Sediment Management Plan Research Articles

Low sediment loads affect survival of coral recruits: the first weeks are crucial

Increased sedimentation due to anthropogenic activities is a threat to many nearshore coral reefs. The effects on adult corals have been studied extensively and are well known. Studies about the impact of sedimentation on the early life stages of scleractinian corals, however, are rare although recruitment is essential for conserving and restoring coral reefs. Laboratory and in situ experiments with recruits of different age classes focused on the broadcast-spawning species Acropora hyacinthus and the brooding coral Leptastrea purpurea. Recruits were exposed to different sediment loads over three to five weeks. Applied sediment loads were more than one order of magnitude lower than those known to affect survival of adult coral colonies. Growth and survival of newly settled recruits were negatively affected by sediment loads that had no effect on the growth and survival of one-month-old recruits. All experiments indicated that newly settled coral recruits are most sensitive to sedimentation within the first two to four weeks post settlement. The co-occurrence of moderate sedimentation events during and immediately after periods of coral spawning can therefore reduce recruitment success substantially. These findings provide new information to develop comprehensive sediment management plans for the conservation and recovery of coral reefs affected by chronic or acute sedimentation events.

Uncertainty in flow and sediment projections due to future climate scenarios for the 3S Rivers in the Mekong Basin

Reliable projections of discharge and sediment are essential for future water and sediment management plans under climate change, but these are subject to numerous uncertainties. This study assessed the uncertainty in flow and sediment projections using the Soil and Water Assessment Tool (SWAT) associated with three Global Climate Models (GCMs), three Representative Concentration Pathways (RCPs) and three model parameter (MP) sets for the 3S Rivers in the Mekong River Basin. The uncertainty was analyzed for the short term future (2021–2040 or 2030s) and long term future (2051–2070 or 2060s) time horizons. Results show that dominant sources of uncertainty in flow and sediment constituents vary spatially across the 3S basin. For peak flow, peak sediment, and wet seasonal flows projection, the greatest uncertainty sources also vary with time horizon. For 95% low flows and for seasonal and annual flow projections, GCM and MP were the major sources of uncertainty, whereas RCPs had less of an effect. The uncertainty due to RCPs is large for annual sediment load projections. While model parameterization is the major source of uncertainty in the short term (2030s), GCMs and RCPs are the major contributors to uncertainty in flow and sediment projections in the longer term (2060s). Overall, the uncertainty in sediment load projections is larger than the uncertainty in flow projections. In general, our results suggest the need to investigate the major contributing sources of uncertainty in large basins temporally and at different scales, as this can have major consequences for water and sediment management decisions. Further, since model parameterization uncertainty can play a significant role for flow and sediment projections, there is a need to incorporate hydrological model parameter uncertainty in climate change studies and efforts to reduce the parameter uncertainty as much as possible should be considered through a careful calibration and validation process.

Reservoir sediments: a sink or source of chemicals at the surface water-groundwater interface.

This study delineates the physical, chemical, and biological effects resulting from anthropogenic and endogenic activities in a sensitive dammed reservoir situated in a semi-arid region. The reservoir is characterized by two major flow regimes: a wet fill hydrologic regime and a dry spill one. A seasonal sampling campaign was carried out over a period of 2 years (2011-2013) where water samples were collected across the water column and from piezometers just outside the perimeter of the reservoir. Similarly, sediments were collected from the corresponding areas beneath the water column. The water samples were analyzed for environmental isotopic ratios, elemental composition, and physical, biological and chemical parameters, whereas the sediment and algal samples were subjected to physical, mineralogical, spectroscopic, and microscopic analyses. This investigation indicated that the dam had resulted in the alteration of the biogeochemical cycle of nutrients as well as the degradation of the sediment and water quality. The hydrological and biogeochemical processes were found to induce vertical downward transport of chemicals towards the fine grained calcareous sediments during the fill mode, whereas the sediments acted as a source of a chemical flux upward through the water column and downward towards the groundwater during the spill mode. The geomorphological characteristics of the reservoir enhanced the strong hydrological connectivity between the surface water and the groundwater where the reservoir responded quickly to natural and anthropogenic changes in the upper watershed. The water and sediments in the sensitive spill mode were of poor quality and should receive more attention due to the potential hazard for the associated hydro-project and the sustainability of the agricultural soil in the long term. Thus, a safe water and sediment management plan should be implemented in order to improve the dam functionality and to safeguard the precious water resources.

