Developing 2015 High-Resolution Impervious Cover Estimates for the 52 Towns in the Piscataqua Region Estuaries Partnership: Final Report

Estimates of 2015 impervious cover (IC) for the 52 towns of the Piscataqua Region Estuaries Partnership (PREP) were generated from 2015 1-foot imagery (for the 42 towns in NH) and 2015 1-meter NAIP imagery (for the 10 towns in Maine). The 2015 IC mapping updated previous high resolution mapping developed from 2010 (New Hampshire) and 2011 (Maine) orthophotography for the study area. Impervious features covered 32,462 acres (5.8% of the land area) in the New Hampshire towns and 13,295 acres (5.3% of the land area) in the Maine towns, with a total of 46,634 (5.6% of the land area) acres mapped in the entire study area. The towns with the highest percent impervious cover in 2015 were in New Hampshire, and included Portsmouth (26.7%), New Castle (20.0%), and Seabrook (20.0%). The largest increases in IC between 2010 and 2015 occurred in Rochester, NH (122 acres), Wells, ME (64 acres), and Seabrook, NH (64 acres). Minimal amounts of IC increases occurred in most towns, with the least amounts in Madbury, NH (4 acres), New Castle, NH (2 acres), and Brookfield, NH (2 acres)

Developing 2010 High-Resolution Impervious Cover Estimates for Selected Towns in the Piscataqua Region Estuaries Partnership: Final Report

Estimates of 2010 impervious cover (New Hampshire) and 2011 impervious cover (Maine) were generated to extend the coverage of previous work in Rockingham and Strafford Counties, New Hampshire, to include all of the Piscataqua Region Estuaries Partnership (PREP) footprint. The newly mapped area comprised the town of Alton in Belknap County, New Hampshire, the towns of Brookfield, Wakefield, and Wolfeboro in Carroll County, New Hampshire, and the towns of Acton, Berwick, Eliot, Kittery, Lebanon, North Berwick, Sanford, Shapleigh, South Berwick, Wells, and York in York County, Maine1. With these new data, standardized, high resolution impervious cover estimates are now available for the entire PREP watershed. Impervious features covered 3,026 acres (2.7%) in the New Hampshire towns and 13,612 acres (4.9%) in the Maine towns, with a total of 16,637 (4.3%) acres mapped in the entire study area. As expected, the more urbanized towns of Kittery (11.3%), Sanford (7.9%), Eliot (7.0%), and York (6.2%) contained the highest percentage of impervious cover

Shoreland Buffer Module for GRANIT Data Mapper

The Complex Systems Research Center at the University of New Hampshire enhanced the GRANIT Data Mapper (http://mapper.granit.unh.edu) by incorporating data describing shoreline buffers in New Hampshire. The project supports an ongoing, comprehensive New Hampshire Estuaries Project (NHEP) outreach initiative that seeks to educate municipal decision-makers about the importance of stream buffers in preserving water quality in coastal New Hampshire. It complements these existing outreach efforts by allowing coastal managers, local land use boards, and the general public to readily visualize the spatial extent of current and/or proposed shoreline regulations in their community. The primary data source for the analysis was the high-resolution New Hampshire National Hydrography Dataset (NHHD). Using standard GIS tools, six concentric buffers incrementing in 50’ widths from 50’ to 300’ were generated around stream and shoreline features recorded in the NHHD. To provide the greatest flexibility to users, two data sets were generated at each buffer increment – one representing shorelines and streams classified as either perennial or intermittent, and the second comprising shorelines and only streams classified as perennial. The resulting buffers were merged with the GRANIT surface water data, and acreage by town and subwatershed was calculated for each buffer category. The shoreline buffer data sets were added to the water resources theme of the Data Mapper, thereby providing the public with the ability to view buffers of varying widths in the context of other data layers (including aerial imagery) available through the viewing tool. The associated acreage data tables were added to the water resources theme tool tab. Findings indicated that aggregated at the HUC-12 level, almost 24,000 acres within the Coastal Basin were covered by 50’ buffers when perennial and intermittent streams as well as shorelines were buffered, with over 133,000 acres covered by 300’ buffers. When only perennial streams and shorelines were considered eligible for buffering, the totals declined to just under 17,000 acres (50’ buffers) and over 96,000 acres (300’ buffers)

Coastal Conservation Lands Update (2005)

