Geological Circular 77-1—Shoreline Changes on Mustang Island and North Padre Island (Aransas Pass to Yarborough Pass): an Anal

TEXAS BCR. OF ECON. GEOLOGY GEGL* CIFX. GEOLOGICAL "7 "7~ -4 CIRCULAR I I \

SHORELINE CHANGES ON MUSTANG ISLAND AND NORTH PADRE ISLAND (ARANSAS PASS TO YARBOROUGH PASS) AN ANALYSIS OF HISTORICAL CHANGES OF THE TEXAS GULF SHORELINE

BY ROBERT A. MORTON AND MARY J. PIEPER

BUREAU OF ECONOMIC GEOLOGY THE UNIVERSITY OF TEXAS AT AUSTIN , AUSTIN TEXAS 78712 * ns,Cfc,l¥fc«L>jpre-3K jxifjfi j/px*tg-=*» IF"ft /*"-*** uT*I*^, W. L. FISHER, DIRECTOROR 1977 JUL 111977

ATLANTIC RfCHFIELD COMPAf^ 6EOSCIENCE LIBRi GEOLOGICAL "7 "T -i CIRCULAR / /~ I

SHORELINE CHANGES ON MUSTANG ISLAND AND NORTH PADRE ISLAND (ARANSAS PASS TO YARBOROUGH PASS)

AN ANALYSIS OF HISTORICAL CHANGES OF THE TEXAS GULF SHORELINE

BY ROBERT A. MORTON AND MARY J. PIEPER

BUREAU OF ECONOMIC GEOLOGY THE UNIVERSITY OF TEXAS AT AUSTIN AUSTIN, TEXAS 78712 W. L. FISHER, DIRECTOR RECEIVED JUL 111977 1977 ATLANTIC RICHFIELD COMPANY 6EOSCIENCE LIBRARY

n(D C cO 5 B 8 9 Contents

Abstract 1 Yarborough Pass 15 Introduction 2 Changes inshorelineposition 15 Purpose and scope 2 Late Quaternary time 15 General statement onshoreline changes 2 Historic time 16 Acknowledgments 3 1860-82 to 1937 16 Historical Shoreline Monitoring— General Methods 1937 to 1956-60 18 and Procedures Used by the Bureau of Economic Geology 4 1956-60 to 1969-70 20 Definition 4 1969-70 to 1974-75 21 Sources of data 4 Nethistoric changes (1860-82 to 1974-75) 21 Procedure 4 Changes inpositionofvegetation line 23 Factorsaffecting accuracy of data 4 1937 to 1956-60 23 Original data 4 1956-60 to 1969-70 23 Topographicsurveys 4 1969-70 to 1974-75 25 Aerialphotographs 5 Factors affecting shoreline and vegetation line Interpretationof photographs 5 changes 26 Cartographic procedure 6 Climate 26 Topographic charts 6 Storm frequency and intensity 26 Aerialphotographs 6 Destructive forces and storm Measurements and calculatedrates 6 damage 27 Justification of methodand limitations 6 Changes in beachprofile during and Sources and nature of supplemental after storms 27 information 7 Local and eustatic sea-level conditions 28 Monitoringof vegetationline 7 Sediment budget 29 Previous work 8 Human activities 30 Present beach characteristics 9 Evaluationof factors 30 Textureand composition 9 Predictions of future changes 32 Beachprofiles 10 References 33 Human alterations of naturalconditions 12 Appendix A. Determination of changes in shoreline AransasPass 12 and vegetationline 38 Corpus Christi Water Exchange Pass 14 Appendix B. Tropical cyclones affecting the Texas Corpus Christi Pass, Newport Pass, Packery Coast,1854-1973 44 Channel 15 Appendix C. List of materials andsources 45

List of Illustrations

Figures 8. Relative changes in position of shoreline and 1. Index map of the Texas Gulf shoreline 3 vegetationline at selectedlocations 24 2. Generalizeddiagram of beach profile 8 9. Generalized diagram of sediment transport 3. Beach profiles, Aransas Pass to Yarborough directions between Aransas Pass and Pass, recordedJune 17-18, 1975 11 YarboroughPass 31 4. Location of significant coastal structures and alterations of Aransas Pass and adjacent areas 13 Tables 5. Proposed sea-level changes during the last 1. Short-termshoreline changes between1860-66 20,000 years 16 and 1937 nearAransasPass 18 6. Location map of points of measurement and 2. Maximum hurricane surge height recorded beach profiles 17 along the central Texas Coast,1916 to 1975 19 7. Net shoreline changes between Aransas Pass 3. Short-term shoreline changes between 1937 and YarboroughPass 22 and 1960 near YarboroughPass 20 Changes Mustang (Aransas Pass to YarboroughPass) ShorelineAn Analysis Of HistoricalOn ChangesIslandOf TheAndTexasNorthGulfPadreShorelineIsland

Robert A.Morton and Mary J.Pieper

Abstract

Historical monitoring along Mustang and Net changes on north Padre Island were north Padre Islands records the nature and magni- predominantly accretionary;however, net erosion tude of changes in position of the shoreline and was recorded from Packery Channel southward for provides insight vegetationline and into the factors a distance of about 7 miles. Minimum net erosion affecting changes. those was 50 feet, whereas maximum net erosion was feet, Documentation of changesis accomplished by 500 and averagenet erosion was 220 feet. The the compilation of shoreline and vegetation line shoreline from 6.5 to 9 miles north of the position from topographic maps, aerial photo- Kleberg/Kenedy county line experienced only graphs, and coastal charts of various vintages. minor net changes of 25 feet or less.Theremaining Comparison of shoreline position based on topo- shoreline of north Padre Island experienced net graphic charts (dated 1860-82) and aerial photo- accretion ranging from less than 10 feet to 275 graphs (taken in 1937, 1956-60, 1969-70, and feet; net accretion, which increased southward 1974-75) indicates short-term changes of accretion along the island, averaged 140 feet. Net rates of and erosion along the Gulf shoreline between change were also low alongnorth Padre Island. Net Aransas Pass and Yarborough Pass. Erosion pro- erosion ranged from less than 1foot to 5.4 feet per duces a net loss in land, whereas accretion pro- year and averaged 2.0 feet per year. Similarly, net duces a net gain in land. Comparison of the accretion varied from less than 1foot to 3.0 feet vegetationline based on the aforementioned aerial and averaged1.5 feet per year. photographs indicates short-term cycles of retreat related to storms (primarily hurricanes) and re- Because of limitations imposed by the tech- covery during intervening years of low storm nique used, rates of change are subordinate to incidence. trends or direction of change. Furthermore, values determined for long-term net changes should be Long-term trend or direction of shoreline used in context. The values for rates of netchange changes averaged over the 115-year time period of are adequate for describing long-term trends;how- this study indicates that Mustang Island has ever, rates of short-term changesmay be of greater experienced net erosion with two exceptions.Net magnitude than rates of long-term changes, partic- accretion adjacent to Aransas Pass, which de- ularly in areas where both accretion and erosion creasedfrom 1,600 feetnear the south jetty to 350 have occurred. feet about 2 miles south of the pass, was caused principally by inlet migration and concomitant Major and minor factors affecting shoreline outbuilding of the north end of the island prior to changes include: (1) climate, (2) storm frequency jetty construction in 1889. Net accretion also and intensity, (3) local and eustatic sea-level occurred about 1.5 miles north of the Nueces/ conditions, (4) sediment budget, and (5) human Kleberg county line attendant with the infilling of activities. The major factors affecting shoreline Packery Channel. Theremainder of MustangIsland changes along the Texas Coast, including Mustang recorded net erosion ranging from 75 to 350 feet and north Padre Islands, are relative sea-level and averaging 225 feet. Net rates of change, conditions, compactional subsidence, and changes however, were low along Mustang Island except in sediment supply. Changes in position of the where net accretion ranged from approximately 3 vegetationline are primarily related to storms. feet per year to 14 feet per year. Net erosion on the island ranged from less than 1footper year to Studies indicate that changes in shoreline and 3.8 feet peryear and averaged 2.0 feet per year. vegetation line onMustang andnorth Padre Islands 2

are largely the result of natural processes,perhaps effects is requisite to avoid or minimize physical expedited by man's activities. A basic compre- and economic losses associated with development hension of these physical processes and their and use of the coast.

Introduction

The Texas Coastal Zone is experiencing adjacent Matagorda Bay area, a cooperative study geological, hydrological, biological, and land use by the Bureau of Economic Geology and the Texas changes as aresult of natural processes and man's General Land Office. In this study, basic tech- activities. What was once arelatively undeveloped niques of historical monitoring were developed; expanse of beach along deltaic headlands, penin- results of the Matagorda Bay project were pub- (1975). sulas, and barrier islands is presently undergoing lished by MeGowen and Brewton Competition for considerable development. space In 1973, the Texas Legislature appropriated exists among such activities as recreation,construc- funds for the Bureau of Economic Geology to tion and occupation of seasonal and permanent conduct historical monitoring of the entire 367 residential housing, industrial and commercial miles of Texas Gulf shoreline during the development, and mineral and resource 1973-1975 biennium. Work versions of base maps production. (scale 1:24,000) for this project are onopen file at the Bureau of Economic Geology. Results of the Studies indicate that shoreline and vegetation project are being published in a series of reports; line changes on Mustang and north Padre Islands each report describes shoreline changes for a and along other segments of the Texas Gulf Coast particular segment of the Texas Gulf Coast. This are largely the result of natural processes. A basic report covering the Gulf shoreline from Aransas comprehension of these physical processes and Pass to Yarborough Pass (fig. 1) is the seventh in their effects is requisite to avoid or minimize that series. physical and economic losses associated withdevel- opment and use of the coast. General Statement on Shoreline Changes

The usefulness of historical monitoring is Shorelines are in a state of erosion, accretion, based on the documentation of past changes in or are stabilized either naturally or artificially. position of shoreline and vegetation line and the Erosion produces a net loss in land, accretion prediction of future changes. Reliableprediction of produces a net gain in land, and equilibrium future changes can only be made from determina- conditions produce no net change. Shoreline tion of long-term historical trends. Topographic changes are the response of the beach to a maps dating from 1860 provide a necessary exten- hierarchy of natural cyclic phenomena including sion to the time base, an advantage not available (from lower order to higher order) tides, storms, through the use of aerial photographs which were sediment supply, and relative sea-level changes. not generally available before 1930. Time periods for these cycles range from daily to several thousand years. Most beach segments Purpose and Scope undergoboth erosion and accretion for lower order events,no matter what their long-term trendsmay In 1971, the Bureau of Economic Geology be. Furthermore,long-term trends can be unidirec- initiated a program inhistorical monitoring for the tional or cyclic; that is, shoreline changes may purpose of determining quantitative long-term persist inone direction,either accretion or erosion, shoreline changes. The recent acceleration in Gulf- or the shoreline may undergo periods of both front development provides additional incentive erosion and accretion. Thus, the tidal plane for adequate evaluation of shoreline characteristics boundary defined by the intersection of beach and and the documentation of where change is occur- mean high water is not in a fixed position ring by erosion and by accretion, or where the (Johnson, 1971). Shoreline erosion assumes shoreline is stable orin equilibrium. importance along the Texas Coast because of active loss of land, as well as the potential damage or The first effort in this program was an destruction of piers,dwellings,highways,and other investigation of Matagorda Peninsula and the structures. 3

Figure 1.Index map of the TexasGulf shoreline.

Acknowledgments and Karen White. Composing was under the direction of Fannie M.Sellingsloh. Assistance in preparation of this report was S. provided by L. W. Epps, M. Amdurer, J.L.Chin, Cooperation of personnel with the U. and S. L. Waisley. Drafting was under the super- Army Corps of Engineers, GalvestonDistrict aided in the acquisition of materials and information. vision of J. W. Macon. Cartographic work was TheTexas General Land Office and Texas Highway performed by D. F. Scranton. Critical review was Department provided access to some of the aerial provided by L.F. Brown,Jr.,and C.G. Groat. The photographs.Meteorological data were providedby report was typed by Elizabeth T. Moore and the National Climatic Center and the National Sharon Polensky and edited by Kelley Kennedy Hurricane Center. Monitoring General Methods And Procedures Used By The HistoricalBureau OfShorelineEconomic Geology

