lake wentworth watershed buildout results · from buildout in the lake wentworth/crescent lake...
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Lake Wentworth Buildout Analysis April 2012
7
Lake Wentworth Watershed Buildout Results
Buildout Results
Table 2: Buildable Area by Subwatershed
Figure 1: Total Area vs. Total Buildable Area by Subwatershed
Watershed Total Area (acres) Buildable Area (acres) Percent Buildable Area
Breezy Brook 68 53 77%
Claypit Brook 1,618 944 58%
Crescent Lake 747 310 42%
Fernald Brook 1,431 943 66%
Frost Brook 614 316 52%
Harvey Brook 820 500 61%
Heath Brook 2,031 822 40%
Red Brook 253 116 46%
Ryefield Brook 900 406 45%
Townsend Brook East 411 236 58%
Townsend Brook West 173 83 48%
Tyler Brook 1,563 1,054 67%
Warren Brook 1,679 777 46%
Lake Wentworth 5,192 862 17%
Whitton Brook 300 130 43%
Willey Brook 4,255 2,250 53%
Brookfield Totals 2,575 1,138 44%
Wolfeboro Totals 19,480 8,664 44%
Grand Totals 22,055 9,802 44%
0
1,000
2,000
3,000
4,000
5,000
77%
58%
42%
66%
52%61%
40%
46%
45%58%
48%
67%46% 17%
43%
53%
Acr
es
Lake Wentworth Buildable Area by Subwatershed
Total Area (acres)
Total Buildable Area (acres)
Lake Wentworth Buildout Analysis April 2012
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Figure 2: Map of Buildable Area by Subwatershed
Lake Wentworth Buildout Analysis April 2012
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Table 3: Full Buildout Results, by Subwatershed
Subwatershed Buildout Units Existing Units Total
Breezy Brook 5 19 24
Claypit Brook 110 86 196
Crescent Lake 209 365 574
Fernald Brook 180 106 286
Frost Brook 34 55 89
Harvey Brook 148 191 339
Heath Brook 153 85 238
Red Brook 21 29 50
Ryefield Brook 50 67 117
Townsend Brook E. 12 49 61
Townsend Brook W. 17 36 53
Tyler Brook 289 138 427
Warren Brook 23 2 25
Lake Wentworth 267 718 985
Whitton Brook 25 49 74
Willey Brook 327 235 562
Wolfeboro Totals 1,870 2,230 4,100
Heath Brook 89 1 90
Townsend Brook E. 68 7 75
Townsend Brook W. 5 0 5
Warren Brook 211 78 289
Lake Wentworth 21 0 21
Brookfield Totals 394 86 480
Grand Totals 2,264 2,316 4,580
WOLFEBORO
BROOKFIELD
Lake Wentworth Buildout Analysis April 2012
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0
100
200
300
400
500
600
700
110
180153
289
23
327
86106
85
138
2
235
Bu
ildin
gs
Wolfeboro Existing & Buildout Units - Full Buildout
Buildout Units
Existing Units
Figure 3: Wolfeboro Full Buildout Results, by Subwatershed
0
20
40
60
80
100
120
140
160
180
200
Heath Brook Townsend Brook E. Townsend Brook W. Warren Brook Lake Wentworth
89
68
5
211
21
17
0
78
0
Bu
ildin
gs
Brookfield Existing & Buildout Units - Full Buildout
Buildout Units
Existing Units
*
*
* Bars with numbers above them represent subwatersheds within the town where the number of new buildout units at full
buildout will exceed the number of existing units.
