Journal of CoastalResearch 1040-1054 Royal Palm Beach, Florida Fall 1999

Rain-Induced Beach Processes; Landforms of Ground Water Sapping and Surface Runoff Ervin G. Otvos

Gulf Coast Research Laboratory and USM Department of Coastal Sciences Ocean Springs, MS 39566, U.S.A. ABSTRACT _

OTVOS, E.G., 1999. Rain-Induced Beach Processes; Landforms ofGround Water Sapping and Surface Runoff. Journal .tflllllll,. of Coastal Research, 15(4),1040-1054. Royal Palm Beach (Florida), ISSN 0749-0208. ~.~ Intensive rainfall events, associated with frequent passage of polar and Pacific maritime weather fronts, influence erosion and sand transfer between backshore and offshore zones during wind-depressed tidal stages on Mississippi ~ ~...... and other microtidal northern Gulf of Mexico beaches. Intensive rainstorms, associated with high tides, due to onshore % S-- winds are likely to result in powerful sheetwash erosion and relatively less significant channel erosion in the back­ shore. Low tides and steeper runoff channel gradients during offshore winds, on the contrary lead to more intensive channel erosion and miniature boxcanyon development. Sizable meandering and braided drainage channels crossand erode the backshore plain. Erosion by sapping involves a progression that starts with small-scale features. Ground water emergence in fluted furrow-and-ridge structures, developedin backwash groove fields and rhythmic sets ofshore­ normal furrows, usually in combination with the sweeping swash currents, initiate dendritic rills and from them, miniature boxcanyons. Although ubiquitous probably on all sand beaches, the first three structures apparently have not been discussed in the literature. Seepage of fresh ground water drives the process during falling and low tide stages. Sea water emission from foreshore sands did not playa appreciable role in the initiation of dendritic rills and miniature box canyons.

ADDITIONAL INDEX WORDS: Swash groove, furrow-and-ridge structure, shore-normal furrow, rhomboidal and den­ dritic rills, box canyon, sheetwash, swash, backshore, beach cusps, GulfofMexico, Mississippi, seasonal beach changes.

INTRODUCTION beaches between Destin and Mexico Beach in northwest Flor­ ida, display rainfall-related landforms and structures similar Mississippi's mainland beaches generally experience low to those that result from the interaction between sheetwash, energy wave conditions, except during infrequent tropical emerging fresh groundwater, and beach processes on the Mis­ storms. However, effects of rainwash, in combination with sissippi coast. rainstorm-related shallow ground water flow, playa signifi­ Dependent on volumes and frequency of rain, as well as on cant role in eroding and transporting sand from the back­ fluctuations in tide-elevation, rainwash and seepage-influ­ shore zone. The purpose of the study was to examine how enced beaches on the northeastern Gulf of Mexico occasion­ small-scale beach landforms and structures develop and in­ ally display seasonal and quasi-seasonal erosion-construction teract with wave swash and surface runoffprocesses and how cycles. ground water flow leads to beach erosion by sapping and pip­ ing. Regularly repeated observations on morphology and pro­ cesses involved in rapidly evolving miniature rill channels Study Methods and box canyons during single tide phases have been very instructive in the present study. General beach surveys have been conducted on Mississippi A proposed genetic relationship between coarse-textured beaches from 1971 to 1998. Since the 1980s, these studies rhomboidal rills and dendritic rills (GARNER, 1976; HIGGINS, focused especially on the impact of intense rain events in two 1982) was also explored. Of the subtle beach structures newly beach areas on Mississippi's mainland shore. Periodic sedi­ designated, the faintly etched swash groove fields that include ment sampling, photography, and beach-profile surveys of more deeply scored furrow-and-ridge and shore-normal fur­ the backshore, foreshore, and the shallow subtidal offshore row structures are expected to occur on foreshores on the zones were undertaken. The surveys often followed major global scale. Dendritic rills, deeply scoured by groundwater rainstorm events. Routine observations also were made on a outflow, prepare the stage for intensive foreshore erosion. weekly to monthly basis during dry periods. Shore-parallel The erosion processes to be discussed are well beyond local beach profile surveys and traverses studied the morphology, significance, especially on wide beaches, seasonally impacted spacing, and cumulative widths of beach-crossing ephemeral by heavy ground water outflow and surface rainwash. In ad­ water courses of varying dimensions. Systematic observa­ dition to the Mississippi coast, Pleistocene bluff-backed tions and photographic recordings were also carried out on the development stages of miniature box canyons during fall­ 98040 received 18 June 1998; accepted in revision 18 September 1998. ing tide stages. Rain- Lnduced Beach Processes 1041

Mlululppl Sound

18ml 'i 'I 30km

Figure 1. Beach locations: Harrison County Beach and East Belle Fon­ tana Beach rEBFB), Mississippi Coast.

Study Area-The Mississippi Sound and its Mainland Beaches Figure 2. Subtidal bar field ofTEBFB (Fig. 1), exposed at extre me low winter tide. Bars ohlique to the shoreline. View toward th e southwest. Climate, Hydrology and Geological Conditions January, 1991. The studied beaches fringe Mississippi Sound's mainland shore (Figure 1). This water body is a 9.5 to 22 km wide and approximately 124 km long lagoon. Except in and winds, despite 306 mm of rain on March 7-8 , 1998, beach degradation was relatively minor on Harrison County immediately landward of passes in the barrier island chain, the Sound is less than 5 m deep. A chain of six barrier islands beaches. Mainland beaches in Mississippi are composed of well- to and a relict Mississippi River delta lobe of the Late Holocene St. Bernard delta separate the Sound from the Gulf of very well-sorted medium sand, reworked from Late Mexico. The average daily tidal range is 0.3 m (JENSEN, Pleistocene barrier sands of the Sangamonian (last) 1983). Calculated mean wave heights range between 15 and Interglacial Gulfport Formation. The 1 to 2 km wide 33 cm. The largest waves range between 0.6 and 1.74 m Pleistocene barrier backs the present beach on the (JENSEN, 1983). Waves approach mostly from the southeast northeastern Gulf of Mexico coast (OTVOS, 1972, 1997). and south, less frequently from the southwest. Dredged from beneath the muddy Sound floor, buried The Mississippi Sound is located in a humid, hot-temperate Quaternary sands periodically are utilized for beach nourishment (OTVOS, 1993). The beach foreshore slopes at climate zone. Strong offshore winds, in combination with 5 to 100. Numerous and sizable runoff channels develop considerable precipitation are rare outside the late fall to early spring period. Annual precipitation from 1942 through rapidly from concentrated rainwash across the backshore and 1994 ranged between 943 and 2148 mm in Biloxi. July and foreshore zones during major rain events. Drainage trunk channels on the wide Harrison County backshore are August usually are the wettest, October and November the perpendicular to the shore, whereas their major tributaries, driest months (INTERNATIONAL CLIMATE SUMMARY, 1996). parallel or oblique . Depressed sea level, typical during the Although winter-rainfall totals tend to be low in comparison passage of late fall and winter weather fronts increases with mid-summer figures, occasional heavy rainstorms from channel gradients and thereby the capacity for Soundward December through March are associated with frequent, almost weekly passages of cold-polar Canadian as well as sand transport. Different characteristics of channels, Pacific maritime frontal systems. Polar and Pacific maritime sheetwash, ground water flow, and eolian processes produced weather fronts from the north-northwest dominate in the late contrasting modes of beach degradation. fall, winter, and early spring. The passage of weather fronts, East Belle Fontaine Beach (EBFB) if associated with offshore winds, may temporarily depress sea levels in excess of 1 m. In contrast, winds blowing onshore This, fast deteriorating, last natural mainland beach in from offshore low pressure centers occasionally raise tides by Mississippi, is 2.5 km long. The Pleistocene barrier strand­ 1.2 m even in the winter season. Late winter-early spring plain that backs the beach is characterized by ridge-and­ storms, associated with strong onshore winds that raise tide swale topography. Since 1850, the 2-to-3.5 m high bluff and levels may result in considerable bluff retreat. the 6-to-8 m wide beach have retreated landward by about Thirteen frontal systems crossed the Mississippi coast in 120 m (Figure 2; and SUHAYDA and OrvANKI, 1993; Table 1). th e period of December 6, 1989 through February 22, 1990, Occasional large, semicircular "theater-headed" indentations during a wet winter. Rain totals during that period ranged of the bluff face indicate that spring sapping at the bluff toe between 8 and 103 mm. An additional 202 mm of rain fell on is a key factor in bluff recession. Sangamonian Interglacial March 15-16, 1990. An unusually late system that also barrier segments flank the rest of the northeast Gulf and th e caused significant rain-related beach degradation, passed southwestern Texas coast sector as well (OTVOS, 1991, 1997). through in early June, 1996. Because of th e strong onshore Semiconsolidated, dark brown, humate-cemented lenses of

