Sediment Balance Research Articles

The late Pleistocene-Holocene changing morphology of the Volturno delta and coast (northern Campania, Italy): Geological architecture and human influence

The present geomorphology of the Volturno River delta system and related strandplain is largely a product of complex, long-lived relationships between geological evolution and human impacts.In order to assess the main drivers of the changed landscape in the last centuries, a multidisciplinary study was carried out by combining geological and historical data. The study was based on geological and geophysical data, including about 1800 stratigraphic well logs to reconstruct the stratigraphic architecture of the delta plain and ca. 180 km of very high resolution single channel reflection profiles to image the stratigraphic pattern of the continental shelf and the offshore delta. Cartographic sources from the last 150 years were acquired, georeferenced and managed into a GIS environment, to support geomorphological interpretation. Land use maps were reconstructed for the 1957, 1990 and 2012. The Late Pleistocene and Holocene reconstruction of the Volturno coastal plain evolution evidenced the control of climatic changes (and consequently sediment supply and global eustatic variations) on the depositional history. The present landscape appears largely inherited by the past MIS5 and LGM landscapes.A progressive increment of anthropic forcing took place in the last 2000 years but the strongest modifications of the landscape occurred since the end of the XVII century, when, during the Spanish vice-kingdom, it was subjected to major land reclamation. More than 500 km of canals were built in the coastal area and resulted in the development of agriculture and farming on reclaimed land, promoting urbanization and increasing landscape fragmentation. A peak of major alterations of the deltaic environment, and retreat of the coastline was attained between the 1960s and the 1990s. Severe urbanization along the coastline, coupled with intensification of agricultural and tourism activities, resulted in a significant loss of natural ecosystems including humid coastal areas, lacustrine/marshy back-dune areas and mostly the beach-dune system. The negative sedimentary balance resulting from the reclamation works on the river courses, along with the interventions along the Volturno river basin, resulted in an accelerated and severe coastal erosion. The latter, coupled with subsidence rates and sea level rise, increase the vulnerability of the coast to flooding and storm surge and aquifer salinization.

A method for estimating stored sediment volumes by check dam systems at the watershed level: example of an application in a Mediterranean environment

PurposeIn this paper a quick, easy and accessible methodology to estimate the sediment volume trapped behind a fully filled check dam system is proposed. As it is well known, check dams play an important role in the sediment balance between watershed and coastline. However, on a large scale, especially in those contexts where a great number of structures was installed, detailed surveys and measurements of sediment storage capacity would be extremely time-consuming and costly in terms of both economic efforts and human resources.MethodsTo this aim, the proposed method considers only four easy-to-obtain morphometric parameters to combine with the number of check dams. The method was calibrated on a sample of 912 check dams located in seven long-term studied watersheds and, therefore, validated in a sample of three regulated Spanish catchments with an independent dataset.ResultsAt watershed level, the comparison between the calculated and estimated values showed a good capability of the method in evaluating the sediment volume trapped by the 912 studied check dams (RMSE ≈ 16,900 m3; R2 > 0.9). The validation revealed encouraging results with estimation errors below 25%.ConclusionThe use of this accessible and easily usable method could represent a supporting tool for planning, monitoring and assessment of the environmental effects of control works. Moreover, these results are useful to carry out actions aimed to mitigate natural hazard and environmental as well as socio-economic problems of the watershed-coast system (e.g. shoreline retreat and morphological instability of the urban and tourist areas).

Sediment bank contribution to form a vortex and maintain a deep scour hole on tidal channel meander in the Bahía Blanca estuary, Argentina

A wide range of processes determine the hydrodynamics and sedimentary balance in tide-dominated estuarine environments. Tidal channels can be subject to the most energetic processes. Therefore, changes in their geomorphology require continuous updates. Through oceanographic surveys, were collected in situ hydrodynamic, bathymetric, and sedimentological data in a section of the Canal del Medio in the Bahia Blanca Estuary (southwest of the Buenos Aires Province, Argentina) to examine the possible effect that the presence of a sediment bank can have on the tidal current pattern within a specific meander. An unusual elliptical deep scour hole was detected with a depth of 12.60 m in the thalweg of the meander (tidal range is about 3 m). Based on the data, it was found that the maintenance of the scour hole is possible because of a vortex forced by the presence of an elongated sandy bank connected to the tidal channel bank that acts as a hydrodynamic barrier to the currents, inducing the modification of the meander pattern.

