.Iournal of Coastal Research 4[)7 4HI Fort Lauderdale, Florida Spring 1992 I

Inlet Migration and Hydraulic Processes at East Pass, Florida

Andrew Morang

Coastal Engineering Research Center U.S,Army Engineer Waterways Experiment Station Vicksburg, MS ;~9180-6199. U.S.A.

ABSTRA{=T _

MOHAN(;, A., 1992. Inlet Migrat ion and Hydraulic Processes at East Pass, Florida. Journal (if Coast.al ,ttlllllll:. Research, Hen, ·1;)7 481. Fort Lauderdale (Florida), ISSN 0719-0208. East Pass, a tidal inlet in the Florida Panhandle between Pensacola and Panama City, connects Choc­ •• • tawhatchee Bay to the Gulf of Mexico. From 198;{ t.o 1991, the U.S. Army Corps of Engineers sponsored ~ ~ a monitoring project to measure waVCH, currents. tidal elevations, bathymetry, and shoreline changes at ass'#" the site. Based on these data and on historical records, a three-phase model has heen developed which --+4 describes the inlet's behavior during the last. 120 years. The first phase (pre-1928) is of spit development 1+-- and breaching and covers the period when the pass was oriented in a northwest-southeast direction between Choctawhatchee Bay and the Gulf. From 1928 to 1968, the inlet was characterized by the second phase: stable throat position but with a main ebb channel that migrated over a developing ebb-tidal delta. This phase covers the time after the inlet breached through Santa Rosa Island in a north-south direction and began to migrate to the east. The third phase, spanning 1968, when rubble-mound jetties were built, to the present is characterized by a stable throat and ebb channel, and ebb-tidal shoal growth. Despite the jetties, East Pass has continued to demonstrate a tendency to move eastward. The driving forces of the eastward migration are hypothesized to be: (I) Wave forces. The predominant wave direction measured in lO-m water depth is from the southwest, while the shoreline trends east-west. (2) Backbay tidal channel and flood-tidal shoal geometry direct ehb currents towards the eastern shore of the inlet. (:n Because of freshwater inputs, the ebb flow is longer in duration and higher in velocity than the flood.

ADDITIONAL INDEX WORDS; Ebb-tidal shoal, erosion, jetties, nearshore wave measurement.s, Santa Rosa Island, tidal hydraulics, tidal inlet.

INTRODUC:TI()N nel may occur. During the 1970's, the beach im­ East Pass is a tidal inlet located in the Florida mediately north of the east jetty was cut back so Panhandle along the north-eastern Gulf of Mex­ severely that the inlet threatened to undermine ico shoreline (Figure 1). Wave energy is generally the landward end of the jetty. Therefore, a 90-m­ low, with less than 10 percent of the waves mea­ long spur jetty was huilt in 1977 to divert the How sured in a 4-year period greater than 1.0 m high of water further towards the center ofthe channel. and wave period typically less than 6.0 sec. 'rides Since then, deep scour holes have formed at the are diurnal, with maximum range less than O.G m. toe of the spur. In February, 1990 the writer ob­ Despite the relatively low energy along this shore, served that the spur was only 60 m long, having the morphology and the behavior of the inlet lost :10 m during the previous winter months. By resembles those of inlets found along the much March, 1991, another ~~o m had disappeared. higher energy Atlantic coast of the lJnited States 1\) assess the causes of instability at East Pass, (e.g. BOOTHROYD, 1985; IIANSEN and KNOWLES, the U.S. Army Corps of Engineers sponsored a 1988). monit.oring project to measure wave and hydraulic Rubble-mound breakwaters were built in 1967­ conditions. 'This paper discusses the data collect­ 1969 by the United States Army Corps of Engi­ ed between 19H:~ and 1991 at the site. Interpre­ neers to stabilize the mouth of the inlet and im­ tations are based on these data and on historic prove navigation. Nevertheless, expensive dredg­ maps and earlier data collected by the Corps of ing and repair have continued to be needed. The f~ngineers. inlet continues to require significant dredging be­ (~E()GRAPHY AND GEOL()GY OF cause of thalweg migration. In addition, the east­ EAST PASS ern shore of the channel has eroded severely, con­ dominiums (built on an ephemeral sand spit) are General threatened, and a breakthrough to a former chan- East Pass, the only direct entrance from the Gulf of Mexico into Choct.awhatchce Bay, is lo­ 91078received 6 September 1991; accepted in revision 12 December 199L cated on the northwest coast of Florida 70 km 458 Morang

I , ( ,i , , ') I ~ I (' ,; -N- .) i A LA. I J " ~ i, \ i I .i i, l, MIS S. i, \, I GA. , ----._------~, MOBILE. FLA. \, ~-~-~~-~----~~--- ~ TALLAHASSEE

". GU LF o F » AI E -r leo ~

,1 SCALES 25 0 25 50 MI -" ...... 40 0 40 80 KM VICINITY MAP ...... I

Figure 1. Vicinity map, Ea~t Pass, Destin, Florida. !

east of Pensacola and 80 km northwest of Panama Choctawhatchce Bay City (Figure 1). Its latitude and longitude are ;10°2:)' Choctawhatchee Hay, landlocked except for East N and HGO:~l' W. The pass lies between Santa Rosa Island on the west and Moreno Point on the east Pass and Santa Rosa Sound, has an area of about ;~16 (Figure 2). Santa Rosa Island is a long, narrow sq krn including the tributary bayous. The barrier beach which extends about 70 km along bay is about 48 km Jong east to west and averages the coast from East Pass to Pensacola Pass. Santa 6 krn in width. Forty-one sq km of the bay are Rosa Sound, imrnediately north of the barrier, is over 9 m deep, and some depressions are 12 m a natural waterway connecting Pensacola and (U.S. CONCHESS, 1950). Santa Rosa Sound enters Choctawhatchee Rays. For Gkm west of the pass, the southwest end of the bay and the Intracoastal Santa Rosa Island is part of ~:glin Air Force Base Waterway canal to St. Andrews Bay enters at the (AFJ~) and has remained mostly undeveloped. east end. Garniers, Boggy, llocky, and La Grange Moreno Point is the western end of the peninsula Bayous flow into the north side of the bay and which separates Choct.awhatchee Hay from the the Choctawhatchee River into the east. The lat­ Gulf of Mexico. The town of I)estin is imrnedi­ ter river is 2HO krn long and drains 1:.3,500 sq km at.ely north of Old Pass Lagoon, the pre-1928 inlet. in west Florida and southeast Alabama. The river The east side of the pass near the jetties consists is heavily loaded with silt and clay sediments, of a sand spit, known as Norriego Point, which which are being deposited in a delta at the eastern formed in 19:i5. This spit and the low beach im­ end of the bay. mediately to the east have been developed with Salinity at the bottom of Choctawhatchee Bay condominiums and canals since the 1970's. ranged Irorn 22 to :HY:;l(' (parts per thousand) in

.lournal of Coastal Resi-arch, Vol, H, No.2, 199:2 88'40' 86'

30'30' ~''l)' ~ -N- ~ I ~ $: 3\:1'20' 30'20'1 ~. ~. ~ :r: 1

rt ~ ;; I J~'lO' 30'10'

FLORIDA

CHOCTAWHATCHEE BAY LEGEND ~ BASED ON NOM CHAATS S11388 ~RN.. 1988 3 4 ? n385 J~ 1978 ~ TIDE C~£ LOCATIONS DEPTHS IN lo4ETERS BELOW .....W , 0 , 2 J 4- 5 8 7 8 9 10 KILD~ETERS 88'40' 880~' 86'20' ""'10'

Figure 2. Choctawhatchee Bay and surrounding region.

*""~

.... ~ 'i:"",,:'~'''':~ ~~~~~'.\ \-\ ) 460 Morang l.

