A geographic information system (GIS) based determination of estuarine and marine wetland and shoreline changes in the Galveston Bay estuary from 1995 to 2002

The purpose of this study was to identify and quantify estuarine and marine wetland and shore changes circa Galveston Bay Estuary (GBE) from 1995 to 2002 by using aerial photography and GIS mapping techniques. Aerial photographs in digital format were acquired from Texas Natural Resource Information System (TNRIS) and the Houston Galveston Area Council (HGAC); these photographs were selected because the images were taken at the time period desired, existed in digital formats at resolutions of 1 m or greater, and were in coordinate systems that were already in or could be properly aligned and georeferenced. Maps for each of thirty quadrangles that include estuarine and/or marine habitats around the GBE were created, depicting wetlands and shorelines for the years 1995 and 2002 as well as changes between the two time periods. Polygons representing different habitats in 1995 were drawn while working at a scale of 1:4,000 or greater. Maps of habitats in 2002 and maps showing changes from 1995 to 2002 were produced by modifying individual 1995 polygons to document boundary shifts or habitat changes from 1995 to 2002. All resulting maps were constructed at 1:24,000 scale in UTM NAD 83 coordinate system to match USGS quad maps. Areas of each habitat in 1995 and 2002 and changes between the two years were calculated in acres and comparisons were made. There were four objectives developed to be examined by the creation of the new set of maps for GBE. They were to determine habitat changes during the time period in question, effectiveness of mapping technique, where differences in change occurred, and what type (i.e. erosion, development, accretion, etc.) of change occurred. My analyses of these maps indicated that there were 117,670 acres of estuarine wetlands and 21,983 acres of unconsolidated estuarine and marine shores present in 1995. In 2002, these values changed to 116,534 acres of estuarine wetlands and 21,630 acres of estuarine and marine shores. The rate of wetland loss was estimated as 162 acres per year or 0.1% of all wetlands annually from 1995 to 2002. This rate has slowed from the previous rate of 405 acres per year or 0.4% in 1979 and remained the same as the 161 acres per year or 0.1% reported in 1993 for the GBE. Further, the results of my analyses indicated that losses from direct human influences (e.g. development, dredging, and filling) were less than losses associated with natural processes like erosion and subsidence.