J ournal of Coastal Resear ch, Vol. 15, No.4, 1999 1042 Ot vos

Table 1. Development stages of sapping -related beach landform s (East Belle Fontaine Beach).

Stage 1 Swash zone at high tide level. Very sha llow, diminutive, eph emer al swash grooves are etched in the foresh ore sur ­ face; dissipating with each swash-backwash sweep. Stage 2 Occasionally aided by scouri ng around incidental beach de­ bris, th e swash grooves, gra dually tapping additional ground water flow deepend into fluted minute furrow-and­ ridge sets. Stage 3 Minu scule dendritic rills form. Shallow fresh ground wat er th at origi na tes from lan d is conducte d to the surface as headward an d downslope erosion, extending the rills, tap into the sha llow subsurface flow. Headward and lateral ero­ sion further enlarges th e rills. Stage 4 Dendrit ic rills, receivin g maximum ground wat er inflow, de­ velop miniature box canyon head sand steep walls. Tribu­ tary canyons develop and erode head ward . Swash-back­ wash currents sweep and enlarge canyons; contribute to seaward sand transport. Stage 5 Enlarged during fallin g tide, by additiona l, captured ground water flow. mat ur e theater-headed box canyons and tribu­ ta ry canyons evolve, gradu ally widen. and deepen by rota­ tional slumping and grainflow. Minor cree ks th at issue from them build small alluvial fans on the lower foreshore. With loss of ground wat er flow, aborte d relict rill networks and canyons are stra nded high and dry in the upper and middle foreshore zones. In the course of continued canyon incision flights of terracettes form along canyon walls an d downstream. off the lower reaches of canyon creek outlets. Sta ge 6 Low tide, Ground water and canyon creek flow. swas h cur­ rents and sediment redeposition gra dua lly cease . Stage 7 Incoming tide reworks and smoothes foreshore surface .

reduced permeability within the Pleistocene barrier sands in­ clude numerous Ophiomorpha tubes. Thes e burrows con­ structed in shallow bottoms by callianassid (ghost) shrimps Figu re 3. EBFB fore shore, backed by bluff of Late Pleistocene Gulfport during the last interglacial marine highstand. Dark brown Fm . (a) dr y season; view to west , November 15, 1991; Width of foresh ore: sandstone lenses and layers crop out between th e low-tide 8 m. (b) incised cross-beach creeks, following hea vy rains, January, 1993. level and, in the bluffs, at maximum + 2.5 m elevation. A Footprints for sca le. broad subtidal sand-bar-studded sandflats apron, well ex­ posed at low sea level (Figure 2) attenuates the approaching waves. Harrison County Beach Periods of heavy surface and ground water discharge across Backed by a low, stepped seawall, the beach is fronted by the beaches and sapping of the beach face alternate with a nearshore sand flat, 50 to 150 m wide, covered by bars, rain-free, non-erosional and constructive intervals that including sand waves. The largest sand bars are 25 to 50 ern smooth foreshore surfaces (Figure 3a). Beach conditions are high . The foreshore, 14 to 18 m wide, usually displays berms stable on this shelt ered shore during th e generally dry fall that mark two previous high tide positions. The foreshore season. Few brooks, springs, or seepages remain. Because of rises about 1 m above low tide level. The backshore plain, 30 the high water table along the coast and to locally extensive, to 70 m wide, slopes gently, declining about 1 m vertically semipermeable humate-rich sand layers of lower permeabil­ from the foot of the seawall to the top of th e foreshore. ity, with return of th e rain, single or multi-day rain events Following construction of the seawall in 1929, designated of 50 to more than 200 mm rapidly saturate the bluff base. to halt erosion by intermittent tropical storms, the original, Seeps and springs issue in great profusion from the bluff toe. narrow natural beach almost disappeared by the late 1940s. They result in heavy dissection of the foreshore. Scores of The present restored and artificially maintained beach dates meandering and straight brooks cross the foreshore (Figure back to 1951. BROWN (1986) calculated an average annual 3b). Some of them emerge by seepage in th e floor of larger sand loss of about 65 to 71 thousand cu m between 1962­ beach-crossing runoff channels. Foreshore seeps reappear at 1985. Up to the present, a total of ca. 6.7 million cu m of sand almost identical locations as before shortly aft er the arrival has been pumped in from nearshore areas (OTVOS, 1993). of heavier rains. Sheetwash, surface runoff, and sapping by Man-made dunes have been constructed by sand fencing and springs convey large quantities of sand to the foot of the fore­ dune grass planting in th e backshore. The dunes contributed shore. greatly to beach-preservation efforts in recent years. Renour-

J ournal of Coastal Research , Vol. 15, No. 4, 1999 Rain- Induced Beach Processes 1043 ished on three separate occasions since 1951 (Figure 1; 0'1'­ vos, 1993), this is one of the oldest and longest (40 km ) ar­ tificially maintained beaches in the world . In contrast with East Belle Fontaine Beach, the Harrison County Beach does not display miniature box canyons. This and the small size of dendritic rills, restricted to th e fore­ shore, may be explained pr imarily by the absence of semi­ permeable sands beneath the beach. Runoff channels that ef­ ficiently dr ain th e backshore during rainstorms may also play a role in this.