.Iune, 1965 (GOLDSMITH, 1966). Salinity may be :~ to 4 In above the clean white Holocene beach. highly variable because during storms the rivers The wide sandy beach just east of the inlet and ( and bayous can supply a significant amount of south of Old Pass Lagoon was part of Santa Rosa fresh water into the bay (U.S. ENCINEER OFFICE, Island before the present channel was cut in 1928. MOHILE, 19:19). Also, freshwater springs How into Since the 1970's, this area has been developed I, the bay bottom (F.F. ESCOFFIEH, personal com­ with canals, roads, and multi-Boor condomini­ munication, 1990). ums. A wide shoal along the edge of Choctawhatchee Longshore Drift Ray contains primarily coarse sand, while silt is the dominant sediment in the deeper parts of the There has been controversy in the technical lit­ bay. A large sand area in the southwest corner of erature and within the Corps of Engineers about the bay, north of Santa Rosa Island, is of notable the predominant drift direction in the vicinity of interest because it is probably a deposit of Hold" East Pass. Many researchers have considered it I reworked sediments (}OLDSMITH, 1966). 'The to be westerly along the western Florida Panhan­ , quartz grains there are yellowish and are rounded dle (KWON, 1969; lJ.S. ENGINEER OFFICE, MOBILE, ~ and well-sorted. This is in contrast to the clean 19~~9; U.S. AHMY ENGINEER DISTRICT, MOBILE, white, angular grains found in ~~ast Pass and along 196:~; WALTON, 197:~; WHIGHT and SONU, 1975). the shorelines facing the (;ulf of Mexico. Puhlished estimates of the amount of net drift vary considerably. STON}<~ (1990) believes that the I. Santa Rosa Island Pleistocene headland east of Destin is the primary ( Santa Rosa Island is the second longest (84 kml source of sand along this part of the coastline and harrier island on the Gulf Coast, hut averages only that net transport is westward towards Pensacola :.100-500 ill in width (OTVOS, 19H2). Dunes up to Pass. Using the Coasta1 Engineering Research about 12 m high occur on the western end of the Center's 20-year Wave Information Studies (WIS) hindcasts (HlJB}<~HTZ and HHOOKS, 1989), STONE ill;!' island, but near East Pass elevations are less than H ill. The Holocene quartz sands are between ;) (1990) computed that the net transport rate was l ( and 10 m thick and are interpreted by OTVOS variable along Santa Rosa Island, reaching a max­ (1982) as being a veneer of shoreface, dune, and imum near Pensacola Pass. At East Pass, he es­ ( beach deposits which overlie a Pleistocene core. tirnated it to be 40,000 cu m/yr. Near the tip of the western jetty, rotary drill cores l ]nder the scenario that the net drift is to the recovered brown, poorly graded sand with silt west, the dynamic behavior of East Pass implies content at a depth of about 12 rn (Mobile District that it is rnigrating updrift. Updrift inlet migra­ archives). This brown sand may represent the top tion has been reported in the literature (AUBREY of the Pleistocene surface. STONE (] 9~)0) considers and SPEEH, 19H4; CAI{TEI{, 1988; FITZGERALD, Santa Rosa Island to be a typical foredune-barrier 19HH). An alternative scenario is that there is a fiat complex along its entire length. Possible relict localized drift. reversal in the vicinity of East Pass. flood tide shoals in Santa Rosa Sound suggest. that. L~;VIN (198:1) noted that there was geological evi­ the present island may have been a series of small­ dence of an anomalous eastward sediment trans­ er ones at one time. 'I'he openings were likely port in this region. The southwest-northeast ori­ short-lived as both STONE (1990) and rrANNEH entation of the beach ridges on the eastern end (19G4) believe that there has been an ample sup­ of Santa H,osa lsland (Figure :~) suggests that this ply of lit torally reworked sediment available dur­ part of the island grew from west to east. TANNER ing the Holocene. (1964) postulated that drift to the east and to the west met at a locus somewhere between Panama Moreno Point (Destin) City and Pensacola. Suhtle changes in wave eli­ Moreno Point peninsula, mapped as the post­ mate rnight cause this locus to move back and Wisconsin-age Silver Bluff shoreline by MACNEIL forth. (1949), has an elevation of up to H ill and may be {;E()L()(;I(: M()DEL OF EAST part of a relict barrier island forrned during the PASS BEHAVIOR peak and regressive phases of the Sangamonian (about 125,000 years HP) (STONE, 1990). No core Phase 1: Pre-t 871 to 1928 data are availahie. Eaat of Destin, facing the Gulf The historic behavior of East Pass inlet can be of Mexico, the oxidized orange bluffs rise about described in terms of a three-phase model, based

.lournal of Coastal Research, Vol. H, No.2, ID9L Inlet Migrat ion and Hyd raulic P rocesses 46 1

Figure 3. Aerial phot ograph of the East Pass area, 28 J une. 1987.

on models described by FIT ZGERA LD (1988) for open while the less inefficient older in let graduall y tidal inlets along the East Coast of th e United closes. By th is process, the older inlet becomes a n States. elonga ted pond that paral lels th e shoreline. The first phase. charact erized by inlet migra ­ Histori c records indicate that East Pass In let tion, is of spit development and breaching (F igur e has a butted Moreno Point since the 1820's. 4) .This usually occurs in a mi xed-energy (neither Wheth er the pass ever occupied a location fu rther wave- nor tide-dom inant) environment whe re the to the west is unknown. The historic data suggest migrati on of the tidal inlet results in an elongation th at Moreno Point ha s been relatively resistant of the inlet channel. Under these cond itions, if to erosion. John Willi am s' 1827 map is not ac ­ thespit is breached during a catas trophic storm, curate enough to use for shore line analyses, but thenew inlet, which is shorte r, will normally stay the sha pe of the peninsu la on his map is contern- 462 Morang-

front were essentially continuous with the outer P[RCENT OCCURR[NCE HISTOGRAMS

30 bars of the adjacent coast and served as the av­ --.- -.J--~-~l·- -- enue of littoral bypassing. The crest of the bar is about ~;-3 m ML W, while the base of the bar front ~ 20 is about -6 m. iii w CL 10 To show changes in the overall size and shape -1- -. . of the shoal over time, the 15-ft (4.6-m) isobath 0+- --~-ii'- ~ .• ~ has been plotted in Figure 10 for each of the seven o 90 180 PEAK 0 I RCCT I UN (OEGR[~5) gridded surveys. The contours have been smoothed

20 for clarity. For the first few years after project construction, the shoal grew to the south in the

f-< form of a symmetrical semi-circle, advancing as ~ U 10--1------+-~I~ ct:: far as Polygon 8. After 1974, the bar front sta­ ~J bilized in 8, and further growth occurred in Poly­ gons 4, 11, and 12 as the shoal bulged to the south­ o west. Q 8 PEAK PER100 (Sr:CONOS) Figure 11 shows the shoal in June, 1967, before 30 the jetties were built. The main channel extends to within 200 m of the edge of the shoal. The [-,r, 20 steepness of the seaward face is shown by the u ,~ converging contour lines. Figure 12 shows the shoal L..J CL 10 in February, 1990. The increase in overall size since 1967 is obvious, as is the northeast-south­ o o .2 west orientation of the channel. Although the WAVE HEI GHT I MlTfR5 ) ij. channel had not been dredged since April, 1988, f Ln~T PRSS, OES1 IN, fLORIUR it appears to have naturally remained over 3 m j CJfl/ - 9U, WflVf:S· \. iJ M deep. There are two areas of serious scour: one at r Figure 9, Percent occurrence histogram for waves higher than ].0 m measured by CERe gage 6.4 km west of East Pass. Pre­ the tip of the west jetty and the other around the ( dominant direction is from the southwest. end of the spur jetty. Changes in sand distribution over time are shown in Figure 13, which depicts the subtraction of the 1967 surface from the 1990 one. Green con­ Zone, Plane Coordinates. The depth points from tours represent accumulation and red, erosion. the survey sheets were digitized and used as input The wide green band shows where the shoal has for CPS:3's surface gridding algorithms. Contours grown seaward, with over 7 m of sand 500 ill south and volumes were based on the gridded surfaces. of the mouth of the inlet. The green immediately The area gridded was a square with 5,OOO-ft (1,524­ east of the east jetty marks the growth of the f m) sides. Eighteen 1,OOO-ft (~)05-m) square poly­ beach in the late 1960's. It has not been possible gons encompassing the present ebb-tidal shoal to determine what proportion of this deposition

were used for the volumetric calculations. These was natural and what was man-made, but the II squares serve as convenient references and are author believes that most was dredge fill depos­ plotted in all the subsequent figures. Manual cal­ ited during project construction. A broad area near } m culations of the shoal's volume compared closely the jetties (Polygon 2) has eroded, and over 11 J with CPS~~ results. Based on an assumed accuracy has been lost from the scour hole at the west jetty. of plus or minus 15 cm for the hydrographic sur­ Within the inlet, the eastward movement of the , veys, the error of the volumetric calculations is channel is evident. Before 1986, a 300-m-Iongweir estimated to he 25-~30 t; existed at the landward end of the west jetty. The ebb-tidal shoal is a wide, If-shaped body While the weir was open, the area to the west in of sand with a fiat top and a crescentic bar at its Polygon 17 was underwater about 1.5 m. Since seaward edge. WRIGHT and SONU (] 975) identified 1986, when the weir was closed, sand has accu­ three units to this inlet-mouth bar: the seaward­ mulated here. The author confirmed that the beach ascending back bar, the bar crest, and the steep is rapidly advancing seaward in this area during bar front. They believed that the bar crest and field visits in 1989 and 1990.

