Sediment Loss Rates Research Articles

Estimation of the soil erosion and sediment trapping using Gerlach troughs in different Land Uses in Luangprabang Province

This study aims to study sediment loss in different areas by collecting data from the Reservoir and Gerlach troughs in the Luangprabang Province, Laos The implementation of this experiment was a selection of study areas to install soil sediment retention tools (Gerlach trough) according to 6 treatments such as T1: No teak+Ruzi grass; T2: No teak + Fallow; T3: Teak with low understory density + Natural regrowth; T4: Teak with low understory density + Ruzi grass; T5: Teak with high understory density+ Natural regrowth; T6: Teak with high understory density+ mixed fodder cover (Ruzi and Napier grass). In 3 replicates/treatments by RCBD design, a total of 18 instruments will be installed by installing them in a row on both sides of the soil, to trap the soil sediment that flows with the water, then there will be a collection of samples that can be collected, and then filter the soil sediment and dry it at a temperature of 105 degrees, for a period of 48 hours and calculate the amount of soil sediment loss in the area. Results found that the highest soil loss (sediment) was in the area planted teak with low understory density + Natural regrowth (T3) followed by the area planted teak with low understory density + Ruzi grass, (T4), and the lowest soil loss was in the area no teak+Ruzi grass (T1) and the area no teak + fallow (T2). While the highest surface water runoff was in the area planted teak with low understory density + Natural regrowth (T3) and the area planted teak with low understory density + Ruzi grass, (T4). On the other hand, factors that are related to surface water runoff and soil sediment loss such as percentage of land cover density, slope of the land, and residue or humus on the land were found that the area no teak with planted Ruzi grass and the area no teak with fallow (natural growth) had lowest rate of surface water runoff and lowest soil sediment loss compared to other areas. It can be concluded that the land cover factor has an important role in helping to reduce surface water runoff and help prevent soil sediments from being lost to runoff in agricultural land and upland cultivation.

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to “re-suspend” and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as “self-digging”. The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and “re-suspension”, which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC “tails” appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of “self-digging” induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the “self-digging” problem to a certain extent and ensure the safety of OWFs.

Plot-Scale Runoff Generation and Sediment Loss on Different Forest and Other Land Floors at a Karst Yellow Soil Region in Southwest China

Yellow soils developed in limestone weathering materials are representative on Guizhou Plateau, Southwest China. As one of the most important cultivated soils in Guizhou Province, karst yellow soils are generally thin and can be significantly damaged by mild soil erosion. This work used the structural equation model (SEM) to analyze the influence of various factors on runoff generation and sediment loss based on a long time series (2015–2020) of natural rainfall-runoff data and soil erosion data collected from 18 runoff plots in the karst yellow soil region of Southwest China, which reflects the erosion dynamics under natural conditions. Slope runoff plots are the most popular and efficient way to collect data on runoff generation and soil erosion. The findings show that: (1) There were 139 rainfall-runoff occurrences between 2015 and 2020, with moderate rain (10–25 mm) and heavy rain (25–50 mm) events making up the majority. Due to its high frequency and prolonged duration, heavy rain had the greatest impact on the overall rainfall erosivity R value (R). (2) Mean surface runoff (SR) values ranged from 17.37 mm to 133.90 mm, while mean sediment loss rates (SLR) ranged from 1.36 t·ha−1·a−1 to 23.49 t·ha−1·a−1. SR and SLR can be successfully reduced by the forest floor. Broadleaf forest, coniferous forest, mixed forest, and orchard had mean SR values of 19.33%, 12.97%, 16.10%, and 33.38% of fallow land, respectively, and had mean SLR values of 6.90%, 5.79%, 6.34%, and 12.64% of fallow land, respectively. (3) SR generation at the plot scale was substantially linked with 30-min maximum rainfall intensity (I30), while vegetation coverage (VC) and antecedent soil water content (ASW) showed negative direct inference on SR and runoff sediment concentration (RSC) according to SEM analysis. The VC and ASW showed the highest indirect impact on SLR. This study will serve as a scientific reference for the water and soil erosion management in karst yellow soil region and serve as a scientific guidance for regional land use in Southwest China.

Responses of Runoff and Soil Loss on Slopes to Land Use Management and Rainfall Characteristics in Northern China.

