Total Suspended Sediment Load Research Articles

Evaluating Wildlife Vulnerability to Mercury Pollution From Artisanal and Small-Scale Gold Mining in Madre de Dios, Peru

Illegal, artisanal and small-scale gold mining (ASGM) often occurs in remote highly biodiverse areas, such as the Madre de Dios region of Peru. Mercury used in gold mining bioaccumulates in the environment and poses developmental, hormonal, and neurological threats to wildlife. The impact of ASGM on biodiversity remains largely unknown. We used geographic information science to create a spatial model of pollution risk from mining sites, in order to predict locations and species assemblages at risk. Multicriteria evaluation was used to determine how flow accumulation, distance from mining areas, total suspended sediment load, and soil porosity influenced the vulnerability of regions to mercury pollution. Results suggest that there is considerable opportunity for protection of areas with high biodiversity and vulnerability north of the Madre de Dios River where much of the land is not protected. Our study highlights the need for future ASGM research to consider more than deforestation risk alone while protecting the areas’ unmatched biodiversity.

Suspended sediment dynamics in the meltwater of Chhota Shigri glacier, Chandra basin, Lahaul-Spiti valley, India

Present study shows suspended sediment dynamics in the meltwater of Chhota Shigri glacier, Himachal Pradesh, India for different melt seasons during the period 2011-2014. Maximum suspended sediment concentration in the meltwater was found during the month of July 2011, 2012 and 2014 constituting to 55.2%, 48.3% and 46.9%, respectively. Whereas in 2013, maximum suspended sediment concentration was observed in August accounting for 46.1% of the total. On the other hand, maximum suspended sediment load was monitored in the month of July 2011, 2012 and 2014 constituting 59.5%, 63% and 55.7% of the total, respectively. Whereas in 2013, maximum suspended sediment load was observed in the month of August accounting for 49.8% of the total suspended sediment load. Annual distribution of suspended sediment concentration (SSC) and suspended sediment load (SSL) in the Chhota Shigri glacier shows higher value of SSC and SSL during the study period 2012 and 2013, which may be due to the presence of high glacial runoff and negative mass balance of the studied area during these time periods. Marked diurnal variation has been observed in the SSC of meltwater. Strong correlation was observed between SSC and SSL with discharge. On the other hand, SSC and SSL also showed strong exponential correlation with air temperature of the studied area. Sediment yield from the catchment of Chhota Shigri glacier is high during the peak melt season (July and August) and low during the late melt season (September and October). The average value of erosion rate for Chhota Shigri glacier basin during the study period 2011-2014 was calculated to be 1.1 mm/yr, which is lower than the average erosion rate of other Himalayan glaciers such as Rakiot, Chorabari and Gangotri glaciers, which may be caused by its geological setting containing high erosion resistant rocks such as granite, granite gneiss and porphyritic granite.

Impact of a two-stage ditch on channel water quality

A two-stage ditch involves modifications of a conventional, trapezoidal drainage ditch to better replicate the features of a natural stream through the addition of adjacent floodplains or benches. Previous research in Indiana and Ohio has shown that two-stage ditches offer the potential to reduce sediment load and extend the interaction time between water, bench vegetation, and bench soil allowing larger uptake of nutrients by the vegetation and increasing the denitrification rates. A two-stage ditch was constructed that drains an area of approximately 267ha of farmland used for corn and soybean production. Discharge, nitrate-N (NO3), total phosphorus (TP), soluble reactive phosphorus (SRP) and total suspended sediment (TSS) were monitored in the two-stage ditch and a control reach immediately upstream. The two-stage ditch was found to significantly decrease TP, SRP and TSS concentrations and loads. Although the two-stage ditch decreased NO3 concentrations significantly, it did not have a significant impact on NO3 loads. More specifically, the two-stage ditch reduced the loads of TP by 40%, SRP by 11% and TSS by 22–40% depending on the stage of vegetation establishment on its floodplain benches, compared to an increase in load of 78%, 2% and 1%, respectively in the control reach.