A new large-scale suspended sediment model and its application over the United States

Abstract. Suspended sediment plays a vital role in the regional and global cycling of carbon and nutrients by carrying carbon and nutrients from headwaters into lowland rivers and the oceans. Sediment transport through river systems is often fundamentally modified by human activities such as reservoir management. However, a physically based representation of sediment transport is still missing in most existing Earth system models (ESMs), which are essential tools for modeling and predicting Earth system changes. Here, we introduce a multi-process river sediment module for ESMs, which includes (1) hillslope soil erosion and sediment discharge into streams, (2) sediment transport processes through river networks, (3) reservoir operation based on the inflows from upstream areas and water demand from downstream areas, and (4) sediment trapping by reservoirs. All model parameters are estimated a priori without calibration. We apply this new sediment modeling framework to the contiguous United States and validate it against historical observations of monthly streamflow and sediment discharges at 35 river gauges. The model reasonably well captures the long-term balance and seasonal variations of suspended sediment in large river systems. Furthermore, our model results show that suspended sediment discharge in managed rivers is affected more by reservoirs' direct trapping of sediment particles than by their flow regulation. This new sediment module enables future modeling of the transportation and transformation of carbon and nutrients carried by the fine sediment along the river–ocean continuum to close the global carbon and nutrient cycles.

Using the River Ecosystem Service Index to evaluate “Free Moving Rivers” restoration measures: A case study on the Ammer river (Bavaria)

AbstractRestoring natural fluvial dynamics is fundamental for sustaining biodiversity and functional integrity of river and floodplain ecosystems. In Central Europe, however, pervasive river regulation and bank protection have greatly impaired ecosystem functioning and many water bodies fail to achieve a good ecological status within the European Water Framework Directive. The “Free Moving Rivers” approach seeks to restore the ecological integrity of rivers and floodplains by creating appropriate conditions for natural fluvial dynamics. Principal goals of the approach include removing artificial constraints on river processes and expanding the river corridor to restore natural river habitats and structures. Lacking, however, are complementary tools that evaluate and predict changes to ecosystem services (ESSs) after implementation. Here, we describe a case study of the Ammer river in Bavaria, Germany, to (i) calculate the extent of the “Free Moving Rivers” corridor, and (ii) assess changes to ESSs of a proposed river restoration measure under two alternative land‐use scenarios. To do this, we apply the River Ecosystem Service Index (RESI), whereby individual ESSs are assessed in a spatially explicit way. We show how a proposed implementation of the “Free Moving Rivers” approach enhances three investigated ESSs: flood retention, sediment balance and habitat provision. We conclude that RESI is a potentially useful tool with wide applicability for restoration planning that synthesises floodplain complexity in such a way that facilitates decision making.

Study of Holocene aeolian morpholithogenesis of the Eastern coast of the White Sea using georadiolocation and palaeolimnological methods

Abstract. Holocene aeolian topography and sediments were investigated at two key sites on the Zimny Coast and one key site on the Kaninsky Coast of the White Sea. Field work included ground penetration radar profiling, paleolimnological and geomorphological study, as well as aerial imagery and topography surveys. Analytical studies including grain-size, geochemical and diatom analyses and radiocarbon dating of lake sediment cores were performed. Accumulative aeolian relief was formed in areas with a positive coastal-marine sediment balance. The sands are brought in by a longshore drift or river discharge. The aeolian topography and the number of stages of aeolian activation vary across the key areas. The present-time coastal dunes have been forming since the late or middle Holocene, when relative sea level became close to contemporary levels.

BEACH PROFILE EVOLUTION IN URBAN AND PERI-URBAN AREAS IN THE VILLA GESELL DISTRICT, BUENOS AIRES, ARGENTINA

The coastal villages with the greatest touristic affluence of the province of Buenos Aires, Argentina, are located on the Eastern Sand Barrier. The characteristics of the beaches of Villa Gesell, one of the most visited districts, have been studied before but there is no recent data available. The present work represents an update of the state of the beaches of this district, comparing data collected between 1994 and 2004 with sporadic measurements taken up to 2010. In 2021, two new seasonal surveys were carried out with the completion of four beach profiles distributed throughout the district and covering urban and peri-urban areas. It was observed that beaches in urban areas, where coastal dunes have been deteriorated or eliminated as a result of urban development and some anthropic practices, presented smaller beach widths and lower slopes. Beaches in peri-urban areas, with less building occupation on the waterfront, had greater beach widths and slopes, as well as larger volumes and sediment balances. Seasonal winter/summer cycles, episodic storm cycles and anthropogenic action have been identified as modifying processes of these beaches. Coastal urbanization and practices linked to sun and sea tourism affect coastal dynamics. Thus, sustained monitoring over time is a necessary tool to evaluate possible changes and preserve the beaches that represent a fundamental tourist resource for these localities.

