Historical Shoreline Change Research Articles

On the Bruun Rule suitability for modelling shoreline change

Modelling and understanding shoreline response to sea-level rise over decadal to centennial timescales is crucial for managing sandy coasts. Globally, the Bruun Rule is one of the most common shoreline model applied to facilitate this. However, there are several limitations to the Bruun Rule, which can compromise coastal management decisions. Here, we provide a novel assessment of the suitability of the Bruun Rule for application in sandy coasts by applying it to hindcast and project shoreline change in three morphologically different sandy beaches over yearly and decadal timescales. We also compare the Bruun Rule predictions against associated observations, published predictions from a hybrid shoreline model, and historical shoreline changes. Results show that the Bruun Rule fails to accurately hindcast and provide realistic projections of future shoreline change in sandy coasts. We attribute this to the Bruun Rule's assumption of linearity between shoreline retreat and relative sea-level rise and its inability to account for nearshore circulation. We, therefore, recommend limiting the use of the Bruun Rule for informing policy and the management of sandy coasts.

Integrated Coastal Vulnerability Assessment: A Study of Karnataka, India

Coastal regions are changing due to environmental pressures and anthropogenic impacts such as coastal development and planning, ultimately becoming sensitive to unpredicted natural and manmade calamities. The scientific assessment requires an understanding of the relative vulnerability of the coast across a region, and, for this purpose, vulnerability indices are often used. This study is an integrated coastal vulnerability index for the Karnataka coastline, incorporating both physical variables and socio-economic indicators. To study the overall vulnerability of a region at the taluka level using the typical physical variables characterizing coastal vulnerability e.g. historical shoreline change, rate of relative sea-level change, coastal regional elevation, coastal slope, mean tidal range, significant wave height and geomorphology. Physical indicators are then combined with the outcomes of an assessment of socio-economic vulnerability developed using population and tourist density and education as indicators like human development index (HDI), composite taluka development index (CTDI) and urban development index (UDI), resulting in a more holistic assessment of vulnerability. The resulting vulnerability map describes the taluka as most vulnerable to physical indicators and also provides information on the nature of vulnerability in terms of its physical and socio-economic components intending to inform adaptation decision-making.

Assessment and Forecast of Shoreline Change Using Geo-Spatial Techniques in the Gulf of California

In coastal regions, the combined effects of natural processes, human activity, and climate change have caused shoreline changes that may increase in the future. The assessment of these changes is essential for forecasting their future position for proper management. In this context, shoreline changes in the Gulf of California (GC), Mexico, have received little attention and no previous studies have addressed future forecasting. In this study, the researchers assessed the historical shoreline changes to forecast the long-term shoreline positions. To address this, shoreline data were obtained from Landsat satellite images for the years 1981, 1993, 2004, 2010, and 2020. The Net Shoreline Movement (NSM), Linear Regression Rate (LRR), End Point Rate (EPR), and Weighted Linear Regression (WLR) geo-spatial techniques were applied to estimate the shoreline change rate by using a Digital Shoreline Analysis System (DSAS) in the GIS environment. A Kalman filter model was used to forecast the position of the shoreline for the years 2030 and 2050. The results show that approximately 72% of the GC shoreline is undergoing steady erosion, and this trend is continuing in the future. This study has provided valuable and comprehensive baseline information on the state of the shoreline in the GC that can guide coastal engineers, coastal managers, and policymakers in Mexico to manage the risk. It also provides both long-term and large-scale continuous datasets that are essential for future studies focused on improving the shoreline forecast models.

Shoreline change on a tropical island beach, Seven Mile Beach, Grand Cayman: The influence of beachrock and shore protection structures

Contemporary and near-future shoreline change is widely regarded as an issue on small tropical islands. While it is widely anticipated that sea-level rise will precipitate shoreline recession on tropical islands, studies to date record both accretion and recession at historical timescales. This study of Seven Mile Beach, Grand Cayman presents a case study of historical shoreline change in which the local geomorphic setting is shown to be an important influence on shoreline behaviour. Consistent with its leeside setting, historic shoreline analysis (1958–2019) reveals erosion on the margins and accretion in the central part of the headland-embayment beach where no beachrock is present. The beach comprises five discrete, but interlinked subcells delineated by low headlands of exposed beachrock. These headlands have emerged through shoreline recession post-1971 but once exposed have become loci of persistent erosion, suggesting a positive feedback between beachrock and waves. A Category 5 Hurricane generated waves directly opposed to long-term modes and throughout the beach, long-term patterns of shoreline change were temporarily reversed, however, the historic pattern of shoreline change was restored within 2 years. The contemporary patterns of erosion and cell development suggest a reduction in sediment supply leading to cannibalization of relict beachridges on the margins of the embayment and emergence of formerly buried beachrock. The effects of coastal structures and erosion abatement measures were assessed and recommendations for coastal management, including development setback lines are presented.