Definition Factors AffectingAccuracy of Data

Historical Shoreline Monitoring is the Documentation of long-term changes from documentation of direction and magnitude of available records, referred to in this report as shoreline change through specific time periods historical monitoring, involves repetitive sequential using accurate vintage charts, maps, and aerial mapping of shoreline position using coastal charts photographs. (topographic surveys) and aerial photographs.This is in contrast to short-term monitoring which Sources of Data employs beach profile measurements and/or the Basic data used to determine changes in mapping of shoreline position on recent aerial shoreline position are near-vertical aerial photo- photographs only. There are advantages and dis- graphs and mosaics and topographic charts. advantages inherentinboth techniques. Accurate topographic charts dating from 1850, available through the Department of Commerce, Long-term historical monitoring reveals trends National Oceanic and Atmospheric Administration which provide the basis for projection of future (NOAA), were mapped by the U. S. Coast Survey changes, but the incorporation of coastal charts using plane table procedures. Reproductions of dating from the 1850's introduces some uncer- originals are used to establish shoreline position tainty as to the precision of the data. In contrast, (mean high water) prior to the early 19305.Aerial short-term monitoring can be extremely precise. photography supplemented and later replaced However, the inability to recognize and differen- regional topographic surveys in the early 19305; tiate long-term trends from short-term changesis a therefore, subsequent shoreline positions are decided disadvantage. Short-term monitoring also mapped on individual stereographic photographs requires a network of stationary, permanent and aerial photographic mosaics representing a markers which are periodically reoccupiedbecause diversity of scales and vintages. Thesephotographs they serve as a common point from which future show shoreline position based on the sediment- beach profiles are made. Such a network of water interface at the time the photographs were permanent markers and measurements has not taken. been established along the Texas Coast and even if a network were established,it would take consid- Procedure erable time (20 to 30 years) before sufficient data were available for determination of long-term Thekey to comparison of various data needed trends. to monitor shoreline variations is agreement in scale and adjustment of the data to theprojection Because the purpose of shoreline monitoring of the selected map base; U. S. Geological Survey is to document past changes in shoreline position 7.5-minute quadrangle topographic maps and to provide basis for the projection of future (1:24,000 or 1inch = 2,000 feet)are used for this changes, the method of long-term historical purpose. Topographic charts and aerial photo- monitoring is preferred. graphs are either enlargedorreduced to the precise scale of the topographic maps. Shorelines shown OriginalData on topographic charts and sediment-water interface mapped directly on sequential aerial photographs Topographic surveys.— Some inherent error are transferred from the topographic charts and probably exists in the original topographic surveys aerial photographs onto the common base map conducted by the U.S. Coast Survey [U. S.Coast mechanically with a reducing pantograph or and Geodetic Survey, now called National Ocean optically with a Saltzman projector. Lines Survey]. Shalowitz (1964, p. 81) states "...the transferred to the common base map are compared degree of accuracy of theearly surveys depends on directly and measurements are made to quantify many factors, among which are the purpose of the any changesinposition with time. survey, the scale and date of the survey, the 5 standards for survey work then in use, the relative source of error in determining shoreline position. importance of the area surveyed, and the ability However, only the central portion of the photo- and care which the individual surveyor brought to graphs are used for mapping purposes, and his task." Although it is neither possible nor distances between fixed points are adjusted to the practical to comment on all of these factors,much 7.5-minute topographic base. less attempt to quantify the error they represent, in general the accuracy of a particular survey is Meteorological conditions prior to and at the related to its date;recent surveys are more accurate time of photography also have a bearing on the than older surveys. Error can also be introduced by accuracy of the documented shoreline changes. For physical changes in material on which the original example, deviations from normal astronomical data appear. Distortions, such as scale changes tides caused by barometric pressure, wind velocity from expansion and contraction of the base and direction, and attendant wave activity may material, caused by reproduction and changes in introduce errors, the significance of which depends atmospheric conditions,can be corrected by car- on the magnitude of the measured change. Most tographic techniques. Location of mean high water photographic flights are executed during calm is also subject to error. Shalowitz (1964, p.175) weather conditions, thus eliminating most of the states "...location of the high-water line on the effect of abnormalmeteorological conditions. early surveys is within a maximum error of 10 meters and may possibly be much more accurate InterpretationofPhotographs than this." Another factor that may contribute to error Aerial photographs.— Error introduced by use in determining rates of shoreline change is the of aerial photographs is related to variation in scale ability of the scientist to interpret correctly what and resolution,and to optical aberrations. he sees on the photographs. The most qualified aerial photograph mappers are those who have Use of aerial photographs of various scales made the most observations on the ground. Some introduces variations in resolution with con- older aerial photographs may be of poor quality, comitant variations in mapping precision. The especially along the shorelines. On a few photo- sediment- water interface can be mapped with graphs, both the beach and swash zone are bright greater precision on larger scale photographs, white (albedo effect) and cannot be precisely whereas the same boundary canbe delineated with differentiated; the shoreline is projected through less precision on smaller scale photographs. Stated these areas, and therefore, some error may be another way, the line delineating the sediment- introduced. In general, these difficulties are re- water interface represents less horizontal distance solved through an understanding of coastal pro- on larger scale photographs than a line of equal cesses and a thorough knowledge of factors that width delineating the same boundary on smaller may affect the appearance of shorelines on scale photographs. Aerial photographs of a scale photographs. less than that of the topographic basemap used for compilation create an added problem of impre- Use of mean high-water line on topographic cision because the mapped line increases in width charts and the sediment-water interface on aerial when a photograph is enlarged optically to match photographs to define the same boundary is the scale of the base map.In contrast, the mapped inconsistent because normally the sediment-water line decreases in width when a photograph is interface falls somewhere between high and low reduced optically to match the scale of the base tide. Horizontal displacement of the shoreline map. Furthermore, shorelines mechanically mapped using the sediment-water interface is adjusted by pantograph methods to match the almost always seaward of the meanhigh-water line. scale of the base map do not change in width. This displacement is dependent on the tide cycle, Fortunately, photographs with a scale equal to or slope of the beach, and wind direction when the larger than the topographic map base cangenerally photograph was taken. The combination of factors be utilized. on the Gulf shoreline which yield the greatest horizontal displacement of the sediment-water Optical aberration causes the margins of interface from mean high water are low tide photographs to be somewhat distorted and shore- conditions,low beach profile, and strong northerly lines mapped on photographic margins may be a winds. Field measurements indicate that along the 6

Texas Gulf Coast, maximum horizontal displace- However, problems do arise when rates of change ment of a photographed shoreline from mean are calculated because: (1) time intervals between high-water level is approximately 125 feet under photographic coverage arenot equal; (2) erosion or these same conditions. Because the displacement of accretion is assumed constant over the entire time the photographed shoreline is almost always sea- period; and (3) multiple rates (^^,where n ward of mean high water, shoreline changes deter- represents the number of mapped shorelines) can mined from comparison of mean high-water line be obtained at any given point using various and sediment-water interface will slightly under- combinations of lines. estimate rates of erosion or slightly overestimate rates of accretion. The beach area is dynamic and changes of varying magnitude occur continuously. Each CartographicProcedure photograph represents a sample in the continuum of shoreline changes and it follows that measure- Topographic charts.— -The topographic charts ments of shoreline changes taken over short time are replete with a 1-minute-interval grid; transfer of intervals would more closely approximate the the shoreline position from topographic charts to continuum of changes because the procedure the base map is accomplished by construction of a would approach continuous monitoring. Thus, the 1-minute-interval grid on the 7.5-minute topo- problems listed above are interrelated, and solu- graphic base map and projection of the chart onto tions require the averaging of rates of change for the base map.Routine adjustments aremade across discrete intervals. Numerical ranges and graphic the map with the aid of the 1-minute-interval displays are used to present the calculated rates of latitude and longitude cells. This is necessary shoreline change. because: (1) chart scale is larger than base map scale; (2) distortions (expansion and contraction) Where possible, dates when individual photo- in the medium (paper or cloth) of the original graphs actually were taken are used to determine survey and reproduced chart, previously discussed, the time interval needed to calculate rates, rather require adjustment; and (3) paucity of culture than the general date printed on the mosaic. alongthe shore provides limited horizontal control. Particular attention is also paid to the month, as well as year of photography; this eliminates an Aerial photographs.—Accuracy of aerial apparent age difference of one year between photographmosaics is similar to topographic charts photographs taken inDecember and January of the in that quality is related to vintage; more recent followingyear. mosaics are more accurate. Photograph negative quality, optical resolution, and techniques of Justification of Method and Limitations compiling controlled mosaics have improved with time; thus, more adjustments are necessary when The methods used in long-term historical working with older photographs. monitoring carry a degree of imprecision, and trends and rates of shoreline changes determined Cartographic proceduresmayintroduce minor from these techniques have limitations. Rates of errors associated with the transfer of shoreline change are to some degree subordinate inaccuracy position from aerial photographs and topographic to trends or direction of change; however, there is charts to the base map. Cartographicprocedures do no doubt about the significance of the trends of not increase the accuracy of mapping; however, shoreline change documented over more than 100 they tend to correct the photogrammetric errors years. An important factor in evaluating shoreline inherent in the original materials such as distor- changes is the total length of time represented by tions and optical aberrations. observational data. Observations over a short period of time may produce erroneous conclusions MeasurementsandCalculatedRates about the long-term change incoastal morphology. For example, it is well established that landward Actual measurements of linear distances on retreat of the shoreline during a storm is accom- maps can be made to one-hundredth of an inch panied by sediment removal; the sediment is which corresponds to 20 feet on maps with a scale eroded, transported, and temporarily stored off- of 1inch = 2,000 feet (1:24,000). This is more shore. Shortly after storm passage, the normal precise than the significance of the data warrants. beach processes again become operative and some 7 of the sediment is returned to the beach. If the sequential shoreline positions are seldom exactly shoreline is monitored during this recoveryperiod, parallel, in some instances it is best to provide a data would indicate beach accretion; however, if range of values such as 10 to 15 feet per year. As the beach does notaccrete to itsprestorm position, long as users realize and understand the limitations then net effect of the storm is beach erosion. of the method of historical monitoring, results of Therefore, long-term trends are superior to short- sequential shoreline mapping are significant and term observations. Establishment of long-term useful in coastal zone planning and development. trends based on changes in shoreline position necessitates the use of older and less precise Sources and Nature of SupplementalInformation topographic surveys. The applicability of topographic surveys for these purposes is discussed by Sources of aerial photographs, topographic Shalowitz (1964,p.79) who stated: charts, and topographic base maps used for this report are identified in appendix C. Additional "There is probably littledoubt but that information was derived from miscellaneous the earliest records of changes inour coastline reports published by the U. S. Army Corps of that are on a large enough scale and in Engineers and on-the-ground measurements and sufficient detail to justify their use for quantitative study are those made by the Coast observations including beach profiles,preparedas a Survey. These surveys were executed by part of this investigation. Laws relating to the competent and careful engineers and were improvement of rivers and harbors are synthesized practically all based on a geodetic network in House Documents 379 and 182 (U. S. Army which minimizedthe possibilityof large errors Corps Engineers,1940, c). being introduced. They therefore represent the of 1968 best evidence available of the condition of our coastline a hundred or more years ago,and the Relative wave intensity, estimated from courts have repeatedly recognized their com- photographs, and the general appearance of the petency inthis respect...." beach dictate whether or not tide and weather bureau records should be checked for abnormal Because of the importance of documenting conditions at the time of photography. Most flights changes over a long time interval, topographic are executed during calm weather conditions,thus charts and aerial photographs have been used to eliminating most of this effect. Onthe other hand, study beach erosion in other areas. For example, large-scale changes are recorded immediately after Morgan and Larimore (1957), Harris and Jones the passage of a tropical storm or hurricane. For (1964), El-Ashry and Wanless (1968), Bryant and this reason, photography dates have been McCann (1973), and Stapor (1973) have success- compared with weather bureau records to deter- fully used techniques similar to those employed mine the nature and extent of tropical cyclones herein. Previous articles describing determinations prior to the overflight.If recent storm effects were of beach changes from aerial photographs were obvious on the photographs, an attempt wasmade reviewed by Stafford (1971) and Stafford and to relate those effects to a particular event. others (1973). Considerable data were compiled from Simply stated, the method of using topo- weather bureau records and the U. S. Department graphic charts and aerial photographs, thoughnot of Commerce (1930-1974) for many of the dates absolutely precise, represents the best method of aerial photography. These data, which include available for investigating long-term trends in wind velocity and direction and times of predicted shoreline changes. tidal stage, were used to estimate qualitatively the effect of meteorological conditions on position of Limitations of the method require that the sediment-water interface (fig. 2). emphasis be placed first on trend of shoreline changes with rates of change being secondary. Monitoring of VegetationLine Although rates of change from map measurements can be calculated to a precision well beyond the Changes in position of the vegetation line are limits of accuracy of the procedure, they are most determined from aerial photographs in the same important as relative values; that is, do the data manner as changes in shoreline position with the indicate that erosion is occurring at a few feetper exceptionthat the line of continuous vegetationis year or at significantly higher rates. Because mapped rather than the sediment-water interface. 8

Figure 2.Generalizeddiagramofbeachprofile.

Problems associated with interpretation of vegeta- appearance of the vegetation line on photographs. tion line on aerial photographs are similar to those For example, the vegetation line tends to be ill encountered with shoreline interpretationbecause defined following storms because sand may be they involve scale and resolution of photography as deposited over the vegetation or the vegetation well as coastal processes. Inplaces, the vegetation may be completely removed by wave action. The "line" is actually a zone or transition,the precise problem of photographic scale and optical resolu- position of which is subject interpretation; in to tion in determination of the position of the other places the boundary is sharp and distinct, vegetation line is opposite that associated with requiring little interpretation. The problems of the mapping vegetation line are not justrestricted to a determination of the shoreline. Mapping geographic area butalso involve changes with time. vegetation line is more difficult on larger scale Observations indicate that the vegetationline along photographs than on smaller scale photographs, a particular section of beach may be indistinct for particularly in areas where the vegetation line is a given date, but subsequent photography may indistinct,because larger scale photographs provide show a well-defined boundary for the same area, or greater resolution and much more detail. Fortu- vice versa.In general, these difficulties are resolved nately, vegetation line is not affected by processes through an understanding of coastal processes and such as tide cycle at the time the photographs were a thorough knowledge of factors that affect taken.

PreviousWork

Originating in the middle 1800's and con- In 1933, the Texas Highway Department tinuing to the present,numerous studies of Aransas made a field reconnaissance to evaluate the feasi- Pass have beenconducted by the U.S. Army Corps bility of constructing a highway on Padre Island. of Engineers. Earlier studies monitored inlet migra- Bailey (1933) described foredune damage and the tion,changesinchannel width,changesindepth of location of washover channels on north Padre water within the channel and over the channel- Island caused by three hurricanes (June, August, mouth bars, and shoreline changes on northern and September 1933) that made landfall while that Mustang Island attendant with jetty construction. study was inprogress. Furthermore,beach profiles surveyed by the U. S. Army Corps of Engineers (1968-1974) document A regional inventory of Texas shores was short-term Gulf shoreline changes adjacent to conducted by the U.S. Army Corps of Engineers Aransas Pass. (1971b); however, between Aransas Pass and 9

Yarborough Pass no areas of critical or non-critical Three isolated points of accretion on north Padre erosion were identified. Island ranged from 1to 4 feet per year.

