USGS National Wetlands Research Center: 2003 Posthurricane Survey of Louisiana and Texas Coasts

Posthurricane Survey of Louisiana and Texas Coasts July 16-17, 2003

Objective:	Survey and document damage from Hurricane Claudette (landfall July 15, 2003) to coastline and adjacent wetlands, uplands, and associated structures along Texas and Louisiana Coast.
Area Surveyed:	Redfish Point, Louisiana, to Padre Island, Texas.
Aircraft:	Cessna 185 amphibious seaplane, N727 (DOI 08)
Pilot:	Thomas C. Michot, Research Wildlife Biologist
Observer:	Christopher J. Wells, Geographer
Affiliation:	USGS – National Wetlands Research Center, Lafayette, Louisiana
Media:	Digital video, digital still photos, digital voice observations linked spatially via GPS/computer system in aircraft

Summary: - impacts minimal to natural resources

shoreline erosion and beach sand displacement, Louisiana and Texas
extensive flooding in some locations
high tides and rough seas, high gulf turbidity
some structural damage in Texas
most vegetation remained intact
bird nesting island in Texas largely unaffected
The shorelines of bay islands and other interior shorelines were largely unaffected with the exception of a few overwashes and erosion areas especially near the path of the northern eye wall
There were occasional marsh balls seen floating in the interior bays and pond
Long parallel striations in exposed sand and shallow water sand flats
digital video, photos, and detailed notes available on request (thomas_michot@usgs.gov)

Background:

Claudette formed in the eastern Caribbean late last week and moved northwest, skirting the northeastern tip of the Yucatan Peninsula in Mexico, then moved across the Gulf of Mexico making landfall about noon July 15 in Matagorda Bay, Texas. The storm strengthened prior to landfall and was upgraded from a tropical storm to a Category 1 hurricane. When it made landfall, Claudette had a well-developed eye wall that was visible on radar images. Reported winds around the eye were 88 mph, but at least one station (Seadrift, Texas) reported sustained winds of 97 mph and gusts up to 110.

On Tuesday July 15 (the day the storm came ashore) we called refuge personnel known to us and to USGS scientist Jim Grace, who has been conducting research for many years in Texas coastal refuges. Obviously, these people had a lot on their minds at that time, but some were still able to direct us to specific areas that were of concern to them. We contacted or sent messages to staff at Anahuac, McFaddin, Brazoria, San Bernard, and Aransas National Wildlife Refuges (NWRs), to the Corpus Christi Field Station of USGS, and to Texas Parks and Wildlife (TXPW). We let them know that we were conducting the survey and that we would be taking video and digital still imagery of the coastline, and requested information on specific points of interest.

Survey Results:

July 16, 2003
We departed from the Lafayette airport at 10:00 CDT Wednesday July 16. Wind was from south 190 degress at 5 knots, cloud cover was 40%. We flew south to Vermilion Bay at about Boston Canal. The effects of Hurricane Claudette in Louisiana were evident along the northwestern shoreline of Vermilion Bay, just north of Redfish Point, in terms of sand having been pushed back from the shoreline into the marsh adjacent to the beach. The USGS camp at Redfish Point looked unaffected. We observed areas of sparse vegetation inside of State Wildlife Refuge that appeared to be recovering deadflats from the marsh dieback episode of the last few years. When we reached the gulf shoreline, just east of Chenier au Tigre, we flew westward parallel to and south of the shoreline. Immediately, we could see fine sand, organic matter, and floating debris pushed up perhaps 5-25 m into the marsh (we will call this “beach sand displacement”). These debris fields were discontinuous; sometimes as much as several miles of contiguous sand splays were evident followed by short spaces in which no effects were evident. For instance, beach sand displacement was significant from Chenier au Tigre to Freshwater Bayou, was less noticeable from Freshwater Bayou to Grand Chenier, then was more noticeable from Grand Chenier to Cameron, etc. We have observed beach sand displacement along the Gulf shoreline following every hurricane or tropical storm. We note that in southwest Louisiana, the sand displacement from Claudette was more substantial than what we had observed in our surveys from Hurricane Lili (October 2002) or Hurricane Bret (July 1999).

The erosion in Louisiana was most easily noticed by the bright whiteness if the sand fans contrasted with the green vegetation. Usually the splay fans were uninterrupted by vegetation, though occasional clumps of Phragmites or various shrubs were not completely overlain by the sediments. Off shore or on the immediate land-water boundary, the effects of the storm were less evident. A closer inspection of the shoreline revealed much darker, probably highly organic silts and clays had been exposed by lifting and transporting of the overlying sand. The wave height and sea level were still higher than normal, so it is quite likely that the shoreline erosion was ongoing at the time of our flight and that large volumes of suspended material would still be transported and redeposited in the unconsolidated near-shore zone.

The exposed substrate resulting from near-shore and shoreline erosion provided abundant feeding opportunities for many birds (brown pelicans, laughing gulls, various terns, white pelicans, white ibis) which were observed foraging near the shoreline along the entire survey. Turbidity was strongly evident all of the way from Chenier au Tigre to Matagorda Bay. This turbidity was evident as far offshore as we could see. Inshore ponds and tidal creeks were highly turbid while bayous and freshwater creeks seemed clear of turbidity, and their outflow was evident from the clear, dark waters which quickly mixed into the brown, silt-laden gulf waters.

