How scarce is developable land? . an imperative for smart growth. by Pat Dunlavey, July 2008. What got me started…. “Depending on how you do the calculations we have already protected between 48.9% and 81% of town ” – an email opposing the proposed wetlands bylaw
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an imperative for smart growth
by Pat Dunlavey, July 2008
Land that is (permanently) excluded from residential or commercial development for purposes of agriculture, conservation or recreation
Upland Conservation District
Protected Open Space
* Hopkins Forest and Clark Art are not actually protected, but we’re counting them anyway
* within Williamstown
[Slope (Percent)]=tan(deg2rad(slope([DEM (Meters)],3)))*100
SELECT * FROM [Slope (Percent)] WHERE [Height (I)] >= 20
SELECT Count(*) * 0.006177634536679134 as Acres FROM [SelectedAreaImage]
WHERE [Selection (I)]
(4) Impervious coverage.
(a) Except in the Village Business District, which is exempt from this limitation, impervious coverage shall not exceed the following percentages of site area, where "impervious coverage" is the area covered by building roof area plus paved areas, "site area" is the smallest single rectangle enclosing the area within which ground vegetation is removed for excavation, grading, drives, lawns or gardens and average slope is measured prior to site preparation.
AverageSite Area Slope
8% or less
24% or more
Maximum Impervious Coverage
Average slope in the site area as delimited here is 25%
With these numbers, according to our bylaw, this house and driveway
should not have been built!
But add a bit of lawn to the plan to increase regulated site area, dropping impervious cover to 20%, and average slope to 20%
(Note that impervious cover outside of the property is counted)
Counting local slopes over 20% as unbuildable does not make sense
We have examples of developments approved with local slopes well over 24%.
A site area with 20% average slope may have up to 20% impervious cover, yet the UMass study says it is unbuildable.
The UMass study’s unbuildable slopes - problems with accuracy and rationale…
Town-owned: 1,359 acres
Other owners: 8,197 acres
Unprotected Open Space
Clark Art Institute:
* within Williamstown
Surface water: 361 acres
RPA 100’ Buffer: 991 acres
100 Year Floodplains
NULA = 9,159 acres, or 31%
* Excluding town-owned
Slopes >= 15%
Water Resources Districts 1 & 2 (minus sewer buffer)
Wellhead Protection District
RPA 200’ buffer
New growth records from 1996 to 2007 with property class of 130 or 132 (new residential lot) joined to the parcels map of 2004
(It doesn’t predict where overall new growth happens)
Average modeled cost on 22 new subdivided parcels compared with all other parcels in NULA
Modeled cost on parcels showing new growth compared to those without (in NULA)
t=1.51, df=286, p<0.2
t=3.58, df=22.78, p<0.002
25% of NULA has a modeled constraint cost under the observed average for the subdivided parcels
Brightest Red = parcels whose modeled development cost is less than the 10 year average of actual subdivided parcels
Ch61 Acres within NULA: 3,384 (37%)
Subtracting Ch61 from NULA…
Parcels <=1.155 in modeled constraint cost, minus Chapter 61 land
“As there is no such thing as a free lunch, there is no such thing as free open space. It comes at a cost—that of forgone income. …
As Mt. Greylock needs to face squarely the tradeoffs in its budget, so does the community need to face more squarely than it has the tradeoff between open space and the quality of municipal services, including education. If we as citizens want open space, as a majority in Williamstown clearly seem to, we must be willing to increase revenue by other means.”
Dumb answer: It’s probably a combination.
Result: a certain rate of new growth becomes a political imperative
Build on unbuilt parcels
Subdivide and build on open land
Mature growth – in the existing footprint:
Improvements (same density)
Infill (increase density)Two kinds of residential growth
Subdivisions averaged19% of annual new growth
Could we satisfy “the growth imperative” without expansive growth?