Soil conservation measures are widely used to control soil erosion and sediment loss; however, their proper usage relies on a deep understanding of the responses of runoff and sediment loss to land management and rainfall characteristics. In the present study, a long-term (2014–2020) monitored dataset derived from ten runoff plots in the upstream catchment of the Miyun Reservoir in Beijing, China, was used to study runoff and sediment loss responses to land use management and rainfall characteristics. The study results show that plots with no soil conservation measures had the highest runoff depth of 75 mm and suffered the highest sediment loss, at a rate of 3200 t km−2 yr−1. The terraced and vegetated plots generated lower runoff depths, with soil loss rates less than 213.0 t km−2 yr−1. With the exception of the contour tillage plots on steep slopes, the vegetation and engineering measures can efficiently reduce runoff and sediment loss, with both runoff and sediment reduction efficiencies higher than 76%. Statistical analyses indicate that, on the plots of bare soil and cultivation without soil conservation measures, runoff and sediment loss were mainly affected by the maximum 30 min rainfall intensity. However, on the plots with soil conservation measures, they were mainly determined by rainfall amount and duration. The sediment loss rate can be well fitted with the runoff depth using a power function. Based on the analyses, water-saving soil conservation measures are recommended for the study area. In addition, the size of terraces should be reconsidered on gentle slopes, and the coverage of forest, shrubs, and grass on slopes should be reduced, thus allowing for more surface runoff generation to ensure drinking water safety. In general, for the study area, soil conservation measures are required on the bare soil and cultivated slopes.

Prioritization of Sub-Watersheds to Sediment Yield and Evaluation of Best Management Practices in Highland Ethiopia, Finchaa Catchment

Excessive soil loss and sediment yield in the highlands of Ethiopia are the primary factors that accelerate the decline of land productivity, water resources, operation and function of existing water infrastructure, as well as soil and water management practices. This study was conducted at Finchaa catchment in the Upper Blue Nile basin of Ethiopia to estimate the rate of soil erosion and sediment loss and prioritize the most sensitive sub-watersheds using the Soil and Water Assessment Tool (SWAT) model. The SWAT model was calibrated and validated using the observed streamflow and sediment data. The average annual sediment yield (SY) in Finchaa catchment for the period 1990–2015 was 36.47 ton ha−1 yr−1 with the annual yield varying from negligible to about 107.2 ton ha−1 yr−1. Five sub-basins which account for about 24.83% of the area were predicted to suffer severely from soil erosion risks, with SY in excess of 50 ton ha−1 yr−1. Only 15.05% of the area within the tolerable rate of loss (below 11 ton ha−1yr−1) was considered as the least prioritized areas for maintenance of crop production. Despite the reasonable reduction of sediment yields by the management scenarios, the reduction by contour farming, slope terracing, zero free grazing and reforestation were still above the tolerable soil loss. Vegetative contour strips and soil bund were significant in reducing SY below the tolerable soil loss, which is equivalent to 63.9% and 64.8% reduction, respectively. In general, effective and sustainable soil erosion management requires not only prioritizations of the erosion hotspots but also prioritizations of the most effective management practices. We believe that the results provided new and updated insights that enable a proactive approach to preserve the soil and reduce land degradation risks that could allow resource regeneration.

Response and recovery of Horn and Petit Bois Islands, Mississippi, USA to tropical cyclone impacts: 2004–2016

Horn and Petit Bois islands are two of five Mississippi (MS) barrier islands that provide physical protection from tropical cyclones threatening the MS Gulf Coast, in addition to critical habitat for the northern Gulf of Mexico (GOM). In September 2004, Hurricane Ivan removed a large volume of sediment from the eastern ends of Horn and Petit Bois islands with its 1 to 2 m storm surge and ~194 kph wind speeds. Then, in August 2005 Hurricane Katrina severely impacted the two islands again with its 3.5 to 5.5 m storm surge on Horn and Petit Bois islands, and estimated maximum sustained wind speeds of 204 kph at landfall in southeast Louisiana. Using topographic light detection and ranging (LIDAR) datasets from 2004 to 2016, spatial and temporal changes of the islands' area, sediment volumes, and shorelines were measured to ascertain their geomorphic responses and recovery rates following the impacts of these devastating tropical cyclones. During the 2004–05 hurricane seasons, Horn Island lost ~13.3% of its pre-hurricane Ivan land area, lost ~35.9% sediment volume, and had a total average shoreline change rate of −10 m/yr. Petit Bois Island also lost ~13.3% of its pre-Ivan land area, lost ~27% sediment volume, and had a shoreline change rate of −33 m/yr. Between 2005 (post-Katrina) and 2016, Horn Island recouped ~6.6% of its pre-Ivan land area and ~4.3% sediment volume, whereas Petit Bois Island recovered ~4% of its pre-Ivan land area and ~22.9% sediment volume. The overall averaged shoreline change rates between 2004 and 2016 were −2 m/yr for Horn Island and −3 m/yr for Petit Bois Island. These changes reflect that Horn Island is no longer stable, as its sediment supply cannot keep pace with the current rate of sediment loss, and that because Petit Bois Island's narrow central shoreline is retreating at a rate of 10 m/yr, the island is at risk of breaching during the next storm. Highlighting complex island response, the relationship between area and shoreline changes to that of volume changes was inconsistent.