Prescribed Burning and Erosion Potential in Mixed Hardwood Forests of Southern Illinois

Prescribed fire has several benefits for managing forest ecosystems including reduction of fuel loading and invasive species and enhanced regeneration of desirable tree species. Along with these benefits there are some limitations like nutrient and sediment loss which have not been studied extensively in mixed hardwood forests. The objective of our research was to quantify the amount of sediment movement occurring on a watershed scale due to prescribed fire in a southern Illinois mixed hardwood ecosystem. The research site was located at Trail of Tears State Forest in western Union county, IL, USA and included five watershed pairs. One watershed in each pair was randomly assigned the prescribed burn treatment and the other remained as control (i.e., unburned). The prescribed burn treatment significantly reduced the litter depth with 12.6%–31.5% litter remaining in the prescribed burn treatment watersheds. When data were combined across all watersheds, no significant differences were obtained between burn treatment and control watershed for total suspended solids and sediment concentrations or loads. The annual sediment losses varied from 1.41 to 90.54 kg·ha−1·year−1 in the four prescribed burn watersheds and 0.81 to 2.54 kg·ha−1·year−1 in the four control watersheds. Prescribed burn watershed 7 showed an average soil sediment loss of 4.2 mm, whereas control watershed 8 showed an average accumulation of sediments (9.9 mm), possibly due to steeper slopes. Prescribed burning did not cause a significant increase in soil erosion and sediment loss and can be considered acceptable in managing mixed hardwood forests of Ozark uplands and the Shawnee Hills physiographic regions of southern Illinois.

SEDIMENTASI DI DELTA SUNGAI CITARUM, KECAMATAN MUARA GEMBONG, KABUPATEN BEKASI (Sedimentation at delta of Citarum River, Muara Gembong District, Bekasi Regency)

One of land use change impacts in the downstream of Citarum watershed is sedimentation. This study aimed to determine the total suspended solid and sediment load in the downstream of Citarum River. The Total Suspended Solid ( TSS ) samples were taken in three locations: the inlet of Jatiluhur reservoir, the outlet of Jatiluhur reservoir, and before the Citarum River estuary. The frequency of TSS samplings was twice a year i.e during the dry season and the rainy season at 2014. Analysis of TSS content was in accordance with SNI 06-6989.3-2004 using gravimetry method. The results showed that TSS at down stream Citarum River flow was 0.44 kg/m 3 , TSS at the inlet of Jatiluhur reservoir was 0.20 kg/m 3 , and TSS at the outlet of Jatiluhur reservoir was 0.02kg/m 3 . The total sediment in the inlet of Jatiluhur was 1.34 x 10 6 ton/year, in the outlet of Jatiluhur reservoir was 0.14 x 10 6 ton/year, and the flow sediment total to the Citarum River estuary was 1.79 x 10 6 ton/year. The Jatiluhur reservoir could reduce the potential for sediment total flowing into the sea as much as 1.20x 10 6 tons/year. Area of sedimentation at the delta of Citarum River was 3,828.26 ha.

Modeling sediment mobilization using a distributed hydrological model coupled with a bank stability model

AbstractIn addition to surface erosion, stream bank erosion and failure contributes significant sediment and sediment‐bound nutrients to receiving waters during high flow events. However, distributed and mechanistic simulation of stream bank sediment contribution to sediment loads in a watershed has not been achieved. Here we present a full coupling of existing distributed watershed and bank stability models and apply the resulting model to the Mad River in central Vermont. We fully coupled the Bank Stability and Toe Erosion Model (BSTEM) with the Distributed Hydrology Soil Vegetation Model (DHSVM) to allow the simulation of stream bank erosion and potential failure in a spatially explicit environment. We demonstrate the model's ability to simulate the impacts of unstable streams on sediment mobilization and transport within a watershed and discuss the model's capability to simulate watershed sediment loading under climate change. The calibrated model simulates total suspended sediment loads and reproduces variability in suspended sediment concentrations at watershed and subbasin outlets. In addition, characteristics such as land use and road‐to‐stream ratio of subbasins are shown to impact the relative proportions of sediment mobilized by overland erosion, erosion of roads, and stream bank erosion and failure in the subbasins and watershed. This coupled model will advance mechanistic simulation of suspended sediment mobilization and transport from watersheds, which will be particularly valuable for investigating the potential impacts of climate and land use changes, as well as extreme events.

