Coastal Alluvial Plain Research Articles

Evolution of Cretaceous to Eocene alluvial and carbonate platform sequences in central and south Jordan

ABSTRACT The Cretaceous to Eocene succession in central and south Jordan is characterised by passive continental margin depositional sequences, which pass upward from alluvial/paralic to carbonate shelf and pelagic ramp settings. Detailed section logging and outcrop mapping have produced robust lithostratigraphic and lithofacies schemes that can be correlated throughout the region and in the subsurface. These schemes are set in a sequence-stratigraphic context in relation to the evolution sedimentation on the Arabian and Levant plates. Three major megasequences are described (Kurnub, Ajlun and Belqa), and these are further subdivided into large-scale depositional sequences separated by regional sequence boundaries that represent maximum flooding surfaces. There is close correspondence between maximum flooding surfaces recording major sea-level rise with those derived for the Arabian and Levant plates, although there are some discrepancies with the precise timing of global sea-level fluctuations. An upward change from braided to meandering stream fluvial environments in central and south Jordan during the Early Cretaceous, reflects a decreasing geomorphological gradient of the alluvial plain, declining siliciclastic sediment flux, and increased floodplain accommodation, associated with a regional Late Albian (second-order) rise in relative sea-level. The Late Albian to Early Cenomanian marine transgression across the coastal alluvial plain marks a major sequence boundary. During Cenomanian to Turonian times a rimmed carbonate-shelf was established, characterised by skeletal carbonates showing small-scale, upward-shallowing cycles (fourth- to fifth-order parasequences) ranging from subtidal to intertidal facies, arranged into parasequence sets. Rimmed carbonate shelf sequences pass laterally to coeval coastal/alluvial plain facies to the south and east. Eustatic (third-order) fluctuations in relative sea level during the Cenomanian and Early Turonian resulted in deposition of ammonite-rich wackestones and organic-rich marls, during high sea-level stands (maximum flooding surfaces). Progradational sabkha/salina facies passing landwards to fluvial siliciclastics were deposited during an Early Turonian sea-level low stand, marks a regional sequence boundary, above which a highstand carbonate platform was established. A second-order, regional rise in sea level and marine transgression during the Early Coniacian marks a Type 2 sequence boundary, and subsequent drowning of the rimmed carbonate shelf by Late Coniacian times. Sedimentation during the Santonian to Maastrichtian was characterised by a hemi-pelagic chalk-chert-phosphorite lithofacies association, deposited in shallow to moderate water depths on a homoclinal ramp setting, although thicker coeval sequences were deposited in extensional rifts. The marked change in sedimentation from rimmed carbonate shelf to pelagic ramp is attributed to Neo-Tethyan mid-oceanic rifting, tilting, intracratonic deformation and subsidence of the platform; this is reflected in changes in biogenic productivity and ocean currents. Oceanic upwelling and high organic productivity resulted in the deposition of phosphorite together with giant oyster banks, the latter developing within oxygenated wave-base on the inner ramp. Chalk hardgrounds, sub-marine erosion surfaces, and gravitational slump folds indicate depositional hiatus and tectonic instability on the ramp. In the Early Maastrichtian, deeper-water chalk-marl, locally organic-rich, was deposited in density-stratified, anoxic basins, that were partly fault controlled. Pulsatory marine onlap (highstand sequences) during the Eocene is manifested in pelagic chalk and chert with a paucity of benthic macro-fauna, indicating a highly stressed, possibly hypersaline, and density-stratified water column. Comparison with global and regional relative sea-level curves enable regionally induced tectonic factors (hinterland uplift and ocean spreading) to be deduced, against a background of global sea-level rise, changing oceanic chemistry/productivity and climatic change.