Previous Work A vast body of literature exists on groundwater sapping, piping processes, and resulting landforms. The Mississippi coastal zone and th e Quaternary history of the northeastern Gulf coastal plain have been also intensively studied in re­ cent decades (OTVOS, 1997). Rotary and vibracore data from southweste rn Jackson County were also included in publi­ cations on th e Belle Fontaine coast (e.g., OIVANKI and OTVOS, 1994).

Definitions-Sapping and Piping Sapping (or spring sapping ; BAKER et al., 1990) in general defines mechanical removal of soil, sediment or rock matter by erosion in the subsurface. It excludes solution (ka rs t) pro­ cesses. Concentra ted spring sapping and more diffuse seep­ age sapping involve sediment entrainment by water through­ flow and emergence from porous sediment or rock. Coulomb's crite rion explains that increased shear stress in consolidated matter reduce s the cohesive strength and causes brittle shear failure (BATES and J ACKSON, 1980). Increased fluid stress (pore or seepage -wate r pressure) in unconsolidated matter re­ Figu re 4. Sub tle "ridge-and-fur row" st ru ctures, in backwa sh groove field, Novemb er 15, 1991, at Meth odist Compound, centra l Biloxi, MS. sults in reduced frictional strength between particles and in Pencil (14 ern) points towar d deeper swas h groove. Foreshore slope; Mis­ th eir forward transport. The process is also called seepage sissi ppi Sound to the right). Super imposed swash marks bend land ward erosion (HIGGINS et al., 1988; DUNNE, 1990). in tr oughs. Piping (BATES and JACKSON, 1980; HIGGINS, 1984) is the nonkarstic erosion and tran sport of debris in steep subsurface conduits formed in essentially insolubl e materials. Locally it In combination with physical and chemical weathering, may be combined with sa pping. Pipe or tunnel development mass-wasting and runoff processes, sapping created spectac­ opens subsurface conduits in un consolidated deposits by ular th eater-head ed canyons and alcoves in sandstone, lime­ scour and oth er processes. Th ese include seepage erosion, stone , ba salt, and oth er rocks , especially where underlain by overland rainstorm-flow, concentrated ground water flow, shale (e.g., LAITY and MALIN, 1985; HOWARD and KOCHEL, eluvi ation, desiccation-crack development in clayey sedi­ 1988; BAKER et al., 1990). Sapping was instrumental in form­ ments, and other forms of differential debris removal from ing certain subma rine can yons and th e vast canyon system the subsurface to th e land surface (BATES and JACKSON, on Planet Mars (HOWARD , 1988; BAKER et al., 1990; ROBB, 1980; HIGGINS, 1984; DUNNE, 1990; PARKER et al., 1990 ). 1990; PAULL et al., 1990; CARR, 1996). These landforms are Sapping (seepage erosion) in bedrock or better consolidated four to six orders of magnitude larger than the beach box sediment may involve concentrated intergranular flow or canyons. seepage along joints, bedding, faults, and exfoliation planes, concave planes of unloading . It is associated with various pro­ Furrow and Rill Microforms cesses, occasionally even with weathering at the water table "Swash grooves", "furrow-and-ridge" structures, and and dissolution of carbona te cement (HIGGINS, 1984; How­ rhythmic, shore-normal furrow sets ARD , 1987; HIGGINS et al., 1988). HIGGINS et al. (1988, p. 392) summarized sa pping-related drainage and valley-network Ubiquitous, yet (to my knowledge) formally not described, characteristic s, as observed at classic Colorado Plateau lo­ subtle features on sandy beach foreshores include closely calities. In part, the characteristics described by Higgins are spaced, finely etched, curved grooves, designated here as analogous to miniature structures th at evolve by spring sap­ swash grooves (Figure 4). Swash grooves are identical with ping in the beach foreshore. "braided scour marks", observed on Connecticut beach berms

J ournal of Coasta l Research, Vol. 15, No.4, 1999 1044 Otvos

a few mm to several em in width and depth, are common along the foreshore toe. Due to the presence of shallow semipermeable sandstone ledges , they also form at high foreshore levels on EBF'B. These rills have been attributed to water percolation from the beach "at low tide or following a storm." (KOMAR, 1976, p. 370). BRENNINKMEYER (J 982, p. 692-693) stated that beach rills" . .. are found only on the lower foreshore .. . (and) ... formed by the escape of ground water when the tide falls below the water table." Rill initiation. Dendritic rills apparently are initiated in both furrow types. They periodically recur in evenly paced bays of beach cusp series on both beaches (Figures 8). Dendritic rills may recur in evenly paced bays of beach cusp sets in both discussed beach areas (Figures 7). Swash scour opens up shallow groundwater pathways through the furrow floor. The emerging flow of groundwater incises landward­ pointed embryonic rills (Figs. 5, Ga). Turbulence around seaweed clumps, shell fragments, and oth er flotsam greatl y enhances scouring and provides percolating wat ers for rill growth. While conveying seepage to the rill head from the immediate surroundings. thus fostering lateral rill expansion and incision , the debris may temporarily or permanently block headward rill extension (Figures Ba).

Fine- and Coarse-Textured Rhombohedral Backwash Rills Minute and large-scale, diamond-shaped (rhombohedral) rills form by backwash deflection around irregularities in the foreshore microtopography. The fine textured, dense, and shallow rhombohedral microrill pattern, commonly with ca. 1 mm or less rill width, have long been recognized on medi­ um- and fine sandy foreshores worldwide (e.g., BUCHER, Figure 5. Dendritic rill initiation and head ward growth in two shore­ 1919; OTVOS, 1964; KOMAR, 1976). A coarse-textured, rarely normal furrows at low tid e; Harrison County Beach, J anuary. 1998. Scale: seen version in Mississippi consists of maximum 26 cm long yardstick with inch-graduation. and 14 cm wide, reticulated rhomboids. It resembling the pat­ tern, reported from Pacific beaches (Figure 4, in: HIGGINS, 1982). BRENNINKMEYER (982) observed coarse-textured rhomboidal rills on th e lower foreshore during falling tide , as and elsewhere (OTVOS, 1964, Figure 2). These grooves are sea water drained the beach during falling tide. induced by the arcuate sweeps of backwash in the swash zone . The variable conditions along the swash front Early Dendritic Rill Stages; Rill Valley Evolution apparently determines the laterally variable strengt h of the swash flow and th e inter-furrow distances. Local swash Seepage points on the foreshore may rapidly develop into turbulence, aided by beach debris in the swash groove fields, dendritic channel networks. A distinction should be made be­ may deepen and widen these ridge-separated, fluted tween the rill-drainage network on one hand, and the enclos­ depressions, named "furrow-and-ridge" structures (Figure 4). ing rill valley , on the other. A miniature scarp outlines the Furrow widths and spacing range from about 0.5 to 2 ern. upslope-pointed, V-shaped valley that penetrate landward Except on the berm backslope, not reached by backwash, into a smooth foreshore surface (Figures 6a ,b,c). A seamless furrows are instantly eliminated, then regenerated by the transition of forms exists between the smallest rills and the next backwash sweep. largest box canyons. By tapping into additional shallow Downslope extended, faint, and semiregularly paced shore­ ground water pathways, the rills acquire additional ground­ normal flutes, apparently related to rhythmic hydrodynamic water sources and expand both by headward- and lateral ero­ conditions, similar to those that initiate beach cusp sets on sion . Spring sapping keeps incising and deepening rill val­ the same central Biloxi beach sector, recur at variable, 20 to leys, as long as ground water still issues from upslope path­ 95 cm intervals. These are 2 to 8 em wide, few mm deep, ways during falling tides. Low-permeability, humate-rich occasionally > 2.5 m long. Gradually growing seaward with sandstone lenses or other impermeable matter, such as the the falling tide , the furrows at times ext end from high- to low shallow bedrock ledges found in certain California beaches tide level. (HIGGINS, 1982, Figure 5), guide ground water pathways. Ad­ Dendritic rills, sma ll-scale braided channels (Figures 5-7), jacent, deeply incised rills may capture the ground water