Challenges of ecosystem restoration in Louisiana – availability of sediment and its management

Abstract. Human intervention has impaired the Mississippi River’s ability to deliver sediment to its delta wetlands, and as a consequence acute land loss in coastal Louisiana has resulted in an unprecedented ecocatastrophe. To mitigate this degradation, an unparalleled restoration effort is underway. For this effort to be successful and sustainable, various sediment input mechanisms must be integrated, including: building appropriate sediment-diversions; beneficially using the millions of cubic metres of sediment dredged annually from navigational channels; harvesting deposits of sand and suitable sediment from the river and offshore; and related sediment management activities that are compatible with other uses of the river. A comprehensive sediment management plan has been developed to identify and delineate potential sediment sources for restoration, and to provide a framework for managing sediment resources wisely, cost effectively, and in a systematic manner. The Louisiana Sediment Management Plan provides regional strategies for improved comprehensive management of Louisiana's limited sediment resources.

Large freshwater and sediment impoundments between the Mississippi River and the Louisiana coastline

Abstract. An innovative system-level sediment and freshwater management plan is proposed for the coastal regions of Louisiana, USA. It involves the construction of large sediment and freshwater impoundments between the river and coastline fed periodically through large spillway structures during the rising hydrograph of the river when the highest concentration of sediment is in the water column. Sediment directing and trapping technologies are proposed for the river channel and spillways to capture the coarser-grained sediments. The embankments can be constructed from dredging and then enlarged by land-based harvesting of coarse-grained sediments from the traps. These impoundments will permit the continuous introduction of freshwater and finer-grained sediments to coastal marshlands for vegetation, land augmentation, protection from storm surges and salt water intrusion, while removing large amounts of sand from the river and decreasing annual maintenance dredging costs.

Quantifying suspended sediment loads delivered to Cheney Reservoir, Kansas: Temporal patterns and management implications

Cheney Reservoir, constructed during 1962 to 1965, is the primary water sup- ply for the city of Wichita, the largest city in Kansas. Sediment is an important concern for the reservoir as it degrades water quality and progressively decreases water storage capacity. Long-term data collection provided a unique opportunity to estimate the annual suspended sediment loads for the entire history of the reservoir. To quantify and characterize sediment loading to Cheney Reservoir, discrete suspended sediment samples and continuously mea- sured streamflow data were collected from the North Fork Ninnescah River, the primary inflow to Cheney Reservoir, over a 48-year period. Continuous turbidity data also were collected over a 15-year period. These data were used together to develop simple linear regression models to compute continuous suspended sediment concentrations and loads from 1966 to 2013. The inclusion of turbidity as an additional explanatory variable with streamflow improved regression model diagnostics and increased the amount of variability in suspended sediment concentration explained by 14%. Using suspended sediment concentration from the streamflow-only model, the average annual suspended sediment load was 102,517 t (113,006 tn) and ranged from 4,826 t (5,320 tn) in 1966 to 967,569 t (1,066,562 tn) in 1979. The sed- iment load in 1979 accounted for about 20% of the total load over the 48-year history of the reservoir and 92% of the 1979 sediment load occurred in one 24-hour period during a 1% annual exceedance probability flow event (104-year flood). Nearly 60% of the reservoir sedi- ment load during the 48-year study period occurred in 5 years with extreme flow events (9% to 1% annual exceedance probability, or 11- to 104-year flood events). A substantial portion (41%) of sediment was transported to the reservoir during five storm events spanning only eight 24-hour periods during 1966 to 2013. Annual suspended sediment load estimates based on streamflow were, on average, within ±20% of estimates based on streamflow and turbidity combined. Results demonstrate that large suspended sediment loads are delivered to Cheney Reservoir in very short time periods, indicating that sediment management plans eventually must address large, infrequent inflow events to be effective.

Sediment changes upstream and downstream of the Altnahinch Dam in the River Bush in Northern Ireland: a preliminary study

The River Bush must reach a standard of good ecological potential (GEP) by 2015 due to the requirements of the water framework directive. The role of sediments within a water body is extremely important to all aspects of a river’s regime. The aim of this research is to investigate the effects of Altnahinch Dam on sediment distribution in the River Bush (a heavily modified water body) with comparison made against the Glendun River (an unmodified water body). Samples collected from the rivers were analysed by physical (pebble count, sieve analysis) and statistical methods (ANOVA, GRADISTAT). An increase in fine sediments upstream of the dam provides evidence that the dam is impacting sediment distribution. Downstream effects are not shown to be significant. The output of this study also implies similar impacts at other drinking water storage impoundments. This research recommends that a sediment management plan be put in place for Altnahinch Dam and that further studies be carried-out concentrating on fine sediment distribution upstream of the dam.

