Human population growth and over-utilization of the biotic resources of the Murray — Darling River system, Australia

Imbalances in aquatic ecosystems of the Murray-Darling Basin reflect 180 years of inappropriate land use practices. Regulation of most rivers in the Basin has reduced frequency or duration of inundation of floodplains, with profound effects on a species-rich, highly specialized aquatic biota. Exotic introductions (e.g. trout, carp) have further modified aquatic ecosystems. Floodplain billabongs (= ox-bow lakes) are critical to maintenance of floodplain biodiversity, yet with isolation of floodplains from the parent rivers, billabongs are being lost or severely degraded. Consideration is given to the apparent carrying-capacity of the Basin, the present over-commitment of its most valuable resource, water, and the prospects for amelioration in view of present conflicting land use and water abstraction requirements.     

Integration of inland and coastal storms for flood hazard assessment using a distributed hydrologic model

Due to increasing flood severities and frequencies, studies on coastal vulnerability assessment are of increasing concern. Evaluation of flood inundation depth and extent is the first issue in flood vulnerability analysis. This study has proposed a practical framework for reliable coastal floodplain delineation considering both inland and coastal flooding. New York City (NYC) has been considered as the case study because of its vulnerability to storm surge-induced hazards. For floodplain delineation, a distributed hydrologic model is used. In the proposed method, the severities of combined inland and coastal floods for different recurrence intervals are determined. Through analyzing past storms in the study region, a referenced (base) configuration of rainfall and storm surge is selected to be used for defining flood scenarios with different return periods. The inundated areas are determined under different flooding scenarios. The inundation maps of 2012 superstorm Sandy in NYC is simulated and compared with the FEMA revised maps which shows a close agreement. This methodology could be of significant value to the planners and engineers working on the preparedness of coastal urban communities against storms by providing a platform for updating inundation maps as new events are observed and new information becomes available.     

Freshwater requirements of a semi-arid supratidal and floodplain salt marsh

When rivers are impounded, the reduction in downstream flow can produce important and often adverse effects, especially in the estuarine environment. One or more dams have been proposed for the Olifants River system in the Western Cape, South Africa. This estuary has an extensive area of salt marsh that was examined to see whether it required occasional flooding with freshwater to wash out accumulated salts. The dominant salt marsh species,Sarcocornia pillansii, occurred in supratidal and floodplain areas where the water table was shallowest, the soil moisture highest, and the soil electrical conductivity lowest. Aerial photographs and simulated runoff data showed that no flood had covered the floodplain during the previous 80 years. The data indicate that salt marsh plants use saline groundwater during the dry months of the year in order to survive, but use the short season winter rainfall period with low salinity conditions to grow and reproduce. This study demonstrated that live roots ofS. pillansii reached the water table during the dry season. Tissue and soil water potentials, the relationship between vegetation cover, depth to the water table, and electrical conductivity of the groundwater support the conclusion that saline groundwater is the only source of water during the drier months of the year. Freshwater flooding of the river in winter may be important because it covers the supratidal area with less saline water and reduces the depth to the water table on the floodplain. This makes the groundwater more accessible to the halophytes growing on the floodplain.     

Understanding a coastal flood event: the 10th March 2008 storm surge event in the Solent, UK

Extreme sea-level events (e.g. caused by storm surges) can cause coastal flooding, and considerable disruption and damage. To understand the impacts or hazards expected by different sea levels, waves and defence failures, it is useful to monitor and analyse coastal flood events, including generating numerical simulations of floodplain inundation. Ideally, any such modelling should be calibrated and validated using information recorded during real events, which can also add plausibility to synthetic flood event simulations. However, such data are rarely compiled for coastal floods. This paper demonstrates the capture of such a flood event dataset, and its integration with defence and floodplain modelling to reconstruct, archive and better understand the regional impacts of the event. The case-study event comprised a significant storm surge, high tide and waves in the English Channel on 10 March 2008, which resulted in flooding in at least 37 distinct areas across the Solent, UK (mainly due to overflow and outflanking of defences). The land area flooded may have exceeded 7 km², with the breaching of a shingle barrier at Selsey contributing to up to 90 % of this area. Whilst sea floods are common in the Solent, this is the first regional dataset on flood extent. The compilation of data for the validation of coastal inundation modelling is discussed, and the implications for the analysis of future coastal flooding threats to population, business and infrastructure in the region.     