Figure 4: Brookfield Full Buildout Results by Subwatershed
Lake Wentworth Buildout Analysis April 2012
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Table 4: Wolfeboro and Brookfield Full Buildout Results, by Zoning District
0
100
200
300
400
500
600
700
Municipal Watershed
Agriculture Village Residential
Commercial - C2
Shorefront Residential
Residential General Residential
Rural Residential
Residential -Agricultural
16 23 3257
133
193
314
444
658
Bu
ild
ings
Zoning District
Wolfeboro - Buildout Units by Zoning District
Figure 5: Wolfeboro Buildout Units by Zoning District
Zoning District Buildout Units
Agriculture 23
Wolfeboro Totals 1,870
Grand Totals 2,264
57
16
Commercial - C2
Municipal Watershed
394
133
32
General Residential
Rural Residential
WOLFEBORO
BROOKFIELD
Commercial - Pine Hill Road
Residential-Agricultural
Shorefront Residential
Village Residential
193
314
0
444
658
0
Residential
Residential - Agricultural
Commercial - Central Business
Lake Wentworth Buildout Analysis April 2012
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Figure 6: Map of Buildable Area by Zoning District
Lake Wentworth Buildout Analysis April 2012
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Discussion
Based on the development constraints and zoning requirements outlined earlier, there are an estimated
9,802 acres of developable land remaining in the Lake Wentworth/Crescent Lake watershed (44% of the
total watershed area within Wolfeboro and Brookfield). Buildout results estimate that this developable
area, under current zoning, can accommodate an additional 2,264 buildings or approximately 98% more
than the current number of existing buildings in the watershed. Although the exact amount of additional
development may vary based on the amount of land protected as open space, zoning and other
regulations, and socioeconomic factors, the buildout analysis indicates that significant additional
development could occur in the watershed. This buildout analysis reinforces the idea that
comprehensive watershed scale planning is needed to address future development impacts.
Development in Lake Wentworth’s Subwatersheds
Table 2 and Figures 1-4 provide information about how much buildable land is available within each
of the 16 subwatersheds that make up the larger Lake Wentworth/Crescent Lake Watershed. As
shown in Figure 1, more than half of the total land area in seven of the sixteen subwatersheds is
buildable. Another way to say this is that the amount of buildable area exceeds the unbuildable area
in those subwatersheds. In the other nine subwatersheds, the remaining buildable area is less than
half of the total land area in that subwatershed. (See also Table 3 for a breakdown of buildable units
by subwatershed.) The subwatersheds with the highest percentage of buildable land include Breezy
Brook (77%), Tyler Brook (67%) and Fernald Brook (66%). Results of the buildout analysis indicate
that the three subwatersheds with the most number of buildout units at full buildout include Willey
Brook (327 new units), followed by Tyler Brook (289) and Lake Wentworth’s direct watershed (288).
In addition, at full buildout, six of the sixteen subwatersheds in Wolfeboro are expected to have
more new buildout units than exist today (Figure 3).
Development by Zoning District
Table 4 and Figures 5 and 6 provide information about how much buildable land is available based
on zoning districts. Since there is only one zoning district in Brookfield (Residential/Agricultural), all
new development will occur in one zone. The Town of Wolfeboro has a number of different zoning
districts and several overlay districts. To simplify the buildout model, overlays were not included in
the analysis, and commercial districts that do not allow for residential development were not
included, leaving nine different districts for the analysis. Figure 6 indicates that the most
development will occur in the Residential-Agricultural zone (658 units), followed by Rural Residential
(444 units) and General Residential (314 units). Given the large area of buildable land in the
Residential-Agricultural zone (Figure 6) it is no surprise that this is the area with the potential for the
most development, despite having the largest minimum lot size (5 acres) across the zones (Table 1).
Lake Wentworth Buildout Analysis April 2012
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Time scope Analysis Results
The time scope analysis estimates are based on a projected per-year population growth rate of 1.8% for
Brookfield and 2% for Wolfeboro (p. 3). This information is based on currently available projections, but
long-term growth rates may vary. If this growth rate remains consistent, which may be unlikely, full
buildout would not occur watershed-wide until the year 2110. On an individual town basis, full buildout
in the Town of Wolfeboro is estimated to occur in 2043, and in 2110 in the Town of Brookfield. If the
growth rate in the towns increases to previous levels, the results could be significant. For example, from
1990 to 2010, Wolfeboro’s overall growth was 30.4%. At this growth rate, full buildout in Wolfeboro
would occur by 2031. Similarly, over the last two decades, from 1990 to 2010, Brookfield’s overall
growth has been 37.5%. At this rate, full buildout in Brookfield would occur by 2056.
The analysis assumes development will occur on parcels closest to existing roads first. (Note: Additional
buildings (6 in Brookfield and 10 in Wolfeboro) were added at the start of the analysis to help account
for any houses that may have been missed in the existing buildings count.) It’s estimated that there is
currently 6,462 acres of developed land in the watershed today. These land uses include commercial,
residential, industrial and agricultural land in addition to bare land areas (e.g. excavation).
