacts on water quality from residential development. Connecticut Department of Environmental Protection, Bulletin No. 11.
Frink, C. R. and W. A. Norvell. 1984. Chemical and physical properties of Connecticut lakes. Connecticut Agricultural Experiment Station, Bulletin 817.
Harris, J. H. 1997. The Clean Water Act and animal agriculture. Journal of Environmental Quality 26:1198-1203.
United States Environmental Protection Agency. 1993. Guidance specifying management measures for sources of nonpoint pollution in coastal waters. Publication 840-B-92-002.