Relationships of nitrogen losses, phosphorus losses, and sediment under simulated rainfall conditions

Losses of nitrogen (N) and phosphorus (P) often occur during the process of soil erosion and are often the primary sources of water eutrophication. Using artificial rainfall experiments, this study analyzed the characteristics of N and P losses and relationships of N losses, P losses, runoff volume, and sediment yield. The results indicated that N, P, and sediment loss rates had significant variations in the beginning and became stable in the middle and late stages of runoff for single rain events. The ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), and dissolved phosphorus (DP) were transported primarily through runoff water, which accounted for approximately 92.6%, 98.1%, and 89.4% of their respective totals. However, the losses of total nitrogen (TN) and total phosphorus (TP) in runoff water only accounted for 50.4% and 9.7% of their respective totals. The loss rates of N, P, and sediment had significant relationships with runoff rate or rainfall, and N and P loss rates had significant relationships with sediment loss rate as well. Ammonium nitrogen, TN, and TP enriched sediment at different degrees for single rain events, and the enrichment with TP was the most significant, especially under the rainfall intensities of 120 mm h−1 and 180 mm h−1.

A method to nourished beach stability assessment: The case of China

Beach nourishment is an effective method for maintaining shoreline position, and it has been preferred to restore beaches in China. However, in the post-nourishment assessment, there are only some single-indicator models (e.g. beach durability, sediment loss rate) which could not fully reflect the actual performance of a nourished beach. This study presents a multiple-indicator model of nourished beach stability assessment, aiming at quantitatively assessing the physical performance of nourished beaches. Geomorphic factors affecting the physical performance of nourished beaches were analyzed and summarized through critical review of literature. An indicator system for assessing the stability of nourished beaches was established by integrating oceanographic parameter (i.e. wave energy, storm intensity, and storm frequency), design parameter (i.e. beach length, grain size, volume density, beach planform, and beach protection structure) and adaptability parameter (i.e. intertidal width, dry beach width, and erosional hot spot). Based on data collecting, each indicator was graded into five classes from 1 to 5, and the associated weight of each indicator was given by the method of variation coefficient. Finally, a multi-indicator and indicator-weighted assessment model for the stability of nourished beaches was established and a new index called Nourished Beach Stability Index (NBSI) was proposed. The physical performances of sixteen nourished beaches representative of China were then quantitatively assessed. The results showed this assessment model could better assess the physical performance of nourished beaches than the single-indicator assessment models for taking beach's characteristics into account. The results can help scientists and managers make appropriate management strategies. This multiple-indicator assessment model can be used to both quantitatively assess the actually physical performance of the beach nourishment projects and to choose the design scheme from multiple alternatives for beach nourishment project.

Applicability of biochar for limiting interrill erosion and organic carbon export of sloping cropland in a semi-arid area of China