Hunter and others (1972) compared Behrens and Watson (1974) studied changes 1860-1882 topographic surveys with more recent in and around the Corpus Christi Water Exchange photographs and concluded that maps and aerial Pass on Mustang Island during its first year of measurable shoreline changes were no consistently operation. Seasonal and short-term net changes in evident on north and central Padre Island. It was shoreline included accretion adjacent both their opinion that relatively stable conditions the to extended to about the southern limit of Big Shell north and south jetties; however, farther south the Beach or approximately 30 miles north of beach experiencednet erosion. Mansfield Channel. Changes in the Gulf shoreline have also been In a recent study, Seeligand Sorensen (1973) mapped by the Bureau of Economic Geology as presented tabular data documenting mean low- part of the Environmental Geologic Atlas of the water shoreline changes along the Texas Coast; Texas Coastal Zone. The active processes maps of values calculated for the rates of shoreline change that publication series delineate four shoreline along Mustang and north Padre Islands were states: (1) erosional, (2) depositional, (3) equilib- included in their report. Their technique involved rium, and (4) artificially stabilized. Although the the use of only two dates (early and recent); the Gulf shoreline conditions presented in the Coastal change at any point was averaged over the time Atlas and in the publications of the historical period between the two dates.Cycles of accretion monitoring project are in general agreement, there and erosion were not recognized and few inter- are certain areas where the acquisition of more mediate values were reported; thus, in certain recent data indicates conditions that are different instances, the data are misleading because of from those presented in the Coastal Atlas. The technique. Furthermore, data retrieval is difficult shoreline conditions published in the present because points are identified by the Texas coor- report are both current and quantitative rather dinate system. Rates of erosion in the area of than qualitative; therefore where there is disagree- interest determined by Seelig and Sorensen (1973, ment, the conditions published herein supersede p. 14-15) range from 0 to -36 feet per year with the conditions presented on the active processes most values falling between -1 and -2 feetper year. maps of the Coastal Atlas.

Present Beach Characteristics

Texture and Composition 1958). Black opaques, hornblende, leucoxene, tourmaline, and zircon are the most common Beach and dune sediment on Mustang and heavy minerals with minor amounts of epidote, north Padre Islands have been the subject of garnet, rutile, and staurolite (Bullard, 1942; numerous investigations (Bullard, 1942; Shepard Shepardand Moore, 1955). and Moore, 1955, 1956; Beal and Shepard, 1956; Curray, 1956; Mason, 1957; McKee, 1957; Padre Island can be divided into a southern Bradley, 1957; Mason and Folk, 1958;Rogers and sedimentologic province, characterized by basaltic Strong, 1959; Hsu, 1960;Shepard,1960a;Shepard hornblende and pyroxene from the Rio Grande, and Young, 1961; Mcßride and Hayes, 1962; and a northern sedimentologic province, charac- Hayes, 1965; Milling and Behrens, 1966; Garner, terized by more durable heavy minerals typical of 1967; Andrews and van der Lingen, 1969; rivers to the north (Bullard, 1942; Shepard and Dickinson and Hunter, 1970; Watson, 1971; Moore, 1955). The two sedimentologic provinces Hunter and others, 1972; Moiola and Spencer, are separated by a transition zone of approxi- 1973; Foley, 1974). The beach between Aransas mately 10 miles (Hayes, 1965) located along Pass and Yarborough Pass comprises well-sorted, central Padre Island. North Padre Island falls fine to very fine sand composed primarily of predominantly within the northern province with quartz, some feldspar,andheavy minerals (Bullard, only the southernmost 8 miles located in the 1942; Shepard and Moore,1955; Mason and Folk, transition zone (Hunter and others,1972).Shell on 10 north Padre Island is restrictedprimarily to Donax except during and immediately following storm sp. Say.It varies from less than1percent to nearly conditions. Therefore, unless beach profiles are 50 percent of the sediment content. The referenced to a permanent, stationary control 50-percent shell content is found on Little Shell point on the ground, comparison of profiles at Beach which falls within the northernmost limits different times may be very similar, but the of the transition zone (Watson, 1971). absolute position of the beach can be quite different. Thus,a beach profile may appear similar Accumulations of tar ranging from less than1 (except after storms) for a longperiod of time,but inch to several feet in diameter are frequently the entire profile may shift seaward (accretion) or found on segments of the coast that are not landward (erosion) during the sameperiod. periodically cleaned. The Writers' Roundtable (1950) referred to "great amounts of asphalt on Except in previously active hurricane wash- the beach" of Padre Island. Geyer and Sweet overs, abandoned tidal inlets, and active blowout (1973) concluded that the tar occurs naturally areas, extant dunes on Mustang Island and north from offshore seeps. Padre Island are relatively continuous and well vegetated.Individual dunes attain heights up to 50 Beach Profiles feet onnorth Padre Island;however, dune heights of 20 to 25 feet are more common. On Mustang The Gulf shoreline of Mustang and north Island,dune heights average from 15 to 20 feet. Padre Islands is characterized by a broad (approximately 200 to 300 feet wide), gently sloping Because foredunes are the last natural defense (between l°3o' and 3°) forebeach. Thebackbeach against wave attack, experiments on dune growth is generally horizontal, but along some segments were conducted by the Corps of Engineers in the the backbeach slopes slightly toward the dunes. washover areas of Packery Channel, NewportPass, Daily changes in beach appearancereflect changing and Corpus Christi Pass (Gage, 1970). These conditions such as wind direction and velocity, experiments utilized junk car bodies and wood wave height, tidal stage, and the like. Accordingly, picket (snow) fences to trap sand and initiate dune beach profiles are subject to change depending on formation. Results of the experiments were en- beach and surf conditions that existed when couraging with regard to establishment of low measurements were recorded. In general, the most (generally less, than 5 feet) dunes in less than 2 seaward extent of a beach profile is subjected to years. However, the project dunes were destroyed the greatest changesbecause in this area breakpoint by Hurricane Beulah in 1967, emphasizing the bars are created, destroyed, and driven ashore. inadequacy of low unstabilized dunes as protection Under natural conditions,the landward portion of against hurricane surge and wave attack. a beach profile is affected only by spring and storm tides of more intense events such as tropical Additional experiments concerned primarily cyclones. With increased use of the beach, how- with dune development using fences and grass ever, minor alterations in beach profiles occasion- plantings on northPadre Island were conducted by ally may be attributed to vehicular traffic and the Gulf Universities Research Consortium in beach maintenance such as rakingand scraping. cooperation with the Corps of Engineers (Otteni and others,1972;Dahl and others,1974). Beach profiles presented in figure 3 were constructed using the method described by Emery Beach profile is controlled primarily by wave (1961). Theprofiles, considered typical of certain action. Other factors determining beach charac- segments of Mustang and north Padre Islands, teristics are type and amount of beach sediment represent beach conditions on June 17 and 18, available and the geomorphology of the adjacent 1975. Beach profiles in the vicinity of Aransas Pass land (Wiegel, 1964). In general, beach slope is and south of Yarborough Pass have also been inversely related to grain size of beach material surveyed by the Galveston District, U.S. Army (Bascom, 1951). Thus, beaches composed of fine Corps of Engineers (1968-1974). Comparison of sand are generally flat. Beach width along the beach profiles and beach scour patterns on Texas Coast is primarily dependent on quantity of Galveston Island by Herbich (1970) suggests that sand available. Beaches undergoingerosion due to a beach condition (breaker bar spacing and size)may deficit in sediment supply are narrower than be similar over a relatively long period of time beaches where there is an adequate supply or 11

Figure 3. Beachprofiles,AransasPass to YarboroughPass,recordedJune 17-18,1975. Locationsplottedon figure 6. 12

surplus of beach sand. For example,the beach on central Padre Island where there is a greater supply south Padre Island is not as wide as the beach on of sand.

Human Alterations Of Natural Conditions

AransasPass mendations of 1871 and also proposed construction of a jetty from San Jose Island parallel to the Aransas Pass was extremely unstable during proposed jetty on MustangIsland. The erection of the middle to late 1800's. Relocation of the a dam across Corpus Christi Pass had also been channel axis, changes in channel depth of several proposed since the pass had decreased in size feet, and shifting of the inlet-mouth bars accom- during the previous 30 years (U.S. Army Corps of panied southerly migration of the inlet. Frequent Engineers, 1880). In May 1880, the work was changes caused navigation problems for trade begun but in August a storm removed most of the vessels traveling over the outer bars and through improvement. the inlet. Not only were the changes frequent but they occurred rapidly as well. It was reported that By 1882, six groins extending from an during one week in 1853, the channel migrated 870-foot breakwater (fig. 4) alongthe channel face from the north to the south breakers. The new of Mustang Island, a revetment along the same channel provided 9 feet of clearance but the old area, and a 450-foot groin from Harbor Islandinto channel shoaled to 4 feet (U. S. Army Corps of Lydia Ann Channel had been built,and construc- Engineers, 1853). Between 1851 and1890,depths tion was proceeding on the south (or Government) over the inlet-mouth bars varied from 7 to 10.5 jetty. When work was suspendedin1885,the jetty feet (U. S. Army Corps of Engineers,1890). was 5,500'feet long; 1,500 feet of this was shore work. During June 1885, the depthof the channel Erosion of the north end of Mustang Island increased to 11 feet and the rate of southward and deposition on the south end of SanJoseIsland migration was reduced (U. S. Army Corps of progressed at a rate of 260 feet per year (U. S. Engineers,1886). However, the jetty was damaged Army Corps of Engineers, 1900). Because of the by ahurricane inSeptember 1885,and the channel importance of Aransas Pass as a route for shoaled. commercial vessels and because of the continuous changes in channel position and depth,numerous A survey made in 1888 revealed that the jetty efforts were made by governmental and private had subsided an average of 6.2 feet in the 3 years interests to stabilize the channel and maintain following its construction;more than 1,750 feet of navigable depths. the total length was submerged. During the same time, the channel shoaled to 8.5 feet (U.S. Army The first attempt at improvement was made Corps of Engineers, 1888). The breakwater and in 1868 when a 600-foot dike of brush- and sand fences on MustangIslandhad beendestroyed, stone-filled cribs was constructed on the southern and the groins had settled 9 to 38 feet into the end of San Jose Island to close a swash channel sand. The revetment along the channel face had (U. S. Army Corps of Engineers,1871). This dike reduced erosion of Mustang Island to 70 feet per was destroyedby storms within 3 years. year even though it had been undermined and isolated from the shoreline which had eroded 100 Recommendations following a survey of the to 200 feet to the south. pass in 1871included construction of groins and a revetment on the northern extremity of Mustang During 1888 and 1889, the revetment was Island and a jetty extendinginto the Gulf from the lengthened to 2,725 feet and strengthened by an northeast side of the island (U.S. Army Corps of 18-inch-thick wall of riprap from the bottom of Engineers, 1871). Between 1871 and 1879, the the channel to the high-water line. These additions channel depth remained about 7 feet, which succeeded in stabilizing the northern tip of prevented the entrance of deeper draft vessels; Mustang Island (U.S. Army Corps of Engineers, therefore, trade in the area was severely curtailed. 1900). On March 22, 1890, the Aransas Pass A report based on an 1879 survey (U. S. Army Harbor Company was incorporated as a result of Corps of Engineers, 1879) reiterated the recom- the limited annual appropriations and because 13

Figure 4. Locationofsignificant coastal structures and alterationsof Aransas Pass and adjacent areas people believed that proposed improvements for The old Government jetty which crossed the Galveston Harbor would receive any forthcoming channel at an angle of 45 degrees and obstructed large appropriations. In exchange for certain rights further operations was partially removed by and privileges granted by Congress, the company dynamite in 1897. The explosion scattered rocks was to provide a deep-water channel (20 feet) over a considerable area of the channel (Welker, through Aransas Pass by 1899 (U. S. Army Corps 1899). Examination revealed that the Nelson jetty of Engineers, 1897-1898). In 1892, the south (or had been extensively damaged and partially Nelson) jetty was constructed 1,800 feet along the removed by storms and teredos. The north jetty, southern edge of Aransas Pass. The north (or which had not been completed,also suffered storm Haupt) jetty was constructed between August damage. 1895 and September 1896. This jetty extended 5,750 feet shoreward from the 15-foot contour The responsibility of the north jetty was line to a point 1,500 feet offshore from San Jose transferred to the Federal Government in 1899 Island.Only 1,250 feet of the jetty was completed after the Aransas Pass Harbor Company was unable breakwater with the remainder being either core to obtain a 20-foot channel required by contract. with partial capping or just core (U. S. Army Corps Although erosion of the north end of Mustang of Engineers,1897-1898). Island had been eliminated, accretion of San Jose 14