The Complex Systems Research Center (CSRC) at the University of New Hampshire has developed, implemented, and coordinated the GRANIT GIS clearinghouse since its inception in the mid 1980’s. One of the primary data sets maintained by CSRC and served through the clearinghouse is the Conservation and Protected Lands Data Layer. This data set contains a digital record of parcels of land of two or more acres that are mostly undeveloped and are protected from future development. Smaller parcels that adjoin previously mapped parcels or represent unique features, such as a bog or state-owned boat ramp, may also be included in this data layer. Through the GRANIT Conservation Lands Data Layer Update project, data on current protected lands were collected, reviewed, and processed for 48 communities in seacoast NH, including the 42 towns within the NH Estuaries Project area. GRANIT staff contacted each community’s conservation commission, as well as all quasi-public entities and land trusts active in the region, to solicit updates and additions to the data set. Concurrently, staff from the NH Office of Energy and Planning contacted the state and federal agencies that manage property in the seacoast to request comparable information. Through this collaborative process, 166 new tracts covering over 6,000 acres were added to the database. In addition, information on 122 existing tracts was modified to incorporate the reported corrections

GRANIT Conservation Lands Data Layer Update

The Complex Systems Research Center (CSRC) at the University of New Hampshire has developed, implemented, and coordinated the GRANIT GIS clearinghouse since its inception in the mid 1980’s. One of the primary data sets maintained by CSRC and served through the clearinghouse is the GRANIT Conservation and Protected Lands Data Layer. This data set contains a digital record of parcels of land of two or more acres that are mostly undeveloped and are protected from future development. Smaller parcels that adjoin previously mapped parcels or represent unique features, such as a bog or state-owned boat ramp, may also be included in the data layer. Through the GRANIT Conservation Lands Data Layer Update project, current protected lands data were collected, reviewed, and processed for the 47-community area within the NH Estuaries Project study area. GRANIT staff contacted each community’s conservation commission to solicit updates. Concurrently, staff from the Society for the Protection of NH Forests contacted the active land trusts in the region. Through this collaborative process, 235 tracts covering 6,997 acres were added to the database. In addition to new tracts, information for existing tracts was modified to incorporate any reported corrections. The resulting, updated data set is available to municipal decision-makers, the land trust community, and the general public through the GRANIT web site (www.granit.sr.unh.edu) and the GRANIT Conservation Lands Viewer (www.granitmap.sr.unh.edu)

Impervious Surface Mapping in Coastal New Hampshire (2005)

Estimates of impervious surface acreage in 2005 were generated and compared to prior estimates for 1990 and 2000 for a 48-town region in coastal New Hampshire, including the 42 towns within Zones A and B of the New Hampshire Estuaries Project (NHEP) area. The estimates were based on applying both traditional and subpixel image classification techniques to 30-meter Landsat 5 Thematic Mapper (TM) satellite data, acquired 3 October 2005. The classifications indicated that impervious surface acreage increased from 4.3% (31,233 acres) in 1990, to 6.3% (45,445 acres) in 2000, to 7.4% (53,408 acres) in 2005. At the subwatershed level, the Portsmouth Harbor subwatershed recorded the highest percentage of impervious surface acreage in 1990 with 19.8% coverage (2,310 acres) and in 2000 with 25.5% coverage (2,975 acres), and this finding continued in 2005 with 28.9% (3,364 acres) of the watershed mapped as impervious. An accuracy assessment was applied to the regional data, and indicated an accuracy of 98.3% for the 2005 data, which compared favorably with the assessment of the 1990 effort (98.6% correct) as well as the 2000 data (93.1% correct). These figures reflect the overall presence/absence of impervious surfaces within the randomly selected pixels. The accuracy was further evaluated against April, 2003 Emerge 1-ft. resolution aerial photography to estimate the validity of the predicted range of imperviousness for a second set of randomly selected pixels. This assessment proved disappointing, as only 7% of the pixels sampled predicted the correct impervious percentage range. The data set representing impervious surface acreage in 2005 has been archived in the GRANIT GIS clearinghouse, thereby making it available to the coastal resource community as well as the general public. The data are appropriate for watershed and subwatershed level characterizations. Users are discouraged from accessing these data to support larger scale mapping and applications

