Abstract:

The shoreline of the Texas Coast was digitized and classified to create an environmental sensitivity index (ESI) dataset. The shoreline was mapped using 2009 Texas Orthoimagery Project (TOP) 0.5m imagery at a scale of 1:2,000, followed by ESI ranking of the entire shoreline based on the 2009 TOP imagery, 2008-2013 low-altitude oblique and orthometric aerial photography from Pictometry, Inc., 2011 low-altitude oblique aerial photography from Red Wing Aerials, and field observations.

Suggested Citation:

Lord, Alistair, Karen Meinstein, William Nichols, Boris Radosavljevic, John Wood, and James Gibeaut. 2024. Environmental Sensitivity Index (ESI) of the Texas coast using 2009 imagery. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/2K9ENKGW

Purpose:

This dataset was developed within the Harte Research Institute for Gulf of Mexico Studies (HRI) for the Texas General Land Office (GLO) Oil Spill Prevention & Response Program, contract #10-094-000-3924, to create up-to-date ESI classifications of the Texas coast. For oil spill response purposes, shorelines are classified according to ESI rankings, which describe the sensitivity of the shore to oil as well as the difficulty and impacts of cleanup activities. Texas and federal partners use the ESI shoreline information to develop contingency plans for protecting the most sensitive environments and to help direct the deployment of limited resources during a spill.

Data Parameters and Units:

List of Fields: Shape_Leng - length of feature in meters (m) ESI - Concatenation of the ESI_1, ESI_2, and ESI_3 fields ESI_1 - Environmental Sensitivity Index Code 1 ESI_2 - Environmental Sensitivity Index Code 2 ESI_3 - Environmental Sensitivity Index Code 3 ESI_CRIT - The most environmentally sensitive ESI ranking specified in ESI_1, ES2_2 and ESI_3. Higher ESI numbers represent more sensitive shoreline habitats, and low numbers represent less sensitive habitats, therefore, the ESI_CRIT value is the highest ESI value from ESI_1, ESI_2 and ESI_3 Shoreline Type (ESI Ranking) ESI No. Shoreline Type 1 Exposed walls and other structures made of concrete, wood, or metal 2A Scarps and steep slopes in clay 2B Wave-cut clay platforms 3A Fine-grained sand beaches 3B Scarps and steep slopes in sand 4* Coarse-grained sand beaches 5 Mixed sand and gravel (shell) beaches 6A Gravel (shell) beaches 6B Exposed riprap structures 7 Exposed tidal flats 8A Sheltered solid man-made structures, such as bulkheads and docks 8B Sheltered riprap structures 8C Sheltered scarps 9 Sheltered tidal flats 10A Salt- and brackish-water marshes 10B Fresh-water marshes (herbaceous vegetation) 10C Fresh-water swamps (woody vegetation) 10D Mangroves

Methods:

Shoreline Delineation: To create the ESI shoreline dataset, the shoreline was manually digitized at a scale of 1:2,000 from 2009 TOP 0.5m imagery obtained from Texas Natural Resources Information System (TNRIS). The shoreline was then dissolved into single part polylines and checked for topological errors. Shoreline Classification: The entire length of digitized shoreline was classified with ESI values in accordance with the ESI scheme (see table below). The shoreline ESI classifications were determined by expert interpretation of the following sources: (1) 2009 TOP imagery; (2) 2008–2013 low-altitude oblique and orthometric aerial photography from Pictometry, Inc.; (3) 2011 low-altitude oblique aerial photography from Red Wing Aerials; (4) wetland maps from the National Wetlands Inventory and the Bureau of Economic Geology; and (5) field observations. Shoreline type interpreters used high-end GIS workstations with large, high-resolution displays to view the multiple imagery sources simultaneously for a single area. Shoreline features with a length of 10 m or greater were captured in the classification. Along many segments of the Texas coast, several shoreline types occur in close proximity in a direction normal to the shoreline, and therefore several ESI rankings are assigned to a shoreline segment where multiple shoreline types are subject to oiling. During the classification process, each length of shoreline was assigned one, two or three ESI rankings depending on how many habitat types existed in proximity to the shoreline in that area. Five fields were ultimately used to store these shoreline types: ESI, ESI_1, ESI_2, ESI_3, and ESI_CRIT. The first ranking was stored in the ESI_1 field, the second ranking (if assigned) was stored in the ESI_2 field and the third ranking (if assigned) was stored in the ESI_3 field. If more than one ranking was assigned, the ESI_1 value always represented the most landward habitat, and each additional ranking was situated progressively seaward. Similarly, the ESI field consisted of a list of the one, two, or three ESI rankings indicated in the ESI_1, ESI_2, and ESI_3 fields and was listed as moving from the most landward shoreline type to the most seaward. The ESI_CRIT field represented the most critical shoreline type that could be damaged or destroyed due to an oil spill. Field Verification Field verifications were performed to aid in classification. The ESI rankings and boundaries were spot checked by boat and from land. Areas were targeted that required additional information due to complexity of shoreline types, significant changes in shoreline types, and for calibration of aerial imagery. In cases where the imagery and ground truth classifications differed or no recent imagery was available, the shoreline classification was changed to the field verified shoreline type.

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