The impacts of this increase in sea level, will vary from place-to-place and depend on a range of factors, including the human response. To initiate a national assessment of sea level rise impacts, the U.S. Environmental Protection Agency (EPA) is working with state, county, and local officials to identify the lands likely to receive shoreline protection. Those judgments incorporate state policies and regulations, local concerns, land-use data, and general planning judgment. The resulting data distinguishes areas likely to receive shoreline protection (e.g., beach nourishment and armoring with seawalls or dikes) from the areas where shores will probably retreat naturally, either because the cost of holding back the sea is greater than the value of the land, or because there is a current policy of allowing the shore to retreat. This data should be used in conjunction with information contained in the corresponding planning report ("Anticipated Sea Level Rise Response s in the Delaware Estuary of Pennsylvania").
Through the development of data on the likelihood of shoreline protection, this research seeks to (1) improve future assessments of the impacts of climate change through incorporation of a richer understanding of local land use policies and trends; (2) improve the understanding among federal, state, and local levels of government on the effect of current coastal policies on coastal development and conservation; and (3) identify opportunities for policy refinement to facilitate a more efficient response to rising seas that limits the impact on coastal property, wetlands, and recreational resources.
For more information on the goals of the study and this data set, please refer to the Introduction section of the report.
Users should display wetlands and the outside-of-study-area layers on top of this data set. This study only focused on dry land that is either below the 20-foot contour or within 1000 feet of the shore. The response data for lands located outside of the study area or beneath non-tidal wetlands is typically misleading and has not been reviewed. Wetlands data and the outside-of-study- area data layers are available separately.
For additional information on sea level rise planning, see EPA publications available at: <A HREF="http://risingsea.net/ERL> or <http://risingsea.net/ERL/PA.html> or <http://plan.risingsea.net>
The study area for the analysis includes all land below the USGS 20-foot contour (based on the National Geodetic Vertical Datum of 1927) or within 1,000 feet of the shore. Given the prospect of, at most, a 1-meter (3- to 4-foot) rise in sea level over the next century, the 20-foot contour may seem over inclusive. However, the 1:24,000 USGS maps are the only comprehensive set of elevation information for the entire study area and their 10-foot contour interval implies that we had to choose between using the 10-foot or 20-foot contours. The later was chosen for several reasons.
First, although the impacts of rising seas in the "near term" are most relevant to current decision-making processes, it is useful to depict the entire area that could be affected by sea level rise over time. A rise in sea level of 10 feet (3 meters) is possible over the next several centuries, and the 20- foot contour would become the approximate floodplain if such a rise were to occur. Second, because Pennsylvania has only a small amount of extremely low- lying land, a lower elevation threshold would have resulted in a study area that is marginal and ignores its overall land use context. Finally, the vertical and horizontal resolution of the existing elevation contour data is poor. Not only does the data have a wide contour interval, but also under National Mapping Standards, those contours can have a vertical error of plus or minus 5 feet (i.e. the mapped 10-foot contour may really be as low as 5 feet in some places). Thus, a margin of error is required to ensure that our analy
To isolate the study area, a digital representation of the USGS (NGVD) 20-foot contour created by ICF Consulting was superimposed onto the project's base map, Year 2000 Land Use layer (1:2,400). The study area includes portions of Delaware, Bucks and Philadelphia counties, including portions of nineteen 19 municipalities, and the City of Philadelphia.
The Delaware Valley Regional Planning Commission (DVRPC) assessed the likelihood of shoreline protection based on the assumption of an approximately 2 to 3-foot rise in sea level over the next century. Chris Linn evaluated Pennsylvania's response to sea level rise based on (1) state laws, policies, and regulations relevant to sea level rise; (2) current and anticipated land uses; and (3) meetings with county planners to determine local conditions, future plans, and areas of importance that would merit protection from rising seas if economically feasible. During the meetings, Linn asked county planners to review conditions along their coasts and, based on aerial photography, identify areas of economic, cultural, and historic importance that would warrant shoreline protection. They discussed anticipated future land uses and considered how coastlines, future county policies, and planning initiatives could be influenced by sea level rise. .
Using this information, he developed decision guidelines for each county, identifying the likelihood of protection for each type of land use based on the "Year 2000 Land Use" GIS data layer. In some cases, area-specific land use designations were modified where county planners anticipated departures from the general guidelines. For information on the relationship between land use and protection designation as well as site-specific departures from the general approach, please see the technical report that documents this study.