-Iournal of Coastal Research, Vol. 8. No.2, 1992 Inlet. Migration and Hydraulic Processes 46~1

CHDCrAWHATCHEE BAY ~ -N- ~ ...... : :.~. '.... ~POND '~::.- . -" .::.',:': ~::.. ~: ..<":. :,' . '.~ J: APRIL 1928 1871 BREACH INLET7 G {J L. F SHORE OLDER o F },/ £ X leo

SCALES 2000 a 2000 4000 FT ... jiii i 1871-1928

Figure 4, Pre-1871-1928 East Pass Inlet. Based on Plate 4 from U.S. Engineer Office, Mobile, 19;~9.

porary and a large Hood-t.ide shoal is depicted in caused by longshore drift which causes a prefer­ the same position as the present one. Some ero­ ential accumulation of sediment on the updrift sion of the western tip of Moreno Point has oc­ side of the ebb-tidal delta, resulting in a deflection curred since 1871, but the south side, facing Old of the main ebb channel (FITZGEHALD, 1988). In Pass, is essentially unchanged. Further evidence some cases, as at East Pass, the main channel that Moreno Point did not extend much further migrates far enough downdrift so that it impinges west is provided by the cores taken along the high­ on the downdrift shoreline, causing erosion. Even­ way bridge between Santa Rosa Island and Des­ tually the channel becomes hydraulically ineffi­ tin, which suggest that there are lagoonal deposits cient in this configuration and it diverts its flow here between 9 and 12 m below rnean low water to a more seaward route through a spillover lobe II <."1 (MLW). channel. This sequence of events describes East Although the northeastern end of the inlet has Pass' behavior between 1928 and 1968, as de­ been anchored by Moreno Point, the seaward end scribed in the following paragraphs. has migrated back and forth. Before 1928, East After the new East Pass inlet was breached in Pass ran in a northwest-southeast direction and 1928, it shoaled while the original course remained entered the Gulf of Mexico about 2 l~ km to the open. During a great storm in 1929, local inhab­ east of its present mouth. A brackish pond about itants dug a pilot channel along the 1928 breach, one-half km east of the eastern end of the present which let t.he high water from Choctawhatchee Old Pass Lagoon suggests that in the past the Bay rush out to the Gulfof Mexico (ANGELL, 1944; inlet extended at least ;~ km east of its present C;OLDSMITH, 1966). Record rains, 40 ern in 48 hr, location. had fallen on Choctawhatchee Hay and its trib­ Santa Rosa Island was breached in April 1928, utary rivers (iLS. ENCINEER OFFICE, MOBILE, during a heavy rainstorm, at about the location 19:39). The rainstorm was accompanied by strong of the present inlet (U.S. CON(;(iESS, 19f)()). south and southwest winds. High-water marks re­ vealed that the water levels rose to 1.65 m above Phase 2: 1928-1968 MLW near Port Washington and 1.5 m near Val­ This phase is characterized by stable throat po­ paraiso, resulting in a tremendous outflow through sition but a main ebb channel that migrates over the breach. As this new channel was shorter and a developing ebb-tidal delta. The migration is more efficient than the longer Old Pass route, it

-Ioumal of Coastal Research, Vol. 8, No.2, 1992 464 Morang captured the tidal flow in and out of Choctaw­ average of 60 m for a distance of 2 1/2 km west of hatchee Bay. The breach widened and by 19~35 the pass. was 760 m across. The main channel'8 trend was northwest-south­ The new channel cut off the eastern tip ofSanta east for over :~O years. Sometime in early 1962, a Rosa Island. Under the influence of waves and north-sout.h-oriented channel breached the ebb­ littoral drift, the Gulf entrance of the old channel tidal delta (Figure 5) (U .S. ARMY ENGINEER began to shoal, and by 1935 only a shallow, narrow DISTHICT, MOBILE, 196~3, Plate 4). The formation opening remained. The old ebb-tide shoal eroded of the new channel appears to have been a natural rapidly, and hydrographic surveys indicate that process, and there is no indication in the literature it had disappeared by 1938 (U.S. ENCINEER OF­ or the project maps that the new channel was FICE, MOBILE, 19~39, Plate 4). initially cut by dredges. Shoals and sandbars rap­ Aerial photographs show that the sand spit along idly formed between the two channels. By Feb­ the east side of the inlet, now known as Norriego ruary, 1964 (based on the hydrographic survey Point, formed in 1935. The source of sand for maps), the new north-south channel was wider Norriego Point's growth appears to have been lit­ and deeper than the older northwest-southeast toral drift carried into the inlet by the Hood tide. one. An oblique aerial photograph taken in Feb­ Drifters released during the 19:~8 study traveled ruary, 1965, shows a large crescent-shaped sub­ into the inlet on the flood, closely following the aerial sandbar near Norriego Point with a shoal , I eastern shoreline (U.S. ENGINEEH OFFICE, MOBILE, extending most of the way across the older north­ 1939, Plate 5). In addition, some sand may have west-southeast channel (Figure 6). The naviga­ come from the erosion of the beaches adjacent to tion channel was rerouted to follow the deeper the inlet's mouth. The amount of sand available north-south channel, and in 1965 dredged sand I was so great that several times in the mid-19~)O's was placed on the sandbar to completely block the channel leading into Old Pass Lagoon was the older channel. completely blocked (based on aerial photographs Phase 2 of the model ends with the construction from the archives at Eglin AFB). When the Gulf of the jetties, starting in December, 1967. The opening to Old Pass Lagoon closed, the east-west north-south channel was stabilized by the jetties and the other one was blocked with a sand dike. channel running south of the highway bridge be­ Several ponds marked the route of the former came the only access to Destin's harbor. Because northwest-southeast channel. One of these ponds of the rapid shoaling, maintaining this navigation still exists, and condominiums have been built channel into Destin's harbor has required frus­ near it. trating and costly dredging for the last 60 years. By 19~~5, East Pass' thalweg was hugging the Phase 3: t 968-Present eastern side of the new channel, a behavior which has continued to the present (Figure 5). Between From 196H to the present, East Pass has been 1935 and 19:38, the east shore moved 90 m north­ characterized by the third phase of the model: east (U.S. ARMY ENGINg£1:R DISTRICT, MOBILE, stable inlet throat and ebb channel, and ebb-tidal 196:3). Despite the erosion on the east shore, Nor­ shoal growth. During this phase, when sand by­ riego Point sand spit continued to grow in overall passes the mouth of the inlet, large bar complexes , width, nourished by a great influx of littoral sed­ form, migrate landward, and weld to the down- I iment. From 1988 to 1961, the east side of the drift sho.reline (FITZG~~HALD, 1988). The bar com- inlet continued to move east, but at a slower rate. plexes form from the stacking and coalescing uf " A comparison of 19:38and] 955 vertical aerial pho­ swash bars on the ebb-tidal delta platform. The I tographs shows relatively little change in the ori­ swash bars move landward because of the domi­ entation of the inlet. nance of landward water How across the swash Between 19:35 and 1938, the inlet's west side platform, creating a net landward transport of I' (the eastern end of Santa Rosa Island) eroded sand on both sides of the main ebb channel. The about 150 m (U.S. ARMY ENGINEER DISTRICT, ebb-tidal platform continues to grow as long as MOBILE, 1963). Between 19:38 and 1961, the end the inlet does not migrate. If of Santa Rosa remained in about the same posi­ An essential question that must be addressed tion but became more pointed in shape. During is how stahle is Phase ~3 at East Pass; if it is un­ F' this time, the Gulf of Mexico shoreline eroded an stable, what physical processes are responsible? ~

Journal of Coastal Research, Vol. 8, No.2, 1992 r Inlet Migration and Hydraulic Processes 465

CHOCTAWHATCHEE BAY IJORENO POINT SHORELINE 1934 ISOBATHS 1941

~ -N-

~ I DEC 1961 I

--- ",

~ . \,- IMAY 19671

.' ...... --- :-_----=--- -<~'--~-- -- -Ie'": " i~ '"' " ,c· '\, r > ..... '

Figure5. East Pass from 1934 to 1967. This covers Phase 2 of the inlet migration model, the period after the present inlet was breached and before the jetties were built. Based on figures in U.S. ARMY ENGINEER DISTRICT, MOBILE (1963). Inlet Migration and Hydraulic Processes 467

Proposed Driving Forces of Eastward Migration

EAST PASS, DESTIN, FLORIDA The remainder of this paper will describe the 30°23"25" N; 86°35"38- W field studies conducted between 198:3 and 1991. 4.0 _ ~ _------~ ------_. A------• Rased on these data, the driving forces of the 3.0 _. _.. - -. - .. ----.------"' --. eastward migration are hypothesized to be the following: (a) Wave forces. The predominant wave direc­ tion, measured off Fort Walton Beach 6.4 km to the west of East Pass from 1987 to 1990, is be­ 10 13 18 18 22 2' tween ] BO and 210 degrees, while the shoreline

20 ------•• - trends at an azimuth of 95 degrees (Figure 2). (b) Backbay tidal channel geometry. Two tidal : 15 ..... ­ c channels lead from Choctawhatchee Bay into East o ~ Pass: one is to the north and the other parallels :llI: Santa Rosa Island in an east-west orientation.