Developing Impervious Surface Estimates for Coastal New Hampshire

Future population growth and the corresponding increase in development in the coastal zone of NH are widely recognized as major threats to the integrity of coastal systems and their watersheds. The potential impacts associated with the expansion of developed land, and specifically with increasing amounts of impervious surfaces – rooftops, sidewalks, roads, and parking lots - may include significant changes in water quantity, degradation in water quality, and habitat loss. Because asphalt, concrete, stone, and other impenetrable materials effectively seal the ground surface, water is repelled and is prevented from infiltrating soils. Instead, stormwater runoff flows directly into our surface waters, depositing metals, excess nutrients, organics, and other pollutants into the receiving bodies. In addition to these environmental impacts, increasing levels of imperviousness can dramatically alter our landscapes, as forested and other natural settings are converted to urban/suburban uses. Many of the impacts associated with impervious surfaces had been well documented by studies in other areas of the country. However, comprehensive studies in coastal New Hampshire had not been undertaken. The primary goals of this project were to provide an accurate, current description of the extent of impervious surface coverage in this region, as well as an estimate of change in the amount of “imperviousness” over a recent, ten-year period

Developing 1990, 2000, and 2005 Impervious Surface Estimates for Southern York County, Maine

Estimates of impervious surface acreage in 1990, 2000, and 2005 were generated for an 11-town region in York County, Maine, covered by the Piscataqua Region Estuaries Partnership (PREP). The project extended previous work done in New Hampshire, relying on comparable satellite-based data sources and image processing methodologies. As a result, standardized impervious surface estimates are now available for the entirety of the PREP region. The impervious surface estimates were derived by applying both traditional and subpixel classification techniques to 30-meter Landsat 5 Thematic Mapper (TM) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) satellite image data. The classifications indicated that 3.3% (9,098 acres) of the study area was impervious in 1990, with increases to 5.3 % (14,646 acres) in 2000 and 6.3% (17,394 acres) in 2005. At the subwatershed level, the Portsmouth Harbor subwatershed recorded the highest percentage of impervious surface acreage in 1990, 2000, and 2005 with 7.8% coverage (1,283 acres), 12.3% coverage (2,009 acres), and 14.5% coverage (2,380 acres) respectively. The regional accuracy assessment indicated an overall accuracy of 97.0% for the 1990 data, 93.0% for the 2000 data, and 92.0% for the 2005 data. These results reflect the overall presence/absence of impervious surfaces within the randomly selected assessment pixels. The three data sets have been archived in the GRANIT GIS clearinghouse, thereby making them available to the coastal resource community as well as the general public. The data are appropriate for watershed and subwatershed level characterizations. Users are discouraged from accessing them to support larger scale mapping and applications

Developing 2010 Impervious Surface Estimates for the Piscataque Region Estuaries Partnership Towns

Estimates of impervious surface acreage for 2010 were generated for the 59-town region covered by the Piscataqua Region Estuaries Partnership (PREP). The project extended previous work done in the region for the years 1990, 2000, and 2005 and relied on the same satellite-based data sources and image processing methodologies. As a result, standardized impervious surface estimates are now available for a 20-year time period in the PREP region. The current project mapped impervious surfaces (buildings, pavement, etc.) based on a Landsat 5 Thematic Mapper (TM) image acquired on April 24, 2010. Processing used both traditional and sub-pixel image classification techniques, as described in previous efforts (see Justice and Rubin, 2006 and Justice and Rubin 2003 for a complete processing description). The current study utilized comparable satellite imagery, and applied consistent techniques to map the PREP area for 2010. It should be noted that since the completion of the 2005 project, the U.S. Geological Survey (USGS) has modified its image offerings and now only serves TM data resampled using cubic convolution techniques. (Resampling algorithms are applied as part of the image registration processing, and describe the way output values are assigned to individual image pixels.) This is an important consideration because our previous sub-pixel classifications were conducted on data sets processed using nearest neighbor resampling (which is the recommended approach). While the classification process can be completed using data resampled using alternative techniques, the results may not be as reliable. Since the three previous data sets (1990, 2000, and 2005) were developed using images processed using the preferred nearest neighbor method, and because it is unlikely that features would revert from impervious to non-impervious status, we opted to use the 2005 impervious surface raster as the starting point for the current iteration. Accordingly, the 2005 impervious surface data was used to mask the 2010 TM image with any remaining, unmasked pixels classified using the techniques described in the documents referenced above. A second departure from previous processing streams is that the TM data is now delivered as a georeferenced, terrain-corrected file. This eliminated the requirement for GRANIT to perform these steps locally. The data set has been archived in the GRANIT GIS clearinghouse, thereby making it available to the coastal resource community as well as the general public. The data are appropriate for watershed and subwatershed level characterizations. Users are discouraged from accessing them to support larger scale mapping and applications