The timescope analysis results for selected years are presented in Table 5 (below) and on the maps on
the following pages. A rough estimate of developed land area associated with the time scope analysis
indicates that an additional 9,802 acres could be developed in the watershed in the future.
Table 5: Wolfeboro and Brookfield Timescope Analysis Results
Years into
Future
Buildout
Date
Brookfield
Buildout Units
Wolfeboro
Buildout Units
Combined
Buildout
Units
Estimated Land
Area Associated
with Buildout Units
(acres)
Watershed
Total (Incl.
Existing
Buildings
5 2017 11 240 251 1087 2567
10 2022 18 495 513 2221 2829
15 2027 28 775 803 3477 3119
20 2032 38 1086 1124 4866 3440
25 2037 48 1428 1476 6390 3792
31 2043 60 1870 1930 8356 4246
40 2052 85 1870 1955 8464 4271
50 2057 115 1870 1985 8594 4301
60 2062 155 1870 2025 8767 4341
70 2072 202 1870 2072 8971 4388
80 2092 259 1870 2129 9218 4445
90 2102 330 1870 2200 9525 4516
98 2110 394 1870 2264 9802 4580
Full
Buildout2110 394 1870 2264 9802 4580
*Full buildout predicted for Wolfeboro in 2043, and 2110 in Brookfield
Lake Wentworth Buildout Analysis April 2012
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Figure 7: Lake Wentworth Watershed Existing Buildings Map
Lake Wentworth Buildout Analysis April 2012
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Figure 8: Lake Wentworth Watershed Buildout Year 2032 Map
Lake Wentworth Buildout Analysis April 2012
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Figure 9: Lake Wentworth Watershed Buildout Year 2043 Map
Lake Wentworth Buildout Analysis April 2012
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Figure 10: Lake Wentworth Watershed Buildout Year 2062 Map
Lake Wentworth Buildout Analysis April 2012
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Figure 11: Lake Wentworth Watershed Full Buildout Map
Lake Wentworth Buildout Analysis April 2012
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Buildout Phosphorus Load Estimate
An increase in watershed development could lead to more phosphorus (P) entering Lake Wentworth and
Crescent Lake from the surrounding watershed each year. Phosphorus serves to “fertilize” the lake and
decreases water clarity. Excess phosphorus can also harm fish habitat and lead to nuisance algae
blooms. A spreadsheet was used to estimate the additional annual phosphorus load that could result
from buildout in the Lake Wentworth/Crescent Lake watershed. For planning purposes, phosphorus load
analyses were conducted for two scenarios:
1. The first analysis estimates phosphorus loads for the year 2032 (20 years from now). At this
point, an additional 1,124 new buildings are estimated to be built in the watershed, making the
total number of watershed buildings 3,440.
2. The second analysis estimates phosphorus loads at full buildout. At full buildout, there would be
an estimated 2,264 additional buildings in the watershed. The total number of buildings in the
watershed at full buildout is estimated to be 4,580.
Below is a description of the methods used to calculate future P loading to Lake Wentworth and
Crescent Lake in Wolfeboro, NH after 20-year buildout and full buildout analyses.
Step 1: Determining zoning coefficients for Wolfeboro and Brookfield.
The minimum lot size for each zone was multiplied by its corresponding maximum buildable lot coverage
(Table 1) and categorized as Urban 1 (Low Residential Development). For lots with NA for lot coverage, 2
acre lots (in Brookfield) were divided into 50% Urban 1 and 50% Urban 5 (Mowed Fields), and 5 acre lots
(in Wolfeboro) were divided into 20% Urban 1 and 50% Urban 5. All zones added 224 square meters of
Urban 3 (Roads) per house. All values were converted to hectares for inclusion in the model.
Step 2: Calculating developed land coverage after 20-year buildout and full buildout projections.