10 13 111 18 22 215 2' Hood-tidal shoal directs the inlet's currents to the east along Norriego Point. Current measurements ~ 3'0 ------_. - - _. - --- _.- -- -. made south of the highway bridge have shown ~ Cl 270 ------_. _. ------. ------_.••. ------.- that while the tide is turning, Hood currents How i o northeast along the west shore while ebb currents ~ 110 flow southeast along the east shore. 4 !, Ci 10 - - _.. ------.- (c) Differences in duration of the ebb and flood i =:llI:

FIELD DATA r:()LLECTI()N AND RESULTS The jetties have temporarily stabilized the inlet by preventing the mouth of the main ebb channel Wave Data 1986-1990 from migrating. Further inland, the inlet has dem­ Directional wave data were collected by the onstrated that it is attempting to continue its long­ Coastal Engineering Research Center (CERC) term tendency to move eastward. This is con­ from 1986 to 1990 at a site 6.4 km west of East firmed by the numerous hydrographic maps made Pass (Figure 2). Sea Data directional wave gages at the inlet, which show that the thalweg hugs the were mounted in a steel tripod at 9.5-m water depth. 'The gages were serviced by divers every east shoreline. Norriego Point has eroded severely two months and the data tapes were processed at and has had to be renourished with dredged sand C:ERC by the author. Wave bursts of 1,024 pres­ numerous times. Hydrographic maps show that sure, u-velocity, and v-velocity samples were col­ the ebb-tide shoal has grown steadily in area be­ lected every 6 hr. The data were spectrally ana­ tween 1967 and 1990. Examples of these data will lyzed using a band-averaging procedure. Pressure be presented later in this paper. Results of this values were converted to water heights using lin­ study suggest that constant maintenance will be ear wave theory. The directional distribution of required to maintain the inlet in its present lo­ wave energy was calculated with a method de­ cation. The condominiums, recently constructed scribed by l~()NClJ}<~T-HICG[NS et al. (196:3). Qual­ on Norriego Point, are in a precarious situation. ity-control procedures used to validate the wave A major storm might cause a breach in the low data are described in MORANG (1990). beach to the east of the present inlet, allowing the Between 1986 and 1990, gages were in the water channel to reoccupy its pre-1928 course. East Pass a total of 1,240 days. Because of gage malfunc­ would thereby return to Phase 1 of the model. tions, a total of 645 days of valid directional wave 468 Morang ( ( data were recorded, a data recovery rate of 52 C(I PLRC[NT OCCURR~:NCE HISTOGRAMS ( (2,515 wave bursts total). The gage failures oc­ 20 - curred randomly and were not related to the se­ ( verity of the weather. During processing, waves f-. [1 below 0.15 m high were rejected because their U 10 ~-- i ~:I energy was too low to calculate realistic estimates l of the directional energy distribution. As a result, ] 444 wave hursts, ] ~3.2 ~';}, were rejected. The fol­ o a l60 270 360 ~ lowing plots represent Hmo spectral wave height, PEAK 0 I RECT I ON (DEGREES) I approximately equal to H, \ significant wave height 30 in deep and transitional water depths (HORIKAWA, 1988; COASTAL ENGIN}<~ERING RESEARCH CENTER, f--. 20 l 1984). ~ f EJ ) From 1987 to 1990, waves were generally low, o. 10 rarely exceeding 2 m. Storms were more frequent l o ------fII6---L..JIl ~ .IL j"l-LL__•. in winter but not necessarily more severe than IS---J a 8 12 20 those which occurred in summer. This part of PEAK PER IOlJ (SECONDS J Florida was not affected by hurricanes during the 30 ( time that CERC's gages were at the site. Figure 7 is an example of the data from .Iune 1989, during ~ 20 ~ U which two storms occurred. Peak period was be­ lY W tween 4 and 10 sec. The peak direction for most 0- 10 of the month was from the southwest, about 200 (JL1L'.L~r¥IT.-~_ I . -+-- _------I degrees. 2 3 Information about the overall wave climate at wnv[ HEI GHT {METfRS) ( the site is shown in Figure 8, which represents the EAST PASS, DEST[N, FLOR [DA , distribution of wave heights, periods, and peak 1987 - 9c), WAVES> 0.\5 M Figure 8. Percent occurrence histogram of all waves measured directions in the form of percent occurrence his­ by CERC directional wave gage 6.4 km west of East Pass be­ r: tograms. The most common wave height was only tween 1987 and 1990. Total wave bursts = 2,515. Predominant 0.2 to 0.3 m, and most periods were less than 7.0 wave direction is from the southwest. sec. The top histogram reveals a distinct south­ west orientation for most of the waves, with the most common direction being 190-200 degrees. ENCIN~~ERINC RES}<~ARCH CENTER, 1984), the wave For waves higher than 1.0 ill, the pronounced data suggest that during these years longshore southwest orientation was still evident, with few drift in this area would have been predominantly waves coming from the southeast (Figure 9). to the east. In the past, slight changes in weather f It must be stressed that these results summa­ patterns may have caused the wave direction to ) rize only the wave climate from 1987 to 1990. They swing back and forth around the 185-degree shore­ ~ are probably representative of long-term, mild normal direction. This would have changed the ( weather conditions, but no extremal statistics have drift direction and might account for the conflict­ , been calculated, and we have no hurricane wave ing interpretations reported in the literature. data for this area. We do not know what effects hurricanes have on the wave climate or the shore­ Ebb-Tidal Shoal 1967-1990 i line near East Pass. Hurricane Camille produced Analyses of the area and volume of East Pass' almost no effects here (TANNEH, 1970). An aerial ebb-tidal shoal were performed on VAX and Cray photograph taken 25 September 1975, after H ur­ computers at the Waterways Experiment Station f ricane Eloise, reveals no detectable changes to the (WES) using Radian Corporation's Contour Plot­ shorelines. ting System :3 (CPS:)) software. Seven hydro­ As the shoreline trends at an azimuth of 95 graphic surveys dating from 1967 to 1990 were degrees near East Pass, the 1987-1990 wave di­ chosen for their comprehensive coverage of the rection was slightly west of perpendicular. Be­ shoal and the mouth of the inlet. All depths were cause longshore sediment transport is driven by referenced to MLW, and all the charts used Lam­ wave radiation stress (KOMAR, ] 976; COASTAL hert Conformal Projection, State of Florida, North

Journal of Coastal Research, Vol. H, No.2, 1992 Inlet Migration and Hydraulic Processes 469

t o -N- o 1~· 17 g~=--~----+------f-JI3r------,------, o ll) \ y\\ I ./ . \ , -\.,~ 'r\"' "'~' o 1 .. o 14 ~ \, gr-----I:---~.---+------..:lu_~~-__+----~~I__-----_+_A:f__----_i o L()

o o 13 2 3 Rt------+--~--\.--~__+---l,--~-----..:lL-__'__.___jI__...... ,.----+_---____e,.,L_....:....:j o L()

o o 11 o ~

~ ( EAST PASS, DESTIN, FLORIDA .) 7 8 9 1363000 1364000 1355000 1356000 1367000 1368000 .J I

SCALE o 1000 FT PROJECT 1"'11 REVISIONS

PWB::IlIlORANC EAST PASS, DESTIN, FLORlOA o 300 600 M I I I EBB-TIDAL SHOAL GROWTH BY DATE 1967 - 1990 K.LT. h1/28/;0 LEGEND f.C.C. 12/12/;0 OESCRIPllON JUNE 1967··········· APRIL 1969 -----­ ALL COORDINATES ARE: MAY 1970 ---­ PLANE COORDINATES, LAMBERT CONFOR~AL PROJECTION JAN 1974 -----­ STATE OF FLORIDA, NORTH ZONE JULY 1983 -._.- (UNES REPRESENT -4.57 M MLLW) OCTOBER 1986 ------­ FEBRUARY 1990 ------Figure 10. Time history of growth of East Pass' ebb-tidal shoal. Contours are -15 ft (-4.6 m) MLW, approx midway up shoal's barfront. Since 1974, growth has been to the southwest in Polygons 4, II, and 12.

Todetermine changes in the volume of the ebb­ seafloor. When the combined volume of all 18 tidal shoal, the shoal was defined as the sand ac­ polygons is plotted against time (Figure 14), the cumulation above -20 ft (-6.1 m) MLW within curve reveals that between 1967 and 1990 the the 18 square polygons. The depth of 20 ft (6.1 shoal's overall volume has increased only 18~'~!, m) was chosen hecause this contour has consis­ from :3,:320,000 to :3,9:30,000 eu m. Although this tently marked where the base of the steep bar increase is less than the estimated error in the front merges into the low-gradient Gulf of Mexico calculations, the trend is physically realistic be- 470 Moran g

g . ~ l - - - ~, ~J\_ - ~ ' ~- " O~~t.. I D ~ ( S '-'1(_ \\1 VI ? ~~ §rS;\I)Jo~ b~R( ' ~ ~ -F.. ~.-/70;- " - ' - 'Jf ~ \J o If) ~'- ' ~ f \ ~~ ~ .._.-- ."U -":\JII :J • »> : _. '--~_ . ~J,-) / - .~ \ \) is ------'-, '~"--. ~ . '------0"/

- - "'=~ - ~ I ~lo 8If) fII..--E- '"",,-,",- - ./.. - ' - , - . ~ 1 EDGE OF SH R~f~~ ' § I N ~/ ---lj VA00 10 ~--4---,/~-- I- -,",,; oI I ( I ERST PRSS. FLORIDR I If)o / is JUNE 1967 •• ~ I~FELOl--J !. _; --r 150 lRTH5 MLl--J I I • j 3630 0 0 : 35"100 0 ! 3GSOOO 135500 0 1367 0 0 01 3580 0 0 I! Figure I I. East Pass ebb-tidal sh oal, June, 1967. Su rveys performed before construction of jellie s commenced. Coordinates are :, Plane coord ina tes (in It) , Lambert Conformal Pr ojection , State of F lorid a, Nor th Zone. Eighteen square areas used for volumetric