Origins, seasonality, and fluxes of organic matter in the Congo River

AbstractThe Congo River in central Africa represents a major source of organic matter (OM) to the Atlantic Ocean. This study examined elemental (%OC, %N, and C:N), stable isotopic (δ13C and δ15N), and biomarker composition (lignin phenols) of particulate OM (POM) and dissolved OM (DOM) across the seasonal hydrograph. Even though the Congo exhibits an extremely stable intra‐annual discharge regime, seasonal variability in OM composition was evident. DOM appears predominantly derived from vascular plant inputs with greater relative contribution during the rising limb and peak in discharge associated with the major November–December discharge maximum. Generally, POM appears to be sourced from soil‐derived mineral‐associated OM (low C:N, low Λ8, and higher (Ad:Al)v) but the relative proportion of fresh vascular plant material (higher C:N, higher Λ8, and lower (Ad:Al)v) increases with higher discharge. During the study period (September 2009 to November 2010) the Congo exported 29.21 Tg yr−1 of total suspended sediment (TSS), 1.96 Tg yr−1 of particulate organic carbon (POC), and 12.48 Tg yr−1 of dissolved organic carbon. The Congo exports an order of magnitude lower TSS load in comparison to other major riverine sources of TSS (e.g., Ganges and Brahmaputra), but due to its OM‐rich character it actually exports a comparable amount of POC. The Congo is also 2.5 times more efficient at exporting dissolved lignin per unit volume compared to the Amazon. Including Congo dissolved lignin data in residence time calculations for lignin in the Atlantic Ocean results in an approximately 10% reduction from the existing estimate, suggesting that this material is more reactive than previously thought.

Assessing the relation of USDA conservation expenditures to suspended sediment reductions in an Iowa watershed

From 1936 to 2010, U.S. Department of Agriculture (USDA) agencies spent $293.7 billion (value adjusted for inflation at the 2009 level) on conservation programs. Of these expenditures, $75.2 billion (26%) were allocated for technical assistance (TA; it is related to costs associated with USDA field staff providing their expert advice to farmers) and $218.5 billion (74%) for financial assistance (FA; monetary incentives for farmers to adopt conservation programs). A major environmental goal of these programs was to reduce soil erosion and sediment leaving the land. In this study, we correlate expenditures on FA and TA programs to a unique long (1937–2009) record of total suspended solids (TSS) and sediment load (SL) for the Raccoon River at Van Meter, Iowa. Study results suggest that three predictors (rainfall, TA and FA) are important in explaining the temporal changes in annual TSS and SL and provide evidence that USDA expenditures helped reduce TSS and SL in the Raccoon River. TA was more effective than FA in reducing TSS levels in the watershed. Our empirical model represents an initial, broad-scale attempt to correlate conservation expenditures to a specific water quality outcome, although more work is needed to disentangle the impacts associated with other unexplored factors.

Control factors and scale analysis of annual river water, sediments and carbon transport in China.

Under the context of dramatic human disturbances on river system, the processes that control the transport of water, sediment, and carbon from river basins to coastal seas are not completely understood. Here we performed a quantitative synthesis for 121 sites across China to find control factors of annual river exports (Rc: runoff coefficient; TSSC: total suspended sediment concentration; TSSL: total suspended sediment loads; TOCL: total organic carbon loads) at different spatial scales. The results indicated that human activities such as dam construction and vegetation restoration might have a greater influence than climate on the transport of river sediment and carbon, although climate was a major driver of Rc. Multiple spatial scale analyses indicated that Rc increased from the small to medium scale by 20% and then decreased at the sizable scale by 20%. TSSC decreased from the small to sizeable scale but increase from the sizeable to large scales; however, TSSL significantly decreased from small (768 g·m−2·a−1) to medium spatial scale basins (258 g·m−2·a−1), and TOCL decreased from the medium to large scale. Our results will improve the understanding of water, sediment and carbon transport processes and contribute better water and land resources management strategies from different spatial scales.