The role of unpaved roads in the sediment budget of a semiarid mesoscale catchment

AbstractHigh erosion and runoff rates have been measured on road infrastructure, indicating that unpaved roads might be significant sources of sediment in catchments. In this paper, the production of surface sediments from unpaved rural roads is assessed in Northeastern Brazil, in a semiarid area of the caatinga biome, vulnerable to desertification. Sediment production data from road surface segments were monitored for 2 years (2013–2014) under conditions of natural precipitation. By using hydrosedimentological modeling and a geographical information system (GIS), the sediment budget was calculated at the meso‐scale catchment (aprox. 930 km2), in order to identify the relative contribution of roads to the sediment balance. The universal soil loss equation (USLE) associated with Maner's sediment delivery ratio (SDR) equation, proved to be an adequate approach for predicting sediment yield on the road segment scale. The best results were obtained for the road without traffic, due to the non‐interference in this segment of external factors, such as traffic and maintenance activities, not explicitly considered in the model formulation. The modeling procedure showed that the roads, which occupy only 0.7% of the catchment surface, were responsible for approximately 7% of soil loss in the area. Furthermore, sediment connectivity might be enhanced by roads, which cross the river network and, therefore, deliver more directly the sediment generated at hillslopes. This is particularly important in the studied environment, where sediment connectivity is low due to limited runoff and the existence of a dense network of surface water reservoirs.

Not just sand: The folly of dismantling the environmental protection of dunes in Brazil

The Brazilian federal government has followed an open agenda and land use policy against existing legislation in the past three years using the false argument that it hinders national development. A recent loss has been the repeal of national resolution CONAMA 303/2002. With the action of the Brazilian government to revoke this resolution, the mobile and eolian dunes are currently without legal national protection, and are available for real estate, industry (e.g., wind farms), and urban development, among other activities. In this context, the occupation of the mobile dunes promoted by the revocation of CONAMA 303 increases the risk of erosion of the beaches, damage to estuaries with mangroves, and destabilization of the coastline as a whole owing to the interruption of wind corridors of sand transport. The dunes are also one of the main freshwater reservoirs in Brazil. Therefore, the occupation of the dunes and encouragement of their impermeabilization by the attempted permanent repeal of CONAMA 303 resolution clearly puts the water security of Northeast Brazil (a semiarid region) at risk. This incentive to occupy mobile dunes by changing legislation will have a synergistic impact and amplify the predicted effects of climate change with negative repercussions on the sedimentary balance, tourist activities, and blue carbon sequestration. In addition, the vast quantity and value of goods and services provided to society and discussed in this article are sufficient to justify their conservation and a permanent decision from Supreme Court to keep the CONAMA 303 active.

Sediment Exchange Between the Created Saltmarshes of Living Shorelines and Adjacent Submersed Aquatic Vegetation in the Chesapeake Bay

Rising sea levels and the increased frequency of extreme events put coastal communities at serious risk. In response, shoreline armoring for stabilization has been widespread. However, this solution does not take the ecological aspects of the coasts into account. The “living shoreline” technique includes coastal ecology by incorporating natural habitat features, such as saltmarshes, into shoreline stabilization. However, the impacts of living shorelines on adjacent benthic communities, such as submersed aquatic vegetation (SAV), are not yet clear. In particular, while both marshes and SAV trap the sediment necessary for their resilience to environmental change, the synergies between the communities are not well-understood. To help quantify the ecological and protective (shoreline stabilization) aspects of living shorelines, we presented modeling results using the Delft3D-SWAN system on sediment transport between the created saltmarshes of the living shorelines and adjacent SAV in a subestuary of Chesapeake Bay. We used a double numerical approach to primarily validate deposition measurements made in the field and to further quantify the sediment balance between the two vegetation communities using an idealized model. This model used the same numerical domain with different wave heights, periods, and basin slopes and includes the presence of rip-rap, which is often used together with marsh plantings in living shorelines, to look at the influences of artificial structures on the sediment exchange between the plant communities. The results of this study indicated lower shear stress, lower erosion rates, and higher deposition rates within the SAV bed compared with the scenario with the marsh only, which helped stabilize bottom sediments by making the sediment balance positive in case of moderate wave climate (deposition within the two vegetations higher than the sediment loss). The presence of rip-rap resulted in a positive sediment balance, especially in the case of extreme events, where sediment balance was magnified. Overall, this study concluded that SAV helps stabilize bed level and shoreline, and rip-rap works better with extreme conditions, demonstrating how the right combination of natural and built solutions can work well in terms of ecology and coastal protection.