SEDIMENT DYNAMICS IN THE RESTORED REACH OF THE KISSIMMEE RIVER BASIN, FLORIDA: A VAST SUBTROPICAL RIPARIAN WETLAND

ABSTRACTHistorically, the Kissimmee River Basin consisted of a broad nearly annually inundated riparian wetland similar in character to tropical Southern Hemisphere large rivers. The river was channelized in the 1960s and 1970s, draining the wetland. The river is currently being restored with over 10 000 hectares of wetlands being reconnected to 70 river km of naturalized channel. We monitored riparian wetland sediment dynamics between 2007 and 2010 at 87 sites in the restored reach and 14 sites in an unrestored reference reach. Discharge and sediment transport were measured at the downstream end of the restored reach. There were three flooding events during the study, two as annual flood events and a third as a greater than a 5‐year flood event. Restoration has returned periodic flood flow to the riparian wetland and provides a mean sedimentation rate of 11.3 mm per year over the study period in the restored reach compared with 1.7 mm per year in an unrestored channelized reach. Sedimentation from the two annual floods was within the normal range for alluvial Coastal Plain rivers. Sediment deposits consisted of over 20% organics, similar to eastern blackwater rivers. The Kissimmee River is unique in North America for its hybrid alluvial/blackwater nature. Fluvial suspended‐sediment measurements for the three flood events indicate that a majority of the sediment (70%) was sand, which is important for natural levee construction. Of the total suspended sediment load for the three flood events, 3%–16% was organic and important in floodplain deposition. Sediment yield is similar to low‐gradient rivers draining to the Chesapeake Bay and alluvial rivers of the southeastern USA. Continued monitoring should determine whether observed sediment transport and floodplain deposition rates are normal for this river and determine the relationship between historic vegetation community restoration, hydroperiod restoration, and sedimentation. Published in 2011 by John Wiley & Sons, Ltd.

Further investigations of underground resistivity structures in coastal areas using grounded-source airborne electromagnetics

Understanding geological and hydrogeological characteristics in coastal areas is an issue of paramount importance considering its socio-economic relevance, whereas, to date, limited information has been acquired due to the lack of suitable survey methods. We have conducted an airborne electromagnetic survey in an alluvial coastal plain, Kujukuri, in southeast Japan, to examine the effectiveness of elucidating the subsurface electric-resistivity structure both on land and offshore. Our approach was to use a grounded electrical dipole source and a helicopter-towed magnetic field receiver. Repeated surveys both at high and low tides revealed that a reliable resistivity structure is available to a depth of 300–350 m in coastal areas where shallow (∼5 m deep) water prevails.

日本列島における沖積層の層厚分布特性―沖積平野における災害脆弱性評価のための地形発達モデルの構築にむけて―

In warm-humid and tectonically active regions such as Japan it is important to investigate the geomorphic development of recent alluvial plains controlled by sea-level changes to prevent natural disasters. This is because human activities concentrate coastal alluvial plains composed of unconsolidated soft sediments (alluvium) including inner-bay mud, which amplify seismic intensity. However, we know little about the general shape of the alluvium quantitatively although several river basins have been investigated in detail. We selected 33 trunk rivers throughout Japan and measured the Present River long-Profile (PRP) along with the Last Glacial River long-Profile (LGRP) defined by the depositional surface of basal gravel layers formed under the influence of falling sealevels during the last glacial period. The thickness of the alluvium given by the relative altitude between PRP and LGRP was basically in proportion to the size of the river basin, and it decreased linearly upstream with the exception of several rivers such as Shinano, Kiso, Oita, and Yoshino. Along these rivers, the alluvium is markedly thicker than expected probably because of tectonic subsidence occurring repetitively after formation of basal gravel layers. This implies that the fluvial response to sea-level change is sensitive enough to distinguish the effects of the accumulation of tectonic movements after deposition of basal gravels. In stable or slightly uplifted areas, the inland distribution of inner-bay mud is basically controlled by river basin size.

Paleoenvironmental evolution and prehistoric human environment, in the embayment of Palamari (Skyros Island, Greece) during Middle-Late Holocene