Managing industrialised coastal fine sediment systems

A high level of concern surrounds the management of industrialised muddy coasts and estuaries. Many centuries of apparently desirable alterations, such as hard defences, training walls and groynes, aided by traditional dredging and disposal, are today recognised as having associated disadvantages. The port and shipping industry is the principal facilitator of world trade, but the trends in its development place ever-increasing strains on conventional methods of management. In particular, inadequacies in “water-side” technologies are constraining the demands of modern societies. The present paper reviews a number of emerging self-sediment engineering technologies to manipulate intertidal zones, many of which are finding wide acceptance by practitioners, although many of these were first used some time ago: salt marsh inducement, set-back, tidal flat regeneration, etc. all have their place. A far greater challenge, and one less readily accepted, is attached to generic Sediment Management Systems for the subtidal zone. A range of more economic, more environmentally desirable methodologies to manage fine sediment for the ports and shipping industry are now well-proven: Auto-flushing, Entrance Flow Optimisation, and various manifestations of the Nautical Depth concept. Although for the moment these apply narrowly to ports, it is shown that they readily have a wider application to the management of whole systems. The technologies and their costs and benefits are herein set out. Bearing in mind that these technologies are well-proven, their wider adoption has now become a “people issue”. The environmental benefits of these methods are also discussed. A challenge facing our highly specialised society is that, in the optimal case, aspects of marine physics, chemistry and microbiology must all be carefully manipulated at the same time. Notably, no port in the world currently has a sediment management plan suited to the modern era.

Ecological Aspects of Coastal Sediment Management in the Gulf of Mexico

Reed, D.J.; Hijuelos, A.C., and Fearnley, S.M., 2012. Ecological aspects of coastal sediment management in the Gulf of Mexico. In: Khalil, S.M., Parson, L.E., and Waters, J.P. (eds.), Technical Framework for the Gulf Regional Sediment Management Master Plan (GRSMMP), Journal of Coastal Research, Special Issue No. 60, 51–65. Water and sediment resource planning is a vital facet of natural resource management. There have been many ecologically disruptive consequences from conventional resource management plans. In the northern Gulf of Mexico (GOM) nearby communities depend on water and sediment resources both ecologically as well as economically. The value of these resources is determined by habitat structure and ongoing sediment dynamics. This article explores how human activities have changed sediment dynamicsin relation to the ecology of the habitats present in the northern GOM. It further presents ideas to prevent future problems through sediment management plans that account for natural processes. The northern GOM contains several habitats that are affected by sediment/water resource management plans such as the shoreface (beaches and dunes), barrier islands, hardbottom (coral and oyster reefs), bays, marshes, and forested wetlands. Many common techniques for water/sediment resource management have been used in these areas such as dredging, hard structures (jetties, groins, seawalls, andbreakwaters),dams, diversions,levees,and coastaldevelopment. The implications of these different management techniques can lead to extensive changes in coastal habitats. Dredging causes disturbances to both borrow and placement sites and can change natural community structure at both sites. The installation of hard structures can cause severe changes in habitat structure that can lead to losses of species diversity. The impacts of river management structures (dams, levees, and diversions) alter the delivery of sediment needed by coastal habitats for growth and sustainability. Anthropogenic development in coastal regions prevents those areas from maturing naturally. Because of the importance of sediments to the ecology of the northern GOM coast and its vulnerability to natural and anthropogenic disturbances, several recommendations are made for holistic future sediment management plans.

Gulf of Mexico Regional Sediment Budget

Abstract Development of dynamic regional sediment management (RSM) plans is needed for future planning, construction, and monitoring of wetland and barrier island restoration. Broadly speaking, RSM refers to the optimum use of various sediment resources (littoral, estuarine, and riverine) in an environmentally effective and economically feasible manner. Coordination of the supply and demand sides of sand resources in a comprehensive manner will be required as project planning develops and evolves. The sediment budget is a planning tool that provides an accounting of sediment sources, sinks, and pathways as well as engineering activities and sediment budgets have generally been characterized as conceptual, interim, and operational depending upon the quality of the data, the level of analysis, and the uncertainty associated with the volume fluxes in the sediment budget. This paper summarizes existing sediment budget data for the entire Northern Gulf of Mexico. The purpose of this work has been to compile av...