Effectiveness of grey and green engineered solutions for protecting the low-lying muddy coast of the Chao Phraya Delta, Thailand

Coastal protection measures can be categorized into grey and green solutions in terms of their ecosystem impacts. As the use of grey solutions has become a serious issue due to environmental consequences during the last few decades, green/nature-based solutions have become prioritized. This study evaluates the effectiveness of grey and green solutions applied along the eastern Chao Phraya Delta (ECPD) based on historical shoreline change analysis and coastal observations using Light Detection and Ranging technology. The results from shoreline analysis indicate that nearshore breakwaters installed 100–250 m from the shoreline have successfully reclaimed the coastline with a sedimentation rate of 17–23 cm/y. Meanwhile, sand-sausage-submerged breakwaters were ineffective at stabilizing the coastline during 2002–2010 due to land subsidence. With a low subsidence rate, the rubble-mound-submerged breakwaters can reduce the shoreline retreat rate with a vertical deposition rate of about 5 cm/y. In contrast, use of a bamboo fence, a green solution widely used along muddy coasts, traps sediment at a rate of less than 1.3 cm/y and typically lasts only for 2–3 years after installation. Decomposed bamboo causes environmental degradation so local communities disapprove of the approach. Results reveal that grey solutions are more effective for stabilizing the ECPD coastline and result in less coastal environmental impact than the nature-based solution using a bamboo fence.

Predicting Shoreline Change for the Agadir and Taghazout Coasts (Morocco)

Aangri, A.; Hakkou, M.; Krien, Y., and Benmohammadi, A., 2022. Predicting shoreline change for the Agadir and Taghazout coasts (Morocco). Journal of Coastal Research, 38(5), 937–950. Coconut Creek (Florida), ISSN 0749-0208. Prediction of the long-term shoreline change under the effect of natural and anthropogenic factors is a fundamental goal for coastal managers. This paper presents a simple model for predicting the shoreline change for the Agadir and Taghazout coasts, which consist of several sandy beaches, in the horizons 2050 and 2100; this coastal area plays a vital economic role in this region. The anticipation of its protection against erosion is necessary in view of the effects of climate change, and it will preserve its potential for tourism and urban development in the long term through the establishment of the construction setback line. The approach proposed here combines the long-term extrapolations of historical shoreline changes (1969–2020) in the future, and the estimate of the shoreline retreat due to sea level rise (SLR) by using Bruun's rule, using the severe RCP 8.5 scenario, and taking into account the contribution of vertical land movements. The model used has been calibrated through incorporating a correction factor (F), calculated by comparing observed and predicted data over a long period. The analysis of the predictions results provided in this work showing a potential risk of erosion threatening all seaside tourist and urban infrastructures along this coast. The average retreat is estimated at 12 m by 2050 and 51 m by 2100.

PREDICTION OF SHORELINE CHANGE USING A NEW LONG-TERM SHORELINE EVOLUTION MODEL BASED ON THE CONCEPT OF SEDIMENT BALANCE

A new model that can predict long-term shoreline evolution in response to climate change for the 21st century has been developed. The developed model is an analytical model, capable of simulating coastal processes that contribute to long-term shoreline change, driven by the concept of sediment mass balance. The model was employed to simulate shoreline change along the 53 Km of coastline on the east coast of Peninsular Malaysia, which includes a variety of beach settings. The model was able to produce results close to the actual historical shoreline change for a hindcast period of 10 years, with an accuracy of 90%, indicating an excellent agreement between observed and predicted shoreline changes. Future coastal evolution predicted by the model indicate that by the year 2100, on average, 65% of beaches that are located along the coast of Pahang are going to disappear completely. Primarily due to the effects of long-term coastal sediment misbalance, the beaches are expected to lose roughly twice the amount of gained sediment as a result of the increasing impact of the coastal processes in the next 80 years.