As a recalcitrant carbon source, the residence time of biochar is estimated to be hundreds to thousands of years. Since biochar is now being applied as a soil amendment in many areas of the world, the effects of long-term stationary biochar and its applicability for limiting soil erosion and nutrient export must be considered. To this end, this study investigated the effects of biochar on interrill erosion processes and total organic carbon (TOC) export by sediment and runoff at five slope gradient levels (5°, 10°, 15°, 20°, and 25°). A silt loam soil was incubated with or without wheat straw-derived biochar for 3 years in the field before carrying out a simulated rainfall experiment, in which a rainfall intensity of 60 mm h–1 was applied for 90 min. Compared with the non-biochar control, biochar-amended soils showed decreased interrill erosion potential by up to 21.34%, due to improved soil aggregate stability and organic carbon (OC) content. No substantial differences in runoff rate were detected between the control and biochar treatments. Light soil particles with a higher OC content were transported preferentially on gentle sloping cropland (≤15°) and there was a negative correlation between the enrichment ratio of OC and sediment loss rate. The OC in sediment was the primary source of TOC export from sloping cropland, while a limiting effect of biochar for reducing this TOC export occurred between 15° and 20° slope gradients. Biochar amendment reduced the relative TOC export and protected sloping cropland from soil degradation. Although the biochar application enhanced soil erosion resistance, it was deemed more appropriate to use biochar as a soil amendment to ≤15°-sloping cropland given its pronounced effect on TOC export.

Sediment Volume and Grain-Size Partitioning Between Submarine Channel−Levee Systems and Lobes: An Experimental Study

The width and depth of submarine channels change progressively as the channels evolve. This is inferred to act as an important control on the rate of sediment loss due overbank and in-channel deposition. Understanding the downstream extraction of sediment from turbidity currents is important for the prediction of grain-size trends and volume distribution in the stratigraphy. However, the partitioning of sediment by individual turbidity currents as a function of channel dimensions has not been investigated previously. We present a series of physical experiments studying the link between channel dimensions and the resulting partitioning of sediment volume and grain size between sub-environments. The experimental set-up consists of a slope (11°) with a straight pre-formed channel and a horizontal basin floor. An identical flow was released repeatedly into channels with different dimensions, resulting in various styles of overspill, erosion, and deposition under varying degrees of channel confinement. The fraction of sediment that was bypassed through the channel to the basin floor varied between 67% and 89%, depending on the amount of levee and in-channel deposition. The volume of levee deposition correlates well with channel depth. A large channel depth relative to flow thickness limits the amount of overspill. The amount of in-channel deposition correlates well with channel width/depth (W/D) ratio, where low-W/D-ratio channels have less deposition. We compare the experiments to natural system to show that the same patterns of volume and grain-size partitioning are present at different scales. The experiments provide snapshots of different phases of evolution of natural submarine channels. Natural submarine channels in an early evolution phase are inferred to be shallow and the experiments demonstrate that this results in significant sediment loss to levee deposition along the channel. The process of levee deposition preferentially extracts the fine-grained sediment fraction, which overspills from the channel. Therefore, we predict that the initial sediment pulse that reaches the basin floor is coarse grained and volumetrically small. As the channel matures and deepens, it will bypass more sediment with a mix of grain sizes to the basin floor.

Assessment of sediment inflow to a reservoir using the SWAT model under undammed conditions: A case study for the Somerville reservoir, Texas, USA

Worldwide, sedimentation represents a major problem for reservoir and dam management due to the related environmental and economic consequences. However, reservoir sedimentation can be significantly mitigated by controlling the rates of sediment loss across a watershed. This article uses a case study to highlight an assessment technique for sustaining effective soil conservation strategies by providing an insight into the spatial variability of sediment loss rates at the watershed scale. The assessment method employs the Soil and Water Assessment Tool (SWAT) and the Modified Universal Sediment Loss Equation (MUSLE) to quantify sediment losses in a case study for the Somerville reservoir, located in Texas. The SWAT model was employed to simulate upstream inflows in the studied reservoir watershed. The goodness-of-fit analyses suggested a realistic representation of the watershed behavior and satisfactory values of Nash-Sutcliffe Efficiency were obtained during the calibration and validation stages (0.76 ≤ NSE ≤ 0.69). Then the calibrated SWAT was used to generate MUSLE estimates of soil losses under undammed conditions. A weight-average formulation was developed to evaluate the rates of sediment loss at the sub-basin level. Meaningful contrasts were outlined between the sub-basins located at the downstream, the midstream, and the upstream. The study was able to pinpoint sub-basins with critical needs of soil conservation (sediment loss > 4 t/ha/year). Overall, the outcomes of the case study demonstrated the value of the methodology and that the outcomes may be used to address the complex problem of sedimentation in watersheds with reservoirs.