Palamari Bay is located on the northeastern coast of Skyros Island (Sporades Islands, Aegean Sea). At the northern edge of the bay a fortified prehistoric settlement is found, dated between 2800 and 1700 BC (Early Bronze Age II–Middle Bronze Age I). Detailed geomorphological mapping of the coastal alluvial plain and paleontological, micropaleontological, palynological, sedimentological and micromorphological studies of the Holocene coastal deposits have been conducted in order to reconstruct the palaeoenvironment and the landscape evolution of the broader area of Palamari Bay. Three main sedimentary units were recognized (A, B and C, from oldest to youngest). The lowermost sedimentary unit A, deposited between before 7500 and 3500 cal BP, consists of sediment deposited from high to moderate energy fresh water flows with some suspended load fallout in established water bodies. The microfauna indicates a shallow fresh water environment. However, a tendency to oligohaline conditions was established gradually. During the same period, the Palamari area was characterized by open mixed deciduous forests that gradually retreated as a possible consequence of the intensification of anthropic activity, associated with the settlement of Palamari. Indications of cultivating and grazing activities in the vicinity of the lagoon were identified, pointing to a strong human presence since the Neolithic. Between about 6000 and 3500 cal BP, the embayment was a lagoon southeasterly connected to the sea, therefore sheltered and protected from northeastern winds. The overlying unit B (ca. 3500–800 cal BP) is characterized by the dominance of brackish water microfauna, indicating a brackish stagnant shallow water depositional environment, which was periodically supplied with fresh water from the surrounding springs. As the result of the continuous sea-level rise during the Late Holocene, part of the northern headland was submerged. The decline of the Palamari settlement at the time of the establishment of Unit B might be related to the observed changes that rendered the embayment a restricted body of water. The uppermost sedimentary unit C corresponds to a backshore environment dominated by aeolian activity modified by fluvial processes.

Late Cenozoic fluvial development within the Sea of Azov and Black Sea coastal plains

Late Cenozoic terrestrial deposits are widespread across the northern coastal regions of the Black Sea and the Sea of Azov and represent diverse fluvial, estuarine and deltaic environments. The dating and correlation of these deposits rely on stratigraphically-associated marine index beds, mammalian and molluscan faunas and magnetostratigraphy. In detail the geometries of these sediment bodies are extremely complex, typically varying between localities and representing many cycles of incision and aggradation. However, the overall disposition of the sediments reflects the transition from the uplifting sediment source region to the north and the subsiding depocentre in the interior of the Black Sea to the south. Since the Middle Miocene the area of the Paratethys/Black Sea depocentre has decreased significantly, but since the Middle Pliocene the hinge zone between uplift and subsidence has been located close to the modern coastline. A combination of regional and local differential crustal movements has given rise to the great variety of fluvial sediment bodies, to the erosion–aggradation cycles, different phases and river activity and to the various fluvial landforms that have all been important in landscape development in this region during the past 12 Ma. The fluvial erosion–accumulation cycles (during the upper Serravillian–Messinian, the Zanclean–late Gelasian, and the Pleistocene) and corresponding cycles of relief dissection and planation are reconstructed against a background of local sea-level changes and climatic variations determined from palaeobotanical data. The maximum fluvial incision occurred in the early Zanclean time with alluvial coastal plains, unique in this area, developing in the Gelasian. Increased climatic aridity during the Pleistocene caused a reduction of fluvial activity in comparison with the Late Miocene and Pliocene. The sea-level oscillations and Pleistocene glaciations affected fluvial processes in different ways. The most remarkable events were the substantial reduction of fluvial activity during the Messinian dessication in the Black Sea and drainage of the shelf, with intensive dissection, coeval with the Last Glaciation.

The Relationship Between the Tectonic Setting of the Lake İznik Basin and the Middle Strand of the North Anatolian Fault

The İznik Basin is an active depression created by a series of faults developed in relation to the Middle Strand of the North Anatolian Fault (NAFMS). The most important of these faults is the oblique Sölöz fault, which runs parallel to the NAFMS. It is interpreted as a releasing bend, and plays a crucial role in the evolution of the 75-m-deep ellipsoid-shaped depression in the southern part of the lake. The faults that limit the coastal alluvial plain on land, some of which developed during the early evolution of the NAFMS, are equally important in the development of the İznik Basin, and correspond to P-shear or secondary synthetic shear faults. These faults are cut by the main fault zone and are right-laterally displaced by approximately 7-8 km. Considering an annual slip rate of 2 mm on the fault, such a displacement is only possible in a time span of 3.5 to 4 million years. An earthquake periodicity of ~2000-2500 years is estimated on the basis of recent GPS data, and a limited number of historical earthquakes. Linear terraces observed on the northern and western parts of the Lake İznik, which have been affected by tectonic activity, show occasional rises of the lake level. The seismic data show that the lake level was approximately 40 m below its present level during the last glacial period.