Journal of Coas ta l Research, Vol. 15, No.4, 1999 Rain-Ind uced Beach Processe s 1045 source of sha llow rills at any tide level. Shallow rill networks rills constitute distinct stages in a three-step scheme of rill and their alluvia l fan s ofte n are abandoned at mid-to-upper and box canyon evolution on California beaches. He had sug­ foreshore levels (Figure Gc) . Flow-tank experiments by Ko­ gested th at th e th eater-headed box can yons represent th e CHE L et al. (1988) and re ports by BAKERet al. (1990) provide th ird stage, related to th e start of ground water sa pping. similar exa mples of ground water pir acy. As th e tid e and However, field observations in Mississippi indi cate th at in ground wate r levels subside, the emerging terracette surfaces initiating rill development, well before th e box canyon for­ displ ay braid ed-an astomosing floodplain patterns of the for­ mation phase, sa pping is instrumental. mer canyon cree k floor (Figures Gb,c), For the form ation of miniature box can yons on beaches, Higgin s required either th e presence of an impermeabl e sub­ Mature Theater-Headed Box Canyons st rate, or th e stabilization of th e ground water table " . .. near th e top of th e swas h zone . .. ". Sta bilization of th e tid e Rill valleys exte nd rapidly by channel incision and inten­ by st rong onshore wind that briefly delays its fall below an sified sa pping, as well as prolonged swash flushing. A 120 cm act ive canyon floor, did not playa determ ining role in th e wide embayed box canyon may develop in less th an 15 min­ observed box canyon formation at EBFB . If it is ind eed a utes. The larger canyons ofte n reached 1.4 m length and wer e valid process under certain conditions, it may sti mulate and 60 ern wide. enha nce canyon growth by prolonging swash curre nt flush ing Terr acettes and occasiona l miniature alcoves flank box­ at temporarily sta bilized tid e levels. canyon and beach-crossing rivulets (Figure 8). Minuscule The und erlying semipermeable sandstone layers are also tunnels of 1 to 2 cm diamet er and products of piping, exte nd helpful in concentra ting ground water seepage at EBFB but 7.5 ern und erground from the alcoves. The variable orienta­ th eir presence on Mississippi beaches either for rill valley or tions and discharge volumes of th e sha llow ground water box canyon initiation and evolution. pathways result in variable elevations, directions, flow vol­ A smooth morphological transition exists between the var­ umes and erosiona l advance ra tes of the rill and box can yon ious beach cha nnel forms that result from sa pping. Grou nd valleys. Small rills and larger box canyons display a variety water access from a single point source at th e head of a rill of parallel, bifurcating, anastomosing, and other configura ­ valley head produces only an upsl ope-pointed, V-sh aped val­ tions. Several of th ese (Figure l Od) resembl e spring head dis­ ley configuration. Small, V-shaped rills require time to de­ tribution patterns, formed by ground water flow-line conver­ velop into larger rill valleys and th en into sizable box can­ gence toward th e valley (DUNNE, 1980). yons . Copious seepage from a wider per colation front, ema­ Percolation in th e high-walled, upp er foreshore level rill s nating from a bluff-reentrant, may almost instanta neously may cont inu e far into the low-tid e stage. Seepage from a tran sform rill ends or sidewall sectors into minuscule, scal­ high er box canyon thus recharges adjacent younger canyons loped box canyon heads even in a very ea rly phase of rill at lower levels. Canyon growth may proceed briefly proceed developmen t (Figure 6c). simultaneously at several levels (Figu re l Oa, b). Aborted rill valleys th at have lost th eir ground water supply due to rill Rhombic Microrills to Dendritic Rill Networks-a piracy frequently leave diminutive alluvial fan s behind at Gradational, Genetic Sequence? mid-foreshore levels, but most fan s form along the low-tidal sa ndflat margin (Figure 11). A pr oposed rill-development scheme, based in part on Slumping and other mass-wast ing processes accompany suggestio ns by GARNER (1974, p. 289 and 554) was adopte d canyon growth (Figures lOa-d). Continued see page gradually by HIGGINS (1982, 1984). Th ey proposed th at the fine soaks th eir walls. Valley incision exposes a sa turated, lower rh omb ic microrills represent the initial stage in a genetic sa nd interval, overl ain by dri er, more cohes ive surface sa nds. sequenc e of rill evolution, in se award directi on microrills Stee p, scalloped headwalls and lateral bluffs form, generally first become dendritic, then take on an anastomosi ng pat­ not higher than th e canyon width (Figures Itla-d). Rounded tern. Higgin s has suggeste d th at the backwash flow th at canyon rims surround evacuated, sca lloped indentations. Un­ dissipates in to the beach , whe n it eme rges from the fore­ dermined by sapping, backward-rotating slump blocks sepa­ shore , is guided by diminutive channels flanked by "lobate ra te along outward-concave , curved tension cracks, and col­ fan s" (H IGGINS, 1984, p. 22- 23; Figure 2.2 ). Combining mi­ lapse on to th e valley floor. Having reached th e liquid limit, crorills and the "fa n"-sepa rating rills under the designa­ the slumped matter turns into a viscous mass th at releases ti on of "reticula te d diamond pattern", he may hav e inter­ gra inflow. The percolating seepage thus rapidly incorporates pr eted lin guoid curre nt ripples (e.g., OTVOS, 1965a , Plate th e decomposin g blocks int o th e sea ward discharging traction 3A) as inte rchannel "fans". tran sport on th e canyon floor. Swash current sweeps speed However, th e incised, essentially erosional rhomboidal mi­ up the sand tran sport (Figures 9- 11). crorills (OTVOS, 1964, 1965a) of swas h currents and th e ag­ graded, const ructive current ripples clearly are not grada tion­ Issues Involved In A Previous Beach Rill-Box Canyon al toward each-othe r, but unrelated, and morph ologically dif­ Evolution Scheme ferent, distinct sedimentary structures, without suggestions Rills to Box Canyon Valleys of genetic linkage. Except for thei r occasion al occurre nce on ra in runoff-excava ted backshore channel floors, or due to Interp ret ing th e coarse-textured rhomboidal rills as den­ swas h-induced return flow behind high-tidal berm s, linguoid dritic rills, HIGGINS (1982, 1984) believed tha t rh ombohedral current rippl es were absen t from Mississippi beaches.