Interplay of water quality and vegetation in restored wetland plant assemblages from an agricultural landscape

Water quality degradation from excessive fertilizer use and runoff is a worldwide problem. While this degradation impacts wetlands, these systems can also be a vehicle for water quality improvement. Restoration of wetlands in agricultural landscapes has recently increased, but little work has evaluated the relationship of plant assemblages and water quality parameters in restored, non-treatment wetlands. This study examines the impact of self-designed wetland plant assemblages on nitrogen and sediment dynamics. Thirty mesocosms were seeded with soil from restored wetlands and allowed to develop from the seed bank to emergent assemblages. During the 2015 growing season (seven to nine months after establishment), these assemblages were exposed to treatment loads of nitrogen and sediment, common stressors to wetlands in agricultural landscapes. Water samples were taken up to five days post-treatment in July and September to quantify interactions between the stressors and plant assemblages. Analyses showed plant assemblage identify was not structured by treatment, but by the site of soil origin. Treatment removal rates were influenced by total amount of the stressor present, with nitrogen removal rates being higher, in relative terms, in low nitrogen amended treatments. Additionally, plant quality, not quantity, was linked to nitrogen and sediment loss rates, and over time, elevated nitrogen and sediment loads were associated with decreased plant assemblage quality. This study demonstrates the ability of plants from restored wetlands to affect nutrient and sediment dynamics, with three significantly differing plant assemblages all exhibiting substantial nutrient and sediment reduction capacity. Nevertheless, we also found that in a relatively short time (seven to nine months) common stressors in agricultural settings can significantly impact wetland plant assemblage quality, and that this may be linked to a reduced capacity for nutrient and sediment removal.

Reef Habitat Type and Spatial Extent as Interacting Controls on Platform-Scale Carbonate Budgets

A coral reefs carbonate budget strongly influences reef structural complexity and net reef growth potential, and thus is increasingly recognised as a key “health” metric. Despite this, understanding of habitat specific budget states, how these scale across reef platforms, and our ability to quantify both framework and sediment production values remains limited. Here we use in-situ census data from an atoll rim reef platform in the central Maldives to quantify rates of both reef framework and sediment production and loss within different platform habitats, and then combine these data with high-resolution habitat maps to quantify contributions to platform wide carbonate budgets. The net reef framework budget for the entire platform is extremely low (0.12 G, where G = Kg CaCO3 m-2 yr-1), with a very high proportion (143,745 kg or 65.1%) of total framework production generated within the platform margin reef zones, despite these comprising only ~8% of platform area. Net platform-scale sediment budgets are higher (1.04 G), but most is produced in the reef and platform margin hardground habitats, of which ~80% derives from parrotfish bioerosion. Significant quantities of new sediment (up to ~1 G derived from the calcareous green algae Halimeda) are produced only in one habitat. All lagoonal habitats have negative or neutral net carbonate budgets. These data demonstrate the marked inter-habitat differences in reef carbonate budgets that occur across reef platforms, and the major dampening effect on overall platform scale budgets when rates are factored for habitat type and size. Furthermore, the data highlights the disproportionately important role that relatively small areas of reef habitat can have on the maintenance of net positive platform scale budgets. Because of the intrinsic link between carbonate production rates and reef-associated landform development and maintenance, these findings also have implications for understanding reef-associated landform stability. In this context the reef island at this site has been highly mobile over the last ~40 years, and we hypothesise that such instability may be being exacerbated by the measured low overall rates of framework and sediment generation.

Stability of artificial beaches in Port Phillip Bay, Victoria, Australia.

Lowe, M.K. and Kennedy, D.M., 2016. Stability of artificial beaches in Port Phillip Bay, Victoria, Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 253–257. Coconut Creek (Florida), ISSN 0749-0208.This study investigates the drivers of beach morphodynamics on the highly modified fetch-limited beaches of the urbanised north-eastern coast of Port Phillip Bay in south-eastern Australia. Repetitive beach profiling, sediment characterization, and aerial photo analysis were conducted to quantify morphodynamic change across six distinct beach systems on a seasonal to annual-decadal scale. The observed morphologies contained features similar to those found on open-ocean wave-dominated and tide-dominated beaches, and included reflective unbarred beaches and intermediate beaches with low-tide terraces or transverse bar-rip systems. Sediment typically ranged from medium to coarse or very coarse in size. The consistency of wave energy across the study sites suggests that sediment size is the primary determinant of beach morphodynamic state, and the relatively low energy of Port Phillip Bay suggests that only storm conditions are energetic enough to mobilise sediment and alter beach morphology. On a seasonal scale, alongshore sediment transport is a major driver of beach change, and groynes and other coastal modifications have considerable influence on planform beach morphology. Over the medium term it appears that these beaches are eroding towards a landward position of equilibrium. With current projections of sea level rise it is expected that rates of beach erosion and sediment loss will accelerate over the coming decades, leading to an increased necessity for beach renourishment or other management interventions if wide beach profiles are to be maintained.