Island continued and the pass narrowed by 300 Extreme hurricanes in 1916 and 1919 caused feet between 1899 and 1900. In turn, flow extensive damage along the central Texas Coast. velocities increased as revealed by the landward The 1919 storm caused the channel to shoal from and seaward 650-foot shift of both the inner and 21to 14.5 feet, and by June 1920, the channel was outer 18-foot contours (U.S. Army Corps of still only 17 feet deep; during the nextyearit was Engineers,1900). redredged to 24.5 feet (U.S. Army Corps of Engineers, 1920). Another hurricane in June 1921 By1900, the outer 1,200 feet of the jettyhad caused shoaling of Aransas Pass to 22.5 feet (U.S. settled or had been washed away,and the inner Army Corps of Engineers,1921). portion, though stable, had been breached in several places (U. S. Army Corps of Engineers, Four spurs projecting at right angles from the 1900). In addition, a second channel, 600 feet north jetty into Aransas Pass were constructed in wide and 6 feet deep, had broken through the 1922 in order to straighten the channel and move shoal between San Jose Island and the landward it southward away from the jetty (U.S. Army end of the north jetty (U. S. Army Corps of Corps of Engineers, 1922). This improvement was Engineers, 1913). During 1902, a mound of riprap relatively successful,but the channelmaintained its was emplaced to connect the jetty with San Jose depth of 22.5 feet for several years (U. S. Army Island; gaps in the north jetty were also repaired Corps of Engineers,1924). (U. S. Army Corps of Engineers,1902). By 1932, the channel between the jettieshad In 1902, the narrow and sinuous channel been dredged to 30.7 feet (U.S. Army Corps of through Aransas Pass was navigable only by boats Engineers, 1932). Both north and south jetties with less than 10 feet of draft. Construction were repaired in 1936 (U.S. Army Corps of continued slowly on the north jetty, and it was Engineers, 1936) possibly as a result of the 1934 completed, as originally planned, in June 1906 hurricane. In 1937, the channel was deepened to (U. S. Army Corps of Engineers,1905, 1910).One 34.5 feet between the jetties and 35 feet over the year later the channel was navigable by boats outer bar (U. S. Army Corps of Engineers, 1937). drawing only 8 feet of water, and it was apparent In 1947, these areas were again deepened to 33 that the north jetty alone was ineffective in feet and 39 feet,respectively (U. S. Army Corps of maintaining a deep channel. Engineers, 1947-1948), and in 1958, the channel was 38 feet deep between the jetties and 39 feet Construction of a south jetty,extendingfrom over the bar (U.S. Army Corps of Engineers, the tip of Mustang Island roughly parallel to the 1958). north jetty,had been proposed since 1887.Owing to rapid channel deterioration, work on this jetty Hurricane Carla (1961) caused extensive was begun in March 1908. The channel deepened damage to the jetties but the damage was later and widened starting at the inner end and pro- repaired (U. S. Army Corps of Engineers, 1962b). gressing outward as the south jetty was extended. The channel was also redredged to 39 feet (U.S. By 1909, a navigable channel 12 feet deep ex- Army Corps of Engineers, 1962c). Hurricane tended across the outer bar (U. S. Army Corps of Beulah caused only minor damage but restoration Engineers,1910). of the channel to its project depth required dredging of over 605,000 cubic yards of sediment The partially completed south jetty was (U. S. Army Corps of Engineers,1968b). slightly damaged by the August 1909 hurricane and attendant high tides that inundated the ends of A 1968 act provided for a deepening of the Mustang and San Jose Islands. As construction channel to 45 feet between the jetties and 47 feet continued, the south jetty was extended from over the outer bar. These depths were attained as 4,000 feet in 1910 to 6,400 feet in 1913,and with reported in 1972 (U. S. Army Corps of Engineers, additional dredging, the channel was deepened to 1972a). 20 feet (U. S. Army Corps of Engineers,1913).By 1916, the 7,385-foot south jetty was completed Corpus Christi Water ExchangePass (U. S. Army Corps of Engineers, 1917) and the channel was 22.5 feet deep (U. S. Army Corps of Intermittent opening and closing of Packery Engineers,1916). Channel, Newport Pass, and Corpus Christi Pass 15

gave impetus to construction of a jettied channel however,the project was soon abandoned because across Mustang Island connecting Corpus Christi of rapid siltation and closure (Lockwood and Bay with the open Gulf. The fish or water Carothers, 1967). The inability of these inlets to exchange pass was completed August 1972. maintain tidal exchange for extendedperiods may Detailed changes of shoreline position andbathym- be due to the deepening of Aransas Pass (Collier etry in and around the pass duringits first year of andHedgpeth,1950; Price,1952).The threepasses operation were studied by Behrens and Watson are reopened periodically by hurricanes but close (1974); analyses of tidal hydraulics and inlet withina relatively short period of time. stability in the first 6 months were alsoconducted by Defehr and Sorensen (1973). Maximum dis- YarboroughPass charge recorded at the fish pass was about 4,000 cubic feet per second. Maximum tidal current Initial dredging of Yarborough Pass, also velocities averaged about 3 feet per second; how- referred to as Murdoch's Landing Pass in the ever, most measured flow velocities were less than literature (Gunter, 1945; Writers' Roundtable, 2 feet per second (Behrens and Watson, 1974). 1950; Collier and Hedgpeth,1950),was authorized by the Texas Legislature around 1931 (Bailey, Corpus Christi Pass,NewportPass, 1933) for the purpose of improving water circula- Packery Channel tion in the Laguna Madre. Dredging commenced December 5, 1940, and was completed in April Three passeslocated within a 4-mile segment 1941, but the pass remained open only for 5 of southern Mustang Island have functioned inter- months before it was closed by littoral processes mittently as natural tidal inlets (fig. 6). Documen- (Breuer, 1957). Additional attempts were made to tation through theliterature of their migration and open the pass in November 1942, May 1944, periods of closure is difficult because Corpus November 1944, and February 1952 (Breuer, Christi Pass, identified on the U.S. Coast Survey 1957);however, all attempts were unsuccessful and topographic chart (1881-1882), was later referred the pass has remained closed. Dunes established to as Packery Channel. The northernmost and naturally in the vicinity of the abandoned pass are middle passes are now Corpus Christi Pass and vegetated and the fore-island area appears to be Newport Pass, respectively. Beginning in 1939, approaching conditions that existed prior to attempts were made to reopenCorpus Christi Pass; dredging.

Changes In Shoreline Position

Late Quaternary Time Vertical accretion of the barrier islands attendant with sea-level rise was augmented by eolian pro- Significant changes in sea level have occurred cesses. Lateral accretion accompanied landward along the central Texas Coast during the past 10,000 years (Shepard, 1956, 1960b). Ridge and transport of sediment from the inner shelf as well swale topography from abandoned beach ridges, as transport of shell and sediment from the bottom visible on aerial photographs along the northern of Corpus Christi Bay andLagunaMadre.Prograda- part of Mustang Island, attests to the fact that tion of Mustang Island and Padre Island, respec- accretion was predominant after sea level reached tively, into Corpus Christi Bay and Laguna Madre its stillstand position about 3,000 years before was associated with hurricane washover and eolian present (fig. 5). Ridge and swale topography on southern Mustang Island and north Padre Island processes. has not been preserved because of inlet migration and eolian processes resulting from a semiarid During the past several hundred years, condi- climate. Radiocarbon methods (Shepard, 1956, tions that promoted seaward accretion have been 1960b) provide dates for the interpretation of altered both naturally and more recently to some sea-level positions along the central Texas Coast extent by man. Consequently, sediment supply to prior to stillstand. the Texas Coast has diminished and erosion is prevalent. The effects of these changes, as well as Barrier island development was initiated the factors related to the changes, are discussed in about 6,500 years ago (Shepard, 1956, 1960b). following sections. 16

Figure 5. Proposed sea-level changes during the last 20,000 years; sketch defines use of Modern and Holocene. After Fisher andothers (1973).

Historic Time Rate (ft/yr) Designation

Shoreline changes and tabulated rates of 0-5 minor change between 1860-82 and 1974-75, at 51 5-15 moderate arbitrary points spaced 5,000 feet apart along the 15-25 major map of Mustang and north Padre Islands (fig. 6), >25 extreme presented appendix Excludingpoints are in A. in 1860-82 to 1937 —Of the 51 points proximity to passes, Mustang Island has experi- monitored for this time interval, 28 experienced enced three periods of erosion (1860-82 to 1937, accretion and 23 recorded erosion (appendix A). 1956-60 to 1969-70,and 1969-70 to 1974-75) and The greatest accretion occurred on MustangIsland one period dominated by accretion (1937 to attendant with migration of Aransas Pass and 1956-60). In contrast, north Padre Island has concomitant outbuilding of the north end of the undergone two periods dominated by accretion island. Accretion also occurred in the same area (1882 to 1937 and 1956-60 to 1969), one period after construction of the south jetty (table 1). of erosion (1969 to 1974-75), and one period of Maximum accretion was 1,650 feet (point 1) and both erosion and accretion (1937 to 1956-60). minimum accretion was 75 feet (point 4). During this same period, however, the shoreline of The following classification of rates of change Mustang Island was dominated by erosion. is introduced for the convenience of describing Between points 5 and 27, erosion ranged from 25 changes that fall within aparticular range: to 450 feet and averaged about 120 feet. From 17

Figure 6.Locationmap ofpoints ofmeasurementand beachprofiles,AransasPass to YarboroughPass 18

Table 1.Short-termshoreline changes between1860-66 and1937 near Aransas Pass.

Dist. Rate Dist. Rate Dist. Rate 'oint Time ft ftper yr Time ft ftper yr Time ft ft per yr

1 1860-66- -+ll5O +31.9 1899- -+775 +32.3 1923- --275 -19.6 1899 1923 1937

2 1867-1899 + 375 +11.7 +600 +25.0 + 50 + 3.6 - 3 75 - 2.3 +550 +22.9 + 25 + 1.8 - 4 1867- -+175 + 3.1 -100 7.1 1923 - - - 5 25 -<1.0 50 3.6 - 6 -200 3.5 +150 +10.7 - 7 -350 6.25 +250 +17.9 - 8 -450 8.0 +325 +23.2 point 27 to Yarborough Pass, however, the shore- Landing (Yarborough Pass), whereas vegetated line accreted between 25 and 250 feet. With the dunes on north Padre Island sustained only exception of minor erosion at point 37, accretion moderate damage (Bailey, 1933). averagedabout 140feet. 1937 to 1956-60— Shoreline changes on Anomalous accretion at point 21 (550 feet) Mustang Island were dominated by accretion was associated withthe closing of Packery Channel between 1937 and 1956-60, but changes on Padre and establishment of a continuous shorelinein that Island were variable. Of the 51 points monitored, area. Therefore, the quantitative data should not 24 experienced accretion, 22 underwent erosion, be construed as an accretion seaward of the general and 5 recorded no change. trend of the shoreline. Similarly, moderate erosion recorded at point 22 reflects realignment of the On Mustang Island, points 1 through 8 shoreline by elimination of the downdrift offset generally experienced both minor accretion and that existed when Packery Channel was perma- erosion. Average accretion for this segment was 75 nently openand functioned as a tidal inlet. feet while average erosion was 25 feet.Frompoint 9 to point 22,accretion ranged from a minimum of Between 1860 and 1937, the central Texas 25 feet to a maximum of 175 feet and averaged Coast was affected by numerous hurricanes approximately 110 feet. The shoreline was rela- (appendix B) which either madelandfall inthe area tively stable at points 20 and 21 where no change or were of sufficient size to cause high tides and wasrecorded. wind damage in the area even though they made landfall elsewhere. Surge heights of 11.1 and 5.0 Shoreline changes between points 23 and 39 feet, respectively, were recorded during the 1919 were dominated by erosion. Minimum erosion of and 1933 hurricanes (table 2). Bailey (1933) less than 10 feet occurred at points 27 and 36 and described damage resulting from three storms that maximum erosion of 275 feet was recorded at made landfall on Padre Island in July, August,and point 30;average erosion for this shoreline segment September 1933 and documented 60 feet of was approximately 115 feet. Minor accretion of 50 foredune erosion at the Nueces/Kleberg county feet was recorded at points 26 and 37. line during the July and August storms. Because field measurements were not possible after the From point 40 to Yarborough Pass, the severe September storm, Bailey made an aerial shoreline was predominantly stable or accre- surveillance of damage to the island and reported tionary. The shoreline remained relatively un- that major damage was south of Murdoch's changed at points 40 and 41, while minimum 19

Table 2.Maximumhurricane surge height recordedalong thecentral Texas Coast,1916-1975.

Surge Height Date (feet) Location Reference 1916 9.2 central Padre Island Cry, 1965 1919 11.1 Port Aransas Sugg and others, 1971 1921 7.1 PassCavallo Cry, 1965 1933 5.0 Port Aransas Price,1956 (July)

1933 4.5 Port Aransas Bailey, 1933 (Aug.)

1933 8.0 Corpus Christi Sugg and others,1971 (Sept.)

1934 10.2 Rockport U. S. Army Corps of Engineers, 1953 1941 11.0 Matagorda Sugg and others,1971 1942 13.8 Port O'Connor Sugg and others,1971 1945 4.0 Port Aransas Sumner, 1946 1949 8.0 Matagorda Sugg and others, 1971 1961 9.3 Port Aransas U.S. Army Corps of Engineers, 1962a (Carla) 1967 8.0 PortAransas U.S. Army Corps of Engineers, 1968a (Beulah) 1970 9.2 PortAransas U. S. Army Corps of Engineers, 1971c (Celia) 1971 3.1 PortAransas U. S. Army Corps of Engineers, 1972b (Fern)

accretion of less than 10 feet occurred atpoint 42. 1942. Surge data were not available for north Maximum accretion of 200 feet occurred at points Padre Island; however, Price (1956) noted that 50 to 51and point 45 recorded no change. Average Corpus Christi Pass was reopened during that accretion for this segment was approximately 110 storm. Storm frequency did not diminish during feet. Aerialphotographs covering the 1956-60 time this time period even though storm intensity was period (appendix C) were not available for points minor in the study area. Most of the tropical 46 and 47; however,coverage was continuous from cyclones affected either the upper or lower coast points 48 through 51. Supplementary 1943 aerial and not the central coast. Except for the 1945 photographs used in the compilation of shoreline hurricane, those few storms that impacted Mustang changes at points 46 and 47 (appendix C) also and northPadre Islands caused only minor damage. included points 48 through 51 (table 3). It is of interest to note that between 1937 and 1943, the Shoreline accretion on Mustang Island shoreline from points 46 to 51 eroded from a between 1937 and 1958 was not restricted to the minimum of 100 feet at points 49 through 51to a Gulf shoreline but occurred on the bay shoreline maximum of 225 feet at point 47, whereas also. Some bay shoreline accretion can be attrib- shoreline changes for points 48 through 51based uted to placement of spoil, but spoil does not on the 1937 to 1960 time interval were accre- account for all the accretion or for its widespread tionary. The short-term erosion between 1937 and and relatively consistent nature. There are several 1943 may have been attributed to a major possible explanations for a period of general hurricane which crossed Matagorda Bay in August accretion, including changes in sediment supply 20

Table 3. Short-termshoreline changes between1937 and 1960 nearYarborough Pass.

