lake wentworth watershed buildout results · from buildout in the lake wentworth/crescent lake...

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)


8

Figure 2: Map of Buildable Area by Subwatershed


9

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


Brookfield Totals 394 86 480

Grand Totals 2,264 2,316 4,580

WOLFEBORO

BROOKFIELD


10

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


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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


12

Figure 6: Map of Buildable Area by Zoning District


13

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).


14

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


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Figure 7: Lake Wentworth Watershed Existing Buildings Map


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Figure 8: Lake Wentworth Watershed Buildout Year 2032 Map


17



18



19

Figure 11: Lake Wentworth Watershed Full Buildout Map


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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


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.


22

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







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)


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


23

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


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.


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.

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