Sediment Dynamics Within Buffer Zone and Sinkhole Splay Areas Under Extreme Soil Disturbance Conditions.

Sedimentation dynamics were assessed in sinkholes within training areas at Ft. Knox Military Installation, a karst landscape subjected to decades of tracked vehicle use and extreme soil disturbance. Sinkholes sampled were sediment-laden and behaved as intermittent ponds. Dendrogeomorphic analyses were conducted using willow trees (Salix spp.) located around the edge of 18 sinkholes to estimate historical sedimentation rates, and buried bottles were installed in 20 sinkholes at the center, outer edge, and at the midpoint between the center and edge to estimate annual sedimentation rates. Sedimentation data were coupled with vegetation characteristics of sinkhole buffers to determine relationships among these variables. The dendrogeomorphic method estimated an average accumulation rate of 1.27 cm year(-1) translating to a sediment loss rate of 46.1 metric ton year(-1) from the training areas. However, sediment export to sinkholes was estimated to be much greater (118.6 metric ton year(-1)) via the bottle method. These data suggest that the latter method provided a more accurate estimate since accumulation was greater in the center of sinkholes compared to the periphery where dendrogeomorphic data were collected. Vegetation data were not tightly correlated with sedimentation rates, suggesting that further research is needed to identify a viable proxy for direct measures of sediment accumulation in this extreme deposition environment. Mitigation activities for the sinkholes at Ft. Knox's tank training area, and other heavily disturbed karst environments where extreme sedimentation exists, should consider focusing on flow path and splay area management.

Remote Sensing and GIS based soil erosion assessment from an agricultural watershed

Soil resource is important for livelihood of the human being. Soil erosion is a global environmental crisis in the world today that threatens the natural environment and agriculture. The present study was undertaken to assess the annual rate of soil erosion from the study watershed using distributed information for topography, land use, soil, etc. using remote sensing (RS) and geographic information system (GIS) techniques and to compare the simulated sediment loss with observed sediment loss. In the present study, the Shakkar River watershed, lying in Narmada river basin situated in Narsinghpur and Chhindwara districts of Madhya Pradesh, India, was selected. The universal soil loss equation (USLE) integrated with RS and GIS approach was used to predict the spatial distribution of the soil erosion on a cell basis occurring in the study area. Thematic maps of USLE factors like rainfall erosivity factor (R), soil erodibility factor (K), topographic factor (LS), crop/cover management factor (C), and conservation/support practice factor (P) were prepared by using annual rainfall data, soil map, digital elevation model (DEM) and executable C++ program, and satellite image of the area, respectively, in the GIS environment. The annual rate of soil erosion was estimated for 10 years (1997 to 2006), and during this period, the annual rate of sediment loss from study area was found to vary between 6.45 and 13.74 t/ha/year with an average annual rate of 10.04 t/ha/year. The percent deviation between simulated and observed values varies between 2.68 and 18.73 % with coefficient of determination (R 2) of 0.911.

Mass-Balance Constraints On Stratigraphic Interpretation of Linked Alluvial-Coastal-Shelfal Deposits From Source To Sink: Example From Cretaceous Western Interior Basin, Utah and Colorado, U.S.A