Dist. Rate Dist. Rate oint Time ft ftper yr Time ft ft per y:

48 1937- --200 -33.3 1943- -+3OO +17.1 1943 1960

49 -125 -20.8 +275 +15.7

50 -100 -16.7 +300 +17.1

51 -100 -16.7 +300 +17.1 and changes in relative sea-level conditions. An 1956-60 to 1969-70 —Between 1956-60 and influx of additional sediment from a nearby source 1969-70, shoreline changes along Mustang Island such as a river could cause accretion. In the were predominantly erosional,but changes along Mustang Island area, however, no new sediment north Padre Island were dominated by accretion. sources are apparent; in fact, recent increases in Of the 51points monitored, 22points experienced San erosion on Mustang and Jose Island suggest erosion, 22 recorded accretion, and 7 recorded no that the amount of sand available is actually decreasing. It is also unlikely that any new influx change. of sediment could affect such widely spaced areas in such asimilar manner. Sixteen of the 22 points that recorded erosion were on Mustang Island between points 1and 19. Another explanation for the anomalous accre- Maximum erosion of 175 feet was reported at tion would be unusual meteorological conditions. points 3 and 4, minimum erosion of less than 10 For example, strong southeast winds could blow feet was reported at point 11, and average erosion water away from the bay shoreline and produce for this segment was approximately 75 feet. apparent accretion. However, this would not Exceptions to this erosional trend were minor account for accretion on both the Gulf and bay accretion of less than 10 feet at point 14 and shorelines. Perhaps the most likely explanation is relative shoreline stability at points 13 and16. that the apparent accretion during the middle fifties was, in part, due to a regional lowering of A transition zone of relative shoreline sea level. Relative sea-level curves for Galveston, stability between points 20 and 26 separated Freeport, and Port Isabel (Swanson and Thurlow, shoreline segments dominated by erosion and 1973), as well as an average sea-level curve for the accretion. All points along that segment recorded United States (Hicks and Crosby, 1975),all show a no change except for minor accretion and erosion minor lowering of sea level in the mid-19505. at points 23 and 25, respectively. The shoreline Therefore, sea-level lowering is postulated as a from point 27 through point 47 experienced mechanism to partially account for the accre- substantial accretion ranging from 50 feet atpoints tionary trend. 37 and 43 to 325 feet at point 47; average accretion was 150 feet. Minor erosion of 25 feet Most of the State was affected by drought was recorded at point 29.The remainingportion of conditions between 1950 and 1956; the most Padre Island (points 48 through 51) experienced severe drought occurred between 1954 and 1956 erosion ranging from 75 feet at point 49 to 150 (Lowry, 1959). This extended drought period was feet atpoints 50 and 51. manifested by reduced riverine discharge into the bays and by excessive evaporation in the coastal Two major hurricanes affected this segment areas. The net effect of these conditions would be of the coast between 1956-60 and 1969-70; a generallowering of water level. Hurricane Carla (1961) made landfall near Pass Cavallo, and Hurricane Beulah (1967) crossed the This lowering is clearly demonstrated by the coast just south of Brownsville. Post-Carla aerial 1956 aerial photographs; however, it is uncertain photographs from Aransas Pass to point 6 indicate what effect the drought had on sea level in 1958 that erosion was greatest adjacent to the south and 1960. jetty. South of the jetty, discontinuous foredunes 21

were eroded approximately 50 feet; however, in Hurricanes Celia (1970) and Fern (1971) areas of a well-developed foredune ridge, little affected this segment of the shoreline between damage was incurred. Based on field observations 1970 and 1975. Celia, an intense storm of rela- on Mustang Island, Mcßride and Hayes (1962) tively small size, is noted for damage associated documented that a belt of low foredunes 60 to 150 with extremely high winds. Although storm surge feet wide was removed by Carla. Wave-cut cliffs up of 9.2 feet was recorded at Port Aransas (table 2), to 10 feet high were observed by Hayes (1967) McGowen and others (1970) reported that no who reportedforedune erosion of 150 to 300 feet foredune erosion was observed on Mustang Island on MustangIsland. after Celia. Hurricane Fern was a relatively small, low-intensity storm that producedopen-coast surge Aerial photographs taken shortly after Beulah of less than 4 feet at Port Aransas (U. S. Army (appendix C) from Packery Channel to Yarborough Corps of Engineers, 1972b). FollowingFern, Davis Pass show that greatest erosion along this segment (1972) observed that storm damage was restricted occurred in the vicinity of Packery Channel which to the beach. was reopened by storm surge. By October 1969, however, the channel had narrowed from approxi- Net Historic Changes (1860-82 to1974-75) mately 600 feet to 15Q feet. In general, storm damage was restricted to areas which lacked a Calculations from previously determined well-developedforedune ridge. changes provide information on the net effect of shoreline retreat and advance along Mustang and 1969-70 to 1974-75.—During this period, north Padre Islands (appendix A and figure 7). shoreline retreat was predominant onMustangand Using the earliest shoreline as a base line, the north Padre Islands as erosion was recorded at 49 comparison is equal to the difference between the of the 51 points monitored. The only exceptions earliest and latest shorelines. were minor accretion (25 feet) at point 3 and relative stability recorded at point 48. Net changes along Mustang Island have been predominantly erosional. Net erosion ranged from Erosion on Mustang Island (points 1through 75 to 350 feet and averaged 225 feet. Net 21) ranged from 50 feet at point 2 to 225 feet at accretion between points 1and 3 was theresult of points 13 and 14; average erosion was 140 feet. On inlet migration and outbuilding of the north end of north Padre Island (points 22 through 51), the island prior to jetty construction in 1889. The minimum erosion of 25 feet was recordedat points shoreline continued to accrete shortly after con- 46, 47, 50, and 51, whereas maximum erosion of struction of the jetties, but subsequent changes 200 feet occurred at point 41;average erosion was along this segment were predominantly erosional. about 100 feet. At point 21, short-term accretion attendant with the infilling of Packery Channel between 1882 and Apparently, magnitudes and rates of erosion 1937 influenced the overall net change. between 1969-70 and 1974-75 are exaggerated because of tidal differences duringrespective times Net erosion along north Padre Island de- of photography. Low tide conditions during the creased southward from 500 feet at point 22 to 50 1969-70 overflight and high tide conditions during feet at point 30; average net erosion for this the 1974-75 overflight tend to reduce estimated segment was 220 feet. amounts and rates of erosion between 1956-60 and 1969-70 and to increase estimated amounts and Net accretion was recorded from point 31 to rates of erosion between 1969-70 and1974-75. To Yarborough Pass except at point 37, which re- compensate for the tidal differences, shoreline corded no netchange,andpoints 38 and 39, where changes were averaged for the entire period minor net erosion (25 feet) occurred. Maximum 1956-60 to 1974-75. These data indicate that the net accretion for this segment was 275 feet and most recent trend is erosion but at reduced rates. minimum net accretion was less than 10 feet; Between 1956-60 and 1974-75, shoreline erosion average net accretion was 140 feet. Since 1960, ranged from 25 to 275 feet and averaged 150 feet however, the shoreline between points 40 and 51 or 9.6 feet per year. A notable exception was the has been erosional. segment between points 30 and 39 where the shoreline either was relatively stable or accreted Rates of change were also calculated for net between 25 and100 feet. change between 1860-82 and 1974-75; the results 22

Figure 7.Netshoreline changesbetweenAransasPass and YarboroughPassbased on the timeperiodfrom 1862-82 to 1974-75 23

are included in appendix A. These figures estimate than 1 foot per year to 3.8 feet per year and long-term net effect, but the values shouldbe used averaged 2.0feet per year.Erosional rates on north in context. The values for rates of net change are Padre Island varied from less than 1 foot to 5.4 adequate for describing long-term trends;however, feet per year. Net erosion along this segment also rates of short-term changes may be of greater averaged 2.0 feet per year.Accretionary rates were magnitude thanrates of long-term changes,particu- also low, ranging from less than 1foot to 3.0feet larly in areas where both accretion and erosion per year; average rates of net accretion were 1.5 have occurred. feet per year. For the time period of this study, the shoreline of Mustang and north Padre Islands has In general, net rates of change were low for been relatively stable, especially between points 29 Mustang Island with the exception of points 1 and 42. The most recent data, however, indicate through 3 where net accretion ranged from 3.3 to that much of the shoreline is experiencing short- 14.4 feet per year. Net erosion ranged from less term erosion.

Changes In Position Of Vegetation Line

Changes in the vegetation line (appendix A) migration (point 20) or revegetated blowouts are considered independently from shoreline (points 1,12, and43 through 50). changes because, in many instances, the nature of change and rate of shoreline and vegetation line Advancement of the vegetation line on recovery are quite dissimilar. Thus, the shoreline Mustang Island varied from 125 to 2,250 feet; advances of and vegetation line should not be viewed as a averaged 670 feet. Similarly, advances the vegetation line on north Padre Island ranged couplet with fixed horizontal distance; this is from 250 to 2,650 feet and averaged 845 feet. The illustrated in figure 8. Although response of the low incidence of storms after 1949 (table 2) was shoreline and vegetation line to long-term changes largely responsible for the recovery of vegetation is similar, a certain amount of independence is by 1956-60. exhibited by the vegetationline because itreacts to a different set of processes than does the shoreline. 1956-60 to 1969-70.—Vegetation line changes Furthermore, documentation of changes invegeta- between 1956-60 and 1969-70 were dominated by tion line for this particular study draws on consid- retreat with only 8 of the 51 points recording erably more data (appendix C) than does docu- advances. On Mustang Island, vegetation line mentation of shoreline changes. retreat from point 1throughpoint 10 ranged from 25 to 225 feet and averaged about 100 feet. The Accurate information on position of vegeta- remaining portion of Mustang Island (points 11 tion line is available neither for the middle 1800's through 21) experiencedboth advance andretreat nor for the early 1900's. Therefore, accounts of of the vegetation line. Points 15, 18, and 20 changes in vegetationline arerestricted to the time recorded retreat ranging from 125 to 300 feet, period covered by aerial photographs (1937 to while points 11, 14, 17, and 21 recorded advance- 1974-75). ment varying from 50 to 475 feet; points 12, 13, and 16 recordedno change. 1937 to 1956-60— Major advances in the vegetation line along Mustang and north Padre Vegetation line changes on northPadre Island Islands between 1937 and 1956-60 were associated between points 22 and 29 were also intermixed, with recovery from the 1933 and 1934 storms as with points 23 and 25 recording retreat,points 24 well as with shoreline accretion. Perhaps drought and 27 recording advancement, and point 28 conditions from 1937 to 1939 contributed to slow recording no change. Data were not available for initial recovery following the storms. During this points 22, 26, and 29 which were located inactive period, only two points (13 and 24) experienced blowout areas. The vegetation line retreated from retreat of the vegetation line; both points were point 30 to point 50 with the exception of points located in areas of localized blowouts. Data were 46 and 47 where minor advances occurred. Retreat not available for points 15, 18, 19, 41, and 51 ranged from 25 to 1,675 feet. Point 50 recorded which were void of vegetation. The greatest no change and 51 was located in a blowout area. advances were located either in areas of pass Averageretreat on northPadre Island was360 feet. 24

Figure 8. Relative changes in positionof shoreline andvegetationline at selectedlocations, AransasPass to YarboroughPass. 25

Retreat of the vegetation line between points recorded advancement thatranged fromless 1956-60 and 1969-70 can be attributed largely to than10 feet to 200 feet and averaged 75 feet. Hurricanes Carla (1961) and Beulah (1967). Aerial photographs taken shortly after Carla (1961, Celia (1970) and Fern (1971) were the only appendix C) show that the entire frontal margin of two storms to affect this segment of the coast low dune vegetation retreated up to 200 feet between 1969-70 and 1974-75. In both cases, between Aransas Pass and point 4. South of point damage to vegetation was minimal and the general 4 through point 6, the continuous dune ridge recovery can be attributed to a lack of storm retreated from 50 to 100 feet; greater retreat was damage. The 1969-70 and 1974 photographs of associated withlocalized dune blowouts. Mustang Island reveal that a row of low, sparsely vegetated dunes had formed gulfward of the Hurricane Beulah made landfall between continuous vegetationline by 1974. This suggests a Brownsville and the mouth of the Rio Grande period of dune stability and potential for future before turning northward parallel to the coast. advancement; however,the volume of sand (dunes) Post-Beulah photographs show considerable accumulated along snow fences in the backbeach damage to the vegetation on north Padre Island area greatly exceeded dune growth observed where especially in areas where the dune ridge was not snow fences were not utilized. Low, sparsely continuous. Only a few measurements were made vegetated dunes also formed along the backbeach because of the lack of control points; however, of Padre Island National Seashore where beach use those few points indicated that the low dunes and has been restricted to non-vehicular traffic since associated vegetation line retreated approximately 1968. 100 feet between Malaquite Beach and Yarborough Pass. Net changes invegetationline were calculated as they were for shoreline changes. However, it 1969-70 to 1974-75— In general, this time should be emphasized that shifts invegetation line interval was dominated by advancement of the are relatedprimarily to storms, and the time period vegetation line with local areas of retreat. Of the over which observations were made was not of 51points monitored,28 recorded advancement,13 sufficient length to establish long-term trends. recorded retreat, and 6 experienced no change. Nonetheless,the general trend of change in vegeta- Four points (19, 22, 26, and 29) were located in tion line has been netadvancement (fig. 8) because active blowout areas which were void of of the changes that occurred between 1937 and vegetation. 1956-60. The 1956-60 vegetationline occupied the most seaward position at the greatest number of Vegetation on Mustang Island advanced points monitored. With the exception of point 13, between points 1 and 7 with the exception of the vegetation line on Mustang Island experienced point 6 where retreat of 100 feet occurred in net advancement that ranged from 25 to 2,300 association with a small blowout. Recovery ranged feet. Greatest advancement occurred inrevegetated from less than 10 feet to 150 feet and advance- washover and blowout areas. Average net recovery ment averaged 70 feet. South of point 8 through in areas unaffected by such drastic changes was point 12, the vegetation line retreated from a 255 feet. Net changes were notavailable for points minimum of 75 feet to a maximum of 100 feet. 15, 18, and 19 as these points were located either Advancement of the vegetation line was also inactive washovers or blowouts in 1937. dominant frompoint 14 throughpoint 21with the exception of point 17, where retreat of 100 feet Net recovery was recorded on north Padre occurred, and point 15, where no change was except at five points.Minor net retreat of 75 feet recorded. Recovery ranged from 50 feet to 400 occurred at point 29 which is situated in a feet and averaged 160 feet. The vegetation line localized blowout. Net retreat was also recorded advanced on north Padre Island with few excep- between points 39 and 42, an active blowout area tions. Minor retreat of 25 to 50 feet was reported since 1956. Greatest net recovery occurred at points 25, 30, 35, and 45. In addition, sub- between points 43 and 51 where advancement of stantial retreat ranging from 150 to 525 feet was the vegetation line ranged from 325 to 2,675 feet recorded from points 39 through 41inassociation and averaged 1,480 feet. Average net recovery for with active blowouts. Other than points 31, 34, the remainder of north Padre Island (points 22 and 37, which recorded no change, the remaining through 38) was 430 feet. 26

Ingeneral, the long-term change inposition of and take place independent of shoreline changes. the vegetation line is similar to that of the This is demonstrated in figure 8 which illustrates shoreline. However, short-term changes inposition that the horizontal separation between shoreline of the vegetation line reflect climatic conditions and vegetation line displays short-term variations.