In Louisiana, there was a nearly continuous wrack line of grasses, sedges, and plastic or wooden litter close to the shoreline. A frequent feature was flattened vegetation immediately adjacent to the shore extending 2-10 m inland to where the sand was deposited as though the transported material slid over the shoreline vegetation. This variable description of the marsh and shoreline extended from Louisiana well into Texas.

In Texas, hurricane effects were similar to Louisiana until we reached High Island where we saw the first instances of sand transported over the marsh and onto the highway. Cuts or tidal channels running perpendicular to shore extended 50 m or more into the marsh, where the transported material was deposited farther from the shoreline than normal. Most of these channels were closed off at the beach by sedimentation, but a few remained open and those seemed to serve as outlets for the flooded marshes behind the beach ridge.

From Gilchrist Beach onward, we saw increasing amounts of damage to human habitation, especially on the northeastern-facing roofs of beach cottages. Several neighborhoods and residential areas were protected by sausage-shaped tubular fabric devices that were placed along the shoreline adjacent to the beach. These devices seemed to have worked very well in stabilizing the shore and minimizing local damage. We noted, however, that sand plumes extended shoreward into the residential neighborhoods from the protection devices, so obviously some water and sediment flowed over, under, or through the devices.

Near the mouth of the Brazos River we noted an abundance of logs and other woody debris deposited on the beach and back into the adjacent marsh. We did not notice any attached root systems or branches on the trunks, which indicated that they probably came from upstream logging operations. After Hurricane Mitch (1998) we had observed a similar abundance of logs on the Caribbean shoreline near the mouth of rivers in northern Honduras.

On Matagorda Peninsula and Matagorda Island, where Claudette made landfall, we noted continued beach erosion, sand displacement, and turbidity along the shoreline. We saw some dune erosion, especially on the dunes that were close to the shoreline, but most dunes appeared intact. Sediment and debris were carried into the adjacent marsh, especially in areas with low or no dunes. Behind the dunes and beach ridge we saw increased flooding in the marsh (50-100 m inland) and adjacent to the bay (200-300 m inward from the bay shoreline toward the gulf), caused by the storm surge, high tides, and precipitation. We also noted flooding in the streets and residential areas. Most buildings in this area had some roof damage, but only a few buildings had other types of structural damage. At the TXPW facility on Matagorda Island, near Port O’Conner, two buildings were completely demolished and one was partially demolished; all buildings had roof damage (we called Todd Merindino of TXPW and gave him a detailed report, per his earlier request). The FWS facility on the south end of the island (Aransas NWR) was largely undamaged except for some missing roof shingles and window screens. Several white-tailed deer family groups, including a fawn, were observed on Aransas NWR.

We had been requested by FWS (Mike Lange) to survey Dressing Point Island, an important bird breeding area in Matagorda Bay, near Carolla Pass, which is between Matagorda Peninsula and Matagorda Island. The vegetation and substrate appeared undamaged. There were two towers (possibly windmills, navigation structures, or observation towers) that were blown down. Nesting and foraging birds were very abundant on and around the island (brown pelicans, gulls, and egrets). We saw one dead brown pelican.

Surprisingly, shoreline damage on Matagorda Peninsula and Matagorda Island was similar to what we had observed up the coast. Shoreline damage quickly tapered off as we surveyed south of the point of landfall. South of Aransas Pass, impacts were not noticeable, and the beach appeared normal. We surveyed Mustang Island and the north end of Padre Island, about five miles south of Kennedy Causeway bridge (17 miles south of the Mustang Island airport). We saw no additional impacts so we ended the survey at that point and flew to Corpus Christi airport.

July 17, 2003
On our return flight to Lafayette we tracked along the inside and surveyed the back sides of the islands, the shoreline marshes, and the shallow bays. Seagrass beds, mangroves, and emergent marsh vegetation seemed largely intact with some exceptions. There was a great difference in hurricane effects between the back bay islands and the Gulf shore. There were only a few areas where erosion, deposition, and shell/sand displacement occurred in any significance. Those were in a few isolated locations in the immediate area of the eye wall path and perhaps 10 miles north, especially in the upper Matagorda Bay area. Also in this area were the only “marsh balls” observed. These were spherical chunks of marsh about 0.5-1.0 m in diameter that had broken free and tumbled downwind so that they ended up floating in the bay over the seagrass beds. We did not see as many as with hurricanes in Louisiana; marsh balls were noticed in abundance there following Hurricane Andrew (1992) and to a much lesser extent, following Hurricane Lili (2002).

Other curious phenomena were long striations or “skid marks” on the islands and peninsulas, evident on unvegetated sand flats and shallow-water with sand bottoms . Some were obviously lines left from dragged debris because the dragged object was visible at the end of the skid mark. The origin of others was not evident because no object was visible. Some were up to 5-10 m wide with parallel lines, others smaller (1 m), possibly from marsh balls. These striations were limited to the area of the eye wall path, i.e., Matagorda Island and Matagorda Peninsula.

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