Length-weight relationship of sucker head, Garra Gotyla Gotyla (Gray, 1830) in different rivers of Nepal and the influence of monsoon

Size structure data particularly that of length and weight is very important fisheries management tool, which is also applied to assess the health, habitat and integrity of the rivers. Nepal is tremendously rich in both fisheries and water resource and thus, this analysis is very important. However, this kind of analysis is not common in fisheries studies and hence the size structure information of all the fish in Nepal is wanting. This study simply tries to open the door for such studies with the study of the sucker head Garra gotyla gotyla, a very common fish in Nepal. The field observation was done in nine rivers of the country in all the seasons of the 2003 by using electrofishing gear. The length-weight relationship was found to vary both spatially and temporally among rivers and seasons respectively indicating different conditions in different rivers. The length weight relationship also showed some interesting facts about the seasonal cycle of the species indicating the period of growth and stress in different rivers. The monsoon event was found to be highly influential in this relationship.     

Understanding the Impacts of Climate Change: an Analysis of Inundation,Marsh Elevation,and Plant Communities in a Tidal Freshwater Marsh

Tidal freshwater marshes around the world face an uncertain future with increasing water levels, salinity intrusion, and temperature and precipitation shifts associated with climate change. Due to the characteristic abundance of both annual and perennial species in these habitats, even small increases in early growing season water levels may reduce seed germination, seedling establishment, and late-season plant cover, decreasing overall species abundance and productivity. This study looks at the distribution of tidal freshwater marsh plant species at Jug Bay, Patuxent River (Chesapeake Bay, USA), with respect to intertidal elevation, and the relationship between inundation early in the growing season and peak plant cover to better understand the potential impacts and marsh responses to increased inundation. Results show that 62% of marsh plant species are distributed at elevations around mean high water and are characterized by narrow elevation ranges in contrast with species growing at lower elevations. In addition, the frequency and duration of inundation and water depth to which the marsh was exposed to, prior to the growing season (March 15–May 15), negatively affected peak plant cover (measured in end-June to mid-July) after a threshold value was reached. For example, 36 and 55% decreases in peak plant cover were observed after duration of inundation threshold values of 25 and 36% was reached for annual and perennial species, respectively. Overall, this study suggests that plant communities of tidal freshwater marshes are sensitive to even small systematic changes in inundation, which may affect species abundance and richness as well as overall wetland resiliency to climate change.     

Feeding ecology of o-group sea bass,Dicentrarchus labrax, in salt marshes of Mont Saint Michel Bay (France)

0-group sea bass,Dicentrarchus labrax, colonize intertidal marsh creeks of Mont Saint Michel Bay, France, on spring tides (e.g., 43% of the tides) during flood and return to coastal waters during ebb. Most arrived with empty stomachs (33%), and feed actively during their short stay in the creeks (from 1 to 2 h) where they consumed on average a minimum of 8% of their body weight. During flood tide, diet was dominated by mysids,Neomysis integer, which feed on marsh detritus. During ebb, when young sea bass left tidal marsh creeks, the majority had full stomachs (more than 98%) and diet was dominated by the most abundant marsh (including vegetated tidal flats and associated marsh creeks) resident amphipod,Orchestia gammarellus. Temporal and tidal effects on diet composition were shown to be insignificant. Foraging in vegetated flats occurs very rarely since they are only flooded by about 5% of the tides. It was shown that primary and secondary production of intertidal salt marshes play a fundamental role in the feeding of 0-group sea bass. This suggests that the well known nursery function of estuarine systems, which is usually restricted to subtidal and intertidal flats, ought to be extended to the supratidal, vegetated marshes and mainly to intertidal marsh creeks.     

Bankline change and the facets of riverine hazards in the floodplain of Subansiri–Ranganadi Doab, Brahmaputra Valley, India

Subansiri?CRanganadi Doab (confluence country), located in Lakhimpur district, Assam, is one of the worst flood-affected areas in Brahmaputra valley. The Doab is well populated, and land around these rivers is extensively used for cultivation. As means of flood protection, embankments were constructed in the 1950s along the banks of both the rivers. On the other hand, these rivers are dynamic in terms of banklines and other forms of channel changes. Progressive migration of bankline, due to erosion, results in loss of cultivable land. Moreover, it causes breaches in the embankments increasing the severity of flood in the Doab. This paper attempts to study the changes in the banklines of two major rivers in the floodplains of the Subansiri?CRanganadi Doab during 1997?C2009 in the context of the riverine hazards it brings to the floodplain dwellers. The shift of the banklines in Subansiri?CRanganadi Doab, downstream of North Lakhimpur, has been estimated using IRS LISS imageries of 1997 and 2009 in GIS environment. The river Subansiri during the study period has migrated westward and has widened substantially resulting in erosion of an area of ~19.137?km². For Ranganadi, the total area that has been eroded due to channel changes is ~0.897?km². The channel changes are mainly due to concave bank erosion associated with high stages of flow. Channel widening in Subansiri and Ranganadi in the study area during the decades of 1990s and 2000 has led to frequent breaches in the embankments. Lateral erosion and inundation due to embankment failure are the most dominant facets of riverine hazards in the study area as these lead to loss of livelihood. Therefore, it is necessary to incorporate geomorphic changes in formulating flood management programmes.     