Factors Affecting Shoreline And Vegetation Line Changes

Geologic processes and, more specifically, included reference to the Brazos and Mission coastal processes are complex dynamic compo- Rivers of Texas. Observations based on geologic nents of large-scale systems. Coastal processes are maps prepared by the Bureau of Economic dependent on the intricate interaction of a large Geology (Fisher and others, 1972) confirm that number of variables such as wind velocity,rainfall, many rivers along the Texas Coastal Plain were storm frequency and intensity, tidal range and larger and probably transported greater volumes of characteristics, littoral currents, and the like. sediment during the early Holocene. This,in turn, Therefore, it is difficult, if not impossible, to affected sediment budget by supplying additional isolate and quantify all the specific factors causing sediment to the littoral drift system. Droughts are shoreline changes. Changes in vegetation line are a potential though indirect factor related to minor more easily understood. However, in order to shoreline changesvia their adverse effect on vegeta- evaluate the various factors and their interrela- tion. Because dunes andbeach sand are stabilized tionship, it is necessary to discuss not only major by vegetation, sparse vegetation resulting from factors but also minor factors. Thebasis for future droughts offers less resistance to wave attack. prediction comes from this evaluation. Severe droughts have occurred periodically in Texas; the chronological order of severe droughts Climate affecting Mustang and north Padre Islands is as follows: 1891-1893,1896-1899,1901, 1916-1918, Climatic changes during the 18,000 years 1937-1939,1950-1952,1954-1956 (Lowry, 1959). since the Pleistocene have been documented by various methods. Ingeneral, temperature was lower Unfortunately, pastchangesin the position of (Flint, 1957) and precipitation was greater vegetation line resulting from storms and droughts (Schumm, 1965) at the end of the Pleistocene than generally cannot be independently distinguished by at the present; the warmer and drier conditions, sequential aerial photography. By monitoring which now prevail, control other factors such as hurricanes and droughts in relation to time of vegetal cover,runoff, sediment concentration,and available photography, however,one can correlate sediment yield. Schumm (1965) stated that the short-term effects of these factors, providing "... an increase in temperature and a decrease in the time lapse between photos is not too great. precipitation will cause a decrease inannual runoff and an increase in the sediment concentration. Storm Frequency andIntensity Sediment yield can either increase or decrease depending on the temperature and precipitation The frequency of tropical cyclones is de- before the change." pendent on cyclic fluctuations in temperature; increased frequency of hurricanes occurs during Changesin stream andbay conditions,as well warm cycles (Dunn and Miller, 1964). Because of as migration of certain plant and animal speciesin their high frequency of occurrence and associated South Texas since the late 1800's, were attributed devastating forces and catastrophic nature,tropical to a combination of overgrazing and more arid cyclones have received considerable attention in climatic conditions (Price and Gunter, 1943). A recent years. Accurate records of hurricanes more complete discussion of the general warming affecting theTexas Gulf Coastare incomplete prior trend is presented in Dunn and Miller (1964). to 1887, when official datacollection was initiated Manley (1955) reported that postglacial air temper- simultaneously with the establishment of the ature has increased 13°F in the Gulf region. Corpus Christi weather station (Carr,1967). Furthermore, Dury (1965) estimated that many rivers carried between 5 and 10 times greater According to summaries based on records of discharge than present-day rivers. His remarks the U. S. Weather Bureau (Price, 1956; Tannehill, 27

1956; Dunn andMiller,1964; Cry, 1965),some 62 large quantities of sand during hurricane approach tropical cyclones have either struck or affected the and landfall. The amount of damage suffered by Texas Coast during this century (1900-1973). The the beach and adjoiningareas depends ona number average of 0.8-hurricane per year obtained from of factors including angle of storm approach, these data is similar to the 0.67 per year average cpnfiguration of the shoreline,shape and slope of reported by Hayes (1967) who concluded that Gulf bottom, wind velocity, forward speed of the most of the Texas coastline experienced the storm, distance from the eye,stage of astronomical passage of at least one hurricane eye during this tide, decrease in atmospheric pressure, and century. He further concluded that everypoint on longevity of the storm. Hayes (1967) reported the Texas Coast was greatly affected by approxi- erosion of 60 to 150 feet along the fore-island mately half of the storms classified as hurricanes. dunes on Padre Island after the passage of Hurricane Carla. Most tropical cyclones have Simpson and Lawrence (1971) conducted a potential for causing some damage, but as study of the probability of storms striking 50-mile suggested by McGowen and others (1970), certain segments of the Texas Coast during any givenyear. types of hurricanes exhibit high wind velocities, The 50-mile segment of the coast, which includes others have high storm surge, and still others are Mustang and north Padre Islands,has a12-percent noted for their intense rainfall and aftermath probability of experiencing a tropical storm, a flooding. 7-percent probability of experiencinga hurricane, and a 5-percent probability of experiencinga great Hurricane surge is the most destructive hurricane. element on the Texas Coast (Bodine,1969).This is particularly true for low-lying areas that lack Comparisons of thedifferent types of some of continuous foredunes that can dissipate most of the morerecent hurricanes are available; the effects the energy transmitted by wave attack.Because of the role hurricane surge plays in flooding and of Hurricanes Carla (1961) and Cindy (1963) on destruction, the frequency of occurrence of high South Texas beaches were compared by Hayes surge on the open coast has been estimated by (1967). Hurricanes Carla, Beulah (1967),and Celia Bodine (1969). Included in his report are calcula- (1970) were compared by McGowen and others tions for Mustang Island, which suggest that surge (1970); individual studies of Hurricanes Carla, height of 10 feet can be expectedapproximately 2 Beulah, Celia, and Fern were conducted by the times every 100 years. Maximum hurricane surge U. S. Army Corps of Engineers (1962a, 1968a, predicted was 12.5 feet. These estimates were 1971c,1972b). based on the most complete records of hurricane surge elevations available for the Texas Coast. Destructive forces and storm damage.—Carla, Surge for specific storms was compiled by Harris one of the most violent storms onrecord, crossed (1963). Wilson (1957) estimated deep-water the Texas Coast at Pass Cavallo and inundated hurricane wave height of between 30 and 40 feet approximately 88 percent of MustangIsland with a once every 50 years for the Brownsville area. recorded surge of 9.3 feet above mean sea level Maximum deep-water hurricane wave height (U. S. Army Corps of Engineers, 1962a).Flooding predicted for the same location was 45 feet with a on north Padre Island was less extreme because of recurrence frequency of once every 100 years. distance from storm landfall and protection Consequently, dissipated energy from breaking provided by a well-developed dune ridge. Storm storm waves can be tremendous under certain surge associated with Hurricane Beulah also caused conditions. major flooding of low-lying areas along the central Texas Coast. High-water elevations in the study Changes in beach profile during and after area ranged from 8.0 to 9.4 feet (U. S. Army Corps storms.— Beach profiles adjust themselves to of Engineers,1968a).Approximately 80percent of changing conditions in an attempt to maintain a MustangIsland was flooded (Morton and Amdurer, profile of equilibrium; they experience their 1974). Major hurricanes also affected the area of greatest short-term changes during and after study in 1887, 1916, 1919, 1933, and 1945 storms. Storm surge and wave action commonly (table 2). plane off preexisting topographic features and produce a featureless, uniformly seaward-sloping High velocity winds with attendant waves and beach. Eroded dunes and washover fans are currents of destructive force scour and transport common products of the surge. The sand removed 28

by erosion is (1) transported and stored tempo- of sand and ultimate burial of the vegetation. rarily in an offshore bar, (2) transported in the Although this causes an apparent landward shift in direction of littoral currents, and/or (3) washed the vegetation line, recovery is quick (usually across the barrier island through hurricane within a year) as the vegetation grows through the channels. Sediment transported offshore and sand and is reestablished. stored in the nearshore zone is eventuallyreturned to the beach by bar migration under the influence The second type of change is characterized by of normal wave action. The processes involved in stripping and complete removal of the vegetation beach recovery are discussed by Hayes (1967) and by erosion. This produces the featureless beach McGowen and others (1970). previously described;oftentimes the wave-cutcliffs and eroded dunes mark the seaward extent of the Foredunes are the last line of defense against vegetation line. Considerable time is required for wave attack, and thus, afford considerable protec- the vegetation line to recover because of the slow tion against hurricane surge and washover. Dunes processes involved and the removal of any nucleus also serve as a reserve of sediment from which the around which stabilization and development of beach can recover after a storm. Sand removed dunes can occur. from the dunes and beach, transported offshore and returned to the beach as previously described, Selective and incomplete removal of vegeta- provides the material from which coppice mounds tion gives rise to the third type of change. and eventually the foredunes rebuild. Thus, dune Frequently, long,discontinuous,linear dune ridges removal eliminates sediment reserve, as well as the survive wave attack but are isolated from the natural defense mechanism established for beach post-storm vegetation line by bare sand. Recovery protection. under these circumstances is complicated and also of long duration. The preserved dune ridge does Whether or not the beach returns to its provide a nucleus for dune development; at times, prestorm position depends primarily on the the bare sand is revegetated andthe vegetationline amount of sand available. The beach readjusts to is returned to its prestorm position. This type of normal prestorm conditions much more rapidly erosion was not observed on Mustang and north than does the vegetation line. Generally speaking, Padre Islands; however,ithasbeen documented on the sequence of events is as follows: (1) return of other segments of the Texas Coast. sand to beach and profile adjustment (accretion); (2) development of low sand mounds (coppice Local and Eustatic Sea-Level Conditions mounds) seaward of the foredunes or vegetation line; (3) merging of coppice mounds with fore- Two factors of major importance relevant to dunes; and (4) migration of vegetation line to land-sea relationships along Mustang and north prestorm position. The first stepis initiated within Padre Islands are (1) sea-level changes, and (2) days after passage of the storm and adjustment is compactional subsidence. Shepard (1960b) usually attained within several weeks or a few discussed Holocene risein sea level along the Texas months. The remaining steps require months or Coast based on C14 data. Relative sea-level changes possibly years and, in some instances, complete during historical time are deduced by monitoring recovery is never attained. This sequence is mean sea level as determined from tide observa- idealized for obviously if there is a post-storm net tions and developing trends based on long-term deficit of sand, the beach will not recover to its measurements (Gutenberg, 1933, 1941; Manner, prestorm position; the same holds true for the 1949, 1951, 1954; Hicks and Shofnos, 1965; vegetation line. Occasionally the vegetation line Hicks, 1968, 1972). However, this method does will recover completely, whereas the shoreline will not distinguish between sea-level rise and land- not; these conditions essentially result inreduction surface subsidence. More realistically, differen- inbeach width. tiation of these processes or understanding their individual contributions,if both are operative,is an Apparently three basic types of shift in academic question; the problem is just as real no vegetation line are related to storms, and con- matter what the cause. A minor vertical rise insea sequently, the speed and degree of recovery is level relative to adjacent land in low-lying coastal dependent on the type of damage incurred. The areas causes a considerable horizontal displacement first and simplest change is attributed to deposition of the shoreline in a landward direction (Bruun, 29

1962). Unfortunately, the tide records at Port uted to (1) transportation offshore into deep Aransas are not of sufficient duration so that a water, (2) accretion against natural littoral barriers definitive statement can be made about relative and man-made structures, (3) excavation of sand sea-level changes. for construction purposes, and (4) eolian processes.