,t l'.; l calc ulatio ns. Contours are in feet below MLW . En glish un its have bee n retained in accorda nce with the units used on the original ~ ; . survey sheets.

cau se t he shoa l's area has increased. T he fact th at bee n in the form of a bu lge to the sout hwest? The t he curve is reasona bly smo ot h suggests that the simplest exp lanation is t hat the sa nd for this underlying data are of good quality . If there had growth came from the west and that the net drift been maj or errors in the echosounder calibrations, since 1974 has been from west to east. Although tidal corrections, or ca rtography, this aut hor ex­ the gross (east and west) amo unt has probably pects that the cu rve would have displayed ab ru pt excee ded 26,000 cu m /yr , t he annual net dr ift may cha nges in volume. In addition, the smoothness have been less. Duri ng field visits between 1989 of the curve suggests that the CPS3 software has and 1991, the author has seen mo rp hologic evi­ not introduced gross errors d urin g its gridd ing or de nce of drift in both directions. As stated earlier, contouring proced ure s. t he beac h west of the former weir has grown, sug­ What do the ana lyses of the shoal's sha pe and gesting eastward d rift. On the opposite side of the volum e tell us ab out lon gshore drift in this region? inlet, the autho r has seen waves brea king on a Over the pa st 23 yea rs, the shoal has increased in very shallow sand bar extendi ng offshore from the volume by 610,000 cu m, an average of about 26,000 bea ch immediately eas t of the east jetty. It seems cu m /y r. T he actual gross drift is pro bably greater likely that this bar has been supp lied with sand than the shoa l's growth rate beca use presumably from the east. the shoa l is trapping less tha n ]00 (}" of the sa nd in littoral tra nsport. T his is supported by the fact Ti da l H ydraulic Dat a that t he beac hes to the east and west are not Tides and curre nts were measured in East Pass ero ding. Why has th e shoa l's post-1974 growth in October 1983, Ma y 1984, an d Apri l 1987. Cur-

J ournal of Coasta l Resear ch , Vol. 8, No. 2, 1992 Inlet Migrat ion and Hydrauli c Processes 471

o o o ro o 1I1

o o ~ +:------r=t<~ \\\'::_._-__1 o 1I1

o o o ill o LI1 . •I o o o tfI o

1 .",G C)(J ( IU Figure 12. East Pass eb b-udal shoal, February, 1990. Conto urs in feet below MLW . There a re major scour holes at th e west a nd east jetti es.

rent measurements were made from boats by per­ were referenced to th e North Amer ican National sonnel from U.S. Arm y Engin eer District, Mobil e, Geodetic Ver tical Datum (NGVD ). and CERC using Price AA cur rent met ers. The Within Ea st P ass, currents were measured at measuremen ts were made hourly over 24-hr pe­ four stations ac ross th e inlet so uth of the highway riods to record complete tid al cycles. Stations were br idge (F igure 15). At each stat ion, me asuremen ts occupied in East P ass, across th e inlet south of were mad e at depths of 0.2,0.5, and 0.8 times th e the highway brid ge, and at vari ous sites in Choc­ to ta l water dep th . In general, maximum near -sur­ tawhat chee Bay (Figure 2). Water depths were face (1 m below th e surface) eb b velocities ran ged measured acr oss the channels with a Raytheon up to 1.5 m/sec , while ma ximum flood was slightly echosounder. lower, up to 1.3 m/sec. Tide gages were esta blished at vari ous locati ons T he significance of th ese data are revealed when in East Pass and Chocta whatchee Bay. T he gages the current vectors ar e plotted on a plan view of in the bay (Figure 2) were strip char t Stephens this part of the inlet (Figure 15). The length of Leupold wat er level recorde rs. The charts were th e arrows rep resents the maximum near- surface digitized at CERC so tha t th e tid e curves could velocity. The 300·degree flood tid e flows towards be plotted on uniform scales. At the Okaloosa th e bridge and th e flood -tid e shoal. The higher­ County fishing pier in the Gulf of Mexico nea r velocity 120-degree ebb flows toward s the eastern Fort Walton Beach and th e Rodeo Dock fishing shore on th e inlet. This autho r believes tha t the pier in Destin, Sea Data internal -record ing TDR ebb curre nts impinging on Norriego P oint are re­ gages were used. Mobile District sur veyors mea­ sponsible for th e serious eros ion there. The sit ­ sured the heights of th e gages, and all tide curves uation is anal ogous to the erosion that occurs at 472 Morang

0 0 0 0 ,- L()

0 0 0 OJ 0 L()

o o [I ---...c., ~ ( " " ~, 1 '~'" oOJ I 7 < I '1,,-----J-/,, =\, " "l <>''" \ " , , -, o L() o o o I ~ I'­ o L() o f o N o ill o L() EAST PASS, o o 1967 o L() g P I I I I I 1 3 6 3 0 00 1 3 640 0 0 1365000 1 366000 136 7000 1 3 68000 Figure 13. Isopach map showing amounts of erosion and deposition within East Pass and on the ebb-tidal shoal. Contours are in feet. Green (l -ft interval) represents accumulation over time; red (2-ft interval) represents erosion. the outer side of a bend in a river, It is noteworthy to flow towards Choctawhatchee Bay along the that the orientation of Old Pass Lagoon is along west side of the inlet, while along the east side a 115-295 degree line, almost identical to that of the water was flowing in the opposite direction. the currents in this region. In Figure 16, the square symbol represents the The current data also reveal that currents may surface (0.2) vector, the triangle the mid-depth flow for a limited time in different directions when (0.5), and the open circle the bottom (0.8). The the tide is turning. An example is provided by the vectors show that at Stations 3 and 4, flow was to measurements from 0210 hr Central Standard the southeast. At Station 2, the direction at each Time on 26 October, 1983, as the tide was chang­ depth was different, suggesting a mixing zone. ing from flood to ebb. Flood currents continued Finally, at Station 1, the surface and mid-depth

J ournal of Coastal Resear ch, Vol. 8, No. 2, 1992 Inlet Migration and Hydraulic Processes 473

EAST PASS, DESTIN, FLORIDA EBB-TIDAL SHOALGROWTH

17~------' JETTY CONSTRUCTION ~ 16 ::::) Qwcn 15 ~ c ::J ~ 14 c5~ > 13 o ~ 12 (j)

11+-"T"'"""--.---...---.----.----r--r----Ir---r----,~___"T_,._,.___,____,___,___,____,____,___r___r____r___1 Jan-67 Jan-71 Jan-75 Jan-79 Jan-83 Jan-87 Jan-91 Jan-69 Jan-73 Jan-77 Jan-81 Jan-85 Jan-89 DATE

1--- POLYGONS 1-18 I

Figure 14. Plot of East Pass' ebb-tidal shoal volume (in cu m), 1967-1990. Curve is summation of volumes from Polygons 1-18. Estimated error is ± 25 ~~(). flow was northwest, while the bottom was north­ The flow through the North channel (circle sym­ east. bol) was about four times that through the West To determine discharge, or volume of flowing channel (triangle symbol). Because the North water, the instantaneous average velocity, V, was channel trends approximately north-south and the multiplied by the cross-sectional area, At"' V was flow through the West channel is much less, it is calculated by averaging the 12 measurements from surprising that the currents south of the bridge Stations 1-4. A", which varied from hour to hour have such a strong east-west component (120-300 depending on the stage of the tide, was calculated degree orientation, as shown in Figure 15). This using the echosounder records and the tide heights orientation suggests that the currents are diverted from the Destin tide station. Similar calculations by a large amount of water flowing over the flood­ were made for Santa Rosa Sound, and the North tide shoal. The combined flow from the North and and West channels. The estimated error for the West channels accounts for only about 50 % of discharge calculations is plus or minus 25 percent. the discharge through the main East Pass chan­ This error was primarily caused by ambiguities nel, indicating that the rest must flow through in determining the cross-sectional area of the minor channels and over the tidal flats. In sum­ channels. The resulting discharge curves for the mary, during the ebb tide, water from the shoal 1984 data are plotted in Figure 17 in units of cu flows towards the bridge in a southeast direction. m/sec. The curves for 1983 and 1987 (not repro­ During the flood, water flows under the bridge in duced in this paper) are similar. a northwest direction. About 50 CJ!o of this water During all three field studies, the ebb discharge proceeds through the North and West channels, waslonger in duration and higher in velocity than while the rest flows over the flood-tide shoal. the flood. The difference in water flowing in and The flood-tide shoal has probably had a major out of the inlet is accounted for by fresh water influence on directing the flow of water through that flows into Choctawhatchee Bay from rivers East Pass since before 1871. The pre-1928 East and springs. Using the 1984 data, tidal prism (av­ Pass had a northwest-southeast orientation, and erage of flood and ebb flow) was 95.4 x 106 CU m. the currents in the northern part of the present The flow of water around and over the broad, inlet still flow in these directions. We do not have shallow flood-tide shoal may be responsible for suitable data to determine how much the fiood­ the orientation of the currents within the inlet. tidal shoal has changed in area or shape histori-