Active overbank deposition during the last century, South River, Virginia

We quantify rates of overbank deposition over decadal to centennial timescales along the South River in Virginia using four independent methods. Detailed mercury profiles sampled adjacent to the stream channel preserve the peak historic mercury concentration on suspended sediment dating from 1955 to 1961 and suggest sedimentation rates of 8 to 50cm/100years. Sediment accumulation over the roots of trees suggest rates of 0 to 100cm/100years, with significantly higher values on levees and lower values on floodplains farther from the channel. Profiles of 137Cs and 210Pb from two eroding streambanks are fit with an advection–diffusion model calibrated at an upland reference site; these methods suggest sedimentation rates of 44 to 73cm/100years. Mercury inventories from 107 floodplain cores, combined with a previously published reconstruction of the history of mercury concentration on suspended sediment, provide spatially comprehensive estimates of floodplain sedimentation: median sedimentation rates are 3.8cm/100years for the <0.3-year floodplain, 1.37cm/100years for the 0.3- to 2-year floodplain, 0.4cm/100years for the 2- to 5-year floodplain, and 0.1cm/100years for the 5- to 62-year floodplain. While these sedimentation rates are relatively low, the total mass of sediment stored from 1930 to 2007 is 4.9±1.7 (95% confidence interval)×107kg, corresponding to an average thickness of 2.5cm (3.2cm/100years). These results demonstrate that floodplains of our 4.5-km-long study reach have stored 8 to 12% of the total suspended sediment supplied to the study reach of the South River. Hydrologic Engineering Center-River Analysis System (HEC-RAS) modeling demonstrates that the floodplain of the South River remains hydraulically connected to the channel: 56% of the 100-year floodplain is inundated every two years, and 83% of the floodplain is inundated every five years. These results, combined with previously published data, provide the basis for a regional synthesis of floodplain deposition rates since European settlement. Floodplain sedimentation rates were high following European settlement, with published estimates ranging from 50 to 200cm/100years. Sedimentation rates decreased by 1 to 2 orders of magnitude during the twentieth and twenty-first centuries; but despite these lower sedimentation rates, floodplains continue to store a significant fraction of total suspended sediment load. Many floodplains of the mid-Atlantic region are active landforms fully connected to the rivers that flow within them and should not be considered terraces isolated from contemporary fluvial processes by post-settlement aggradation.

Sediment transport in two mediterranean regulated rivers

Mediterranean climate is characterized by highly irregular rainfall patterns with marked differences between wet and dry seasons which lead to highly variable hydrological fluvial regimes. As a result, and in order to ensure water availability and reduce its temporal variability, a high number of large dams were built during the 20th century (more than 3500 located in Mediterranean rivers). Dams modify the flow regime but also interrupt the continuity of sediment transfer along the river network, thereby changing its functioning as an ecosystem. Within this context, the present paper aims to assess the suspended sediment loads and dynamics of two climatically contrasting Mediterranean regulated rivers (i.e. the Ésera and Siurana) during a 2-yr period. Key findings indicate that floods were responsible for 92% of the total suspended sediment load in the River Siurana, while this percentage falls to 70% for the Ésera, indicating the importance of baseflows on sediment transport in this river. This fact is related to the high sediment availability, with the Ésera acting as a non-supply-limited catchment due to the high productivity of the sources (i.e. badlands). In contrast, the Siurana can be considered a supply-limited system due to its low geomorphic activity and reduced sediment availability, with suspended sediment concentration remaining low even for high magnitude flood events. Reservoirs in both rivers reduce sediment load up to 90%, although total runoff is only reduced in the case of the River Ésera. A remarkable fact is the change of the hydrological character of the River Ésera downstream for the dam, shifting from a humid mountainous river regime to a quasi-invariable pattern, whereas the Siurana experiences the opposite effect, changing from a flashy Mediterranean river to a more constant flow regime below the dam.

Factors Controlling the Suspended Sediment Yield During Rainfall Events of Dry and Wet Weather Conditions in A Tropical Urban Catchment

The catchments of the Klang and Ampang Rivers are two sub-catchments that drain into the main Klang River, Selangor, Malaysia. Due to the development and siltation processes, the current capacity of the Klang River in the city centre is insufficient for accommodating the excess flood flow during major events, and, therefore overflows the riverbanks causing flash floods to occur in the Kuala Lumpur city centre. This study investigates the relationship between the rainfall, discharge and suspended sediment transport and its variations during the dry and wet periods in tropical sub-catchments; identifies the different hysteresis types of single flood events in the suspended sediment concentration/discharge relationships in the dry and wet periods, and determines the relationship between the types of single event hysteresis loops and the hydrological and sediment responses. Principal component analysis was performed to examine factors that have a major influence on the suspended sediment yields during both the dry and wet periods. The clockwise and counter-clockwise hysteresis loops occurring mostly during the dry period, can be described as events with moderate total rainfall, rainfall intensity (less than 10 mmh−1), average discharge and suspended sediment load. Counter-clockwise events occurring during the wet period are associated with low total rainfall, rainfall intensity, average discharge and suspended sediment load. The clockwise and counter-clockwise events that occurred in the wet period are related to events with a relatively high and low moisture condition, respectively. The figure-eight and complex hysteresis loop events occur predominantly during the wet period. The complex loop events occurred mostly during the wet period generates the highest suspended sediment load. The complex loop events occur mostly during the wet period generated the highest suspended sediment load.