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Figure Ba-c, Rill valley development, accompa nied by ra pid cha nnel incisio n and latera l shift, January, 1991. Rill valleys widen downslope. a-scouring around debri s initiat ed rill and ea rlies t stage of cha nnel incisio n; b-segme nted remn ants of seve ra l genera tions of braid ed te rracettes left high as th e

J ourn al of Coastal Research, Vol. 15, No. 4, 1999 Rain -Induced Beach Processes 1047

HIGGINS (1982, p. 149; Figures 5 and 6) also suggested lo­ cal structural control by the rhombic configuration of pre­ existing, higher permeability zones in the formation of ':0" straight rill outlines. In his view, buried rhombic microrill grooves, formed "during the phase of swash-zone accretion during the preceding rising tide . . . ", acting like a template, guided the process. The idea of such an "imprinting" is not sustainable for several reasons. It is obvious that reworking of the foreshore surface laminae by the breaker and swash zones during the next incoming tide destroys all preexisting surficial sedimentary structures (OTVOS, 1965bl. In addition, rhomboidal rills of neither type are associated with dendritic rills on Mississippi beaches. The morphological similarity between rhombic microrills on New Jersey beaches (GARNER, 1974; Figure 9.13) and in Mississippi strongly suggests that Garner's dendritic rills on the lower foreshore also formed by spring sapping. Upslope penetration of dendritic rills into a field of rhomboidal mi­ crorills by headward erosion may provide a more reasonable explanation for the coexistence of the two rill types than the suggested genetic-gradational interrelationship.

Fresh or Saline? The Ground Water Source The literature implies that sea water infiltration into the foreshore and its subsequent outflow during low tide play the determining role in beach rill formation te.g., KOMAR, 1976). GRANT (1946, p. 1252) noted the effects of" . .. large waves, heavy rainfall, or wet-weather rills (including "miniature streams") from the land back of the shore" .. . , that soak into the backshore and raise the beach water table to the surface. This condition facilitated wave erosion. Recognition of the ground water source, associated with rill Figure 7. Rill valley set, formed in beach cusp bays, 30 to 70 ern apart. development, may provide an important guidance in clarify­ They recur often following heavier rains. Westward view across foreshore ing beach rill formation conditions. While several publica­ and exposed low tide sandflat . Chalmers Drive, central Biloxi, MS, Feb­ tions imply that infiltrated salt water is responsible for the ruary 19, 1990. rill formation process, few mention explicitly the land-based, fresh or marine nature of the groundwater involved. Al­ though GRANT (1946) stated that both fresh and salt waters tral Biloxi, offset seaward by the exposed end of a concrete did percolate through a California beach, emerging from the drainage culvert that periodically discharges ground water, foreshore, he did not relate the water types to rill genesis. displayed daily recurring rills along the lower foreshore. The On the other hand, on California beaches HIGGINS (1982, dendritic rills reform daily along the foreshore toe as long as 1984) implied the marine origin of the seepage that he as­ fresh water outflow lasts. They start to vanish, two to three sociated with rhombic and dendritic rill development. weeks into the following dry spell and reappear with the next Areas of recurring dendritic rills on Mississippi foreshores soaking rain. Depending on the saturation stage of beach have been clearly and consistently associated with rainstorm­ sand following even moderate rains (30 to 60 mm per day), related ground water discharge. Where the emission of salt rills and miniature box canyon head of maximum 6 cm width water evenly dispersed in the beach sand body, responsible did abound along the toe of the adjoining foreshore sector, for dendritic rill formation and growth these structures would downdrift from the culvert. While ground water discharge be reasonably evenly spaced at least along the Harrison continued along this stretch of beach for some time, the sea­ County beach. This is not the case at all , except in rhythmic ward offset, updrift-adjacent beach sector ceased to display sets of shore-normal swash furrows and beach cusps. sapping structures only a few days after major rain events. A frequently revisited beach sector at Chalmers Drive, cen- A direct causative relationship between rain events and fresh

(- trunk channels extend and cut deeper (inch graduation); b-Triangular-shaped valley heads that stopped headward erosion, point landward. Note sets of young, deep trunk channels and shallow tributary rill s, with braided terracette surfaces; c-headward erosion continues due to active seepage from U­ shaped, finely-scalloped head- and sidewalls. Percolation eventually stops, as the shallow rill system is intersected by more deeply incised new rill valley (right), leaving it "hanging". Ruler : 30.5 em.

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Figure 8. Stairsteps of braid -surfaced ter racettes in miniature box can­ yon (sets 1-through-1O), incised during falling tide. St eep slopes of de­ scending ter racettes form left canyon bank. White vertical scarplets sep­ ara te terraces. Vertical right canyon wall (55 cm high ) casts dark sha dow. F- foreshore; C-box canyon floor. Scale: ru ler (30.5 ern). EBFB, J anuary 23, 1990.

ground water discharge along certain shallow subsur face pathways, on th e one hand, and the appearance of rill fea­ tures at th e foreshore toe, on the other, is evident here.

Sheetwash and Cross-Beach Channeled Flow Rainstorms dissect and degrade the backshor'e and fore­ shore by sheet flow and runoffchannel erosion. In EBFB pro­ file flanked by cross-beach runoff channels, sheetwash had lowered the flat mid-foreshore surface by 30 cm. After 202 Figure 9. Scalloped head of braid-floored mini ature box canyon head , mm of rain fell between March 15-16, 1990 the surface ele­ with slump blocks. J anuary 7, 1990, EBFB. Ruler ; 30.5 em, vation of the upper foreshore was reduced by 3-18 em (7- 10 em on the average) by sheetwash along a surveyed Edgewater cross -beach profile in west Biloxi. Sheetwash-related sand loss on th e west Biloxi beaches equaled or exceeded sand vol­ erosion, somewhat resembling sastrugi structures (erosion umes, that were removed by channel excavation. ridges in snow), recur occasionally. On one occasion, their de­ When the temporary erosional base level, i.e., the tide level, velopment was partly influ enced by interference betwe en is high, due to the gentler channel gradients and despite sheetwash and vehicle tracks in the west Biloxi beach. These heavy rains, channel development tends to be weak. Because faint structures have been observed after major rainstorms, of onshore wind -induced high tide that accompanied the in particular between J anuary 6 and March 16, 1990 and in downpour and despite the more than 310 mm of rain that fell January, 1998 (Figures 13a,b). Parabola structures developed within ca. 27 hours on March 7-8, 1998, cross-beach runoff in March, 1990. On that occasion only, th ey formed by a com­ channel development was relatively weak on Harrison Coun­ bination of erosion and accretion, at intersections between ty beaches. Two new berms formed as the tid e slowly fell. shore-normal, shallow, 45-to-90 cm wide shee twash furrows Sheetwash that was conducted and concentrated into the and th e long tracks of heavy beach maintenanc e vehicles. shore-parallel inter-berm lows excavated highly unusual, Sand from th e upper backshore, including from higher pa­ > 25 em deep channels between the berms. Megaripples of rabola structures and from occasional upturned vehicle 2.25 m in wavelength and 10-20 ern height, covered by cur­ tracks was carried downslope by sheetwash and molded into rent ripples, filled the backberm channels on that foreshore the headwalls of the parabola structures. The seaward-con­ sector (Figure 12). cave headwalls and th eir seaward-pointed "tails" rose less than one centimeter, on one occasion higher, above the ad­ Parabola Structures jacent she etwash-eroded backshore surface and the slightly Rainst orm related sheetw ash commonly forms small anti­ depressed parabola centers. Downslope-extended parabola dunes on th e Harrison County backhore plain. In addition, walls formed the subtle margins of th e original furrows, rows of shore-normal, parabola-shaped residual structures of shaped by th e channeled sheetw ash . Narrow, incised grooves