Prediction\ufeff research on sedimentation balance of Three Gorges Reservoir under new conditions of water and sediment

Influenced by climate change and human activities, especially the completion and operation of cascade reservoirs in the middle and lower reaches of Jinsha River since 2012, new changes have taken place in the water and sediment characteristics of the Three Gorges Reservoir (TGR) in recent years. In this paper, a one-dimensional unsteady water and sediment mathematical model of the main and tributary rivers of the TGR is established, and the main calculation parameters of the model are calibrated with the measured water and sediment data from January 1, 2008 to December 31, 2017. In view of the different combinations of inflow water and sediment that may occur in the TGR under the condition of new water and sediment, the long-term changes of sediment erosion and deposition and the balance of reservoir deposition in the TGR are studied using the model. The results show that: (1) Under the new conditions of water and sediment, the amount of sediment in the TGR accounts for only 14.8% and 35.8% of that in 1956–1990 and 2003–2012, respectively; (2) The variation process of water level, discharge and sediment concentration of each station along the route calculated by the model is basically consistent with the measured results, and the calculated values of total deposition amount and deposition distribution are also basically consistent with the measured results. The verification results of the model are in accordance with the measured values; (3) Under the water-sediment conditions during 1961–1970 and 1991–2000, the model predicted the estimates of 320 and 430 years for the TGR to reach a sedimentation balance, respectively. Under the new water-sediment conditions, it takes 560 years at most and 450 years at least to reach the sedimentation balance for the TGR, and the corresponding condition is the typical year with less water-less sediment and more water-more sediment, respectively. The research results of this paper can provide a new reference for the long-term safe operation and operation optimization of the TGR.

Upstream morphological effects of a sequential check dam adjustment process

AbstractSediment flushing and the morphological responses to the procedure of check dam removal are still unclear. Following laboratory experiments that revealed three stages (deepening, widening, and volume release) of check dam adjustment, a check dam built in 2007 at Landao Creek in central Taiwan was adjusted in 2015 by removing central bars and cutting 2.5 m from the middle two piers (stage 1 + 2), with the purpose of regulating sediment transfer and keeping the thalweg at the center of the channel, while also preventing hill slope toe erosion. In 2019, four central piers were removed (stage 3) to increase the volume of sediment released. Annual surveys were conducted after the initial adjustment in 2015 through to 2020 using unmanned aerial vehicles (UAVs). The check dam adjustments revealed that the channel had narrowed and stabilized as indicated by regenerating riparian vegetation. Additionally, distinct terraces had formed on the hill slope toes of the creek channel in proximity to the check dam. The meander upstream weakened following the dam adjustments. This study combining laboratory experiments with actual field observation contributed immensely to check dam decommissioning. Additionally, this study illustrated how an adjustable check dam may aid regulation of sediment transport and thereby sediment balance. It can be adjusted accordingly based on the prevailing channel condition.

Mean Dynamics and Elevation‐Contributing Area Covariance in Landscape Evolution Models

AbstractThe temporal dynamics of the land surface are commonly modeled by so‐called landscape evolution models, consisting of coupled partial differential equations accounting for the balance of sediment and water. An average sediment budget equation for a landscape evolution model in detachment‐limited condition is derived in terms of curvature‐dependent and curvature‐independent components. This highlights the role of plane curvature and spatial distribution of surface divergence/convergence on the average erosion rate. Performing a Reynolds‐type averaging of the original equations leads to a decomposition of the erosion into an unchannelized erosion sink and a channelization sediment flux. The latter is the derivative of a potential (referred to as “channelization sediment potential”) that arises from the negative correlation of elevation and specific drainage area and closely resembles, in both form and behavior, the Reynolds stress in fluid turbulence. The negative elevation‐area covariance emerges as a statistical signature of surface channelization. Building on analogies between landscape channelization and fluid turbulence, these theoretical results may provide a path to estimate model parameters from observations and offer useful benchmarks for numerical simulations in the channelized regime.