COASTAL REGIONAL SEDIMENT MANAGEMENT PLAN

Regional Sediment Management (RSM) is a planning approach that seeks to address coastal sediment processes on a broader geographic scale. It recognizes that sand, cobble, and fine sediment are important natural resources that are critical to the environmental health and economic vitality of the coastal zone. The relevant sediment processes overlap multiple geopolitical boundaries which explains why a regional planning perspective is needed. To be effective a comprehensive road map is needed to addresses how to conserve and restore the valuable sediment resources, reduce shoreline erosion and coastal storm damages, protect sensitive environmental resources, increase natural sediment supply to the coast, preserve and enhance beaches, improve water quality along the shoreline, and optimize the beneficial use of material dredged from ports, harbors, and other opportunistic sediment sources. The plan that was prepared for the diverse 144-mile long Santa Barbara and Ventura Counties coastline was developed systematically using traditional planning processes to understand the baseline science and relevant physical processes; identify the challenges that currently exist and the corresponding opportunities that can be seized to positively move forward; and formulate appropriate action plans and solutions that have unanimity of purpose. It is demonstrated that in order to be technically, environmentally, economically, and politically effective regional sediment management plans should consist of a suite of diverse study, management, policy, and capital project activities.

Conceptual framework and interdisciplinary approach for the sustainable management of gravel-bed rivers: The case of the Drôme River basin (S.E. France)

Geomorphic responses to changes in bedload transport in gravel-bed rivers are complex. Such responses occur over long time scales and vary as a function of distance from sediment sources and local channel characteristics. As a result, different types of cascading ecological and social consequences are observed in different parts of a drainage network. This paper presents the results of an interdisciplinary research project, conducted by geomorphologists, ecologists, social scientists, and river managers that focused on changes in bedload transport in the Drome River catchment in south-eastern France. Our objective was to document a general conceptual framework of the historical and current physical, ecological, and social implications of human-caused bedload transport changes in the Drome River watershed that could be used to develop sediment management plans for similar gravel-bed river catchments. First, we synthesized the historical trajectory of the Drome River over the past two centuries from a geomorphic perspective in relation to the evolution of socio-economic activities. Then, we summarized typical ecological responses to gravel-bed channel adjustment. Third, we reviewed how the problems of water and sediment management in the Drome have been addressed over the past 20 years. We identified the best technical solutions for the replenishment of incised reaches by considering practical interdisciplinary questions including each technique’s juridical feasibility, ecological impacts, and its degree of acceptance by managers and the public. Finally, we integrated geomorphic processes, ecological dynamics, and socio-economic values into a functional river reach typology that was used to map target restoration reaches and potential sediment sources throughout the Drome River catchment.

Sediment management and the renewability of floodplain clay for structural ceramics

Background, aim, and scope: The Netherlands has vast resources of clay that are exploited for the fabrication of structural ceramic products such as bricks and roof tiles. Most clay is extracted from the so-called embanked floodplains along the rivers Rhine and Meuse, areas that are flooded during high-discharge conditions. Riverside clay extraction is-at least in theory-compensated by deposition. Based on a sediment balance (deposition versus extraction), we explore the extent to which clay can be regarded as a renewable resource, with potential for sustainable use. Beyond that, we discuss the implications for river and sediment management, especially for the large engineering works that are to be undertaken to increase the discharge capacities of the Rhine and Meuse. Materials and methods: Extraction rates are based on production statistics for clay, as well as those for fired end-products. Deposition rates are estimated from published and unpublished geological data (clay volumes and thicknesses, datings, etc.) and from morphological modeling studies. Comparisons between extraction and deposition are made at three different time-space scales: (1) long term (post-1850)/large scale (all Dutch floodplains), (2) present/large scale, and (3) present/site scale. The year 1850 is relevant because it approximately marks the beginning of the current, fully engineered river systems, in which depositional processes are constrained by dikes and groynes. As the Industrial Revolution began in the same period, post-1850 sediments can be identified by their pollution with heavy metals. Results: (1) We estimate the post-1850 clay volume in situ at about 0.20 km3, and the total extracted volume in the same period at about 0.17 km3. This puts the net long-term average deposition rate of clay at ∼1.3 million m3/year and the corresponding extraction rate at ∼1.1 million m3/year. (2) Current accumulation is approximately 0.4 million m3/year and expected to increase, and current extraction is about 0.7 million m3/year and expected to decrease. (3) Clay extraction creates a depression that has an increased sediment-trapping efficiency. This local effect is not considered explicitly in large-scale morphological modeling. Based on maximum observed sedimentation rates, we estimate that replenishment of a clay site takes in the order of 150 years. As clay extraction lowers some 0.5 km2 of floodplain yearly, a surface area of approximately 75 km2 would be required for sustainable clay extraction. This is about 1/6 of the total surface area of the embanked floodplains. Discussion: On the long term, clay extraction from the embanked floodplain depositional environment has been sustainable. At strongly decreasing deposition rates, the ratio between extraction and replenishment seems to have shifted towards unsustainable. However, current sedimentation is estimated conservatively. The site-scale approach suggests that, even if extraction would currently exceed deposition, this could be resolved with sediment management, that is, with site restoration measures aimed at higher sediment-trapping efficiency. Our results have implications for river engineering, especially where substantial digging is involved (floodplain lowering, high-discharge bypass channels, obstacle removal). First, this inevitably affects the clay resources that we studied, while resource sterilization should be avoided. Secondly, the effect that any form of digging has on subsequent sedimentation-increased rates-relates to long-term river maintenance. Conclusions, recommendations, and perspectives: We conclude that floodplain clay is a renewable resource, especially if managed accordingly. Beyond that, we established that clay extraction is a significant, lasting factor in floodplain evolution along the Rhine and Meuse Rivers. The interests of the extractive industry and river managers could be served jointly with sediment management plans that are based on sediment-budget analyses. © 2009 The Author(s).