Shepard and Moore (1960) speculated that The sources of sediment and processes re- coastwise subsidence was probably an ongoing ferred to by Johnson have direct application to the process augmented by sediment compaction. More area of interest. Sources of sand responsible for the recent data tend to support the idea of land incipient stages of development and growth of subsidence along the Texas Coast (Swanson and Mustang and north Padre Islands probably include Thurlow,1973). sand derived from shelf sediment, the Colorado and Brazos Rivers, and perhaps some sand derived Through geologic time, the central Texas from updrift shoreline erosion. Van Andel and Coast, ina regional sense, has been situated over a Poole (1960) and Shepard (1960a) suggested that more stable and positive tectonic element, the San sediments of the Texas Coast are largely of local Marcos arch, than the adjacent areas that occupy origin. Shelf sand derived from the previously the Rio Grande embayment to the south and the deposited sediment was apparently reworked and East Texas embayment to the northeast. Further- transported shoreward by wave action during the more, stream gradients for the Guadalupe and Holocene sea-level rise (fig. 5). McGowen and Nueces Rivers suggest that uplift has been greater others (1972) also concluded that the primary in areas updip of the hingeline over the SanMarcos source of sediment for Modern sand-rich barrier arch than inadjacent areas. islands such as Mustang and north Padre Islands was local Pleistocene and early Holocene sources Because Swanson and Thurlow were inter- on the inner shelf,based on the spatial relationship ested in the subsidence component reflected in tide of the different age deposits. level variations, their data were intentionally adjusted so that the contribution from sea-level rise Sediment supplied by major streams is trans- would be eliminated from their analysis. Neverthe- ported alongshore by littoral currents. It is less, tidal data gathered from numerous coastal generally recognized that the combination of basin areas indicate that sea level continues to rise at the configuration and shoreline orientation plus pre- rate of approximately 1foot per century. dominant wind direction produce southwesterly littoral drift along the upper and central Texas In the overall analysis, it would appear that Coast, whereas littoral drift is northerly along the the balance between factors of tectonic stability lower coast (Lohse,1955). Apparently,the zone of and sea-level rise would favor continued sea-level convergence is located near 27° N latitude, but rise relative to the land surface. seasonal conditions can cause the convergence to shift up the coast toward north Padre Island Sediment Budget (Curray, 1960). Although the direction of littoral drift at any given time is dependentprimarily on Sediment budget refers to the amount of wind direction, the net direction of drift alongthe sediment in the coastal system and the balance central Texas Coast is southwesterly. This is among quantity of material introduced, tempo- documented historically by the migration of rarily stored, or removed from the system.Because Aransas Pass and inlets in the Corpus Christi beaches are nourished and maintained by sand- Pass/Packery Channel area. Remote sensing tech- sized sediment, the following discussion is limited niques have also been used to document the to natural sources of sand for Mustang and north characteristics and southwestward direction of Padre Islands. suspended-sediment transport (Berryhill, 1969; Hunter,1973). Johnson (1959) discussed the major sources of sand supply and causes for sand loss along Because of the seasonal reversals in direction coasts. His list, modified for specific conditions of littoral transport associated with changing wind along the Texas Coast, includes two sources of direction (Blankenship, 1953;Kimsey and Temple, sand: major streams and onshore movement of 1962, 1963; Watson and Behrens, 1970; Hunter shelf sand by wave action. Sand losses are attrib- and others, 1974; Hill and others, 1975), net 30 littoral drift along the central Texas Coast is only channels. Sand removed by man-made structures about 10 to 20 percent of the gross littoral drift and for construction purposes is discussed in the (Carothers and Innis, 1962; Behrens and Watson, following section on humanactivities. 1974). Gross littoral drift in the vicinity of Corpus Christi fish pass from July 1972 to June 1973, HumanActivities and Watson (1974), was computed by Behrens Shoreline induced by man are yards (Behrens and Watson, changes about 1million cubic difficult to quantify because human activities 1974); net littoral drift (southward) was from promote alterations and imbalances in sediment 39,250 to 85,200 cubic yards. A sediment bypass budget. For example, construction of dams, erec- system utilizing the outer bar was not established tion of seawalls, groins, and jetties, andremoval of until the pass was dredged open. Prior to its sediment for building purposes all contribute to opening, the jettiesentrapped1million cubic yards changes in quantity and type of beach material of sediment. Net loss downdrift from the pass delivered to the Texas Coast. Even such minor exceeded 120,000 cubic yards. activities as vehicular traffic and beachscraping can contribute to the overall changes, although they Carothers and Innis (1962) estimated that are in no way controlling factors. Erection of southward drift of 30,000 cubic yards of sediment impermeable structures and removal of sediment occurred in the vicinity of Mustang and north have an immediate, as well as a long-term effect, Padre Islands, whereas a net annual volume of whereas a lag of several to many years may be 146,000 cubic yards was transportednorthward at required to evaluate fully the effect of other Yarborough Pass. changes such as river control and dam construction. The highest dunes and most extensive dune fields along the Texas Coast occur south of Construction of the jettiesat Aransas Pass was Yarborough Pass; however, eolian transport is an initiated in 1880 and completed in 1916; the important factor in the distribution of sand on Corpus ChristiWater ExchangePass was completed north Padre Island. Active blowouts and migrating in 1972. Aransas Pass has been dredged period- dune fields (Blankenship, 1953; Boker, 1956; ically to maintain and deepenthe channel.Projects Hunter and Dickinson, 1970;Price, 1971) indicate such as these serve to alter natural processes such that a substantial volume of sand supplied to as inlet siltation, beach erosion, and hurricane beaches by longshore currents is removed from the surge. Their effects on shoreline changes are littoral drift system by eolian processes. subject to debate, but itis an elementary fact that impermeable structures interrupt littoral drift and Sand losses listed by Johnson (1959) do not impoundment of sand occurs at the expense of the include sedimentremoved by deposition from tidal beach downdrift of the structure. Therefore, it deltas and hurricane washovers; these are two appears reasonable to expect thatany sand trapped important factors on the Texas Coast (fig. 9). west of the south jetty is compensated for by During storms, sand may be moved offshore in removal of sand downdrift, thus increasing local deeper water or into lagoons through washover erosion problems.

Evaluation Of Factors

Shore erosion is not only a problem along Tropical cyclones are significant geologic United States coasts (El-Ashry, 1971) but also a agents and during these events, fine sand, which problem worldwide. Even though some local condi- characterizes most of the Texas beaches, is easily tions may aggravate the situation, major factors set into motion. Silvester (1959) suggested that affecting shoreline changes are eustatic conditions than storm waves (compactional subsidence on the Texas Coast) and swell is a more important agent and a deficit in sediment supply. The deficit in sand in areas where longshore drift is interrupted supply is related to climatic changes, human sand is not replenished offshore. For the purposes activities, and the exhaustion of the shelf supply of this discussion, the individual effects of storms through superjacent deposition of finer material and swell is a moot question. Suffice itto say that over the shelf sand at adepthbelow wave scour. water in motion is the primary agent delivering 31

Figure 9. Generalizeddiagramof sediment transport directionsbetweenAransasPass andYarboroughPass. 32

sand to or removing sand from the beach and storms are the primary factor related tochangesin offshore area. There is little doubt, however, that vegetationline.

Predictions Of Future Changes

The prediction of future shoreline changes on approximately 45 to 50 feet of sand under Mustang and north Padre Islands is more specula- southern MustangIsland (in the vicinity of Packery tive than along most other segments of the Texas Channel), and Dickinson and others (1972) Coast because short-term trends have varied con- reported 60 feet of sand from borings on north siderably. Based on information from this study,it Padre Island (in the vicinity of point 32). Although appears reasonable to assume that long-term net total sandthickness isimportant in terms of barrier changes of the future will occur at relatively low island stability, it should be noted that the sand rates. A critical factor which has not been eval- sequence probably represents two distinctly uated fully is sediment budget, especially the different stratigraphic units based on their origin balance between sand supplied to north Padre and age.For example, Wilkinson and others (1975) Island by updrift erosion and sand removed by concluded that the lower 22 feet of sand under eolian processes. Until sources and sinks of sand southern Mustang Island was depositedas a strand- along the Texas Coast are known, prediction of plain during a Pleistocene interglacial. In contrast, future shoreline changes in the zone of con- the overlying sand was interpreted as Holocene vergenceis uncertain. barrier island deposits.

The logical conclusion drawn from factual The shoreline could be stabilized at enormous information, however, is that the position of expense by a solid structure such as a seawall; shoreline and vegetation line on Mustang Island however,any beach seaward of the structure would andnorth Padre Island will retreat landward as part eventually be removed unless maintained artifi- of a long-term erosional trend. The combined cially by sand nourishment (a costly and some- influence of interrupted and decreased sediment times ineffective practice). The U.S. Army Corps supply, relative sea-level rise, and tropicalcyclones of Engineers (1971a, p. 33) stated that "While is insurmountable exceptin very local areas such as seawalls may protect the upland, they donot hold river mouths. There is no evidence that suggests a or protect the beach which is the greatest asset of long-term reversal inany trends of the major causal shorefront property." Moreover, construction of a factors. Weather modification research includes single structure can trigger a chain reaction that seeding of hurricanes (Braham and Neil, 1958; requires additional structures and maintenance Simpson and others, 1963), but human control of (Inman andBrush, 1973). intense storms is still inincipient stages of development. Furthermore, elimination of tropical storms Maintenance of some beaches along the Outer entirely could cause a significant decrease in Banks of North Carolina has been the respon- rainfall for the southeastern United States sibility of the National Park Service (Dolan and (Simpson, 1966). others, 1973). Recently the decision was made to cease maintenance because of mounting costs and Sand stored in the barrier islands should tend the futility of the task (New York Times, 1973). to minimize erosion and keep rates relatively low. Foundation borings and jet-down samples indicate It seems evident that eventually nature will that sand thickness beneath the barrier islands have its way. This should be givenutmost consid- increases southward from Aransas Pass. Sand eration when development plans are formulated. thickness on MustangIsland is generally from 33 to While beach-front property may demand the 38 feet but is greater than 45 feet near Aransas highest prices, itmay also carry with it the greatest Pass. Wilkinson and others (1975) encountered risks. References

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4 3 3 6 8 3 3 6 3 1 9 1 8 0 4 14. 7.7 3. 1.0 2. 2. 2. 3. 2. 2. 2. 2. 1. 1.0 1.0 1. 3. 3. 1. Pass NetRate + + + -< ------3.0 - - -< -< - 825 350 75 250 275 300 350 250 275 325 250 225 200 75 100 125 350 275 125 NetDist. +1600 + + - - - - -

1 1 Pass-Yarborough Net Time 1860-66 1974 1867 1974 ii ii ii n ii ii 1 ii n ii ii ii ii 1862 1974 11882 1974 ii ii

5 6.2 2 2 8 8 4 0 3 3 8 4 2 Aransas Rate per -18.7 -12. + -25.0 -22. -16.7 -22. -27. -27. -44.4 -44.4 -44. -50. -50.0 -33. -33. -27. -44. -44.4 -22. segment ft 75 50 25 75 ft - - + - beach Dist. -100 -100 -100 -125 -125 -200 -200 -200 -225 -225 -150 -150 -125 -200 -200 -100

1 1 ii ii 1 ii Time 1970 1974 ii ii ii 1969 1974 ii n n ii ii ii ii ii ii 1 ii

2 2 2 5 1 3 5 5 5 2. 4. 6.8 9. 2. 1.0 1.0 4. 4. 6.8 4. Rate per -10.9 -15. -15. -11.4 -11.4 - - -< -2.3 +< - - - - ft

A 25 50 75 25 10 25 10 50 50 75 50 Changes ft - - - Appendix Dist. -125 -175 -175 -125 -125 -100 -< +< Shoreline Time 1958 1970 ii ii ii 1958 1969 it ii n ii it n ii ii ii ii ii ii ii ii 19591969

3 2 8 0 1 5 6 6 6 1 5 2. 1. 1-0 5. 2.3 1.2 7. 8. 3. 4. 4. 4. 8. 7.0 7.0 2.3 3. per + + + - + + + + + + + + + Rate -< -2.3 -1.2 + + ft

50 25 10 50 25 50 25 75 50 75 ft 150 100 100 150 Dist. + -< 125+ + + 175+ + + + 100+ 175+ +150 + + +

Time 1937 1958 n ii ii ii ii ii ii ii ii ii ii ii ii ii ii it n ii 19371959

3 6 1 1 1 5 1 .0 3 per 14. 7. 1. 1.- 1.0 1.4 1.8- 2.- 1.8 1.4 1.- 1 1. 1.8 1.0 Rate +22. + + + -< - -3.2 -2.9 -< -1.3 -2.3 _< ft

500 75 75 50 100 125 175 225 200 125 100 75 50 100 100 125 100 25 Dist. ft +1650 1025+ + + - - -

1 Time 1860-66 19371867 1937 n ii ii it ii ii ii n ii ii n ii ii 1862 1937 ii 1882 1937 1 n

1 10 11 12 13 14 15 16 17 18 19 20 accretion+ erosion- Point 39

6 4 9 8 3 4 1 1 3 3 9 0 0 0 4. 5. 4. 3. 2. 1. 1. 1. 1.0 1.0 1.0 1. 1. 1. 1. 1. 1. 1.0 1.0 + - < - + + + Pass Net Rate -< -< +< +< +< -< -< + h 425 500 450 350 250 125 100 100 75 50 25 125 125 175 75 50 25 25 25 Net Dist. + - - + + + + + + - +

1 1 1 1 ii ii ii ii ii 1 Pass-Yarborou; Net Time 1882 1974 it ti 1 ii ii 1882 1975 ii ii ii ii v n

8 2 9 3 3 3 2 2 7 7 8 2 1 6 2 3 Aransas Rate per -27.8 -16.7 -27. -22. -38. -33. -27. -27. -18. -18. -22. -22. -31.8 -31. -18. -22.7 9.- -13. -18. -27. segment ft 75 50 75 ft - - beach Dist. -125 -125 -100 -175 -150 -150 -150 -100 -100 -125 -125 -175 -175 -100 -125 -100 -150

ii 1 ii ii ii ii ii ii H Time 19691974 ii ii n ii 19691975 ii 1 it ii ii ii

8 1 5 7 7 7 5 0 3 4. 7. 9. 1.8 16. 16. 16. 18. 7.4 3.7 5.6 9. 7.4 Rate per + -2.4 + + 14.8+ + + + + +13. + + + + + ft

50 25 25 50 75 ft 75 100 175 100 125 100 Changes Dist. + + + - +200 +225 +225 +225 +250 + + + + + + Shoreline Time 19591969 ii ii n it ii ii 1956 1969 ii ii ii ii ii ii ii ii ii ii ii fVy 1 1 5 5 3 3 1. 1. 4. 5. l.'O 5. 2.3 1.0 2.6 7.9 9.2 7.9- - < 2.6 6.6- Rate per + -5.7 -5.7 + -< - - -14. -11.8 - + ft