Abstract Experimental work suggests that the rate of upstream-to-downstream loss of sediment from an active depositional system to permanent storage exerts a fundamental control on stratigraphic architecture. This rate of sediment (mass) loss is determined by the spatial distribution of tectonic subsidence and rate of sediment supply. The character of input sediment (grain-size distribution and composition) is the third parameter that affects stratigraphic architecture. We apply this concept in a mass-balance framework to linked alluvial–coastal–shelfal deposits of the Upper Cretaceous Castlegate Sandstone, Blackhawk Formation, Star Point Sandstone, and Mancos Shale (Western Interior Basin, Utah and Colorado, USA). Facies partitioning and sediment budgets are estimated for eight stratigraphic intervals, in order to compare temporal dynamics of the sediment routing system from erosional source to depositional sink. Mapping of each stratigraphic interval and its constituent segments, from upsystem to downsystem, was achieved along a representative, dip-oriented 2D cross section over a distance of c. 350 km using extensive outcrop exposure and densely spaced subsurface wells. The cross section provides time-averaged estimates of the spatial distribution of deposition. Grain-size data show that there is limited downsystem fining of any particular facies within the Castlegate Sandstone, but that the proportion of facies changes systematically downsystem to accommodate an overall fining trend. Therefore, it is reasonable as a first approximation to use facies proportions as a “textural replacement” for grain size. Sediment supply characteristics for each of the eight stratigraphic intervals are constrained by total facies proportions in each interval. For each stratigraphic interval, we assess the level of interaction between alluvial and coastal-to-shelfal segments of the routing system. Comparison of the downsystem mass-balance characteristics of the eight stratigraphic intervals suggests that there were depositional gains and losses of shallow-marine shale in the five youngest intervals, which can be attributed to along-strike sediment transport. This result is consistent with increased interaction through time with vigorous wave- and tide-driven circulation in the seaway, as the sediment-routing system advanced out of a sheltered embayment in response to decreasing tectonic subsidence. In the youngest stratigraphic interval, the upstream-unconformable base of the Castlegate Sandstone is marked by a pronounced increase in the sand- to gravel-grade mass fraction of the fluvially supplied depositional volume. This marked increase can be attributed to hinterland unroofing and/or cannibalization of wedge-top basins, leading to import of coarse-grained sediment into the Castlegate fluvial system. Our results demonstrate the value of analyzing downsystem sediment loss (i.e., downsystem mass extraction) within a mass-balance framework as a simple and practical tool to quantify the relationship between accommodation and sediment supply, and thus to decode past external forcing mechanisms from stratigraphic architecture.

An improved method for determining dredging source terms

The determination of sediment loss rates from dredging activities is important for quantifying the potential impact on the surrounding physical and biological environment. This paper describes an improved method for measuring and analysing data to determine measurable dredging ‘source terms’ using Sediview software and data from two vessel-mounted acoustic Doppler current profiler devices, one of which is mounted with a vertical beam. The methodology is described in detail and an example data set is presented based on measurements undertaken around a working back hoe dredger. The technique described in this paper offers an improvement over the traditional application of the software used to measure dredger source terms (i.e. the use of one vessel-mounted acoustic Doppler current profiler in a Janus configuration). The use of a vertically orientated acoustic beam allows for a greater range (depth) of acoustic backscatter measurements to be acquired, as the data are not contaminated by side-lobe reflections. Although partially dependent upon the dredging methodology, this improvement is important as high suspended sediment concentrations tend to occur near to the bed. Subject to robust calibration, an improved source term can be collected using two acoustic Doppler current profiler instruments and the software allows the determination of suspended sediment flux (kg/s) across an entire survey transect, by using discharge data from one instrument and calibrated concentration data from the other, rather than the use of a series of water column turbidity profiles and subsequent spatial interpolation (an alternative method to the use of the software).

Streambank erosion in two watersheds of the Central Claypan Region of Missouri, United States

This study was undertaken to assess the importance of streambank erosion to the total in-stream sediment of two agricultural watersheds within the Central Claypan Areas. The objective of this research was to determine the effect of stream order, adjacent land use, and season on streambank erosion rates. Thirty-four study sites were established in 2007 and 2008 within Crooked and Otter Creek watersheds, two claypan watersheds located in northeastern Missouri. At each site, field assessments of severely to very severely eroding bank length were determined along 300 to 400 m (984 to 1,312 ft) stream reaches. A factorial experimental design was implemented with four land uses (crop, forest, pasture, and riparian forest), three seasons, and three stream orders (1st, 2nd, and 3rd). Each treatment was replicated three times for each stream order, except for the cropped 3rd order treatment as only one suitable treatment site could be found. Streambank erosion was measured using erosion pins, which were installed in randomly assigned plots that included at least 20% of the eroded bank length within each site. The effect of different seasons was assessed by measuring the length of the exposed pins three times per year (March, July, and November). The bulk density and carbon and nitrogen content of bank material were also determined. Sediment loss rates showed that season and the three-way interaction between season, land use, and stream order were highly significant. Erosion rates were consistently higher in the winter months than spring/summer and fall seasons; however, the significant three-way interaction precluded a simple interpretation of the seasonal effect. Soil nutrient concentration data showed that forest sites had significantly lower C and N concentrations than other land uses. At the watershed scale, bank sediment accounted for 79% to 96% of the total in-stream sediment and 21% to 24% of the total N exported from the study area. These results indicate that streambanks are the dominant source of sediment and a significant source of N in these streams. Therefore, improved management of riparian areas to decrease streambank erosion would result in significant water quality improvement in streams of the Central Claypan Areas in northeastern Missouri.