Delft3D as a Tool for Living Shoreline Design Selection by Coastal Managers

Coastal risk reduction features are often built to protect infrastructure and ecosystems from damaging waves, sea level rise, and shoreline erosion. Engineers often use predictive numerical modeling tools, such as Delft3D to help design optimal intervention strategies. Still, their use by coastal managers for optimizing the design of living shorelines in complex geomorphic environments has been limited. In this study, the Delft3D modeling suite is used to help select the optimum living shoreline structure for a complex inlet and bay system at Carancahua Bay, Texas. To achieve this goal, an extensive array of sensors was deployed to collect hydrodynamic and geotechnical data in the field, and historical shoreline changes were assessed using image analysis. The measured data were then used to parameterize and validate the baseline Delft3D model. Using this validated model, the hydrodynamics resulting from a series of structural alternatives were simulated and compared. The results showed that the mouth of this complex inlet has widened greatly since the 1800s due to wave erosion and sea level rise. The analysis of the structural alternatives showed it was not advisable to attempt a return of the inlet to its historical extent, but rather to create a hybrid design that allowed for limited flow to continue through a secondary inlet. The numerical modeling effort helped to identify how to best reduce wave and flow energy. This study provides a template for the application of Delft3D as a tool for living shoreline design selection under complex shallow-estuary and inlet dynamics.

Spit Evolution and Shoreline Changes Along Manamelkudi Coast Using Geo-Spatial Techniques and Statistical Approach

The historical shoreline changes from 1980 to 2020 along the Manamelkudi coast is studied using toposheet, satellite time-series Landsat data, and observed data. An attempt is made to recognise possible factors which are responsible for shoreline changes and spit growth at south Manamelkudi coast (Palk Strait), Eastern part of Pudukkottai district, Tamilnadu. During 1980–2020, the regions showed distinct spatio-temporal variability, which is discussed in relation to spit evolution and shoreline changes. The study also generated a long-term (1980-2020) shoreline change statistics (EPR, LRR, SCE and NSM, WLR) using the Digital Shoreline Analysis System (DSAS) at every 150 m interval for the Manamelkudi coast covering 42 km, identified the erosion and accretion and divide the shoreline into different classes of erosion and accretion. Identified lengths of shoreline with high erosion, low erosion, stable, low accretion and high accretion are, respectively, based on LRR. The results indicate that spit evolution is predominant along the Manamelkudi coast, with the highest percentage of erosion and accretion.

Multi-criteria coastal environmental vulnerability assessment using analytic hierarchy process based uncertainty analysis integrated into GIS

Changes in environmental conditions influence vulnerability due to interacting stresses and pressures across the nations and regions. Coastal resources are under severe stress due to climate change, growing trade and commerce, and the human population depends on them. The coastal vulnerability to changing climatic variables has created a major concern at regional, national and global scales. The present model study assessed the coastal vulnerability of the densely populated districts in South India, which are prone to extreme climatic events at a higher frequency. The seven crucial influencing variables that have been selected for the study were sea-level rise, coastal elevation, coastal slope, extreme rainy days, historical shoreline change, tidal range, and geomorphology. The identified variables were ranked by relative importance and linked by weightage using analytical hierarchy process-based uncertainty analysis. Mapped and reclassified variables have been integrated to derive the overall vulnerability using geospatial techniques. The study shows that the coast has experienced high vulnerability to SLR impact, extreme rainfall, geomorphology, and elevation; medium vulnerability to the shoreline change and least vulnerable to coastal slope and tidal range. Of the coastal regions studied, 29% and 14.3% had high vulnerability; 70.5% and 85.7% had medium vulnerability in the two selected densely populated districts (Kancheepuram and Tiruvallur District). Applying geospatial techniques to assess the environmental vulnerability resulted in reliable and informative maps which will serve as a model to determine the critical coastal regions to plan for the conservation and adaptation measures.

