Land Development Risk Around Southern Sebago Lake, Maine: Identifying at-Risk Parcels

Methods This analysis uses GIS to determine a numeric value between 1 and 100 for an undeveloped land parcel’s relative risk for development and reduction in water quality. The analysis includes parcels in the Town of Standish that are within a 5km radius of the PWD intake pipes and within 1km of the lake shore. The development risk is calculated for each undeveloped parcel that is not currently under indefinite conservation by the PWD. The analysis uses the Maine Office of GIS land parcel map (GISVIEW.MEGIS.Parcels_new), and development status from the Standish assessor’s 2015-16 owners list (http://www.standish.org/ assessor). Sebago lake, roads, and elevation are represented by the Maine Office of GIS lake and pond layer (water_poly), road layer (gisview.E911.NG_ROADS), and a Lidar slope raster (Maine DEM 2 SLOPE). Additionally a map of future growth areas produced by Standish was digitized to create “growth area,” “transition area” and “critical area” designations (http://www.standish.org/sites/standishme/ files/uploads/generalized_future_land_use_map.pdf). The PWD intake location was approximated from the street address and its location in the 1971 amendment to the law governing water quality in Sebago Lake (Maine State Legislature 1971). Land use type was classified as developed, undeveloped, or conserved by PWD, and converted to a raster with 2m pixels. Raster layers were generated for distance from roads, distance from the lake, location in a growth, transition, or critical area and distance from the nearest developed pixel. A summary layer was generated to combine and weight all factors (Table 1). The values of all cells in each undeveloped land parcel were averaged. This Parcels were further weighted by distance to the lake shore and to the PWD intake. Pixels within 0.5km of either were multiplied by three, and pixels between 0.5km and 1.0km were multiplied by two to determine parcel risk values (Table 2). The map is projected in UTM zone 19N using NAD83. Results and Discussion The areas containing the most at risk parcels are the most builtup parts of Standish and those near other shore-line development. These parcels are close to developed parcels and roads, and are relatively flat, making them very likely parcel to be developed. The largest “very high risk” parcel it is located very close to the lake and the PWD intake (just north) showing that its development poses a greater risk to water quality (Figure 1).