Mass balance of Neogene sediments in the Colombia basin relationship with the evolution of the Magdalena and Cauca River basins

The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.

An Ecogeomorphic Framework Coupling Sediment Modeling With Invasive Riparian Vegetation Dynamics

AbstractFeedbacks between geomorphic processes and riparian vegetation in river systems are an important control on fluvial morphodynamics and on vegetation composition and distribution. Invasion by nonnative riparian species alters these feedbacks and drives management and restoration along many rivers, highlighting a need for ecogeomorphic models to assist with understanding feedbacks between plants and fluvial processes, and with restoration planning. In this study, we coupled a network‐scale sediment model (Sediment Routing and Floodplain Exchange; SeRFE) that simulates bank erosion and sediment transport in a spatially explicit manner with a recruitment potential analysis for a species of riparian vegetation (Arundo donax) that has invaded river systems and wetlands in Mediterranean climates worldwide. We used the resulting ecogeomorphic framework to understand both network‐scale sediment balances and the spread and recruitment of A. donax in the Santa Clara River watershed of Southern California. In the coupled model, we simulated a 1‐year time period during which a 5‐year recurrence interval flood occurred in the mainstem Santa Clara River. Outputs identify key areas acting as sources of A. donax rhizomes, which are subsequently transported by flood flows and deposited in reaches downstream. These results were validated in three study reaches, where we assessed postflood geomorphic and vegetation changes. The analysis demonstrates how a coupled model approach is able to highlight basin‐scale ecogeomorphic dynamics in a manner that is useful for restoration planning and prioritization and can be adapted to analogous ecogeomorphic questions in other watersheds.

Sediment Balance Estimation of the ‘Cuvette Centrale’ of the Congo River Basin Using the SWAT Hydrological Model

In this study, the SWAT hydrological model was used to estimate the sediment yields in the principal drainage basins of the Congo River Basin. The model was run for the 2000–2012 period and calibrated using measured values obtained at the basins principal gauging station that controls 98% of the basin area. Sediment yield rates of 4.01, 5.91, 7.88 and 8.68 t km−2 yr−1 were estimated for the areas upstream of the Ubangi at Bangui, Sangha at Ouesso, Lualaba at Kisangani, and Kasai at Kuto-Moke, respectively—the first three of which supply the Cuvette Centrale. The loads contributed into the Cuvette Centrale by eight tributaries were estimated to be worth 0.04, 0.07, 0.09, 0.18, 0.94, 1.50, 1.60, and 26.98 × 106 t yr−1 from the Likouala Mossaka at Makoua, Likouala aux Herbes at Botouali, Kouyou at Linnegue, Alima at Tchikapika, Sangha at Ouesso, Ubangi at Mongoumba, Ruki at Bokuma and Congo at Mbandaka, respectively. The upper Congo supplies up to 85% of the fluxes in the Cuvette Centrale, with the Ubangi and the Ruki contributing approximately 5% each. The Cuvette Centrale acts like a big sink trapping up to 23 megatons of sediment produced upstream (75%) annually.

Coastal geology of the Holocene progradant plains of sandy beach ridges in Santa Catarina state, Southeastern Brazil

Beach ridges are indicators of supratidal and intertidal depositional environments built by waves. The major factors that influence on the ridge’s formation is related to antecedent topography, sediment supply, sedimentary balance, and substrate gradient. They consist of siliciclastic and/or bioclastic sediments whose grain size varies from very coarse sand to very fine sand. At Santa Catarina state, progradant plains are related to Pleistocene and Holocene regressive marine processes. The Holocene marine terraces, object of this study, predominate in the coastal plains of Passo de Torres, Pinheira, Jurerê, Tijucas and Navegantes, presenting heights from 3 to 6 m in elevations and 1 to 2 m in depressions. The ridge deposits are constituted by sandy sediments, medium to very fine, composed by quartz, opaque and heavy minerals and shell fragments. The runnel deposits comprehend silt-sand-clayey sediments enriched by organic matter. The evolution of Holocene Santa Catarina beach ridges is connected to the regressive events occurred after 5,1 ky BP that indicate the position of paleo coastlines and mean sea level of the Holocene.