SHORELINE MAPPING OF TELUK NIPAH USING DIGITAL SHORELINE ANALYSIS SYSTEM (DSAS) IN ARCGIS WITH TIDAL CORRECTION

Shoreline characterization using remote sensing technologies is a useful tool to determine the historical shoreline changes of a specific coast. Tidal variation is one of the important factors that should be considered in the shoreline mapping exercise. However, the tidal correction has often been neglected due to the need to access the historical tidal data series for the study site. As a result, the accuracy of the shoreline mapping without tidal correction is ambiguous. Hence, this study aims to establish the historical shoreline mapping of Pantai Teluk Nipah, Pangkor Island, Malaysia, with a tidal correction, using ArcGIS software. For 30 years of the study period, Landsat satellite imageries were processed via ArcGIS to quantify the shoreline change rate. Based on the previous shoreline mapping study without the tidal correction, transect 23 of Pantai Teluk Nipah has undergone severe erosion where the erosion rate is up to –6.83 m per year. With consideration of tidal correction, the shoreline erosion rate at the same transect has reduced to –3.87 m per year, which is consistent with the current beach condition at Pantai Teluk Nipah.
 Keywords: coastal, shoreline extraction, remote sensing, tidal effect, erosion, coastal retreat, tidal correction

Shoreline change rate dynamics analysis and prediction of future positions using satellite imagery for the southern coast of Kuwait: A case study

The studied shoreline extends 73 kilometers, starting from the Kuwait-Saudi Arabia borders northward. This work represents a limited work that analyses the historical shoreline positions. Five-dates satellite images along a period of 35 years between 1986 and 2021 were used to calculate the historical shoreline change rates and predict future shoreline positions in 2030 and 2050. First, the historical shoreline was extracted using the Normalized Difference Wader index (WI 2015). Then, the shoreline change rates were quantified statistically using the End Point Rate (EPR) and the Linear Regression Rate (LRR) models of the Digital Shoreline Analysis System (DSAS) tool in ArcMap. It has been found that the maximum erosion rate is –9.73 m/year, and the highest accretion is 10.88 m/year. Also, the positions of shorelines in the year 2030 and 2050 were predicted and defined on the map, with mapping of gain and loss surfaces. The results defined the most stable areas for future development and the areas needing urgent protection. It has been found that the resulting model can be affected by the topographical changes of the beaches due to human activities, where the coast alongside the Al-Khiran project will be eroded and accreted less than predicted because of the presence of protection facilities.

Assessment and prediction of shoreline change using multi-temporal satellite data and geostatistics: A case study on the eastern coast of India

Abstract Climate change and rising sea level is transforming global coastlines as corroborated by significant changes in the position of shoreline witnessed through coastal erosion or accretion. Andhra Pradesh has the second longest (972 km) coastline in India. The present study analyzed shoreline change and its future prediction by employing satellite-derived data and geographic information system. End point rate (EPR) and linear regression rate (LRR) statistical tools in the Digital Shoreline Analysis System (DSAS) were used to estimate historical shoreline change rate between 1973 and 2015. Erosion and accretion of the coastline were delineated from Landsat satellite images for 1973, 1980, 1990, 2000, 2010, and 2015; subsequently, shoreline is predicted for short-term (2025) and long-term (2050) periods. The study showcased that the river mouths of Krishna and Godavari experienced higher rate of change in shoreline position influenced by the deltaic environment and fluvial processes. LRR model prediction depicts the average rate of shoreline change during 2015–2025 will be −4.64 m, while between 2015 and 2050 it will increase to −16.25 m. The study observed that the error between predicted and actual shoreline is higher in the river mouth and deltaic plains. Predicted shoreline position will provide baseline information for adaptation strategies and policy framework for coastal management.

Coral Reef Geometry and Hydrodynamics in Beach Erosion Control in North Quintana Roo, Mexico

Coral reefs are increasingly recognized for their shoreline protection services. The hydrodynamic performance of this ecosystem is comparable to artificial low-crested structures often used in coastal protection, whose objective is to emulate the former. Coral reefs also provide other important environmental services (e.g., food production, habitat provision, maintenance of biodiversity and social and cultural services) and leave almost no ecological footprint when conservation and restoration actions are conducted to maintain their coastal protection service. However, studies have focused on their flood protection service, but few have evaluated the morphological effects of coral reefs through their ability to avoid or mitigate coastal erosion. In this paper, we investigate the relation between shoreline change, reefs’ geometry and hydrodynamic parameters to elucidate the physics related to how the Mesoamerican Reef in Mexico protects sandy coastlines from erosion. Using numerical wave propagation and historical shoreline change calculated from satellite imagery, a direct correlation was found between shoreline movement, the depths and widths of reef flats, changes in the wave energy flux, and the radiation stresses of breaking waves. The findings indicate that the most remarkable efficacy in preventing beach erosion is due to reefs with shallow crests, wide reef flats, a dissipative lagoon seabed, located at ∼300 m from the coastline. The results provide essential insights for reef restoration projects focused on erosion mitigation and designing artificial reefs in microtidal sandy beaches. Results are limited to wave-dominated coasts.