Hydro‐meteorological drivers and sources of suspended sediment flux in the pro‐glacial zone of the retreating Castle Creek Glacier, Cariboo Mountains, British Columbia, Canada

AbstractGlaciers are major agents of erosion that increase sediment load to the downstream fluvial system. The Castle Creek Glacier, British Columbia, Canada, has retreated ~1.0 km in the past 70 years. Suspended sediment concentration (SSC) and streamflow (Q) were monitored independently at five sites within its pro‐glacial zone over a 60 day period from July to September 2011, representing part of the ablation season. Meteorological data were collected from two automatic weather stations proximal to the glacier. The time‐series were divided into hydrologic days and the shape and magnitude of the SSC response to hydro‐meteorological conditions (‘cold and wet’, ‘hot and dry’, ‘warm and damp’, and ‘storm’) were categorized using principal component analysis (PCA) and cluster analysis (CA). Suspended sediment load (SSL) was computed and summarized for the categories. The distribution of monitoring sites and results of the multivariate statistical analyses describe the temporal and spatial variability of suspended sediment flux and the relative importance of glacial and para‐glacial sediment sources in the pro‐glacial zone. During the 2011 study period, ~ 60% of the total SSL was derived from the glacial stream and sediment deposits proximal to the terminus of the glacier; during ‘storm’ events, that contribution dropped to ~40% as the contribution from diffuse and point sources of sediment throughout the pro‐glacial zone and within the meltwater channels increased. While ‘storm’ events accounted for just 3% of the study period, SSL was ~600% higher than the average over the monitoring period, and ~20% of the total SSL was generated in that time. Determining how hydro‐meteorological conditions and sediment sources control sediment fluxes will assist attempts to predict how pro‐glacial zones respond to future climate changes. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Spectral calibration of CBERS 2B multispectral satellite images to assess suspended sediment concentration

In this study, 11 CBERS 2B and 1 LANDSAT 5-TM satellite images from 2008 were used to estimate the suspended sediment concentration and the total suspended sediment load of the Parnaíba River (NE-Brazil). The calculation of the amount of sediment in suspension was performed using Tassan’s algorithm, which was originally developed for use on LANDSAT 5-TM images; therefore, the CBERS 2B images were spectrally calibrated using LANDSAT 5-TM at-satellite radiance. The application of atmospheric correction to the images was necessary to account for meteorological influence on the spectral data prior to the calculation of the suspended sediment concentration. Three types of dark object subtraction and the 6S model were tested, and one type of dark object subtraction was chosen as the appropriate atmospheric correction method. Tassan’s algorithm requires in situ calibration; therefore, suspended sediment concentrations measured in water samples from the Parnaíba River mouth were used to calibrate the algorithm. The results revealed that the variation of suspended sediment concentration was strongly influenced by seasonal precipitation. In 2008, the suspended sediment released by the Parnaíba River was approximately 2.54×106tons. The discharged sediment formed a sediment plume on the inner continental shelf. The extension of the plume depended on the specific hydrodynamic conditions that were forced mainly by the strength of river runoff, longshore currents, tidal currents and amplitudes, and wind and wave climate.

Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses.

Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for movement of sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine the reduction in drainage effluent total suspended sediment (TSS) and phosphorus (P) concentrations and loads when open surface inlets were replaced with blind (in gravel capped with 30 cm of soil) or gravel (in very coarse sand/fine gravel) inlets. In Indiana, a pair of closed depressions in adjacent fields was fitted with open inlet tile risers and blind inlets in 2005 and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season for years 2006 to 2013 showed that TSS loads were 40.4 and 14.4 kg ha event for tile risers and blind inlets, respectively. Total P (TP) and soluble reactive P (SRP) loads were 66 and 50% less for the blind inlets, respectively. In Minnesota, TSS and SRP concentrations were monitored for 3 yr before and after modification of 24 open inlets to gravel inlets in an unreplicated large-field on-farm study. Median TSS concentrations were 97 and 8.3 mg L and median SRP concentrations were 0.099 and 0.064 mg L for the open inlet and gravel inlet periods, respectively. Median TSS and SRP concentrations were elevated for snowmelt vs. non-snowmelt seasons for open and gravel inlets. Both replacement designs reduced suspended sediment and P concentrations and loads. The Indiana study suggests blind inlets will be effective beyond a 10-yr service life.