Assessment of suspended sediment load variability in the Tonle Sap and Lower Mekong Rivers, Cambodia

The Mekong River in Southeast Asia, one of the world’s great rivers, has been facing disruption of its sediment balance and resultant impacts on nutrient fluxes, aquatic ecology, floodplains and the delta. Using monitoring data from 1993 to 2018, we estimated the temporal variability of sediment loads in Tonle Sap and Lower Mekong Rivers in Cambodia, assessing the sediment linkage between the Tonle Sap Lake and the Mekong mainstem, which are connected by a seasonally reversing flow through the Tonle Sap River. We estimated the annual sediment in the Mekong mainstem of 72 ± 38 Mt/year at Kratie (upstream) and 78 ± 22 Mt/year at Chroy Changvar from 1993 to 2018 (just upstream of the Chatumuk confluence). Our sediment load estimation of the Mekong River is consistent with other recent estimates of sediment load on the Lower Mekong. However, the result is lower than reported in some older studies (prior to the 2000s), which is consistent with sediment trapping by dams on Upper Mekong mainstem and major tributaries. Our analysis indicates that Tonle Sap Lake provided 0.65 ± 0.6 Mt/year of sediment annually to the Lower Mekong River from 1995 to 2000. However, since 2001, Tonle Sap Lake has become a sink for sediment, accumulating an average of 1.35 ± 0.7 Mt annually. Net storage of sediment in Tonle Sap Lake reduces the annual sediment transport to the delta, further compounding the effects of reduced sediment delivery to the delta resulting from upstream dam development and instream sand mining.

Hydro-morphological simulation for Blue beach, Gaza Strip, Palestine

Man-made improvements to the coastal areas can have a drastic short- and long-term impact on the sediment balance. This paper investigates the morphological changes at the Blue beach, Gaza Strip, Palestine. The Blue Beach resort is extremely deteriorated due to shoreline recession, where the width of the beach at some locations is less than 0.5 m. On the other side, the new recreational groin is unstable because it is not adequately designed to serve as a breakwater from a technical point of view. Firstly, this paper uses the integrated Digital Shoreline Analysis System (DSAS) with the Geographic Information System to detect changes in the coastline along the Blue Beach coast in Gaza during the 2011–2019 period. Shoreline change rates in the form of erosion and accretion patterns are automatically quantified by the End Point Rate. In addition, a proposed plan consists of two main stages to mitigate the current problems raised by severe erosion through numerical investigation; restoration of the existing beach by sand nourishment in addition to reducing the exposure of the coast to erosion and boost the protection of the recreational groin by implementing submerged offshore breakwaters. Hydro-morphological modeling is applied to study the processes of the coastal zone, hence, evaluating the diverse alternatives mentioned above. Delft3D software package is used to numerically simulate the different scenarios at different times: 1, 5, and 8 years, respectively. In addition, the existing structures are rehabilitated in accordance with current conditions. DSAS results show that during the period (2011–2019) there was a major recession to the shoreline with a peak erosion rate of -4.16 m/year. From the numerical modeling, it is concluded that the two submerged breakwaters managed to restore the beach by minimizing the amplitude of the wave and thus trapping the sediments behind it. In fact, the sediments grew offshore beyond the submerged breakwaters for the long term.

Theoretical Investigation of Equilibrium Dynamics in Braided Gravel Beds for the Preservation of a Sustainable Fluvial Environment

Gravel bars have an important role in the exchange between surface and subsurface waters, in preventing and mitigating riverbank erosion, in allowing the recreational use of rivers, and in preserving fluvial or riparian habitats for species of fishes, invertebrates, plants, and birds. In many cases, gravel bars constitute an important substrate for the establishment and development of ground flora and woody vegetation and guarantee higher plant diversity. A sustainable management of braided rivers should, therefore, ensure their ecological potential and biodiversity by preserving a suitable braiding structure over time. In the present study, we propose an analytical–numerical model for predicting the evolution of gravel bars in conditions of dynamical equilibrium. The model is based on the combination of sediment balance equation and a regression formula relating dimensionless unit bedload rate and stream power. The results highlight the dependence of the evolving sediment particles’ pattern on the ratio of initial macro-bedforms longitudinal dimension to river width, which determines the gradual transition from advective and highly braiding to diffusive transport regime. Specifically, the tendency to maintain braiding and flow bifurcation is associated with equilibrium average bed profiles and, therefore, equilibrium average stream power characterized by the maximum period that does not exceed transverse channel dimension.