Coastal Vulnerability Index for Kuwaiti Coast

Kuwait is investing significantly for the development of coastal infrastructures in many of its coastal areas. It is essential to know the vulnerability of the coast of Kuwait for the future sea level rise and other physically influencing parameters. For this purpose, a detailed study is carried out and the Coastal Vulnerability Index (CVI) is established for the Kuwaiti coast including the coasts of Islands. The CVI is assessed based on the data on coastal geomorphology, historical shoreline change rate, landward side of the coastal slope, mean significant wave height, mean tidal range and the particle size of the sediments along the beach. The total Kuwaiti coastline of 499 km is divided into two groups with a total of 162 coastal segments. The group 1 contains 138 segments and covers the mainland, Boubyan and Failaka Island. The group 2 contains 24 locations and covers Umm Al-Maradim, Qaru and Kubbar Islands. Field data collection is carried out for all these segments. From this study it is found that 5% of the Kuwaiti coastal area in group 1 are very low vulnerable; 34% low vulnerable; 31% moderately vulnerable; 18% highly vulnerable and 12% are very highly vulnerable. Similar results are obtained for group 2 coastal segments. The results of this study will be useful while preparing the Integrated Coastal Zone Management plan for Kuwaiti coast and for its sustainable coastal infrastructure development.

The Comparative Study of Adaptation Measure to Sea Level Rise in Thailand

In the 21st century, global sea level rise associated with climate change will affect beach areas, which provide a number of benefits that include benefits to the recreational sector of the economy. In Thailand, the adoption of structural measures in order to slow down beach erosion and handle the impact of sea level rise is commonly implemented. However, structural measures often bring about negative effects on nearby coastal areas. For this reason, suitable adaptation measures should be determined, in order to protect beach areas and to sustain the tourism carrying capacity of the beach. This study analyzed historical shoreline changes using satellite images, and assessed beach value with the hedonic pricing method. We used a benefit–cost ratio analysis to evaluate the economic valuation assessment of Pattaya beach and Chalatat beach. The results showed that the beach values of Pattaya beach and Chalatat beach were 1,072,250 and 92,092 USD, respectively. The benefit–cost ratio analysis proposed that it is worth implementing beach nourishment for the adaptation measure to address all climate change scenarios. In response to climate change, recommendations could be applied to support beach tourism.

Geomorphic and temporal evolution of a Mississippi delta flanking barrier island: Grand Isle, LA

Barrier islands throughout the world are increasingly stressed due to accelerating sea-level rise (SLR), increasing storminess, and diminishing sediment supplies. This condition is particularly evident along the Louisiana coast because it has one of the highest rates of relative SLR in the world and very limited sand sources. One of the keys in predicting how barrier islands will change in the future is to understand how they have evolved since their formation. Historical shoreline changes are usually insufficient, because those records only provide a glimpse of a barrier's history. Moreover, the data needed to decipher barrier evolution at an intermediate scale (~101–103 years) is lacking for many coastal Louisiana barrier systems. One method for tracking barrier island development through time makes use of optically stimulated luminescence (OSL) dating of beach ridge sediments. This study combines OSL and the analysis of aerial imagery and previous core logs to document the timing of beach ridge formation, rates of progradation, and geologic framework of the only developed barrier island in Louisiana.Grand Isle is composed of prograding beach ridges organized in distinct, unconformable sets. Ridges increase in spacing from west to east, due to increased rates of shoreline progradation caused by decreased accommodation space. Proto-Grand Isle began forming approximately 750 years ago, prograded northeastward until approximately 620 years ago when sediment supply slowed and/or major storms impacted the island. During that time, much the seaward portion of the existing ridges were eroded. Following truncation of the first set of beach ridges (Group 1), the island once again began to prograde in a slightly more eastward direction (Group 2 ridge sets). OSL dates indicate the island's central ridges (Group 2, ridge sets 7–9) formed between 370 ± 30 and 170 ± 10 years ago at an average rate of one ridge every 14.8 years, or progradation rate of 14.9 m/yr.The island's sediment source comes from an eroding beach ridge plain of the Caminada headland to the west. The volume of Grand Isle's barrier lithosome is 9.26 × 107 m3, which computes to an average northeasterly longshore transport rate of 128,625 m3/yr. This is a high longshore transport rate for the relatively low wave energy of this coast (Hs = 0.6 m) but is explained by hurricane impacts that substantially increase average sand transport conditions. The substantial thickness of the Grand Isle barrier lithosome (~10 m) and its steady supply of sediment contribute to the island's stability in contrast to other barrier systems along the Louisiana coast.