Natural fisheries,marsh management,and mariculture: Complexity and conflict in Louisiana

Most of Louisiana’s economically important saltwater fishes and crustaceans spawn in the Gulf of Mexico, but their young must use the vast coastal marsh as their nursery. Marsh management in Louisiana usually consists of emplacement of levees and water-control structures in the marsh. These structures significantly reduce fisheries production and offshore recruitment. In addition, in 1987 private entities were authorized to use 32,380 ha of the marsh for experimental mariculture, which (if successful) will likewise lead to greatly reduced natural fisheries production and offshore recruitment. Private interests also nearly succeeded in legalizing entrapment and eventual harvest of the wild fisheries from 100,000 ha, and 20,000 ha, of the marsh in 1991 and 1992, respectively. The effects of all these threats to natural fisheries production are further complicated by Louisiana's confused legal situation regarding coastal land ownership.     

Multiple scenario analyses of Huangpu River flooding using a 1D/2D coupled flood inundation model

Huangpu River floodplain is historically vulnerable to flooding due to its location in the path of tropical cyclones, low elevation, relatively flat topography, rapid changes in sea level and fast rate of land subsidence due to urbanization. This paper presents a scenario-based study that investigates the fluvial flood potentials in the Huangpu River floodplain. Flood scenarios with return periods of 50, 100, 200, 500 and 1,000 years were designed to cover the probable situations. Further, a flood inundation model (FloodMap) that tightly couples a river flow model with a 1D solution of the full form of the St. Venant equations and a 2D floodplain flow model was used to predict the river flow and inundation extents. Flood characteristics obtained from the simulations were used in the exposure analysis to determine the spatial distribution of susceptible land uses under different scenarios. Results suggest that overtopping inundation mainly occurs within 1–2 km of the banks of the Huangpu River, with larger inundation extent predicted in the upper and middle reaches of the channel, a result of varying protection levels from relatively rural upstream to high urbanized floodplain in the vicinity of the middle reaches.     

Geomorphological zoning for flood inundation using satellite data

The authors investigated geomorphological features on the central plain of Thailand utilizing satellite remote sensing data and made geomorphological land classification map showing flood-stricken area. Land classification maps showing flood-striken area tell us former flood inundation area, such as inundation depth, inundation width, flood flow course and flood direction, as well as estimating of the features of flooding. Thus map is useful for planning of flood control works.We classified land form units in the central plain of Thailand as following; delta, tidal flat, lagoon, mud spit, back marsh, natural levee, fan and former river course and so on. After that, the principal component analysis is applied to Landsat TM data and gives good results for photo interpretation of land form units and we transfer geomorphological land classification map to make zoning map of flood risk for the purpose of evaluating the flood damages.     

Storage of sediment-associated nutrients and contaminants in river channel and floodplain systems

Samples of fine-grained channel bed sediment and overbank floodplain deposits were collected along the main channels of the Rivers Aire (and its main tributary, the River Calder) and Swale, in Yorkshire, UK, in order to investigate downstream changes in the storage and deposition of heavy metals (Cr, Cu, Pb, Zn), total P and the sum of selected PCB congeners, and to estimate the total storage of these contaminants within the main channels and floodplains of these river systems. Downstream trends in the contaminant content of the <63 μm fraction of channel bed and floodplain sediment in the study rivers are controlled mainly by the location of the main sources of the contaminants, which varies between rivers. In the Rivers Aire and Calder, the contaminant content of the <63 μm fraction of channel bed and floodplain sediment generally increases in a downstream direction, reflecting the location of the main urban and industrialized areas in the middle and lower parts of the basin. In the River Swale, the concentrations of most of the contaminants examined are approximately constant along the length of the river, due to the relatively unpolluted nature of this river. However, the Pb and Zn content of fine channel bed sediment decreases downstream, due to the location of historic metal mines in the headwaters of this river, and the effect of downstream dilution with uncontaminated sediment. The magnitude and spatial variation of contaminant storage and deposition on channel beds and floodplains are also controlled by the amount of <63 μm sediment stored on the channel bed and deposited on the floodplain during overbank events. Consequently, contaminant deposition and storage are strongly influenced by the surface area of the floodplain and channel bed. Contaminant storage on the channel beds of the study rivers is, therefore, generally greatest in the middle and lower reaches of the rivers, since channel width increases downstream. Comparisons of the estimates of total storage of specific contaminants on the channel beds of the main channel systems of the study rivers with the annual contaminant flux at the catchment outlets indicate that channel storage represents <3% of the outlet flux and is, therefore, of limited importance in regulating that flux. Similar comparisons between the annual deposition flux of specific contaminants to the floodplains of the study rivers and the annual contaminant flux at the catchment outlet, emphasise the potential importance of floodplain deposition as a conveyance loss. In the case of the River Aire the floodplain deposition flux is equivalent to between ca. 2% (PCBs) and 36% (Pb) of the outlet flux. With the exception of PCBs, for which the value is ≌0, the equivalent values for the River Swale range between 18% (P) and 95% (Pb). The study emphasises that knowledge of the fine-grained sediment delivery system operating in a river basin is an essential prerequisite for understanding the transport and storage of sediment-associated contaminants in river systems and that conveyance losses associated with floodplain deposition exert an important control on downstream contaminant fluxes and the fate of such contaminants.     