Cambrian paleosols and landscapes of South Australia*

Cambrian marine, grey shales are widespread, and so are Cambrian intertidal, redbeds with weakly developed marine-influenced paleosols. A broader view of Cambrian landscapes and soilscapes now comes from paleosols of alluvial coastal plains of the Cambrian (to Ordovician?) Parachilna, Billy Creek, Moodlatana, Balcoracana, Pantapinna and Grindstone Range Formations in the central Flinders Ranges of South Australia. Paleosols are recognised by soil structures such as calcareous nodules (caliche) and cracked ridges (mukkara). They also show gradational changes down-profile in minerals, grainsize and chemical composition comparable with soils. Some of these Cambrian paleosols are thick (>1 m) and well developed (large caliche nodules). They indicate stable alluvial and coastal landscapes of quartzo-feldspathic and locally tuffaceous sediments. Paleoclimates were generally semiarid, although several intervals of subhumid paleoclimate coincide with local marine transgression. Drab-haloed filaments in red claystones, and elephant-skin and carpet textures in sandstones of some of the paleosols may be evidence of biological soil crusts, and some waterlogged marginal marine and lacustrine paleosols had animal burrows. Cambrian paleosols of the Flinders Ranges are assignable to the modern soil orders Vertisol, Aridisol, Inceptisol and Entisol. Modern soils of the Flinders Ranges and central Australia are within the same orders as the Cambrian paleosols, supporting evidence from paleogeomorphology that some Australian landscapes and soilscapes are very ancient indeed.

Analytical description of tidal dynamics in convergent estuaries

Analytical solutions of the one‐dimensional hydrodynamic equations for tidal wave propagation are now available and, in this paper, presented in explicit equations. For given topography, friction, and tidal amplitude at the downstream boundary, the velocity amplitude, the wave celerity, the tidal damping, and the phase lag can be computed. The solution is based on the full nonlinearized St. Venant equations applied to an exponentially converging channel, which may have a bottom slope. Two families of solutions exist. The first family consists of mixed tidal waves, which have a phase lag between zero and π/2, which occur in alluvial coastal plain estuaries with almost no bottom slope; the second family consists of “apparent standing” waves, which develop in short estuaries with a steep topography. Asymptotic solutions are presented for progressive waves, frictionless waves, waves in channels with constant cross section, and waves in ideal estuaries where there is no damping or amplification. The analytical method is accurate in the downstream, marine part of estuaries and particularly useful in combination with ecological or salt intrusion models. The solutions are compared with observations in the Schelde, Elbe, and Mekong estuaries.

Late Quaternary Geomorphic Evolution of the Coastal Zone of Kachchh, Western India

The present study attempts to delineate the late Quaternary morphotectonic evolution of the coastal zone of Kachchh on the basis of detailed field mapping of the various coastal and fluvial landforms and lithostratigraphic studies of the associated sediments. The entire coastline has been divided into five morphologically distinct segments from west to east—Narayan Sarovar–Jakhau, Jakhau–Khuada, Khuada–Bhada, Bhada–Mundra, and Mundra–Surajbari segments. Major geomorphic features of interest are the variable width of the intertidal zone; development of beaches, bars, and spits; width of active and stabilised coastal dunes; raised mudflats; raised beaches; uplifted estuarine tidal terraces; and the development of a coastal alluvial plain in the Jakhau–Khuada and Bhada–Mundra segments. The coastal alluvial plain was formed by deposition of fluvial sediments over the peneplained Tertiary rocks during upper late Pleistocene in two separate tectonically created basins. Deeply incised fluvial valleys were formed in response to tectonic uplift of the coast due to movements along E-W trending faults further north during the early Holocene. The sea level was higher than present during 6–2 ka, which led to the deposition of coastal sediments, fluvial terraces along incised fluvial valleys, and formation of a cliffy coast in the Narayan–Sarovar–Jakhau segment. Emergent coastal features consisting of raised beaches, raised mudflats, abandoned coastal cliffs, uplifted estuarine tidal to fluvial terraces, and stabilised coastal dunes developed because of uplift during the last 2 ka. The various morphotectonic divisions of the coast are attributed to the role played by the inherent structural fabric, the subsurface Median high, and general uplift of the coast due to tectonic activity along the E-W trending faults to the north of the study area during the early Holocene and the last 2 ka.