J ourna l of Coastal Research, Vol. 15, No. 4, 1999 Rain-Ind uced Beach Processes 1049

Figures l Oa-d. Head ward- eroding box canyons discha rge simultaneously at different foreshore levels. Note scalloped valley crest and braided terrace surfaces. J anuary 8, 1990, EBFB. a- a nd b- parallel gulli es of variable lengths. Note aba ndoned high-tidal rill relicts in (a ) in upp er-left corner and front­ cente r (compare with Fig. 6a). Scale: rul er (30.5 em) and 56 em-long section of ya rdstick; c- two converging box canyons with bra ided terra ce su rfaces; d­ mai n valley and severa l side canyons . Multiple terraces have formed during falling tide stages. Sa turated slump block, lower right, gra dua lly disintegrates into slurry.

Jo urna l of Coasta l Research, Vol. 15, No.4, 1999 1050 Otvo s

.. -: ~ O( :,. _ . "' ~~_ ,,~ -:~ ••• 4 ..

Figure 11. Min iature box canyons ; alluvial fans coalesced as tide fell. Edge of low tid al sa nd flat , EBFB, January 9, 1990. Scale: yardstick (91.5 em).

occasionally flank the parabola head- and sidewalls (Figu re 13a).

Runoff-Excavated Backshore and Foreshore Channels Heavy runoff accumulates in sizable but only few em deep, ephemeral backshore ponds during he avy rains. Almost im­ perceptibly outlined dr ainage divid es separate individual backshore "drainage basins" rapidly drained by sheetflow and overland channels (Figu res 14, 15). The degree of saturation is critical in runoff channel development. After the backshore Figure 13 a ,b. (a ) Closeu p an d (b) rows of parabolic shee twas h features becomes saturated during a rain event just below the thresh­ on backsh ore plain , Edgewat er Mall beach in west Biloxi, J anuar y 7, old level for runoff channels to be initiated, even a minor 1990. Note fa int pre-ra inst orm vehicl e track s an d distinct, more recent additional rainfall may trigger formation of a substantial ones . View to th e southeast , foreshore on right. Ya rdstick = 91.5 em. channel network in the backshore and foresh ore zones. In contrast, only narrow and short channels form on the fore-

Figure 12.Cu rre nt ripple-covered very ra re megaripples in back-ber m Figure 14. Storm run off in mea ndering backshore cha nnel (flow toward cha nnel. Flow was toward viewer , Mar ch 8, 1998, Harrison County beach. th e viewer) . Bank c. 45 em high. Note rot at ional slump blocks in both Maximum cres t spaci ng : 2.25 m; height: 20 em. Sca le: yardstick. banks. Harrison County Beach, J anuary 22, 1998.

J ourn al of Coasta l Research. Vol. 15. No.4, 1999 Rain-Indu ced Beach Processes 1051

Figure 16. (a) Old high-tid al berm, breached by drainage channel (cen­ te r-right, middle ground ).Cha nnel throa t subsequently was blocked by new berm (left, back ground ), formed du ring new high tid e. (b) New ber m blocks dr ainage channel throa t. Note st eep ber m slip slope and landward­ oriented pre-berm current ripples, deposited on cha nne l floor du rin g ris­ ing tid e. Mississippi Sound to th e right. Ha rrison County Beach, January 22, 1998. Scale: yardstick.

shore, or none at all, following a long dry spell , succeeded by a minor (30- 50 mm) rain event. In the latter case, the back­ shore surface shows few sign s of channel erosion. Widely spaced miniature runoff channels are initiated and steadily enlarged as a storm tide starts to recede from its highest level. The channels extend simultaneously headward and seaward. Following the outgoing tide, the evolving back­ Figure l fia-c . Large runoff cha nnels across back shore. Edgewater , Har­ shore channels seek out and cut acros s saddles that develop rison County . View to north-northwest, March 19, 1990. (a) meander along the berm crest and gradually extend seaward across bend , flanked by descending terracette s. Scale: yardstick, 91.5 cm; (b) cutb anks, braided trunk-channel floor , and incised seconda ry tribu taries th e drained foreshore slope, down to low tid e level. Where (scale: camera case 15 cm long); (c) meander in main cha nnel with a nas­ sa pping-related beach drainage also plays a significant role, tomosinglbra ided sma ller cha nnels within; cutbank (foreground) with th e head ward eroding box canyon and rill channels also con­ point bar opposite . tribute to foreshore dissection. The largest Harrison County Beach drainage channels, straight and meandering, were flanked by miniature bluffs, maximum 25--45 em high (Figures 15, 16). Channel lengths reached 15 to 25 m; widths, 1.5 to 3.4 m. During major rain­ storms th e runoff channels may extend halfway across the

Journal of Coastal Resear ch, Vol. 15, No. 4, 1999 1052 Otvos

west Florida (Drs . J . S. and T. F. Lytle, pers. comms., 1992­ 95).