Coastal vulnerability assessment using GIS-Based multicriteria analysis of Alexandria-northwestern Nile Delta, Egypt

This study intends to map the relative coastal vulnerability index (CVI) for the administrative governorates of Alexandria and adjacent Behera in the northwestern coastal margin of the Nile delta. In addition to other common environmental stresses, these governorates are under threat due to accelerated sea level rise induced from climate change. Of special interest is that the coastal margin of the study area is characterized by markedly constructing geology, morpho-dynamics and land surface topography that varies from low-lying (−3 m below MSL) to high land (~20 m height). Therefore, nine physical and geological variables influencing the vulnerability of the coast are used in this study, including land elevation, seabed/beach composition, beach type (dissipative to reflective), relative sea level, historical shoreline change, tidal range, significant wave height, shore protection measures, and land cover. Results obtained from performing multi-criteria analysis of GIS indicates that about 16.58%, 15.45, 42.03%, 18.16 and 7.78% of the shoreline is under very high, high, moderate, low and very low vulnerability respectively. Of great concern is that although the low-lying broad depression (−1 to −3 m below MSL) east and southeast of Alexandria is protected now by a combination of natural shore-parallel elevated ridges (up to 10 m) and artificial shore-parallel detached structures, it is likely to be accidently flooded by unexpected extreme storm or tsunami events at the lowest waterfront points.

The State of the World\u2019s Beaches

Coastal zones constitute one of the most heavily populated and developed land zones in the world. Despite the utility and economic benefits that coasts provide, there is no reliable global-scale assessment of historical shoreline change trends. Here, via the use of freely available optical satellite images captured since 1984, in conjunction with sophisticated image interrogation and analysis methods, we present a global-scale assessment of the occurrence of sandy beaches and rates of shoreline change therein. Applying pixel-based supervised classification, we found that 31% of the world’s ice-free shoreline are sandy. The application of an automated shoreline detection method to the sandy shorelines thus identified resulted in a global dataset of shoreline change rates for the 33 year period 1984–2016. Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr, while 28% are accreting and 48% are stable. The majority of the sandy shorelines in marine protected areas are eroding, raising cause for serious concern.

Luminescence dating of Holocene beach-ridge sands on the Yumigahama Peninsula, western Japan

Abstract We applied infrared stimulated luminescence (IRSL50) and post-infrared (post-IR) IRSL150 dating to K-feldspar sand obtained from Holocene beach ridges on the Yumigahama Peninsula, Japan, to investigate the rate of progradation of the beach, which has been affected by 17–18th century iron mining in a local river catchment. All samples showed higher equivalent doses for the post-IR IRSL signal. Fading tests indicated that IRSL yielded relatively high g-values (11–13%/decade), while post-IR IRSL yielded negative g-values (–5 to –8%/decade). The corrected IRSL age of the oldest sample, 8.1 ± 1.3 ka, was slightly overestimated with respect to its expected age of 5–6.7 ka. The corrected age is highly dependent on the g-value, which if slightly inaccurate would have caused the overestimate. The uncorrected post-IR IRSL ages were underestimated, and we consider that the post-IR IRSL signal faded. However, given the negative g-values, application of an appropriate fading correction was not feasible. The corrected IRSL ages of the younger samples, coupled with an assumption of residual dose, roughly agreed with the historical shoreline changes, indicating that the rate of shoreline progradation increased markedly during the recent period of mining-related enhanced sediment discharge.