Journal of Coastal Research, Vol. 8, No.2, 1992 474 Morang

DESTIN

~ -N- ~

~ ~~ ~ ~ VELOCITY SCALES \. ?~ ___ 4 FTISEC "\. « ... o______2i t.C/SEC f't :' t•

~\, ·.l,.:-. ' EAST PASS OCT 25-26. 1983 MAX. CURRENTS

Figure 15. Maximum near-surface (0.6-1.2 m below surface) currents measured 25-26 October, 1983, in East Pass at Stations 1-4. Flood direction about 300 deg; ebb direction about 120 deg. Stations 1-4 were reoccupied during the 1984 and 1987 field studies.

cally, but even the earliest maps indicate that it 1.3 phi (0.44 mrn). One sample from 6.1-m depth was a prominent feature immediately northwest at the base of the shoal's bar front was bimodal, of Moreno Point. with peaks at 1.0 phi (0.5 mm) and 1.8 phi (0.29 mm). The fine component may be brought by the Sediment Grain Sizes ebb tide from Choctawhatchee Bay. As the ebb Surface sediments were sampled in 1989 within jet expands over the shoal, it slows and drops its East Pass and from the flood-tide and ebb-tide sediment load (OERTEL, 1988). Over the shoal it­ shoals. The samples were washed, dried and sieved self, wave action keeps the finer sediments in mo­ at CERC. Examples of the results are presented tion, but some settle in deeper water at the base in Figures 18 and 19 in the form of weight percent of the bar front. This hypothesis is supported by plots. aerial photographs that show black streaks ex­ In general, within 1.0 phi standard deviation, tending radially from the inlet's mouth over the all the samples were the same size, ranging from shoal and black patches seaward of the bar. The ~ about 1.0 to 2.0 phi (0.25 to 0.5 mm). The samples black material may be humate-stained sands and from the ebb-tidal shoal had a mean size of about silts from the shores of Choctawhatchee Bay l (

Journal of Coastal Research, Vol. 8, No.2, 1992 ~ j Inlet Migration and Hydraulic Processes 475

OW PASS LAGOON ~ 4 -N- ~

LEGEND • CURRENT METER LOCATION o SURFACE 6. ~IDDEPTH o BOTTOM . •I

VELOCITY SCALES 2 FT/SEC &iiiiiiiiiiil===::Jiiiiiiiiiiiiiiiiiii~==:::::J

EAST PASS OCT 26. 1983 02:10 CST

Figure 16. Currents measured at 0210 hr CST on 26 October 1983 in East Pass at Stations 1-4.

(SWANSON and PALACAS, 1965). The quantity of across the inlet. Profiles from Station 32+00, ad­ fine-grained sediment being flushed out of Choc­ jacent to the southernmost of the condominiums tawhatchee Bay appears to be small. on Norriego Point, are shown in Figure 20. The Samples from within the inlet and from the x-axis of the plot is the distance from the center­ flood-tide shoal had a mean size of about 1.5 phi line of the west jetty. Depths are corrected to (0.35 rom). The similarity in size and color of these MLW. These data were digitized from bathy­ sands to the ones sampled at the ebb-tidal shoal metric charts prepared by the Panama City Area suggests that their source was the Gulf of Mexico Office. The February and June curves show the side of the inlet and not Choctawhatchee Bay. inlet before and immediately after dredging. By September, 40 percent of the sand had returned Analysis of Channel Shoaling to the navigation channel, and the bottom had Information on sedimentation patterns and the shoaled from -4.6 m MLW to about -4 m. How­ effect of dredging are revealed by plotting profiles ever, during this time the natural channel along

Journal of Coastal Research, Vol. 8, No.2, 1992 476 Morang

3000 (+) = FLOW INTO CHoeTAWHATCH!!! BAY

2000 ,.... . u W fn ...... :-...... I ,-:.-:.-:.-:.~ . 2 1000 ..... : ,.- ., u III i :::» ...... ~,/~;;;r...... I' ...... ,U o ~ . . . ~ o.... II. a:: -1000 w l- e ~

·2000

(.) = FLOW OUT OF CHOCTAWHATCH!! B. -3000"" ", ,, """ 15 1. 17 MAY, 1984 STATIONS: [] EAST PASS MAIN CHANNEL EAST PASS, FLORIDA _~ __ ~g_I!!~_ ~_I-!~!4_ ~~_LJ_~~~_C?~_-:-_-':'I~~ _~~_~~~ _6_~EST.CHA~NEL~ FLO~D_~IDE .SHO~~ DISCHARGE CURVES

+ FOR~ WALTON,_W. END C~OC. BAY Figure 17. Discharge hydrograph based on data collected 15-16 May, 1984, in East Pass and Choctawhatchee Bay. Error estimated to be ±25%. the east shore remained over 5 m deep. The east the east shore of the inlet have eroded. Recent shore was steeper in June and September because hydrographic data show that the inlet may be dredged sand was placed along the beach, which generally deepening, suggesting that sand in lit­ had suffered serious erosion. Profiles from other toral transport is bypassing the mouth of the inlet. parts of the inlet also show that the thalweg hugs Some of this sand may be accumulating on the the east shore while the navigation channel shoals ebb-tidal shoal, but because the beaches to the rapidly. east and west of the shoal are not eroding, it is reasonable to assume that only some of the littoral SUMMARY AND DISCUSSION drift is trapped on the shoal. Recent evidence suggests that East Pass inlet The geological model developed in this study may now be sand-starved. Bayward transport of proposes that East Pass inlet periodically breaks sand in the past is indicated by the large flood­ through Santa Rosa Island and subsequently turns tide shoal, the similarity of sand samples from and migrates in a northeast direction until it reoc­ within the inlet to those found along the Gulf of cupies its original, prebreakout channel. We do Mexico shore, the growth of Norriego sand spit not have historical data to measure how many in a northwest direction, and constant shoaling years are required for a complete cycle. Based on in the mouth of Old Pass Lagoon. Before the erec­ the stability of the inlet from 1871 to 1928 and tion of the jetties, erosion and deposition along on the eastward movement of the inlet after the Norriego Point were in balance. However, since 1928 breakthrough, it appears that a cycle might project construction ended, Norriego Point and take about 100 years.

Journal of Coastal Research, Vol. 8, No.2, 1992 Inlet Migration and Hydraulic Processes 477

EAST PASS SEDIMENT SAMPLES

----- ~::~:'.... N ". .... " CHD~TA\JHA;CHEE "BAY f I- I : I I \ I, \ "

LEGEND

01 SAMPLING STATION

MEAN GRAIN SIZE (PHD AND STD. DEVIA TIDN GULF OF MEXICO

1) E of Ee.st Jetty, 2) N of Spur Jetty, 3) Edge of Ebb-Trocl water's edge we. ter's edge Shout, 20 ft \JD 5/18/89 5/18/89 6/28/89

t 40 II •. 30

20 to

I- Z W U 0::: W o, I- 4) I [dae of Ebb-Tidal 5) Ebb-Tidal Shoal, 6) Off tip of Ea.st LJ Shoa.l, 7 ft \JD 10 Ft \.ID 6/28/89 JettYJ 14 ft 'wiD w 6/28/89 6/28/89 ~ 40

30

20

10

2 2

SEDUviENT SIZE (PHD Figure 18. Sediment grain-size analyses, ebb-tidal shoal. Above each curve is plotted the mean grain size of the sample along with a bar representing plus or minus 1.0 phi standard deviation.

The following evidence supports the hypothesis driving forces of the eastward migration are be­ that physical processes are still attempting to force lieved to be: the inlet east: (a) Norriego Point is eroding. (b) (a) Wave forces. The predominant wave direc­ The thalweg migrated east within the inlet after tion from 1987 to 1990 was from the southwest the jetties were built. It now hugs the east shore­ while the shoreline trends approximately east­ line from the spur jetty north for about 600 m. west. Based on field data collected in this project, the (b) Currents within the inlet. The geometry of 478 Morang

EAST PASS SEDIMENT SAMPLES

j~-::-- ... .N " ~---..... , /" -...... ' CHOCTA\.JHATCHEE:\!'BAY.:,_...:.: , ~ I / 4 1':1 -, DESTI , ,'~a Ilrj; ,. N \ I :-.-. " \ - , -,~~ LEGEND

01 SAMPLING STATION

MEAN GRAIN SIZE (PHD AND STD. DEVIATION GULF OF MEX reo

1) Off Coast Guard 2) N o f H\JY 98 3) E side of N Channel Sta.ticn, 12 Ft \lD bridge a:t share 26 Ft ~D 6/28/89 6/28/89 5/17/89