Weather and Beach Conditions; Sand Exchange Between Beach Zones The combination of occasional rainstorms, offshore winds, and extreme low tides, typical of winter months on the north­ ern Gulf, results in modest to major degradation of the back­ shore and foreshore zones and in seaward transfer by water and wind . The amount of sand permanently lost, primarily from wide beach backshore plains to the offshore is yet un­ known. In contrast with the northerly, cold front-driven de­ structive winter storms in south Louisiana that devastate its open Gulf mainland and fragile island beaches (DINGLER and REISS, 1990), the sheltered Mississippi mainland shore is se­ riously impacted only by tropical cyclones. Rising tides under constructive wave conditions return part of the sand, previously removed from the offshore and lower foreshore (SHEPARD, 1973). High-tidal berms, 20-40 cm thick, commonly form during periods of normal tides. They Figure 17. Wind-blown and slumped sand fills backshore rain channel. may block the throats of the previously excavated cross-beach Edgewater Beach, west Biloxi. March 24, 1990 (sec : Fig. 5). Scal e: yard­ discharge channels (Figure 16), stick (91.5 ern) and camera case. Unless re-excavated by returning heavy rainwash, the rel­ ict channels quickly loose their identity due to erosion by hu­ man traffic, slumping, rainwash, and eolian fill (Figure 16). Due to rain runoff-related intensive beach degradation, the backshore; occasionally even reaching the seawall. Rain in beach foreshore during the low-tidal late fall-early spring re­ excess of 180 mm had fallen on January 6-7, 1990. In addi­ gime may retreat landward by 2 to 10 m. Waves, associated tion to the multitude of rills and narrow channels, a host of with high tides during the spring season often form berms on channels > 35 cm wide crossed the foreshore at 8.0 to 13.4 m two levels along the foreshore that has retreated during the intervals. In four sectors, studied in detail, the cumulative rainy season. These berms rise 20 to 80 ern above the high length of the channel transects, measured shore-parallel berm level of the previous winter season. along the foreshore edge, equaled 16 to 22% of the corre­ Constructive summer and fall swell waves of distant sponding longshore beach length. storms that raise tide levels, may also add 15 to 20 ern high Following 243 mm of rainfall on December 30-31,1989, the berms to the foreshore. Along with construction of new high cumulative channel transect width in one beach sector rep­ berms, backshore-foreshore channel erosion in the summer resented 35.4% of the sector's shore-parallel length. The sand also accompanied the nearby passing and distant landfall of volume, eroded from runoff channels during the rainstorms Hurricanes Andrew (1992) and Danny (1997). Because of the of January, 1990, was estimated as 0.05 to 0.10 cu m per 1 elevated low tide level that accompanied Danny's passage on m beach length. To illustrate the volume of sand transferred July 18-19, 1997, even the significant ca. 125 mm rain total to the shallow subtidal zone: a 4.5 m wide trunk channel that failed to cause intensive channel excavation. drained a sizable backshore basin at Edgewater Mall, west Biloxi, constructed a 9.5-m wide, 1 to 4 em thick, semicircular CONCLUSIONS alluvial fan during a single tidal period. Small fans frequent­ ly form 10-20 em apart along the low-tide margins of EBFB Heavy runoff in the form of sheetwash, channeled surface after heavy rainfall events. flow, and fresh ground water-driven spring sapping processes Wind-elevated tide levels may neutralize effects of even often results in appreciable seaward sand transfer and deg­ record rainstorms. For example, high tides in the Mississippi radation of the northern GulfCoast beaches. Even if partially Sound, set up by strong onshore winds that accompanied 275 returned to the foreshore, the sand that is removed from the mm of rainfall between January 5 and 7, 1998, precluded wide backshore of Harrison County Beach is permanently channel development on the Harrison County backshore. lost to the backshore plain. Previously unreported and ap­ While large shallow rain pools did accumulate in backshore parently ubiquitous, "ridge-and-furrow" structures and drainage basins, the headward eroding foreshore channels shore-normal furrows, and wash current-generated current did not extend back into the backshore plain. After the fore­ on the wetted foreshore surface, also illustrate the role of shore channel were excavated, the winds shifted and started swash scouring in opening up shallow ground water path­ to blow toward the shore. Rising waves constructed a new ways. Seepage of fresh ground water was responsible for den­ smooth foreshore surface, crowned by a high tidal berm. Sim­ dritic rill formation; the contrasting beach conditions during ilar runoffchannels develop regularly after rainstorms on the periods of alternating wet and dry periods indicate that sea bluff-backed beaches at Seagrove Beach and Seacrest, north- water emission played no appreciable role in the process .

Journal of Coastal Research, Vol. 15. No.4, 1999 Rain-Induced Beach Processes 1053