Sediment management options for the lower Ebro River and its delta

Past and present management of the Ebro catchment have altered water, sediment and nutrient fluxes of the lower Ebro River and its delta. The construction of the Mequinensa and Riba-Roja dams during the 1960s disrupted the sediment transport continuity. As a result, the lower Ebro River and its delta are facing a reduction in sediment delivery which is estimated to be up to 99% of its original yield (about 3 × 107 t/yr). Consequently, about 45% of the emerged delta will be under the mean sea level by 2100 due to subsidence and sea level rise, whereas the delta coast is retreating at a rate of several meters per year in the mouth area. This paper aims to establish the basis for a sediment management plan directed to offset the effects of the sediment delivery deficit of the Ebro delta. A new management plan named ‘Integrated Plan for the Protection of the Ebro Delta’ (PIPDE) is being presently elaborated in order to develop sustainable management of the Ebro River and delta through an integrated management of water, sediment and habitats, in order to achieve European Union (EU) Water Framework Directive (WFD) requirements. Among other aspects, the plan aims to restore the sediment flux of the lower Ebro River by means of both the removal of the sediment trapped behind the dams and the transport of the sediment downstream of the reservoirs to the river mouth and delta plain. Preliminary studies show that the ‘flushing flood’ method has lower costs and is the most adapted method to transfer the sediments retained into the Riba-Roja dam. The required sediment load to stop coastal retreat in the mouth area and to compensate relative sea level rise represents 10 times the present suspended load (0.021 g/l), but is 10 times lower than the total volume of sediment delivered to the sea under natural conditions. Sediment delivery to the delta plain can be accomplished through the rice irrigation system, a method used prior to dam construction. Problems of achieving a sustainable management of water and sediment are mostly linked to reservoir management. Technical problems associated with by-passing sediments through the reservoirs can be solved through operational and structural changes. Benefits of sediment flow recovery are multiple, including maintenance of the reservoir capacity, possible decline of invasive species, reduction of elevation loss and coastal retreat in the delta. The partial restoration of sediment fluxes in the lower Ebro River and its delta is technically feasible and environmentally desirable, but further detailed studies need to be carried out before the plan can be implemented. Overall, the sustainability of the lower Ebro River and delta can only be guaranteed by the implementation of a new reservoir management concept where the ecological and morphological values, as well as the economical and social values, have to be taken into consideration.

Cyclic Erosional Instability of Sandbars along the Colorado River, Grand Canyon, Arizona

The study and management of regulated rivers have become important issues. A prime example is Glen Canyon Dam and its operational impacts on the downstream environment in Grand Canyon National Park, Arizona. We present an overview of the Glen Canyon Dam environmental issue, a novel methodology for monitoring dam impacts on alluvial sediments, and three years of study relating to the stability of alluvial deposits along the Colorado River. This research uses oblique photographs taken daily, automatically, from twenty-one fixed-position programmable cameras. Digital image-processing techniques created planimetric models of sandbar area from the photos for the period of March 1993 through May 1995. The technique allowed daily tracking of sandbar areas for detection of rapid erosional events. We demonstrated that rapid erosional events occur commonly on Grand Canyon sandbars. Sandbars are unstable over the study period, especially the first two years. Most of the rapid erosional events are associated with weekend or seasonal reduction in flow. Sandbar area frequency is bimodal with negative kurtosis, indicating that measurements taken at long time-steps are not likely to document mean area but rather minima or maxima. Time-series analysis suggests that periods of relative stability occur between rapid area-reducing events. Sandbars appear to adjust in two modes, a short-term adjustment mode occurring over hours and a long-term adjustment mode over days to weeks. The understanding and minimization of rapid-failure events should be increased, and the phenomenon needs to be addressed in any comprehensive sediment management plan.