Introduction
Texas has a variety of shoreline types along its coastal bays
and open Gulf of Mexico coast that are constantly shifting
and mostly retreating landward. This retreat results in loss
of private and public property and important natural habitats
such as beaches, dunes, and marshes. To address this problem
the Texas Legislature passed the Coastal Erosion Planning
and Response Act in 1999. This act authorized the Texas
General Land Office (GLO) to conduct a coastal-erosion
response program. In support of the program, Bureau coastal
researchers are identifying and studying eroding areas along
the Gulf of Mexico and coastal bay shorelines of Texas, quantifying
data gleaned from research and creating a comprehensive, digital
database of historical shoreline positions and average annual
rates of shoreline change that are being made available to
the public through the Internet. Funding is provided by the
Texas General Land Office, the Texas Coastal Management Program,
and the National Aeronautics and Space Administration (NASA).
Goals
The goal of the Texas Shoreline Change Project is to develop
a modern shoreline-monitoring and shoreline-change analysis
program that will help guide coastal-erosion and storm-hazard-mitigation
projects along bay and Gulf shorelines. This goal is being
accomplished through digital rectification of historical photographs
to extract past shoreline positions, airborne topographic
lidar surveys for acquiring new and future shoreline data,
selection of ground topographic transects, and establishment
of Global Positioning System (GPS) reference points to support
the monitoring.
Funding from NASA has enabled the Bureau to develop the application of lidar
and geodetic GPS surveys for tracking coastal change. The Bureau owns
and operates an Optech Inc. lidar instrument and is continually developing
new and improved coastal survey techniques. During 2002, we conducted
lidar surveys of the upper Texas Gulf shoreline and the bay shorelines
of West and East Bays in the Galveston Bay System. We have developed
processing techniques for extracting shoreline positions from the
lidar data, as well as mapping sediment volumes alongshore. Spatial
variation in the sand volume and elevation and shape of the beach/dune
system are primary controls on the amount of damage to landward structures
that can occur during storms. This work involves mapping of these
variations and developing new parameters to describe them for use
in hazard mitigation.
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Objectives
and Methods
The TSCP will
be implemented in a series of study areas defined by Gulf shoreline
segment and bay system. The project includes mapping and analysis
of the following Gulf of Mexico shoreline segments: Sabine
Pass to Brazos River, Brazos River to Pass Cavallo, Port Aransas
to North Padre Island (to the north boundary of the Padre Island
National Seashore), and Mansfield Channel to Rio Grande; and the
following bay systems: Matagorda, Copano/Aransas, Baffin,
Corpus Christi, and West and Christmas Bays of the Galveston Bay
System.
For each area,
the tasks required to achieve the following objectives will vary
because of differences in the current status of shoreline data and
because of differences in mapping methods for bay and Gulf shorelines.
The overall objectives and the methods for achieving them include
| 1. |
Digitize
and integrate into a Geographic Information System (GIS) historical
shorelines that were previously mapped and are currently on
paper base maps at the Bureau of Economic Geology. |
| 2. |
Map,
digitize, and integrate into the GIS additional historical shorelines
so that all bays have data from at least the 1930's, 1950's
through 70's, and 1982 and so that Gulf shorelines will have
data at least every 16 years dating back to the 1950's. |
| 3. |
Map
select Gulf shorelines using airborne LIDAR
mapping techniques. |
| 4. |
Map
bay shorelines using georeferenced 1995/96 photography from
the Texas Orthoimagery Program (TOP) and U. S. Geological Survey. |
| 5. |
Establish
topographic ground-survey transects at select locations. |
| 6. |
Compute
shoreline rates of change and, where appropriate, project at
least one future shoreline position. |
| 7. |
Integrate Environmental Sensitivity Index (ESI) shoreline types
with rate of change information and energy level as derived
from fetch, shoreline orientation, and wind climate. |
| 8. |
Compute
statistics for bay systems and shoreline segments related to
rate of change, such as (1) acres of land lost or gained and
(2) average erosion rates for particular shoreline types and
energy levels. |
| 9. |
Work
with GLO staff to identify "critical coastal erosion areas." |
| 10. |
Generate
reports that present and describe the data and explain the general
causes of shoreline change in the area. |
| 11. |
Serve
maps, data, and reports on the Internet. |
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