Contrary to earlier suggestions, th e delicately etched, fine­ sion and overwas h in the central part of th e Isles Dernieres, a textured and coarse-pattern ed rh omboidal (diamond-shaped) Louisian a barrier-island arc . Marine Geology, 91, 177-1 94. DUNNE, T., 1980. Formation and controls of cha nnel networks: Pro­ rills are not genetically gradational toward dendritic rill de­ gress in Physical Geography, 4, 211-239. velopment. Rill format ion and its subsequent headward prop­ DUNNE, T., 1990. Hydrol ogy, mechanics and geomorphic implica­ agation, widen ing, and deepening involve spring sapping tions of erosion by subsurface flow, p.I-28, In : Groundwater Geo­ from th e very sta rt. It is not confined to an assumed, distinct morphology, Higgin s, C.G. and Coates, D.R. Editors, Geological America Sp ecial Paper, No. 252, 368 pp. "box canyon stage". Slumping, grainflow, traction transport, EMERY, K.O. and FOSTER, J .F., 1948. Wat er tables in marine beach­ and flushing by swash currents all participate in th e evolu­ es. Jour. Marine Research, 7, 644--B54. tion of miniature box canyons. The rill valleys and box can­ GARNER, H.F., 1974. The Origin of Landscapes. New York , Oxford yons displ ay diverse sizes and orientati ons, reflecting the in­ Univ. Pr ess, 734p. fluence of multiple ground water sources and pathways. GRANT, U.S., 1946. Effect of grou nd-wate r table on beach erosion. . Bull . Geological Society America (abstr. ), 57,1252. Aided by increased fres hwater supply from subsurface HIGGINS, C.G., 1982. Drainage syste ms developed by sa pping on sources following heavy ra infall , large foreshore box canyons Earth and Mars. Geology, 10, p. 147-1 52. evolved by headward extension of th e trunk channels and HIGGINS, C.G., 1984. Piping and sa pping: development of landforms tributaries. The presence of a uniform groundwate r table un­ by groundwat er outflow. In: Lafleur, RG., Editor, Groundwater as a Geomorphic Agent. Boston, Allen and Unwin p. 18-58. der th e foreshore, nearly coincident with the tide level, could HIGGINS, C.G. and twelve coau th ors, 1988. Ground wate r as a geo­ not be ju stified from field observations. Varied flow durations logic age nt, Cha pter 41, p. 381-4 00, In : Back , W., Rosenshein , and simultan eous freshwater discharges from different levels J.S., an d Seabe r, P.R, Editors, Hyd rogeology: Geological Soc. suggest th e highly uneven distribution of groundwater path­ America, The Geology of North America, V. 0 -2. ways beneath the beach surface. In part due to lower per­ HOWARD, A.D., 1988. Introduction; Groundwat er sa pping on Mars and Ea rth. pp. 1-5. In: Howard, A.D., Kochel, R.C., and Holt, H.E. meability intervals te.g., humate-cemented sand layers), sev­ (Editors), Sapping Features of the Colorado Plateau. A Comparative eral local (perched) groundwater horizons and active path­ Planetary Geology Field Guide: National Aeronautics and Space ways may coexist beneath a given foreshore sector. Administration Sp ecial Publication SP-491, Scientific and Techni­ Respond ing to depressed tide levels, surface- and ground cal Inform ation Division, 108p., Washington, D.C. HOWARD, A.D. and KOCHEL, R C., 1988. Introduction to cuesta land­ water runoff may play an important subsidiary role in sea­ forms and sa pping processes on th e Colora do Plateau. National sona l beach degradation.Sand, tran sferred from the back­ Aeronau tics and Space Administration Sp ecial Publication SP-491, shore and upper foreshore to th e lower foreshore and shallow pp.6-56. offshore contributes to beach erosion. Sheetwash , runoff­ INTERNATIONAL STATION METEOROLOGICAL CLIMATE SUMMARY, channel, and sa pping/seepage erosion impact most , if not all 1996, Keesler AFB, Biloxi, MS.Unpublished, compute rized Dat a Base: Federal Climate Complex, Ashe ville , N.C. beaches worldwide. They are expected to be significant in J ENSEN, RE., 1983. Mississipp i Sound wave-hindcast study: U.S. sediment redistribution, especially on coasts of high rainfall Army Engineers Wat erways Experiment Station, Vicksburg, MS, and wide beaches, backed by permeable high bluffs. an d Mobile, AL. Techn . Report UHL-83-8, pp. C-l through E 272. KOCHEL, RC., 1988. Role of groundwater sapping in the develop­ ment of large valley network s on Hawaii. In : Howard, A.D., Ko­ ACKNOWLEDGMENTS chel, R C., and Holt, H.E., (Editors), Sapp ing Features of the Col­ orado Plateau: National Aeronautics and Space Administration My sincere thanks go to Robert Q. Oak s, Jr. for his pains­ Sp ecial Publication SP-491, p. 10D-101. tak ing reading of th e original man uscript and the construc­ KOCHEL, R C., SIMMONS, D.W., and PIPER, J .F., 1988. Groundwater tive comments. Bruce Hegge and an unnamed review er have sa pping experi ments in weakly consolidated layered sediments: A quantitative summary, In: Howard, AD., Kochel , R C., and Holt , has also contributed valuable suggestions. The Weather H.E.,(Editors), Sapp ing Features of the Colorado Plateau:National Squadron Office at Keesler Air Force Base, Biloxi, Mississip­ Aeronautics and Space Administration Sp ecial Publ ication SP-491, pi, provided th e wind and pre cipitation data during the study p. 161-1 83. period. KOMAR, P.D., 1976. Beach Processes and Sedimentation. En glewood Cliffs, New Jersey, Prenti ce-Hall , 429p. LAITY, J .E. and MALI N, M.C., 1985. Sapping processes and th e de­ liTERATURE CITED velopment of theater-hea ded valley network on th e Colora do Pla­ teau . Geol. Soc. America Bull ., 96, 203-217. BAKER, V.R, KOCHEL, R C., LAITY, J .E., an d HOWARD, AD., 1990. OIVANKI , S.M. and OTVOS, E.G., 1994. Geologic framework , erosion Spr ing sa pping and valley network development In: Higgin s, G. hist ory , and physical setting of the Belle Fontain area. Mississippi and Coates , D.R Editors, Geol. Soc. America Spec. Paper 252, p. Office of Geology Bulletin. No. 130, 21--BO. 235-265. OTVOS, E.G., 1964. Observations on rh omboid beach mark s. Jour. BATES, RL. and J ACKSON, J .A, 1980. Glossary of Geology. Second Sedi ment Petrol. 34, 683--B87. Edition. The American Geological Institute, 751p. OTVOS, E.G., 1965a. Type of rhomboid beach sur face patterns. Amer. BRENNINKM EYER, B.M., 1982. Rill Marks. In: Schwartz, M.L. Editor: Jour. Science, 263, 271- 276. Encyclopedia of Beach and Coastal Processes, Hutchinson Ross, OTVOS, E.G., 1965b. Sedim entation-erosion cycles of single ti dal pe­ 940p. riods on Long Island Sound beach. Jour. Sedi ment . Petrol., 35, 604­ BROWN, J.L. , 1986. Sa nd Beach Master Plan, Harrison County, Mis­ 609. sissippi. Unp ublished Report. Brown Engineering Inc., Gulfport, OTVOS,E.G., 1972. Pre-Sangamon beach ridges along th e north­ MS, 172 p., with Appendices A th rough F. eastern Gulf Coast -fact or fiction? Trans. GulfCoast Assoc. Geol. BUCHER, W.H., 1919. On rippl es an d relat ed sedimentary surface Socs., 22, 223-228. forms and their paleogeographic inte rpretation. Amer. Jour. Sci . OTVOS, E.G., 1991. Quat ernary geology of the Gulfof Mexico coastal 197, 149-210. plain (with J .R DuBar et al.). In : Morri son, RB., Editor, Quater­ CARR, M.H., 1996. Water on Mars. Oxford Univers ity Press, 229p. nary Nonglacial Geology. Conterminous U. S . The Geology ofNorth DINGLER, J .R and REISS, T.E., 1990. Cold-front driven storm ero- America, v. K-2, Geological Society of Americ a pp. 583-610.

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OTVOS, E.G., 1993. Mississippi-Alabama: natural and man-made PAULL, C.K., SPIESS, F.N.,CURRAY, J .R., and TWlcm;LL, D.C., 1990. shores. A study in contrast: Coastal Zone '93. Proceedings Eighth Origin of Florida Canyon and th e role of spring sa pping in th e Symposium on Coastal and Ocean Mana gement , 3, 2600-2615. formation of submari ne box canyons. Bull. Geol. Soc. Am er., 101, OTVOS, E.G., 1997. Northeastern Gulf Coasta l Plain Revisited. Neo­ 502-515. gene and Quaternary Units and Events-Old and New Concepts. ROBB, J .M., 1990. Groundwater processes in th e submarine environ­ ment. In: Higgins, Ch.G., and Coates , D.R.,(Editors) Groundwat er Guidebook: Gulf Coast Assoc. Geological Societies-New Orleans Geomorphology. Geol. Soc. America Special Paper 252., 267- 281. Geol. Society , 143p. SHEPAR D, F.S., 1973. Marine Geology, New York , Harper Row, 517p. PARKER, G.G., S.R., HIGGI NS, CH.G., and WOOD, W.W., 1990. Piping SUHA YDA, J .N. and OIVAN KI, M., 1993. Coasta l erosion an alysis of and pseudokarst in drylands, p. 77-110. In: Higgin s, Ch.G. and th e Belle Fontan a area, J ackson County, Mississippi. Coastal Zone Coates, D.R. (Eds.), Groundwater Geomorphology, Geological Soc. '93. Proceedings of the Eighth Symposium on Coastal and Ocean America Special Paper No. 252, 368p. Management (American Society of Civil Engineers) 3, 2907- 2917.

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