Antecedent alluvial morphology and sea‐level controls on form‐process transition zones in the lower Trinity river, Texas

AbstractAn important aspect of river science and management is the identification of key boundaries, transition zones and hinge points. Such critical areas are likely to be important foci or indicators of the effects of environmental change on river systems. While geological controls on such features are widely recognized in upland streams, inherited or antecedent forms may also be important controls of key transitional points or reaches in alluvial coastal plain rivers. The critical zone of the lower Trinity River, Texas marks an important transition in river channel and valley forms, dominant processes and resulting geomorphological, hydrological and ecological characteristics. Its location is not a transient result of upstream or downstream propagation of effects. Rather, the location marks the contemporary upstream extent of the effects of Holocene sea‐level rise, which in turn coincides with the point at which the Pleistocene upper Deweyville alluvial terrace surface is encountered. A more rapid rate of change and relatively sudden upstream displacement of this zone is likely when the upper Deweyville surface is flooded. Antecedent fluvial and alluvial topography inherited from previous aggradation, degradation and lateral migration episodes is likely to be an important control over modern fluvial forms and processes in other alluvial coastal plain rivers as well. Identification and mapping of such features may be extremely useful in pinpointing critical transition zones for water resource managers. Copyright © 2008 John Wiley & Sons, Ltd.

Sequence architecture within a low-accommodation setting: An example from the Permian of the Galilee and Bowen basins, Queensland, Australia

The coal-bearing, Upper Permian Betts Creek Beds (BCB) of the northeastern intracratonic Galilee Basin in north-central Queensland, Australia, record sedimentation within an alluvial-coastal plain in a low-accommodation basin-margin setting. Six third-order depositional sequences are preserved within the BCB and are characterized by a sequence architecture that is overall relatively thin (15 m; 49 ft), condensed, and top truncated. Sequences have a lowstand systems tract composed of extensive braided fluvial sheet sandstones, a transgressive systems tract characterized by tidally influenced fluvial sheet sandstones and bioturbated estuarine mudrocks, and a highstand systems tract composed of coastal-plain mudrocks and coals. Sequences can be correlated throughout the entire Galilee Basin and related to the lithostratigraphy established in the adjacent Bowen Basin, a foreland basin to the east. The overall Late Permian fill is considered a second-order sequence. The stacking patterns show an overall retrogradational to progradational architecture suggestive of relatively low accommodation space. Sequences show an extremely laterally continuous geometry (1000 km; 600 mi) and are relatively uniform in thickness. Sequences do not show evidence of onlap, toplap, or erosional truncation, but instead are thin in areas of low accommodation and expand into areas of higher accommodation. That these third-order sequences can be traced across basins with differing tectonic regimes, together with the persistent, sheetlike nature of the sequences, suggests that tectonic effects on the sequence architecture were minimal. The basin fill covers a time interval during which two glacial events occurred in the final stages of the late Paleozoic Ice Age, suggesting that changes in glacioeustasy may have been the dominant controls on the sequence architecture of the Late Permian succession in the Galilee Basin of northeastern Australia.

Cenozoic graben facies in the Middle Amur sedimentary basin as inferred from seismic and electrical exploration

Most of the grabens of the Middle Amur sedimentary basin (MASB) are usually characterized by similar structures typical of continental rifts. Based on models elaborated for the sedimentary infill in well-studied rift basins, seismic facies developed in grabens of the MASB are first analyzed. The analysis revealed seismic facies characteristic of different parts of asymmetrical basins: facies of fans developed on steep slopes and facies of coastal shoals, alluvial plains, and deltas occurring on gentle slopes. Seismic facies peculiar of deep lacustrine settings that are considered promising with respect to oil-and gas-bearing source rocks is recognized. Correlation of seismic and drilling data confirms the correctness of the interpretations and shows that boreholes penetrated a thin sequence of deep-water lacustrine sediments. Using the vertical electrical sounding method, a low-resistivity sequence that is most promising for discovery of lacustrine sediments is defined in the southwestern and eastern parts of the MASB. The lowest values of the specific resistivity in this sequence (7–8 Ohm · m) are recorded in its southeastern part, where a borehole partly recovered a relatively thick silty-clayey sequence.