40 I r+I r+l '.'1 ::~LA~ I'll II" ~ lO l I ...'t ,'" ~ 0 ! "I I W ' \ U ~ ,. w I, o, l ~ Cente~ T 4) of North 5) 'vi side of' Nor"th 6) N Channel off ~ Channel, 14 Pt \lD Channel, 6 Pt \JD shoal, 19 Ft \JD w 6/28/89 6/28/89 6/28/89 ~ 40 , 30~ r+l rl r+1 20 l 10....; ! I I .. 2 SEDIMENT SIZE (PHD Figure 19. Sediment grain-size analyses, flood-tidal shoal, Choctawhatchee Bay.

the flood-tidal shoal and its associated channels flowing against it. Because of freshwater inputs, cause the currents south of the highway bridge to the ebb often is longer in duration and higher in flow northwest-southeast. Because the currents velocity than the flood. In 1984, the ebb flow was flow through the jetties in a north-south direction, measured to be almost 2,800 cu m/sec for over8 they must turn in the region between the jetties hr. Flowing towards 120 degrees in the area south and the highway bridge. The inlet's east shore of the highway bridge, the ebb flow is forced against (Norriego Point), being the outer side of this turn, the inlet's east shore. is eroded by the tremendous amount of water An important question at this juncture is how

Journal of Coastal Research, Vol. 8, No.2, 1992 Inlet Migration and Hydraulic Processes 479

WEST CHANNEL EAST

-"' ~ ·6 t---t1--Jlt---1l---+------1--i.---.....L..------IL..------rl-----_ .J 2 ~ o ..J W III ·10 r------~r____ff_+------IL..------_4't___f---_ ... W W I&. '-' ::c ... ·15 f__------....I.....lI.,.,.a&4I~~~,;,."....",.\___-----_r_\_:jf__---__ a.. w a a: ...w ~ ---fl------J~------_____i ;: .20 I------...L------ll-----__

.~ I .26 '--- --'------'- ....L...-_------IU------'-- _ o eoo 1000 1500 2000 2500 DISTANCE IN FEET FROM WEST JETTY

PROFILES: D 32+00, FEB 1987 EAST PASS, FLORIDA _~ __ ~~~_o_~,_ ~~!'!~ _~S!~! ~ ~-=!~_~ ~~~_l!~~~_~ _"_32+00, SEP 1987 _ BATHYMETRY PROFILES Figure 20. Profiles across East Pass Inlet, Line 32+00 (adjacent to the southernmost of the condominiums on Norriego Point), 1987. Depths are in feet below MLW.

hasthe Federal project affected the geologic cycle and breaching, include Murrells Inlet, South Car­ proposed in the model? Temporarily, the jetties olina (DOUGLASS, 1987), Kiawah River Inlet, South have arrested the eastward movement of the in­ Carolina (FITZGERALD, 1988), the mouth of the let's mouth. However, how long can man-made Piave River, Italy (POSTMA, 1989), the mouth of structures retard powerful natural forces? And at the Senegal River, Senegal (GUILCHER, 1985). what maintenance costs? These troubling ques­ Phase 2, relatively stable throat but migrating ebb tions have no simple answers, but all evidence channel, has been observed at Matanzas Inlet on indicates that maintaining the present inlet will the Atlantic coast of Florida (BRUUN, 1966), New

beincreasingly difficult. Pass, on Florida's Gulf coast (BRUUN t 1966), at Drum and other inlets along the Georgia coast SIMILARITY OF EAST PASS TO (OERTEL, 1975), and at many river mouths such OTHER TIDAL INLETS as the River Braan in Northern Ireland (CARTER, East Pass Inlet is not a unique situation. Prob­ 1988). Phase 3, stable throat and ebb channel and lems ofshoaling, migration, and erosion have been shoal growth, can be seen at Pensacola, Florida reported from natural and jettied tidal inlets (STONE, 1990), at Ocean City, Maryland (personal throughout the world. observation by the author), and at an inlet in All three phases of the East Pass tidal inlet Ninety Mile Beach in Victoria, Australia (BIRD, migration model can be seen at other inlets. Ex­ 1985). Instability and erosion within an inlet amples of Phase 1, large-scale spit development caused by jetty construction have been reported 480 Morang

at Torsminde, Denmark, by MOLLER (1983). Sim­ Engineers, U.S. Government Printing Office, Wash­ ilar to East Pass, the beaches to either side of the ington, D.C. (2 volumes). jettied entrance to Gippsland Lakes in Victoria, DOUGLASS, S.L., 1987. Coastal Response to Navigation Structures at Murrells Inlet, South Carolina. Tech­ Australia, have prograded because longshore drift nical Report CERC-87-2, U.S. Army Engineer Wa­ is in both directions and is roughly in balance terways Experiment Station, Vicksburg, Mississippi, (BIRD, 1985). 40p. Clearly there is room for more research on how FITZGERALD, D., 1988. Shoreline erosional-depositional processes associated with tidal inlets. In: AUBREY, D.G. inlets in such diverse environments apparently and WEISHAR, L. (eds.), Hydrodynamics and Sedi­ behave in similar ways. Inlets are complex fea­ ment Dynamics of Tidal Inlets. Lecture Notes on tures situated in the world's most dynamic en­ Coastal and Estuarine Studies, v. 29. New York: vironment, and many aspects of the interaction Springer-Verlag, pp. 186-225. between inlet geometry, sediment type, anteced­ GOLDSMITH, V., 1966. The recent sedimentary environ­ ment of Choctawhatchee Bay, Florida. Unpublished ent geology, tidal prism, wave and tide conditions, M.S. Thesis, Department of Geology, Florida State and meteorology are still unknown. Further University, Tallahassee, Florida, 89p. knowledge on tidal inlet behavior will be gleaned GUILCHER, A., 1985. Senegal and Gambia. In: BIRD,E.C.F. from interdisciplinary studies that examine both and SCHWARTZ, M.L. (eds.), The World's Coastline. New York: Van Nostrand Reinhold, pp. 555-560. details of the hydraulic and physical factors that HANSEN, M. and KNOWLES, S.C., 1988. Ebb-tidal re· affect inlets and the ways that these factors in­ sponse to jetty construction at three South Carolina fluence, and are influenced by, the overall geolog­ inlets. In: AUBREY, D.G. and WEISHAR, L. (eds.), Hy­ ical setting of the site. drodynamics and Sediment Dynamics of Tidal In­ lets. Lecture Notes on Coastal and Estuarine Studies, v. 29. New York: Springer-Verlag, pp. 364-381. ACKNOWLEDGEMENTS HEYDORN, A.E.F. and FLEMMING, B.W., 1985. South Af­ The author wishes to thank Nicholas Kraus, rica.In: BIRD, E.C.F. and SCHWARTZ, M.L. (eds.), The World's Coastline. New York: Van Nostrand Rein­ William Preslan, Gregory Stone, and Per Bruun hold, pp. 653-667. "'l,., for advice and constructive criticism. This re­ HORIKAWA, K. (ed.), 1988. Nearshore Dynamics and search was conducted at the Coastal Engineering Coastal Processes, Theory, Measurement, and Pre­ ",M' 1"1 Research Center of the Army Engineer Wa­ dictive Models. Tokyo: University of Tokyo Press, .1111 u.s. 'II terways Experiment Station, and was funded by 522p. HUBERTZ, J.M. and BROOKS, R.M., 1989. Gulf of Mexico 1\ the Monitoring Completed Coastal Projects Pro­ '.. Hindcast Wave Information. Wave Information ..u gram. Permission was granted by the Chief of Studies WIS Report 18, U.S. Army Engineer Water­ Engineers to publish this paper. Citation of trade ways Experiment Station, Vicksburg, Mississippi. names does not constitute an official endorsement KOMAR, P.D., 1976. Beach Processes and Sedimenta­ tion. Englewood Cliffs, New Jersey: Prentice-Hall, ~' or approval of the use of such commercial prod­ 429p. ucts by the United States Government. KWON,H.J., 1969. Barrier Islands of the Northern Gulf ofMexico Coast. Sediment Source and Development. LITERATURE CITED Technical Report TR-75, Coastal Studies Institute, Louisiana State University, Baton Rouge, Louisiana, ANGELL, J.W., JR., 1944. History of the Army Air Forces 5Ip. Proving Ground Command, Part One, Background of Eglin Field 1933-1940. Air Force Development Test LEVIN, D.R., 1983. East Pass: Evidence of anomalous Center, Office of History, Eglin Air Force Base, FL eastward longshore sediment transport. In: Sedimen­ (Reprinted March, 1989), 104p. tary Processes and Environment Along the North­ AUBREY, D.G. and SPEER, P.E., 1984. Updrift migration east Coast of the Gulf of Mexico. Coastal Research of tidal inlets. Journal of Geology, 92, 531-545. Technical Report 83-2, Louisiana State University, BIRD, E.C.F., 1985. Victoria. In: BIRD, E.C.F. and Baton Rouge, Louisiana, pp. 122-129. SCHWARTZ, M.L. (eds.), The World's Coastline. New LONGUET-HIGGINS, M.S.; CARTWRIGHT, D.C., and SMITH, York: Van Nostrand Reinhold, pp. 899-911. N.D., 1963. Observations of the directional spectrum BOOTHROYD, J.C., 1985. Tidal inlets and tidal deltas. In: of sea waves using the motions of a floating buoy. In: DAVIS,R.A., JR. (ed.), Coastal Sedimentary Environ­ Ocean Wave Spectra. Englewood Cliffs, New Jersey: r ments. New York: Springer Verlag, pp. 45-532. Prentice-Hall, pp. 111-136. BRUUN,P., 1966. Tidal Inlets and Littoral Drift. Trond­ MACNEIL, F.S., 1949. Pleistocene Shore Lines in Flor­ heim, Norway: H. Skipnes Offsettrykker, 192p. ida and Georgia. Shorter Contributions to General CARTER, R.W.G., 1988. Coastal Environments: An In­ Geology, Geological Survey Professional Paper 221­ troduction to the Physical, Ecological and Cultural F, Washington, D.C., pp. 95-106. I Systems of Coastlines. London: Academic Press, 617p. MOLLER,J.T., 1983. Artificial structures on a North Sea COASTAL ENGINEERING RESEARCH CENTER, 1984. Shore coast-The Barrier Coast at Torsminde, Denmark. Protection Manual (4th edition). U.S. Army Corps of In: RITCHIE, W. (ed.), Northeast Scotland Coastal I