Effects of Suspended Sediment on Early‐Life Stage Survivalof Yaqui Chub, an Endangered USA–Mexico Borderlands Cyprinid

AbstractHigh levels of total suspended sediment (TSS) can have negative consequences on fishes, such as altering food supply, lowering food acquisition, clogging gills, and disrupting reproduction. While effects of TSS on salmonids and estuarine fish are well studied, less is known about possible negative impacts of suspended sediment on desert fishes. Several imperiled desert fishes inhabit streams and springs near the U.S.–Mexico border and are potentially threatened by increased sediment loads from borderlands activity such as livestock grazing, road building, illegal traffic, and law enforcement patrols. One such species is the Yaqui Chub Gila purpurea, a federally listed endangered cyprinid. We exposed Yaqui Chub embryos and fry (mean TL = 12.6 mm; SE = 0.42) to a range of TSS levels commonly found in one of the only streams they inhabit, Black Draw, which crosses the Arizona–Mexico border. We tested effects of 0; 300; 500; 1,000; 5,000; and 10,000 mg/L TSS loads on fry and embryos over a 5‐d period in three replicate containers for each treatment. Fifty percent hatch rate (i.e., median lethal concentration, LC50) was 3,977 mg/L for embryos. The LC50 for fry (concentration at which half died) was 8,372 mg/L after 12 h of exposure; however, after 5‐d exposure, LC50 leveled at 1,197 mg/L. The TL of fry did not change significantly in any treatment over the 5‐d period. Suspended sediment in Black Draw reached concentrations lethal to Yaqui Chub embryo and fry during four floods in 2012. Although some desert fishes have evolved in rivers and streams subject to elevated TSS and are tolerant to high TSS concentrations, other fish species are less tolerant and may be impacted by land practices which increase erosion into stream systems. Management of critically endangered desert fishes should include considerations of the effects of increased suspended sediment.Received September 5, 2014; accepted November 10, 2014

Estimation of Sediment and Nutrient Loads to Bays from Gauged and Ungauged Watersheds

<abstract> <bold><sc>Abstract. </sc></bold>Due to the lack of water quality data in the lower watersheds of the Texas coastal region, a Soil and Water Assessment Tool (SWAT) version 2009 model was used to estimate terrestrial sediment and nutrient loads from non-tidal fresh water inflows to Texas bays in this study. The Texas Water Development Board (TWDB) has used the TxRR (Texas Rainfall-Runoff) model to estimate the total fresh water inflow and annual sediment, nitrogen, and phosphorus loads from measured and simulated stream flows to the bays in Texas. Applying newer methods, such as distributed hydrologic models, e.g., SWAT, enables the temporal and spatial distribution of freshwater, sediment, and nutrient loads to also be predicted. To develop the SWAT model for the estimation of sediment and nutrient loads from two watersheds, the Matagorda as a rural watershed and Galveston as an urbanized watershed, the average of the calibrated model parameter values were applied to the ungauged lower sub-watersheds in consideration of land use homogeneity. The monthly sediment calibration showed good agreement compared with the observed total suspended sediment, with Nash Sutcliffe Model Efficiency (NSE) values ranging from 0.55 to 0.75 and Percent Bias (PBIAS) values ranging from +10.3% to +51.0%. The predicted monthly total nitrogen (TN) and total phosphorus (TP) at gauge stations exhibited poor correlation with the observed values in the urbanized sub-watersheds but good-to-acceptable correlation in the other watersheds, with NSE values ranging from -0.15 to 0.85 and PBIAS values ranging from+13.3% to +84.0%. The comparison of the SWAT and available estimations from previous studies showed good agreement for the mean annual total suspended sediment and nutrient loads from ungauged sub-watersheds to the bays. Using parameter settings from gauged watersheds for ungauged watersheds, SWAT can be applied to other Texas coastal watersheds to estimate flow and sediment and nutrient loads. However, extending the global average values of the adjusted parameters to the highly developed ungauged sub-watersheds may lead to poor results, and limited regionalization in parameter allocation to these areas should be considered.

