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2013-07-25

Commishes hear SARA's LiDAR pitch

By Judith Pannebaker & Carolyn B. Edwards

John Refolo, CMF, a GIS analyst with the San Antonio River Authority, recently outlined the LiDAR (Light Detection and Ranging) mapping procedure and its use as a part of the FEMA RiskMAP program to Bandera County Commissioners.
Refolo had anticipated bringing the county onboard as one of the project's participating sponsors, along with the City of Bandera, Bandera Electric Cooperative and the Economic Development Corporation, among other entities. On Thursday, July 11, he indicated SARA was seeking $50,000 of local funding. The total cost of mapping Bandera County would be $230,000.
As Refolo explained, LiDAR had already partnered locally with the Bandera County River Authority and Groundwater District (BCRAGD). The mapping project would create a database for clarifying flood plain boundaries and more.
Under the direction of the Texas Water Development Board, the LiDAR mapping process uses pulses of light from an airborne sensor to measure the elevation of the ground below. "It gives us four or more elevation points in a square meter," Refolo explained, "yielding high quality elevation data." Parts of Bandera County already mapped include the southeast border from Medina Lake eastward, a small block just north of Bandera along Highway 173, a swath in the center of the county that comes down from Kerr County and a block in the Vanderpool area.
"Eventually the entire state will be mapped," Refolo said, "and this area is the last major frontier in Central Texas."
Once LiDAR mapping is completed, SARA will use the collected data to participate in the FEMA RiskMAP program. This nationwide project uses high quality risk data to increase awareness of flood risk, promote community mitigation action and reduce risk to lives and property.
As a participant in RiskMAP, Bandera County would receive a Flood Risk Database, Flood Risk Report and a Flood Risk Map. Datasets would include flood depth and analysis grids, flood risk assessments and areas of mitigation interest. Bandera County is part of Hydrologic Unit Code (HUC) 8, a classification number in the FEMA program, which includes the Medina River and Leon Creek watersheds. In the county, 5.31 miles of the watershed have been verified, with 399.19 miles still unknown.
The program, which would clarify flood plain boundaries, would help predict the percentage of risk for a location for 10-year to 500-year flood events, Refolo said.
"The LiDAR is data your community can utilize for many years, in various ways, say in emergency management," Refolo told the court.
"How does cedar affect the resolution?" asked Precinct 2 Commissioner Bobby Harris. According to Refolo, the technology penetrates through cedar and thick brush to capture the desired information. "There are ways around cedar," he said.
Other uses for Bandera County would be measuring the amount of sediment that has accumulated in a channel leading into the Medina River and determining how much fuel would be available in the event of wildfires. "This information would determine where to put the most effective firebreaks," Refolo said.
"Once you get the information, you can dream big and use it for many purposes," he added. Other uses include building footprint and land development information. "This aerial mapping won't replace surveying, but will give accurate high precision mapping for planning," Refolo said. "As the data is accumulated, you will find more applications."
Wendy Grams, chief appraiser for the Central Appraisal District, said the CAD has no aerial maps of the county. She believed that the project would make CAD's job easier. "Most properties are behind locked gates. This would make it easier to find new structures that are not on the tax rolls," she said. "That $50,000 could eventually bring as much as $4.2 million in appraisals. The program would pay for itself in a year."
To a query, Refolo admitted that county officials could access the information without contributing to the project. "It's all public information that is stored by the state," he said. However, he commented that the county would have to purchase a software program to access the data.
And, as was indicated, state officials would be more amenable to assisting partners who have put some skin - read "funding" - into the LiDAR project.