Formation of braided river floodplains, Waimakariri River, New Zealand

Floodplains along the braided gravel-bed Waimakariri River are discontinuous although generally extensive landforms composed predominantly of gravel bars capped with vertically accreted fines. In order of importance, three mechanisms lead to floodplain formation. River bed abandonment by lateral migration of the braid-train initiates the formation of the largest floodpiains, which usually occur downstream of tributary fans and valley bedrock spurs. In the headwater reaches, localized river bed aggradation during high magnitude events leads to floodplain formation by producing a surface resistant to erosion by lesser events due to either the coarse nature of the deposit, or by its elevation over the river bed, or both. The least important mechanism initiating floodplain development is localized river or channel incision. A six stage model is proposed for the sequential development of floodplains on the Waimakariri River from: (i) active river bed; (ii) stabilizing bar; (iii) incipient floodplain; (iv) established floodplain; (v) mature floodplain; and to (vi) terrace. Two mechanisms, lateral migration by the braid-train and reactivation of abandoned channels within floodplains, operating separately or in combination, are responsible for floodplain reworking and their relatively young age (<250 years). Clearly, braided rivers can construct substantial areas of well developed floodplain.     

Denitrification capacity in a subterranean estuary below a Rhode Island fringing salt marsh

Coastal waters are severely threatened by nitrogen (N) loading from direct groundwater discharge. The subterranean estuary, the mixing zone of fresh groundwater and sea water in a coastal aquifer, has a high potential to remove substantial N. A network of piezometers was used to characterize the denitrification capacity and groundwater flow paths in the subterranean estuary below a Rhode Island fringing salt marsh.¹⁵N-enriched nitrate was injected into the subterranean estuary (in situ push-pull method) to evaluate the denitrification capacity of the saturated zone at multiple depths (125–300 cm) below different zones (upland-marsh transition zone, high marsh, and low marsh). From the upland to low marsh, the water table became shallower, groundwater dissolved oxygen decreased, and groundwater pH, soil organic carbon, and total root biomass increased. As groundwater approached the high and low marsh, the hydraulic gradient increased and deep groundwater upwelled. In the warm season (groundwater temperature >12 °C), elevated groundwater denitrification capacity within each zone was observed. The warm season low marsh groundwater denitrification capacity was significantly higher than all other zones and depths. In the cool season (groundwater temperature <10.5 °C), elevated groundwater denitrification capacity was only found in the low marsh. Additions of dissolved organic carbon did not alter groundwater denitrification capacity suggesting that an alternative electron donor, possibly transported by tidal inundation from the root zone, may be limiting. Combining flow paths with denitrification capacity and saturated porewater residence time, we estimated that as much as 29–60 mg N could be removed from 11 of water flowing through the subterranean estuary below the low marsh, arguing for the significance of subterranean estuaries in annual watershed scale N budgets.     