Delaware Valley Regional Planning Commission (DVRPC) staff gave county planners a copy of the masp and report for review. The maps were generally at a scale of approximately 1:100,000. In some cases, minor changes were suggested by county planners based on the substance of the draft report and the 8.5" x 11" maps included therein. Chris Linn implemented each change by selecting the associated polygon(s) that existed within the area and revising the likelihood of protection identified in the layer attributes. Afterwards, he added the new layer to the county project. When the boundaries of the site-specific change did not overlap with the boundaries of land use polygons, he used ArcGIS's edit functions. All edits were then implemented through heads-up digitizing using ArcGIS software.
The fact that the review took place at a scale of approximately 1:100,000 could potentially reduce the resolution of our maps, if the reviewer changes were not as precise as the 1/50 inch assumed by National Map Accuracy Standards. We do not believe that the deterioration was significant. The types of changes that the officials sought were generally for relatively large areas corresponding to the size of parks and new communities. The primary source of error for these maps is not the precision of well-defined boundaries, but rather the uncertainty of how land use will evolve in undeveloped areas.
During this step, the EPA project manager performed a final review of the GIS data and planning report. This review sought to identify map changes that were still needed. These changes usually involved cases where the requested stakeholder review changes had not been implemented correctly, or the GIS data failed to recognize recent development or newly planned development and the resulting map showed an area as less likely to be protected than anticipated (for example, a recent development might show as unlikely to be protected because the land use data did not reflect the presence of residences that would likely protect their land if ever threatened). Using the same approach described in Step 3, Brit Poole and Kevin Wright of ICF Consulting then made the necessary edits and incorporated the data into the GIS project.
Prior to finalizing the data, ICF created a series of "transfer confirmation maps", which the EPA manager reviewed to confirm that the maps were unchanged.
Kevin Wright and Brit Poole of ICF Consulting then developed several geoprocessing models, using ESRI's Model Builder, to "flatten" the data into single state-wide files. The process of flattening the data involves combining or unioning each of the source data layers together to create the single file.
The models take the data layers that collectively create a state's sea level rise protection scenarios and flatten them into a single file. During the flattening process, all files are projected into an appropriate projection for the state. The models assign common attributes of shore protection, an appropriate source, whether or not it is military owned land, county name, state name, and if it is to override wetland data. Counties are flattened individually and then another model is used to combine all counties into a single state layer. Any edits that have been made to the protection scenarios are flattened and all attributes are verified.
Using this "flattened data", ICF created 1:100,000 "comparison maps" for the EPA manager to review. Those maps explicitly highlighted areas that had been erroneously masked (as wetland or high ground) during previous phases of the study, and hence not received the same level of scrutiny as most of the study area. The comparison maps included 1:24,000 TIGER road layer data.
The project manager examined the comparison maps and made three types of corrections.
First, these maps used better elevation and wetlands data (see data at <http://maps.risingsea.net/data.html>) . The new data unveiled areas that had been covered by the draft elevation and wetlands masks, for three reasons. (a) the newer wetlands data often reclassified wetlands to dry land due to development and other land use changes taking place after the older (NWI) wetlands data was created (b) the original elevation mask was created from a draft version of the elevation data and did not include the 1000 foot buffer from the shore; and (c) the original elevation mask mis-located the head-of-tide along the Schuylkill River. The EPA project manager provided the map showing the unveiled areas to Delaware Valley Regional Planning Commission (DVRPC) staff, who corrected the maps to ensure that the designations fit with the decision rules noted by the planners. Second, the project manager looked for lands that would not be protected due to our decision rules, but would be inherently protected by the protection of nearby lands. For example, if a land area were shown as unlikely to be protected but surrounded by land almost certain to be protected, then the protection level for the surrounded polygon would be set to match the nearby area. If an area was on high ground (and thus only at risk of erosion), then only the adjacent property closest to the shoreline had to be at the higher protection category to be changed. On lower ground, where properties could become inundated from any direction, the polygon had to be surrounded by a higher protection level to be changed.
Along relatively high ground shores, where erosion is the primary risk, protecting shorefront developed lands has the direct effect of protecting undeveloped inland farms, whether or not protection is otherwise expected for that land use category. In lower areas, lands can be submerged from the back side even if shorefront homes are protected. For those areas, he edited the protection designation only if a polygon is entirely surrounded by land that are more likely to be protected.
Kevin Wright and Brit Poole of ICF Consulting then implemented the final changes by selecting the corresponding polygons in the final response data and changing the source and scenario response fields accordingly.