Galveston Bay 100 km Tide range = 0.65 m Wave ht. = 1.1 m

1961 – post Carla Jamaica Beach Galveston Isl. This is a photograph of the town of Jamaica Beach on western Galveston Island right after Hu Carla in 1961. Carla caused massive washover and erosion along the upper Texas coast. We have not had a large “clear the slate event” like this since 1983 when Hurricane Alicia came ashore. What we have had, however, are smaller tropical storms that, when combined with the ongoing development

2002 Jamaica Beach Galveston Isl. and overall shoreline retreat of the upper coast, have created a lot of pressure to change coastal management rules and laws and to spend private and public money to protect property.

Coastal Studies Group Threshold Conditions for Episodic Beach Erosion along the Southeast Texas Coast James C. Gibeaut, Roberto Gutierrez, and Tiffany L. Hepner Bureau of Economic Geology John A. and Katherine G. Jackson School of Geosciences The University of Texas at Austin Therefore, it is important to examine the effects of sub-hurricane events and to determine the threshold conditions of waves and storm surge that when reached cause significant changes in the beaches from a management point of view. Knowing this threshold will contribute to better mitigation efforts whether they are in the form of coastal management rule changes or project designs.

This is what a 10-foot storm tide looks like plotted on the topography of Bolivar Peninsula. Hurricane Alicia in 1983 caused this level of storm surge on Galveston Isl., but the level of storms I’m talking about here are on the order of 5 or 6 foot surges.

Bermuda Beach on Galveston, Island Even though a storm may not cause wholesale washover and destruction, they can suddenly strand structures on the open beach. Texas has a law called the OBA that gives the public the right to access the beach up to the line of vegetation. This house is obstructing that access and, therefore, may be considered in violation of the law.

Post Tropical Storm Fay 1998 Post Tropical Storm Fay Surfside, Texas A single storm may suddenly place many structures on the “public beach” and therefore cause a coastal management and law enforcement nightmare.

Rollover Pass Beach Nourishment June 1997 Efforts to stem shoreline retreat brought to the forefront by tropical storms since 1996 include small-scale beach nourishment projects such as this one where muddy sand dredged from the ICW behind Rollover pass was placed on the beach.

Pirate’s Beach on Galveston Island And the installation of geotubes such as this project on Galveston Island.

Lidar Topographic Images Gilchrist East Geotube Area 1,000 ft 1997 Nov Rollover Pass Gulf of Mexico 1998 Pre- Frances 1998 Post- Frances 2000 May geotube This is a series of lidar surveys showing how these geotubes have changed the geomorphology of the shoreline. 2001 July geotube QAd496

In an attempt to quantify the effects and determine the conditions of threshold-level storms. We looked at a series of beach profiles since 1994. We also examined open-coast tide gauge data and wave height measurements from an offshore buoy.

These are the tropical systems that affected the northern GOM from 1994 through 1997. Only TS Josephine, highlighted here, caused significant erosion that resulted in emergency response measures. Note that Josephine never got closer than about 500 km to Galveston.

These are the storms that occurred in 1998 These are the storms that occurred in 1998. Only TS Frances, highlighted here, caused significant changes and as I will show you, Frances caused much more damage than Josephine. So 2 of the 8 tropical cyclones that sent waves to the upper Texas coast from 1994 to 1998 caused episodic changes resulting in emergency coastal management procedures. But just last month we had another storm that reached the threshold, TS Fay; Fay tracked just to the west of Galveston Island.

Let’s look at changes in beach profiles caused by these storms Let’s look at changes in beach profiles caused by these storms. The next slides are from the BEG02 profile location at Galveston Isl. State Park.

BEG02 Galveston Island State Park

Galveston Island State Park, Pre-Frances, August 8, 1998, (profile BEG-02)

Galveston Island State Park, Post-Frances, September 16, 1998, (profile BEG-02)

BEG02 Galveston Island State Park

BEG02 Galveston Island State Park

The next location is on Bolivar Peninsula where bluff retreat is cutting into a relict beach ridge.

Bolivar Peninsula, June 13, 2001, (profile GLO-20)

GLO20 Bolivar Peninsula

The last location we will look at is back on Galveston Island at a location of relatively low long-term shoreline retreat and a high and wide dune complex.

GLO04 Galveston Island

Galveston Island, Pre-Frances, August 8, 1998, (profile GLO-04)

Galveston Island, Post-Frances, September 16, 1998, (profile GLO-04)

Alongshore Change This shows the alongshore distribution in profile volume change caused by Josephine. Near San Luis Pass, the beach actually gained for a period of 1-yr following Josephine. This is due to alongshore drift toward the pass.

Shoreline Change Caused by TS Frances Measured by Topographic Lidar

Water Level Standard Deviation (Sigma) Tide gauge records water level once a second for 180 seconds These levels are averaged and standard deviation (sigma) computed Levels greater than 3 x sigma from the average are discarded and new average is determined, which is the reported water level Sigma is directly related to wave height and is a parameter that indicates the amount of wave energy arriving at the gauge

Tropical Storm Josephine 1996 Extreme Area EA= 12.7 m2,hr

Tropical Storm Frances 1998 Extreme Area EA= 36 m2,hr

Storm Comparison

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 3 2 1 Water level Relative to station datum (m) 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 0.5 0.4 0.3 0.2 0.1 0.0 Sigma (m) 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 1.2 0.8 0.4 0.0 Water level times sigma (m2) TS Lili TS Arlene TS Dean TS Josephine TS Frances TS Allison TS Fay HU Opal TS Charley TS Isadore

Conclusions The threshold condition for episodic beach/dune/bluff erosion is an EA of greater than 12. This approximates to water levels that exceed 1 m above sea level with coincident wave heights exceeding 2.5 m for more than 24 hrs. These conditions can occur during distally tracking tropical storms. For example, TS Josephine was 500 km south of Galveston Bay when peak wave heights and water levels occurred.

Conclusions TS Frances (3-times “stronger” than threshold conditions) did not erode and washover dunes that were more than 3-m above the berm tops or where the dune system was more than about 40-m wide. These areas are also where long-term shoreline retreat rates are relatively low. Real-time data from the open-coast tide gauge could be monitored to give an indication of damage to expect. Officials should also be aware of the present condition of the beach and structures to anticipate the effects of the next storm.