Radioisotopic age constraints for Glacial Terminations IX and VII from aggradational sections of the Tiber River delta in Rome, Italy

Buried sedimentary aggradational sections deposited between 800 ka and 600 ka in the Tiber River coastal alluvial plain have been studied using borecores from around Rome. 40Ar/ 39Ar ages on sanidine and/or leucite from intercalated tephra layers and paleomagnetic investigation of clay sections provide geochronologic constraints on the timing of aggradation of two alluvial sections, demonstrating that they were deposited in response to glacio–eustatic sea level rise caused by Glacial Terminations IX and VII. 40Ar/ 39Ar age data indicate ages of 802 ± 8 ka (1σ full errors) and 649 ± 3 ka (1σ full errors) for Glacial Terminations IX and VII, respectively, providing a rare test, beyond the range of U-series dating for corals and speleothems (∼ 500 ka), of the astronomically calibrated timescale developed for oxygen isotope records from deep sea cores.

Sedimentology and stratigraphic architecture of the Late Permian Betts Creek Beds, Queensland, Australia

The Late Permian Betts Creek Beds form a succession of coal-bearing alluvial-coastal plain sediments in a basin marginal setting within the northeastern Galilee Basin, Queensland, Australia. The unit is ∼ 50–60 m in thickness at Porcupine Creek National Park where outcrop is laterally continuous for several kilometers. Eight facies have been identified within the formation and can be grouped into 2 facies associations: (A) channel deposits and (B) floodbasin deposits. The channel association consists of conglomerate (A1) and trough cross-bedded multistorey sandstone facies (A2), both interpreted as deposits of low-sinuosity river systems, tidally influenced fluvial channels (A3), interbedded sandstone and siltstone (A4) interpreted as the abandonment fill of the alluvial systems, and diamictite (A5) interpreted as debris flows. The floodbasin facies association is composed of sandy siltstone (B1; proximal–distal floodbasin), carbonaceous siltstone (B2; mire), and bioturbated siltstone (B3; estuarine) facies. The overall sediment body architecture can be resolved into 6 unconformity-bounded cycles interpreted as sequences in the genetic sense, which are sheet-like in geometry and, in general, consist of amalgamated multistorey, multilateral braided fluvial deposits at the base overlain by extensive sheet-like overbank mudstones, carbonaceous shales, and coals. Sea-level change is interpreted as the primary control on the sequence architecture of the formation, while the internal stratigraphic architecture, however, varies between sequences and is a function of a combination of sea level, tectonic, and autogenic controls.

Whole-rock geochemistry of upper Paleozoic loessite, western Pangaea: Implications for paleo-atmospheric circulation

Average bulk (major and trace-element) chemical composition of upper Paleozoic loessite (lithified loess) from several widely scattered sites in western equatorial Pangaea (western North America) approximates Upper Continental Crust (UCC), but is more similar to the bulk composition of Precambrian basement coring uplifts of the Ancestral Rocky Mountains. However, distinct compositional signatures occur among the various loessite deposits, controlled primarily by differences in Al 2O 3, MgO, Na 2O, K 2O and Rb. Furthermore, values of the Chemical Index of Alteration (CIA) of these loessites are low (55–63, skewed toward lower values), closely matching values for North American loess and Precambrian basement. Although diagenesis can account for some of the compositional differences (e.g. local SiO 2 or K 2O enrichment), it fails to explain the major differences among the sites. Rather, these differences are best explained as a result of variations in regional basement that sourced the loess, coupled with transport (wind) pathways, which varied from zonal easterlies to monsoonal westerlies in this region of tropical Pangaea from late Carboniferous to early Permian time. The low CIA values generally reflect first-cycle derivation from regional basement uplifts of the ARM and, for younger deposits, a variable contribution from the suture zone uplifts and volcanism of the Appalachian–Ouachita–Marathon collisional belt. The variations in bulk chemical composition of the loessite, coupled with previously collected detrital zircon geochronology, suggest that these low-latitude loessites are not simply the result of deflation of mid-latitude erg deposits or coastal alluvial plain sediments. These data represent a first attempt at geochemical characterization of pre-Quaternary loess, and demonstrate the utility of loess geochemistry as a proxy for paleoatmospheric circulation in Earth′s deep-time past.