The number of houses per subwatershed per zone was determined by intersecting the
Wolfeboro/Brookfield buildout shapefiles with subwatershed delineations and zoning polygons in GIS
for both projections (20-year and full buildout). The zoning coefficients per urban land use category
(from Step 1) were multiplied by the number of houses in each subwatershed in each zone for both
projections. The total hectares for Urban 1, Urban 3, and Urban 5 land use categories for each
subwatershed was determined by summing the hectares in each zone.
Step 3: Incorporating land use changes to LLRM for P Loading predictions.
The total area to be developed for each projection was summed by subwatershed, and was subtracted
out of Forest 1-3 land use categories. Each land use category for Urban 1, 3, and 5 was added to the
corresponding land use category for each subwatershed. In this way, the total land use area for each
Lake Wentworth Buildout Analysis April 2012
21
subwatershed remained unchanged. We assumed forested areas would be primarily impacted by future
development.
The new land use values were entered into the Lake Wentworth LLRM for P Loading predictions. The
predicted median P for post-calibration LLRM was used as P input concentration to Crescent Lake LLRM.
Crescent Lake land use values were changed accordingly as well to obtain accurate future P Loading
predictions for each projection (20-year and full buildout).
At full buildout, the total P load is predicted to be greatest in the Willey Brook subwatershed, followed
by the direct drainage area to Lake Wentworth and the Fernald Brook subwatershed. However, if we use
the tool from the LLRM model to predict which subwatershed will have the greatest concentrated P load
(P load/water load), then Townshend Brook (East) will have the greatest followed by Whitton Brook and
Fernald Brook (Table 6). Factors that affect P delivery to downstream waterbodies include the ability of
these watersheds to attenuate (or hold onto) P. In watersheds with large wetland systems, P is more
easily attenuated then areas with little or no wetlands since wetlands provide natural filters and act as
“P sinks” along with other nutrients that may affect water quality. Townshend Brook, Fernald Brook and
Whitton Brook do not attenuate P very well, and have relatively high P concentrations compared to the
other subwatersheds (FBE, 2012b).
Based on the methods outlined above, at a 20-year buildout there would be an 63% increase in Lake
Wentworth watershed P runoff loads and a 46% increase in Crescent Lake watershed P runoff loads
(note: the increased P load for Crescent Lake includes loading from Lake Wentworth). At full buildout,
there would be a 143% increase in Lake Wentworth watershed P runoff loads and an 87% increase in
Crescent Lake watershed P runoff loads (Table 8 and Figure 12). The increased P loading to Lake
Wentworth and Crescent Lake is predicted to result in a dramatic increase in in-lake phosphorus
concentrations (Figure 13). Within 20-years the in-lake P concentration in both lakes could increase to
8.9 ppb in Lake Wentworth and to 10.6 ppb in Crescent Lake. These increases would exceed the
standards set by the NH Department of Environmental Services (NH DES) for oligotrophic lakes
(currently 8 ppb). At full-buildout, the in-lake concentration of Lake Wentworth is expected to almost
double from 6.4 ppb to 12.2 ppb, a difference of approximately 6 ppb. Lakes that do not meet state
water quality criteria are assessed for not meeting water quality standards and could be listed as
impaired.
Lake Wentworth Buildout Analysis April 2012
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Figure 12: Estimated Existing and Future Phosphorus Loads, Lake Wentworth
& Crescent Lake
Bre
ezy
Bro
ok
Cla
ypit
Bro
ok
Fern
ald
Bro
ok
Fro
st B
roo
k
Har
vey
Bro
ok
Hea
th B
roo
k
Isla
nds
Red
Bro
ok
Rye
fie
ld B
r
Tow
nse
nd
E
Tyle
r B
roo
k
War
ren
Br
Dir
ect
Dra
inag
e
Wh
itto
n B
roo
k
Will
ey B
roo
k
Tow
nse
nd
W
TOTAL
Total Input
P Conc.
(mg/L)
Median In-
Lake P
Prediction
(mg/L)
Total Input
P Conc.