Large-scale dam removal on the Elwha River, Washington, USA: Fluvial sediment load

The Elwha River restoration project, in Washington State, includes the largest dam-removal project in United States history to date. Starting September 2011, two nearly century-old dams that collectively contained 21±3millionm3 of sediment were removed over the course of three years with a top-down deconstruction strategy designed to meter the release of a portion of the dam-trapped sediment. Gauging with sediment-surrogate technologies during the first two years downstream from the project measured 8,200,000±3,400,000tonnes of transported sediment, with 1,100,000 and 7,100,000t moving in years 1 and 2, respectively, representing 3 and 20 times the Elwha River annual sediment load of 340,000±80,000t/y. During the study period, the discharge in the Elwha River was greater than normal (107% in year 1 and 108% in year 2); however, the magnitudes of the peak-flow events during the study period were relatively benign with the largest discharge of 292m3/s (73% of the 2-year annual peak-flow event) early in the project when both extant reservoirs still retained sediment. Despite the muted peak flows, sediment transport was large, with measured suspended-sediment concentrations during the study period ranging from 44 to 16,300mg/L and gauged bedload transport as large as 24,700t/d. Five distinct sediment-release periods were identified when sediment loads were notably increased (when lateral erosion in the former reservoirs was active) or reduced (when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport). Total suspended-sediment load was 930,000t in year 1 and 5,400,000t in year 2. Of the total 6,300,000±3,200,000t of suspended-sediment load, 3,400,000t consisted of silt and clay and 2,900,000t was sand. Gauged bedload on the lower Elwha River in year 2 of the project was 450,000±360,000t. Bedload was not quantified in year 1, but qualitative observations using bedload-surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam. Using comparative studies from other sediment-laden rivers, the total ungauged fraction of <2-mm bedload was estimated to be on the order of 1.5Mt.

Statistical modelling and power analysis for detecting trends in total suspended sediment loads

The export of sediments from coastal catchments can have detrimental impacts on estuaries and near shore reef ecosystems such as the Great Barrier Reef. Catchment management approaches aimed at reducing sediment loads require monitoring to evaluate their effectiveness in reducing loads over time. However, load estimation is not a trivial task due to the complex behaviour of constituents in natural streams, the variability of water flows and often a limited amount of data. Regression is commonly used for load estimation and provides a fundamental tool for trend estimation by standardising the other time specific covariates such as flow. This study investigates whether load estimates and resultant power to detect trends can be enhanced by (i) modelling the error structure so that temporal correlation can be better quantified, (ii) making use of predictive variables, and (iii) by identifying an efficient and feasible sampling strategy that may be used to reduce sampling error. To achieve this, we propose a new regression model that includes an innovative compounding errors model structure and uses two additional predictive variables (average discounted flow and turbidity). By combining this modelling approach with a new, regularly optimised, sampling strategy, which adds uniformity to the event sampling strategy, the predictive power was increased to 90%. Using the enhanced regression model proposed here, it was possible to detect a trend of 20% over 20 years. This result is in stark contrast to previous conclusions presented in the literature.

Fine‐suspended sediment and water budgets for a large, seasonally dry tropical catchment: Burdekin River catchment, Queensland, Australia

AbstractThe Burdekin River catchment (∼130,400 km2) is a seasonally dry tropical catchment located in north‐east Queensland, Australia. It is the single largest source of suspended sediment to the Great Barrier Reef (GBR). Fine sediments are a threat to ecosystems on the GBR where they contribute to elevated turbidity (reduced light), sedimentation stress, and potential impacts from the associated nutrients. Suspended sediment data collected over a 5 year period were used to construct a catchment‐wide sediment source and transport budget. The Bowen River tributary was identified as the major source of end‐of‐river suspended sediment export, yielding an average of 530 t km−2 yr−1 during the study period. Sediment trapping within a large reservoir (1.86 million ML) and the preferential transport of clays and fine silts downstream of the structure were also examined. The data reveal that the highest clay and fine silt loads—which are of most interest to environmental managers of the GBR—are not always sourced from areas that yield the largest total suspended sediment load (i.e., all size fractions). Our results demonstrate the importance of incorporating particle size into catchment sediment budget studies undertaken to inform management decisions to reduce downstream turbidity and sedimentation. Our data on sediment source, reservoir influence, and subcatchment and catchment yields will improve understandings of sediment dynamics in other tropical catchments, particularly those located in seasonally wet‐dry tropical savannah/semiarid climates. The influence of climatic variability (e.g., drought/wetter periods) on annual sediment loads within large seasonally dry tropical catchments is also demonstrated by our data.