Modeling groundwater flow and its associated environmental problem in a lowland coastal plain: a first step towards a sustainable development plan

Groundwater is an important resource in the alluvial coastal lowland plains. In the Shiroishi lowland plain, southwestern Kyushu Island of Japan, land subsidence due to groundwater development has long been recognized as an environmental issue. Land subsidence can have several negative economic and social implications. In this study, an integrated numerical groundwater and land subsidence model, which combines a three-dimensional numerical groundwater flow model and a one-dimensional soil consolidation model, was used to simulate the dynamic groundwater flow and ground subsidence due to pumping. On the other hand, a groundwater optimization model was also formulated to search for an optimal safe yield of groundwater pumping without violating physical, environmental, social-economic constraints. The model results reveal that groundwater levels in the aquifers greatly vary from season to season in response to varying climatic and pumping conditions. Consequently, land subsidence has rapidly occurred throughout the area with the central prone in Shiroishi plain. The study also proposes a countermeasure against subsiding process in the area by means of numerical models. The optimization model result suggests that pumping can be increased in the northern part of the study area without leading to significant land subsidence.

Groundwater resources and management for paddy field irrigation and associated environmental problems in an alluvial coastal lowland plain

Groundwater is an important resource for water use in the alluvial coastal lowland plain. In the Shiroishi lowland plain, southwestern Kyushu Island of Japan, land subsidence and salinity intrusion due to intense withdrawals of groundwater have become the main environmental issues for public concern. In this study, an integrated surface and groundwater model was established and applied to the Shiroishi site to simulate groundwater flow hydraulics, aquifer compaction and solute transport in the alluvial lowland plain. Moreover, a groundwater optimization model was also formulated to search for an optimal safe yield of groundwater extraction without violating salinity intrusion and other constraints. The simulated results show that groundwater levels in the aquifer greatly vary in response to varying climatic and pumping conditions. Consequently, land subsidence has rapidly occurred throughout the area with the central prone in Shiroishi basin. As a result of pumping and land subsidence, seawater has been intruded along the coast. In case of relative sea level rise, seawater intrusion appears to extend much farther in land from the coast. From the viewpoint of agricultural water management, pumping for irrigation with an optimal pumping amount that is a new finding from the optimization model will sustain groundwater quality in the study area.

Groundwater flow modelling within a coastal alluvial plain setting using a high-resolution hydrofacies approach; Bells Creek plain, Australia

Ground penetrating radar (GPR) has proved to be an extremely useful geophysical tool, in conjunction with direct geological data, to develop a realistic, macroscopic, subjective-based conceptual model of aquifer architecture within a shallow coastal alluvial plain. Subsequent finite-difference groundwater modelling has not only enabled determination of the dominant groundwater flow paths for the plain, but has also quantified the effects of within-facies and between-facies sedimentary heterogeneity on those flow paths. The interconnection of narrow, unconfined alluvial channels and a broad, semi-confined alluvial delta is ensuring that most fresh groundwater that enters the plain in the form of precipitation or recharge from lateral bedrock hills, is discharged into the eastern coastal wetlands via that alluvial delta aquifer.

Salinization processes in an alluvial coastal lowland plain and effect of sea water level rise

In coastal areas, groundwater and aquifer systems are easily prone to pollution and contamination. Moreover, sea level rises also threaten the viability of many coastal zones and small islands. In the Shiroishi lowland plain, southwestern Kyushu Island of Japan, some environmental problems such as land subsidence and salinity intrusion due to over pumping of groundwater have long been recognized as water problems and become causes for public concern. In this study, an integrated surface and groundwater model was established and applied to the Shiroishi site to simulate groundwater flow hydraulics and predict the salinity intrusion process in the alluvial lowland plain. The simulated results show that groundwater levels in the aquifer greatly vary in response to varying climatic and pumping conditions. It is also found that sea water intrusion would be expected along the coast if the current rates of groundwater exploitation continue. Furthermore, sea water intrusion with a relative rise in sea water level due to aquifer compression and global climatic change was also considered. As a result, sea water intrusion appears to extend much farther in land from the coast compared to a reference case. The study also suggests a possible alternative to mitigate the inverse effects by pumping groundwater.