(mg/L)
Median In-
Lake P
Prediction
(mg/L)
Water Load (cu.m/year) 153,087 3,700,727 3,745,998 1,415,135 2,118,800 5,861,878 106,734 661,647 2,109,995 1,085,813 4,047,688 3,851,816 5,367,983 809,492 11,175,403 516,318 46,728,516
Phosphorus Load (kg/year) 6.56 50.14 82.26 34.56 47.37 60.86 4.27 13.47 32.59 32.13 60.89 52.77 160.29 29.31 251.09 12.77 931.34
Phosphorus Load (mg/L) 0.043 0.014 0.022 0.024 0.022 0.010 0.040 0.020 0.015 0.030 0.015 0.014 0.030 0.036 0.022 0.025
Water Load (cu.m/year) 152,489 3,689,302 3,735,584 1,411,609 2,109,304 5,853,934 106,734 660,212 2,103,560 1,083,739 4,028,257 3,846,272 5,348,851 806,774 11,153,556 513,688 46,603,867
Phosphorus Load (kg/year) 9.16 90.11 140.66 56.70 76.67 93.79 4.27 20.66 59.17 38.56 136.44 65.15 284.50 48.98 374.18 22.46 1521.47
Phosphorus Load (mg/L) 0.060 0.024 0.038 0.040 0.036 0.016 0.040 0.031 0.028 0.036 0.034 0.017 0.053 0.061 0.034 0.044
Water Load (cu.m/year) 152,489 3,680,396 3,717,782 1,408,826 2,103,267 5,829,293 106,734 659,136 2,100,797 1,070,277 4,009,140 3,848,570 5,342,076 806,415 11,109,372 513,249 46,457,820
Phosphorus Load (kg/year) 9.16 125.68 253.86 76.69 98.02 168.18 4.27 26.28 66.84 89.98 217.52 66.41 336.30 53.02 646.33 22.44 2260.97
Phosphorus Load (mg/L) 0.060 0.034 0.068 0.054 0.047 0.029 0.040 0.040 0.032 0.084 0.054 0.017 0.063 0.066 0.058 0.044
Model Results under Full Buildout Scenario
0.033 0.0122 0.0159 0.0134
Model Results under 20 yr Buildout Scenario
0.024 0.0089 0.013 0.0106
Lake Wentworth Crescent Lake
Model Results under Current Conditions
0.017 0.0064 0.0087 0.0074
Existing P Load
(kg/yr)
20-Year
Buildout P
Load (kg/yr)
Full Buildout P
Load (kg/yr)
Lake Wentworth 931 1521 2261
Crescent Lake 467 682 874
0
500
1000
1500
2000
2500
Existing P Load (kg/yr) 20-Year Buildout P Load (kg/yr)
Full Buildout P Load (kg/yr)
Ph
osp
ho
rus
(kg/
yr)
Existing & Future P Loads, Lake Wentworth & Crescent Lake
Lake Wentworth
Crescent Lake
Table 7: Estimated Existing and Future Phosphorus Loads, Lake Wentworth &
Crescent Lake
Table 6: Estimated Phosphorus Loads by Subwatershed & In-Lake Concentrations
Lake Wentworth Buildout Analysis April 2012
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Summary
The buildout analysis for the Lake Wentworth/Crescent Lake watershed provides estimates about the
potential for new residential development, including the number of new buildings and the amount of
land area that could be developed in the watershed based on current zoning standards. The buildout
also presents information about where the development is expected to occur, and how total
phosphorus exported from the watershed is expected to increase in Lake Wentworth as a result of this
development. buildout analysis provides a “worst-case scenario” based on current zoning standards, and
should be viewed as an estimate only- a planning tool that can be used to guide future development
activities in the watershed, or to target subwatershed areas for land conservation. For example, the
buildout analysis estimates that the land area that drains to Breezy Brook, Willey Brook and Tyler Brook
has the potential to have the most new development, which will increase runoff to these streams and
result greater amounts of phosphorus delivery to Lake Wentworth.