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Field Guide and Geographical Essays. Department TANNER, W.F., 1964. Nearly ideal drift system along the of Geography, University of Aberdeen, pp. 151-157. Florida Panhandle Coast. Annals of Geomorphology, MORANG, A., 1990. Quality Control and Management 8(3), 334-:342. of Oceanographic Wave-Gage Data. Instruction Re­ TANNER, W.F., 1970. Significance of Camille. South­ port CERC-90-1, U.8. Army Engineer Waterways Ex­ eastern Geology, 12(2), 95-104. periment Station, Vicksburg, Mississippi, 33p. U.S. CONGRESS, 1950. Letter from the Secretary of the OERTEL, G.F., 1975. Ebb-tidal deltas of Georgia estu­ Army. East Pass from the Gulf of Mexico into Choc­ aries. In: CRONIN, L.E. (ed.), Estuarine Research, Vol. tawhatchee Bay, Fla. 81st Congress, 2nd Session, 2. New York: Academic Press, pp. 267-276. House Document 470, 18p. OERTEL, G.F., 1988. Processes of sediment exchange be­ U.S. ARMY ENGINEER DISTRICT, MOBILE, 1963. Survey tween tidal inlets, ebb deltas and barrier islands. In: Report on East Pass Channel from the GulfofMexico AUBREY, D.G. and WEISHAR, L. (eds.), Hydrodynam­ into Choctawhatchee Bay, Florida. Report to the Di­ ics and Sediment Dynamics of Tidal Inlets. Lecture vision Engineer, South Atlantic Division, Atlanta, Notes on Coastal and Estuarine Studies, v. 29. New Georgia, 23p. York: Springer-Verlag, pp. 186-225. U.S. ENGINEER OFFICE, MOBILE, 1939. Study of East OTVOS, E.G., 1982. Santa Rosa Island, Florida Panhan­ Pass Channel, Choctawhatchee Bay, Florida. Report dle, origins of a composite barrier island. Southeast­ to the Division Engineer, Gulf of Mexico Division, ern Geology, 23(1), 15-23. New Orleans, Louisiana, 37p. POSTMA, R., 1989. Erosional trends along cuspate river­ WALTON, T.L., JR., 1973. Littoral Drift Computations mouths in the Adriatic Coast. In: FABRI, P. (ed.), Along the Coast of Florida by Means of Ship Wave Coastlines of Italy, Coastlines of the World Series. Observations. Coastal and Oceanographic Engineer­ New York: American Society of Civil Engineers, pp. ing Laboratory Technical Report No. 15, University 84-97. of Florida, Gainesville, Florida, 80p. STONE, G.W., 1991. Differential sediment supply and WILLIAMS, J.L., 1827. A View of West Florida. Bicen­ longshore sediment transport along coastal northwest tennial Floridiana Facsimile Series (1976 facsimile Florida and southeast Alabama since the late Holo­ reproduction), University of Florida, Gainesville, cene. Ph.D. Dissertation, Department of Geology, Florida, 178p. . University of Maryland,College Park, 365p. WRIGHT, L.D. and SOND, C.J., 1975. Processes of sedi­ •. SWANSON, V.E. and PALACAS, J.G., 1965. Humate in ment transport and tidal delta development in a strat­ Coastal Sands of Northwest Florida. Contributions ified tidal inlet. In: CRONIN, L.E. (ed.), Estuarine Re­ to Geochemistry, Geological Survey Bulletin 1214-B, search, v. 2. New York: Academic Press, pp. 63-76. U.S. Government Printing Office, Washington, D.C., 29p.

o RESUME 0 East Pass, qui est un goulet tidal situe entre le Florida Panhandle et la ville de Panama, relie la baie de Choctawhatchee au Golfe du Mexique. De 1983 a 1991, le corps des Ingenieurs de I'Armee americiane a soutenu une campagne de mesures de la houle, des courants, de la maree, de la bathymetrie et des changements du rivage sur ce site. Ces donnees et des enregistrements historiques on permis de developper un modele en trois phases qui decrit le comportement du goulet durant les 120 dernieres annees, La premiere phase (avant 1928) voit Ie developpement de la fleche, sa rupture et recouvre la periode OU la passe etait orientee NW -SE. De 1928 a 1968, le goulet entre dans une seconde phase: la position de l'etranglernent est stable mais cornporte un chenal principal de jusant qui migre sur Ie delta de jusant qui s'est forme. Cette phase couvre la periode OU le goulet s'est ouvert it travers Santa Rosa Island, en direction N-S et commence it.migrer vers l'Est, La troisieme phase, depuis 1968, date OU ont ete construites des jetees de blocs, jusqu'a nos jours ou I'etranglement du goulet, le chenal de jusant et la croissance du delta de jusant sont stables. En depit des jetees, East Pass tend toujours ase deplacer vers l'Est. Les forces qui contribuent acette migration sont supposees etre 1) la force de la houle. La direction predominante de la houle mesuree it -10 m est du SW, alors que celle de la cote tend Ii E-W; 2) Le chenal de rnaree de fond de baie, la geometric du delta de jusant dirigent les courants de fiot vers la cote Est du goulet; 3) du fait des apports en eau douce,le jusant dure plus longtemps et a une vitesse plus que le Rot.-Catherine Bousquet-Bressolier, Geomorphologic E.P.H.E., Montrouge, France.

o ZUSAMMENFASSUNG 0 East Pass ist eine schmale Tidenbucht im Florida-Korridor zwischen Pensacola und Panama City und verbindet die Choctawhatchee Bucht mit dem Golf von Mexico. Zwischen 1983 und 1991 unterstiitzte das Pionierkorps der U.S.-amerikanischen Streitkrafte in diesem Raum ein Projekt in dem Wellen, Strornungen, Tidenhohen, Bathymetrie and Veranderungen der Kiistenlinien gemessen bzw. aufgezeichnet wurden. Anhand dieser Daten und historischen Aufzeichnungen wurde ein Drei-Phasen-Modell entwickelt, welches die Entwicklung dieser Bucht wahrend der vergangenen 120 Jahre beschreibt. Die erste Phase (vor 1928) ist gekennzeichnet durch die Entwickling und Zerstorung von Nehrungen. In dieser Phase wies die Bucht eine Nordwest/Sudost-Orientierung zwischen Choctawhatchee Bucht und dem Golf auf. Die zweite Phase lag zwischen 1928 und 1968 und war dadurch charakterisiert, dan die Bucht zwar eine stabile verengte Offnung aufwies, gleichzeitig aber ein Hauptebbkanal tiber ein sich entwickelndes Ebbtidendelta wanderte. Diese Phase umfaflt den Zeitraum nach dem Nord/Sud­ Durchbruch der Bucht durch Santa Rosa Island und dem Beginn der Ost-Wanderung. Die dritte Phase begann 1968, als Molen/Walle aus Detritus entstanden, reicht bis in die Gegenwart und ist durch eine stabile Offnung und ebbtidales Wachsen von Sandbanken gekennzeichnet. Trotzder erwahnten Walle weist die East Pass Bucht tendenziell eine kontinuierliche Bewegung in ostlicher Richtung auf. Als Antriebskrafte ftir diese ostwartige Wanderung werden vermutet: (1) Wellenkrafte, In zehn Meter Wassertiefe liegt eine vorherrschend siidwestliche Wel­ lenrichungvor, wohingegen die Kiistenlinie sich in Ost/West-Richtung bewegt. (2) Tidenkanale des hinteren Buchtabschnitts und die Geometrie der Sandbanks. die wahrend der Flut entstehen, leiten die Ebbstrome in Richtung des ostlichen Strandes der Bucht. (3) Wegen der Fri­ schwassrerzufuhr ist der Ebbstrom Hinger und schneller als der Flutstrom.-Ulrich Radtke, Geographisches lnstitut; Universitiit Dusseldorf, F.R.G.

Journal of Coastal Research, Vol. 8, No.2, 1992