Wetland Loss Patterns and Inundation-Productivity Relationships Prognosticate Widespread Salt Marsh Loss for Southern New England

Tidal salt marsh is a key defense against, yet is especially vulnerable to, the effects of accelerated sea level rise. To determine whether salt marshes in southern New England will be stable given increasing inundation over the coming decades, we examined current loss patterns, inundation-productivity feedbacks, and sustaining processes. A multi-decadal analysis of salt marsh aerial extent using historic imagery and maps revealed that salt marsh vegetation loss is both widespread and accelerating, with vegetation loss rates over the past four decades summing to 17.3 %. Landward retreat of the marsh edge, widening and headward expansion of tidal channel networks, loss of marsh islands, and the development and enlargement of interior depressions found on the marsh platform contributed to vegetation loss. Inundation due to sea level rise is strongly suggested as a primary driver: vegetation loss rates were significantly negatively correlated with marsh elevation (r ²?=?0.96; p?=?0.0038), with marshes situated below mean high water (MHW) experiencing greater declines than marshes sitting well above MHW. Growth experiments with Spartina alterniflora, the Atlantic salt marsh ecosystem dominant, across a range of elevations and inundation regimes further established that greater inundation decreases belowground biomass production of S. alterniflora and, thus, negatively impacts organic matter accumulation. These results suggest that southern New England salt marshes are already experiencing deterioration and fragmentation in response to sea level rise and may not be stable as tidal flooding increases in the future.     

Flood inundation mapping sensitivity to riverine spatial resolution and modelling approach

An innovative approach in the investigation of complex landscapes for hydraulic modelling applications is the use of terrestrial laser scanner (TLS) that can lead to a high-resolution digital elevation model (DEM). Another notable factor in flood modelling is the selection of the hydrodynamic model (1D, 2D and 1D/2D), especially in complex riverine topographies, that can influence the accuracy of flood inundation area and mapping. This paper uses different types of hydraulic–hydrodynamic modelling approaches and several types of river and riparian area spatial resolution for the implementation of a sensitivity analysis for floodplain mapping and flood inundation modelling process at ungauged watersheds. Four data sets have been used for the construction of the river and riparian areas: processed and unprocessed TLS data, topographic land survey data and typical digitized contours from 1:5000-scale topographic maps. Modelling approaches combinations consist of: one-dimensional hydraulic models (HEC-RAS, MIKE 11), two-dimensional hydraulic models (MIKE 21, MIKE 21 FM) and combinations of coupled hydraulic models (MIKE 11/MIKE 21) within the MIKE FLOOD platform. Historical flood records and estimated flooded area derived from an observed extreme flash-flood event have been used in the validation process using 2 × 2 contingency tables. Flood inundation maps have been generated for each modelling approach and landscape configuration at the lower part of Xerias River reach at Volos, Greece, and compared for assessing the sensitivity of input data and model structure uncertainty. Results provided from contingency table analysis indicate the sensitivity of floodplain modelling on the DEM spatial resolution and the hydraulic modelling approach.     

Influence of Wind-Driven Inundation and Coastal Geomorphology on Sedimentation in Two Microtidal Marshes, Pamlico River Estuary, NC

Marsh sediment accumulation is predominately a combination of in situ organic accumulation and mineral sediment input during inundation. Within the Pamlico River Estuary (PRE), marsh inundation is dependent upon event (e.g., storms) and seasonal wind patterns due to minimal astronomical tides (<10 cm). A better understanding of the processes controlling sediment deposition and, ultimately, marsh accretion is needed to forecast marsh sustainability with changing land usage, climate, and sea level rise. This study examines marsh topography, inundation depth, duration of inundation, and wind velocity to identify relationships between short-term deposition (tile-based) and long-term accumulation (²¹⁰Pb and ¹³⁷Cs) recorded within and adjacent to the PRE. The results of this study indicate (1) similar sedimentation patterns between the interior marsh and shore-side marsh at different sites regardless of elevation, (2) increased sedimentation (one to two orders of magnitude, 0.04–4.54 g m^?2 day^?1) within the interior marsh when the water levels exceeded the adjacent topography (e.g., storm berm), and (3) that short-term sea level changes can have direct effects on sediment delivery to interior marshes in wind-driven estuarine systems.     

Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia

Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e., the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land subsidence plays an important role in long-term coastal zone management in Semarang.     

Natural hazards in Central Java Province,Indonesia: an overview

Central Java Province, Indonesia, suffers from natural hazard processes such as land subsidence, coastal inundation, flood, volcanic eruption, earthquake, tsunami, and landslide. The occurrence of each kind of natural hazard is varied according to the intensity of geo-processes. It is necessary to learn from the historical record of coastal inundation, flood, volcanic eruption, earthquake, tsunami, and landslide hazards in Central Java Province to address issues of comprehensive hazard mitigation and management action. Through the understanding about the nature and spatial distribution of natural hazards, treatments can be done to reduce the risks. This paper presents the natural hazard phenomena in Central Java Province and provides critical information for hazard mitigation and reduction.