The analysis indicates that 2,264 new buildings could be added to the watershed by the year 2110,
affecting 9,082 acres of buildable land remaining in the watershed. The analysis also indicates that full
buildout could occur in the Town of Wolfeboro as soon as the year 2043 based on projected growth
rates within Wolfeboro’s Master Plan. The buildout also predicts where the most development will occur
by zoning district. In Wolfeboro, the Residential-Agricultural and Rural Residential zones are expected to
have the largest increase in new development. Development standards that result in no net increase of
stormwater should be considered for all new development, including low impact development (LID),
which utilizes smart site design principles to capture and treat polluted runoff from rooftops, driveways
6.4
8.9
12.2
7.4
10.6
13.4
6
7
8
9
10
11
12
13
14
Existing Concentration 20 Years Full Buildout
Ph
osp
ho
rus
Co
nce
ntr
atio
n (p
pb
)
Effects of Future Development
on In-Lake P Concentrations
Lake Wentworth
Crescent Lake
Declining Water Quality
Figure 13: Effects of Future Development on In-Lake P Concentrations
Lake Wentworth Buildout Analysis April 2012
24
and other impervious surfaces so that they don’t end up in nearby streams and lakes. Similarly
phosphorus control standards which require the installation of best management practices (BMPs),
including LID, could be adopted to limit the amount of phosphorus allowed to be exported from an
individual property. Other tools such as conservation or cluster subdivisions should be encouraged for
zones with large minimum lot sizes (2-5 acres) to protect open space, wildlife habitat and water quality,
and to discourage sprawl.
The buildout analysis also provides estimates of future phosphorus loading based on a 20-year
projection, and at full buildout when all the land has been developed. These estimates indicate that in
just 20 years, the phosphorus levels in Lake Wentworth could increase by 63% and by 43% in Crescent
Lake. These increases are expected to result in dire consequences for sensitive lake systems that by
nature are phosphorus limited. Any new increases in phosphorus in these lakes can “tip the scales” of
nature to favor increased algal growth, resulting in decreased water clarity, increased algae production
and algal blooms, and increased presence of other aquatic plant growth in the shorezone, including well
established invasive plants. Projected in-lake phosphorus levels would exceed NH State Water Quality
Standards for High Quality Waters and possibly result in a federal listing of these waters as impaired, and
result in costly efforts to restore water quality.
The analysis did not include an assessment of the watershed area in the Town of New Durham, which
represents just 2% of the watershed area (468 acres). Based on hydrological features such as streams,
ponds and wetlands (> 5% of the land area), as well as analysis of topography, a large percentage of this
area is unbuildable land. However, any development that does occur in this portion of the watershed
could result in damaging effects to Heath Brook and Lake Wentworth and Crescent Lake downstream, as
a result of increased levels of phosphorus from road building and other earth work to build new homes
near these sensitive natural resources. Fortunately, the Town of New Durham already had stormwater
management and erosion control ordinances in place that should help minimize impacts associated with
this development (New Durham, 2012).
In March of 2012, the Lake Wentworth Watershed Steering Committee set a water quality goal that
would allow up to a 4% increase in phosphorus from new development in Lake Wentworth as part of the
watershed management planning process. The large projected increases in phosphorus from the
buildout analysis indicates that new development in the Lake Wentworth/Crescent Lake watershed
needs to be curtailed significantly to reach this goal. Development standards as described above need to
be considered in order to protect these precious natural resources into the future, and to maintain the
vivacious local economy that depends on these resources.
Lake Wentworth Buildout Analysis April 2012
25
References
FBE (2012a). Wolfeboro Municipal Ordinance Review. Town of Wolfeboro, NH. FB Environmental
Associates. April, 2012.
FBE (2012b). Lake Wentworth and Crescent Lake Nutrient Modeling: Using Lake Loading Response
Modeling to Estimate Phosphorus Loads. FB Environmental Associates. April, 2012.
Houseman, Robert. Director of Planning and Development, Town of Wolfeboro, NH. Personal
Communication, February 6, 2012.
Lingeman, J. & Bradt, S. (2008, December). CommunityViz Level 1: Using ESRI ArcView 9.3, CommunityViz
Scenario 360 3.3, City of Nashua NH Data, and NH GRANIT Data. UNH Cooperative Extension &
UNH Complex Systems Research Center, Nashua, NH.
New Durham (2012). Stormwater Management & Erosion Control Regulations. Town of New Durham,
NH. Adopted January 17, 2012.
Placeways, LLC. (2007, July). Scenario 360 v. 3.3 Quick Reference Guide. Orton Family Foundation &
Placeways, LLC. 61pp.
Wolfeboro (2007). Wolfeboro Master Plan Summary (Population). Town of Wolfeboro, New Hampshire,
2007.