Hidrogramas e sedimentogramas associados à erosão hídrica em solo cultivado com diferentes sequências culturais, com diferentes condições físicas na superfície

Estudos hidrossedimentológicos detalhados são de grande valia para o melhor entendimento e controle do processo de erosão hídrica e, por conseguinte, para se aprofundar a pesquisa no assunto e, assim, praticar a conservação do solo e da água de modo mais eficaz e duradouro. Considerando isso, realizou-se este trabalho com o objetivo de desenvolver hidrogramas (taxas instantâneas de descarga da enxurrada versus tempo) e sedimentogramas (concentrações instantâneas de sedimento na enxurrada e taxas instantâneas de perda de solo versus tempo) individualizados (cada repetição de tratamento), associados à erosão hídrica ocorrida em solo cultivado com diferentes sequências culturais (gramíneas e leguminosas de inverno e verão, implantadas em semeadura direta, nos modos de cultivo isolado e consorciado), com diferentes condições físicas na superfície (solo não mobilizado, solo recém-escarificado, solo previamente escarificado e solo recém-gradeado, com presença e ausência de crosta e de completa, pouca e nenhuma cobertura por resíduos culturais). O estudo foi desenvolvido em campo, na EEA/UFRGS, em Eldorado do Sul (RS), usando-se chuva simulada e um Argissolo Vermelho distrófico típico com textura franco-argiloarenosa na camada superficial e declividade média de 0,115 m m-1. No início da pesquisa esse solo encontrava-se bastante degradado. As chuvas simuladas (seis no total, sendo uma para cada teste de erosão) foram aplicadas com o aparelho simulador de braços rotativos, todas elas na intensidade planejada de 64 mm h-1 (neste trabalho usaram-se as intensidades observadas das chuvas, as quais variaram de 59,1 a 74,6 mm h-1) e com duração variando de 1 a 3 h (devido almejar-se atingir a condição de equilíbrio da enxurrada em todos os testes de erosão). Observou-se que os hidrogramas e sedimentogramas, de modo geral, resultaram coerentes com as condições das quais foram desenvolvidos. Assim, na maior parte das vezes, os hidrogramas diferenciaram-se mais entre os testes de erosão do que entre os tratamentos de sequência cultural, e o inverso ocorreu com os sedimentogramas. As superfícies de solo não mobilizadas e com pequena rugosidade e pouca cobertura, de modo geral, proporcionaram hidrogramas e sedimentogramas com menor tempo de partida e maior magnitude, independentemente da presença ou ausência de crosta e do tipo de sequência cultural. As superfícies de solo recém-mobilizadas e com média e grande rugosidade, de modo geral, proporcionaram hidrogramas e sedimentogramas com maior tempo de partida e menor magnitude, praticamente independentemente da cobertura e do tipo de sequência cultural. As superfícies de solo com completa cobertura tiveram suas enxurradas diminuídas e suas erosões eliminadas, independentemente da sua mobilização e do tipo de sequência cultural. A sequência cultural com teosinto proporcionou hidrogramas e sedimentogramas com os maiores tempos de partida e as menores magnitudes, seguida das com milho+feijão-miúdo e milheto, as quais diferenciaram pouco entre si. As repetições dos tratamentos proveram valores das taxas instantâneas de descarga da enxurrada que se pareceram mais e se distribuíram no tempo de modo mais uniforme do que os providos para as correspondentes concentrações instantâneas de sedimento e taxas instantâneas de perda de solo. Os dados obtidos foram valiosos no que diz respeito a poder entender melhor a variação comumente observada nos resultados de pesquisas de erosão hídrica realizadas em campo.