25 25 50 10 50 10 50 ft - Dist. + -125 -125 + -< -100 -275 -225 -150 -175 -150 -100 _< + -125 -100

Time 1937 1959 n ii ii ii n ii ii 1937 1956 it it ii ii v ii n ii ii ii ii

5 3 .0 5 5 8.2 4. 2. 1.0 1.0 1.0 1 1.8 2.3 2.7 3.2 4. 4. 1.8 1.4 1.0 1.8 1-0 1.4 per 10.0+ - - - -< -< -< +< + + + + + + + + -< + +< + Rate ft 550 450 250 125 25 25 25 50 100 125 150 175 250 250 100 75 50 100 50 75 Dist. ft + - - + + + + + + + + + + + +

Time 1882 1937 !I ii ii ii ii II I! II II II II II II II II II II II

5 22 23 24 2 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 +accretionerosion- Point 21 40

0 9 9 0 0 7 9 4 1.0 1. 1. 1. 3. 1.9 3. 2. 1.9 1. 2. Pass < < + + + + + + + + + h Net Rate + + 50 10 175 175 275 175 275 250 175 175 225 < + + + + + + + Yarborou; Net Dist. + + + + 5

1 1 1 Pass- Net Time 1882 197 it ii ii ii it it ii 1 1 1

1 1 5 5 1 5 5 Aransas Rate per -36.4 -22.7 9. -18.2 9.- 4.- 4.- 9. 4.- 4.- segment ft 50 50 25 25 50 25 25 beach Dist. ft -200 -125 - -100 - - - - -

1 1 1 ii ii 1 it 1 M Time 19691975 1 ii it ii

0 5 0 8 9.3 7.4 3.7 5.6 13. 8. 7.9 Rate per + + + + + + 12.3+ -25. - -15.8 -15. ft

50 75 75 ft 100 175 Changes Dist. 125+ + + + + +225 +325 -100 - -150 -150 line Shore Time 1956 1969 it ii ii ii 1943 1969 ii 196.0 1969 ii. ii ii r y 5 3 5 7 1.0 2.6 2.6 4. 6. 8. 8.7 per < + + + + Rate + + + -25.0 -37. ft

10 50 50 ft < + + 100+ 150+ Dist. + -150 -225 +200 +200

Time 1937 1956 ii M ii 1937 1943 ii 1937 1960 ii ii ii

9"ry 3 0 3 5 2. 1. 2.3 2.7 2.7 2. 3.6 4. 2.7 2.7 3.6 Rate per + +< + + + + + + + + + ft

25 50 125 125 150 150 125 200 2 150 150 200 Dist. ft + + + + + + + + + + +

Time 1882 1937 ii ii ii ii tt ii ii ti ii ii

41 42 43 44 45 46 47 48 49 50 51 accretion+ erosion- Point 41

2 8 1 Q 0 5 4 4 7 5 7 6 3 7 4 12. 4.7 1. 2. 9. 7. 5. 1.3 4. 4. 17. Pass Net Rate +62. + +10. + +< + + + + + + +40. - + +34. +25. +53. h 5 25 50 47 375 175 75 350 275 200 175 1500 175 650 1200 950 Net Dist. +2300 + + + + + + + + + + + + + + 1975+

Yarborou: 1 1 1 1 1 1 1 1 ii ii ii ii 1 1 1 1 ii 1 Pass- Net Time 1937 1974 ii 1 ii 1 1 ii

7 2 5 0 7 2 2 2 2 2 9 2 7 18. 6. 37. 1. 18. 22. 22. 22. 16.7 22. 22. 1.0 88. 22. 11.1 16. per - - - + Aransas Rate + + + +< + + +< + + segment ft 75 25 10 75 75 10 50 75 ft + 150 100+ - + + beach Dist. + + +< + -100 -100 -100 -100 +< +400 -100

1 1 1 1 1 Time 1970 1974 it ii 1969 1974 ii ii ii 1 1 1 ii 1 ii ii 1 ii it

2 0 5 2 4 5 8 3 5 2 6 2 4 6 fi'y 2. 8.7 13. 6. 15. 11.4 20. 4. 6. 2. 4. 43. 13. 18. 11. 28. Rate per + + + - ft

5 Changes 25 100 150 75 50 75 25 50 47 150 ft 175 125 225 200 125 300 Line Dist. + + +

! I Time 1958 1970 II II II II 19581969 It II I II II II II l II M It II 19591969

Vegetation 1 1 1 1 5 6 6 4 8 9 4 0 5 4 2 0 /■ry 25. 17. 5. 13. 22. 15. 17. 7. 10. 74. 8. 8. 37. 39. per 11.6 + 100. Rate +104. + + + + + + + + + + + + + + ft Channel

5 550 375 250 125 300 47 325 375 150 225 175 175 washover 800 850 washover ft 1600 Dist. +2250 + + + + + + + + + + + + + + Packer +2200

1 1 1 ii Time 1937 1938 ii n 1 1 it ii ii 1 it n ii n ii ii ii 19371959 Rate per ft

Dist. ft Time

1 5 10 1 12 13 14 1 16 17 18 19 20 accretion+ erosion- Point 42

3 6 2 0 4 4 2 8 8 1 5 5 5 5 8 5 5 2. 5. 9. 12. 12. 8. 12. 5.9 Pass Net Rate +22. 17.+ 12.+ + + + +13. +11. 11.+ 17.+ + + + + + +16.4 +13. -10. -12. h 5 5 825 650 450 75 200 350 500 450 450 650 47 475 325 475 225 625 525 400 Net Dist. + + + + + + + + + + + + + + + + + - -47

Yarborou I I I II II I II II II I II II II Pass- Net Time 1937 1974 ii II ii I 1937 1975 I! II II 3 8 7 2 1 6 7 6 4 6 1 7 /ry per 27. 16. 22. 11. 5. 16. 5. 44. 5. 11. 5.6 16. 33. Aransas Rate + + + + + + + + + -116.7 segment ft 75 50 25 75 25 25 50 25 75 ft 125 100 - + - + + + beach Dist. + + + + +200 -525 -150 Time 19691974 it ii ii 19691975 ii ii ii ii ii ti it ii ii ii ii

9 5 2 8 5 6 1 1 5 2 1 6 9 srry 30. 9. 4. 9. 3.7 5. 24. 11. 9.3 9.3 18. 22. 24. 29. 88. Rate per + 145.+ + - - - - Changes ft 100 50 blowout blowout 50 75 150 125 125 300 325 400 ft 325 construction 100 325 250 - Line Dist. + >ark +1525 + - - -1200

Vegetation Time 19591969 ii ii ii ii ii ii 1956 1969 ii ii ii ii ii ii ii ii ii it ii

4 6 6 9 0 0 6 2 6 6 2 8 6 17.0 11. 21. 70.4 13. 15. 17. 17.0 25. 27. 38. 31. 31. 23.7 34. 23.7 48.7 40. 27. 46.0 Rate per + + + - + + + + + + + + + + + + + + + + ft

5 5 375 250 47 300 350 375 375 47 525 725 600 600 450 650 450 925 775 525 875 Dist. ft + + + -1550 + + + + + + + + + + + + + + + +

Time 1937 1959 it ii ii ii ii ii n 19371956 ii n ii ti ii ii it ii ii it ii yr Rate per ft

Dist. ft Time

6 8 5 3 38 40 accretion erosion Point 21 22 23 24 25 2 27 2 29 30 31 32 33 34 36 37 43

4 3 2 5 5 5 9 4 8. Pass NetRate -22. +24. +47.4 +36. +62. + +39. +28. +70. h 850 925 325 - 1800 1375 + 1100+ Yarborou; Net Dist. + + + +2375 +1500 +2675

1 1 1 ii ii Pass- Net Time 1937 1975 M 1 ii ii ii

5 8 5 2 5 1 1 5 2 5 7 per 54. 31. 4. 18. 4. 9. 9. 4. 18. 4. 22. Aransas Rate + + + + + + + + + segment ft 25 25 50 50 25 25 ft 175 100 - 100 125 beach Dist. -300 + + + + + + + + + Time 1969 1975 ii ii ii ii ii it ii ii ii

8 1 2 1 8 6 8 fTy per 51. 14.8 22. 11. 3.7 1. 2. 15. Rate - -124. - + + Changes ft 5 700 200 300 150 50 25 2 150 Line Dist. ft - -1675 - - + +

Vegetation Time 1956 1969 ii ii ii ii ii ii 1960 1969 11 ii

2 9 3 7 2 0 8 rry 34. 57. 81.6 119. 13.2 65. 50. Rate per + + 105.+ + + + + + +203. ft blowout 650 250 blowout Dist. ft + 1100+ 2000+ 1550+ +2275 + 1500+ 1150+ +2650

Time 1937 1956 II II II II II 1937 1943 1937 1960 II II II

rxy Rate per ft

Dist. ft Time

42 50 51 accretion+ erosion- Point 41 43 44 45 46 47 48 49 44

Intensity- minimal minor minimalminimal minimal major minimal minor minor extrememinor minor minimal major minor minimal minor minimalminimal minimalminimal minor extrememinimal minor major minor major minor minimal minor Island coast Bay Island Grande Padre coast coast Christi southernChristi RioPassChristi Pass coast coast coast coast coast Arthur Brownsvilleof Pass Padre Island Island Island in. in. UpperUpperMatagorda UpperUpperMatagorda Upper Freeport Corpus Corpus High Sargent Corpus High High in. 40 00 less Area Galveston CentralMiddle PortLower Galveston South Beaumont SabineExtreme Galveston SouthPalacios Mouth Aransas Aransas 29. 29. or 1965). Pressures 29.40 to to in. Minimum 03 01 00 19401940 19411941 1942 1942 1943 1943 194519451946 1947194719491954 1955 1957 19571958 1958 19591960 19611963 19641967 1968 1970 1970 19711973 Cry, Central above 29. 28. 28. Year and 1854-1973 1964; Miller Coast and Intensity major major major Miller, Dunn extrememinor minimal minor minimal minor minimalminimal minor extremeextrememinimal extrememinimal minor minor minor minimal minor minor minor minimalminimal minor minimal minor minor B Texas and Winds 74 higher the from 100 135 than to and Dunn to Appendix Maximum Less 74 101 136 Affecting1956; Island Bay CyclonesTannehill, Classification coast coastChristi coast coast coast coast coast coast coast coastPass Christi coast coastPadre coastO'Connor coast coast coast Aransas coast coast Intensity Area UpperUpper Corpus Lower VelascoLowerLowerLowerLowerLower UpperLowerSabine CorpusEntireLower SouthLower PortLowerFreeportLowerMatagorda Rockport Entire PortLower Upper Tropical from Brownsville BrownsvilleBrownsville (compiled Year 1900 1901 1902 19081909 190919091910 1910 1912 191319151916 1918 191919211921 19221925 1929 19311932 1933 1933 1933 193319341934 193619361938 MinorMinimal MajorExtreme Intensity major minimal major minimal minorminimalminimal minimal minor extreme minimal minor major major minimalminimal minor extrememinimalminimalminimalminimal minor minimalminor minor minimal minor southward southward Isabel Christi Isabel coast Island coast coast coast coast coast coast coast coast coast coast coast coastcoast coast coast coast Area Galveston Port GalvestonGalveston CorpusGalvestonGalveston PortIndianola LowerIndianola PadreEntire Upper Lower SargentBrownsville LowerEntire UpperEntireLower UpperBrownsville UpperUpperEntireLowerLower Upper Upper Year -18541857 186618671868 187118711872 1874 18741875 1876 18771879 188018801880 18811885 18861886 188618861887 18881888 18911895 18951897 1898 45

CAppendix

List ofMaterials and Sources

List of aerial photographs used* in determination of changes in vegetation line and shoreline. Indicates that vegetation line and/or shoreline wasused inmap preparation.

Date Source of Photographs * Apr. 1937 * Tobin Research Inc. Feb. 1943 * U. S. Dept. Agriculture Feb.,Mar. 1956 * U. S. Dept. Agriculture Dec. 1958 * TobinResearchInc. Jan. 1959 * Tobin Research Inc. Apr. 1960 Tobin Research Inc. Sept. 1961 U. S. Army Corps Engineers Sept. 1961 Natl.Oceanicand Atmospheric Adm. June 1967 U. S. Army Corps Engineers Nov. 1967 * InternationalBoundary Comm. Oct. 1969 * Natl. Oceanic and Atmospheric Adm. Aug. 1970 * Natl. Oceanicand Atmospheric Adm. June 1974 Texas GeneralLandOffice May, June 1975 * Texas General Land Office July 1975 Texas General LandOffice

List of Maps Used inDetermination of Shoreline Changes

Date Description Source of Maps

1860-1866 topographic map 823 Natl. Oceanicand Atmospheric Adm. 1867 topographicmap 1044 Natl.Oceanicand Atmospheric Adm. 1881 topographicmap 1679 Natl.Oceanicand Atmospheric Adm. 1881-1882 topographicmap 1626 Natl. Oceanic and Atmospheric Adm. 1881-1882 topographicmap 1628 Natl. Oceanicand Atmospheric Adm. 1881 topographicmap 1627 Natl. Oceanicand Atmospheric Adm. Feb.1899 topographicmap 2354 Natl. Oceanicand Atmospheric Adm. 1923 topographicmap— U. S. GeologicalSurvey 15-minute quadrangle

List of 7.5-minute quadrangle topographic maps used in construction ofbasemap. Source of thesemaps is the U. S. Geological Survey.

Port Aransas, Texas SouthBirdIsland, Texas Crane Islands NW, Texas South Bird IslandSE, Texas Crane IslandsSW, Texas YarboroughPass,Texas PitaIsland, Texas