Lindy Dingerson, Virginia Institute of Marine Science, College of William and Mary

Lindy Dingerson Lindy is pursuing two masters degrees through a concurrent degree program. One is a masters degree in marine science from the Virginia Institute of Marine Science. The other is in public policy from the Thomas Jefferson Program in Public Policy at the College of William and Mary. Her research focuses on land use and shoreline condition in the context of climate change and sea-level rise.

Click here for a link to Lindy's thesis "Predicting Future Shoreline Condition Based on Land Use Trends, Logistic Regression, and Fuzzy Logic."

Predicting Future Shoreline Condition Based on Land Use Change and Increased Risk Associated with Climate Change
Carl Hershner and Lindy Dingerson, Center for Coastal Resources Management, Virginia Institute of Marine Science

Coastal communities in Virginia have made efforts to preserve natural habitat on the shoreline. Benefits include public access, runoff buffer, spawning habitat, nursery grounds, water quality, and ecosystem health. Protection of these areas is often in the form of restrictions and regulations on land use and permitting requirements. Marshland and riparian buffers face an increased risk of degradation from sea-level rise and storm surge.

The human population along the shoreline of the Chesapeake Bay and its tributaries collectively can make a significant difference in the amount of riparian lands that are preserved. As wetlands move landward and the composition of the shoreline changes, the natural succession of habitat will likely be altered by "armoring" of the shoreline. Armoring includes use of riprap, bulkheads, and other shoreline hardening. These will, by design, hamper the natural processes associated with a rise in sea level. The actions of property owners will, in the long term, affect the amount and quality of the resources within the coastal region. As the land use in the study area continues to change, land types will be converted to other uses. As land use changes, the shoreline condition also can change. By examining these relationships, a more realistic model of future shoreline condition can be developed.

The site of the study will be in South Gloucester County, Virginia in an area called Guinea Neck. This region is characterized by very low relief and a sizable rural population. Guinea Neck residents span a wide range of education levels, income, and property values. The area historically has been home to many watermen and their families, but increasingly, wealthier residents are purchasing waterfront land to build their homes. As land use changes and sea-level rises, actions of property owners in response to this increased risk will affect the amount of natural habitat in Gloucester County. Preliminary assessments of land use change in the study area has shown rapid change in land use. In the five-year time span from 1992 to 1997, Gloucester County as a whole lost 23.5 acres of natural habitat and gained 30.5 acres of developed land. To put this into perspective, 2.13% of its natural habitat was lost, and Gloucester County increased developed land by 115.97%.*

Guinea marshes

Figure 1: Guinea Neck Land Use Change (1992-1997)

 

Probable land use change and the likelihood of significant sea-level rise and climate change in the region, are important factors in the prediction of shoreline condition. Sea-level rise in Virginia has been tracked by NOAA_NOS in the study area for 50 years and the surrounding regions for up to 72 years. Local trends indicate that there may be an acceleration of sea level rise in recent years. Seven stations record sea level trends as well as inter-annual variation. These stations can be put into three general categories: those that have been recording for 72 years, those that have been recording for 49 to 52 years, and those that have been recording for 24 to 27 years. Rough analysis of the mean sea level data indicates that there is considerable variability in the rate of sea level in the Chesapeake Bay region. The 72-year mean sea-level rise is calculated to be 4.42 mm/yr, while the 49 to 52 year estimates range from 3.59 and 3.95 mm/yr.** The stations that have been recording for shorter amount of time, and therefore the mean sea level is averaged over a smaller number of years, indicate a rate of sea-level rise that ranges from 4.85 to 7.01 mm/yr. This would suggest that the rate of sea-level rise could be increasing at a greater rate than recorded previously.

Sea Level Trend

Figure 2: Gloucester Point Mean Sea Level Trend (1950-2000)

In order to adequately assess the change in shoreline condition, an elevation model will be constructed using Digital Raster Graphs (DRGs) with a contour interval of 5 feet. The zero to five-foot intervals will be estimated, and the resulting elevation countours will serve as the base of the model. The Center for Coastal Resource Management has an extensive digital shoreline condition inventory, which includes riparian and littoral zone resources, structures, and shoreline stability. The shoreline condition inventory and information from the Gloucester County government will be incorporated into the base elevation model. The information from the Gloucester County Department of Information Technology/GIS and the Office of the Commissioner will include parcel value (property value or property tax), parcel boundaries, landowner characteristics, and other relevant information. The combination of these databases will allow for investigation of the correlations between land use and shoreline condition.

The land use prediction model 1978 or 1982, and 2001 will be scanned, georectified, and made into a mosaic. Each unit of the mosaic will be digitally classified for land use and the surrounding land uses. The prediction of future land use will be based on the rate and proportion of conversion from one land use to another land use histo nd land use change has taken place in the study area. The project may also evaluate the historical photos from 1994 in order to capture some of the more recent trends in land use in Guinea Neck.

In the face of an increase in sea-level rise landward movement of the marshlands. Once land use change can be predicted, sea level change will be estimated for the low-lying study area. This assumes a constant rate of sea-level rise for the associated time period. Using a constant rate will give us an underestimate of the true impact of sea-level rise on the study area and a conservative estimate of the impact.

The land use change and sea level change model will then be assessed in the context of the correlations between land use and shoreline condition. The result will be an informed estimate of future shoreline condition. In order to ensure protection of riparian benefits, realistic prediction of future conditions is integral to accurately estimating the future shoreline condition.

* Bradley, P., L. Dingerson, K. France, D. Lambert, S. Lerberg, L. Liguori, F. Santos, J.W. Stanhope, A. Walker, and R. Chuenpagdee.  2003. A case study of growth and management planning in coastal Virginia .  In: Coastal Zone 03. Proceedings of the 13th Biennial Coastal Zone Conference, Baltimore, MD, July 13-17, 2003.  NOAA/CSC/20322-CD. CD-ROM. Charleston, SC: NOAA Coastal Services Center.
**Mean Sea Level Trends for stations in Virginia