The Impact of Hurricane Ike on Oyster Reefs in Galveston Bay and ...

<strong>The</strong> <strong>Impact</strong> <strong>of</strong> <strong>Hurricane</strong> <strong>Ike</strong> on OysterReefs in Galveston Bay and On-goingRecovery EffortsJennie Rohrer*, Jennifer Bauer, William Rodney, DavidWestbrook, Lance Robinson -TPWDJoseph Carlin*, Austin Baker, Timothy M. Dellapenna - TAMUG

as an important driver <strong>of</strong> Holocene coastalevolution (Duane 2006). Biokarst featuresdeveloped on beach rock surfaces serve aseco-geomorphic indicators <strong>of</strong> present sealevel variations. Biokarst landscape can alsosufice as a miniaturized ield laboratoryto study several coastal landforms andmodel their development. <strong>The</strong>se landscapesresult from a complex interplay <strong>of</strong> coastal,weathering and ecological processes and<strong>of</strong>fer excellent research area to study thecomplexities present in carbonate coastalenvironments (Spencer and Viles 2002).Bioclastic, carbonate, Quaternary shoredeposits or beach rocks associated withIndian coral reef coasts have mostly beenstudied from geological (Krishna Kumaret al. 2012; Bhonde and Desai, 2011;Bhatt, 2003; Khadkikar and Rajshekhar,2003) and ecological (Rajshekhar andReddy, 2002; Pillai and Appukuttan, 1980)perspectives. Bhatt, 2003 and Bhonde andDesai, 2011 have reported karstiication <strong>of</strong>exposed beach rock surfaces from certainparts <strong>of</strong> Saurashtra coast <strong>of</strong> Gujarat whichlies in close proximity to present reefformations in Gulf <strong>of</strong> Kachchh. <strong>The</strong>se beachrocks lithologically comprise <strong>of</strong> bioclasticlimestone and conglomerate. Bhatt, 2003 hasclassiied these beach rocks as calcirudites(coarse and shell rich variety) which belongto Okha Shell Limestone Member <strong>of</strong> ChayaFormation <strong>of</strong> Middle to Late Pleistoceneage (Bhonde and Desai, 2011). Trenhaile(1987) has considered parts <strong>of</strong> Saurashtracoast as one <strong>of</strong> the typical example <strong>of</strong> littoralzonation in coral limestone coasts <strong>of</strong> warmseas. However, a detailed appraisal <strong>of</strong> suchkarst (more precisely biokarst) features onbeach rock surfaces and their geomorphicevolution from Indian reef coasts stillremains unexplored.This paper documents the differencesobserved in biokarst morphology in two sitesfrom Dwarka coast <strong>of</strong> Gujarat, India andtries to account these differences in the light<strong>of</strong> site-speciic, subtle variations in coastal,weathering and ecological processes that areshaping their development.2. Study AreaTwo coastal locations (Fig.1 see page 235)from Dwarka coast (a subset <strong>of</strong> Saurashtracoast <strong>of</strong> Gujarat) were selected as testcases for this study on biokarst landscapedeveloped on beach rock exposures inOkhamandal area <strong>of</strong> coastal Saurashtra. <strong>The</strong>irst site is located in the northern beach<strong>of</strong> Bet Shankhodhar or Bet Dwarka Islandadjacent to coral reef area and shares theenvironmental characteristics <strong>of</strong> Jamnagar-Okha segment (Merh, 1995) <strong>of</strong> Saurashtracoast. <strong>The</strong> second site is located in thewest-facing rock-shore platform to thesouth <strong>of</strong> Bhadkeshwar Temple in Dwarka.This site is representative <strong>of</strong> environmentalcharacteristics <strong>of</strong> Dwarka-Diu segment<strong>of</strong> the Saurashtra coast. <strong>The</strong> sites wereselected as ideal representations <strong>of</strong> biokarstlandscape after preliminary field visitscarried out in February and April, 2008.3. Materials and Methods3.1. Remote Sensing:For this study, an initial attempt wasmade to visually identify the signatures <strong>of</strong>known biokarst landscape in Okhamandalarea from high spatial resolution (5.8m),multi-spectral images as captured byResourcesat-1 (IRS-P6) LISS-IV imagingsensor on different dates and tidal conditions.Seven LISS-IV MX scenes (precision geo-226 | Transactions | Vol. 35, No. 2, 2013

Bolivar Peninsula

ObjectiveUtilize acoustic techniques to evaluate<strong>Hurricane</strong> <strong>Ike</strong>’s impacts on Galveston Bayoyster reefs and to determine sedimenttransport as a result <strong>of</strong> the storm

• TAMUG R/V CavallaMethods– Edgetech Subbottom Chirp seismic sonar towfish– 3 in. Diameter Vibra-cores

Post-<strong>Hurricane</strong> Pre-<strong>Hurricane</strong> <strong>Ike</strong>East Galveston Bay

Post-<strong>Ike</strong> Pre-<strong>Ike</strong>Pre- & Post-<strong>Hurricane</strong> <strong>Ike</strong>East Galveston Bay

Post- Pre- <strong>Hurricane</strong> <strong>Ike</strong>Mid-Galveston Bay

Post- <strong>Hurricane</strong> <strong>Ike</strong>Mid- Galveston Bay7.5 m100 mReefStorm Deposit

East Galveston Bay CHIRP2 m*100 m* Vertical scale based on 1500 m/s speed <strong>of</strong> sound Storm Deposit

0Percent Composition~30% ~50% ~50%0 20 40 60 80 100 0 20 40 60 80 100 0 20 40 60 80 10000505050100Depth (cm)100~100 cm150100~90 cm ~90 cm150150200200200250250HRVC2EGB2EBVC1250300300Gravel (>2 mm) Sand (2 mm-63 µm) Mud (

East Galveston Bay Core DataDeposit Thickness(CI=25 cm)Sand Fraction(CI=10%)Core LocationsReef

Data courtesy <strong>of</strong> Harris County Flood Control District

Data courtesy <strong>of</strong> Harris County Flood Control District

Summary• Overwash from <strong>Hurricane</strong> <strong>Ike</strong>’s initial storm surge transported anddeposited sand from Bolivar into East Galveston Bay.• Houston Ship Channel acted as a funnel for retreating storm surge throughthe main stem <strong>of</strong> Galveston Bay.• Storm surge ebb, draining inundated lands to the north and east <strong>of</strong> EastGalveston Bay, transported and deposited fine-grained sediment in EastGalveston Bay as waters flowed through the bay exiting Bolivar Roads intothe Gulf.• <strong>The</strong>se data and results are being used to direct oyster reef restorationefforts and develop predictive models <strong>of</strong> storm surge and ebb flowsthroughout Galveston Bay.

Acknowledgements• Funding for this work was provided by the NationalOceanographic and Atmospheric Administration throughGulf States Marine Fisheries Commission.• <strong>The</strong> authors would like to thank the staff <strong>of</strong> Texas Parks& Wildlife Department, Coastal Fisheries Division andTAMUG Marine Science undergraduate students forassisting with data collection.