Showing papers on "Siltation published in 2018"

Estimating the Sediment Flux and Budget for a Data Limited Rift Valley Lake in Ethiopia

Abstract: Information on sediment concentration in rivers is important for the design and management of reservoirs. In this paper, river sediment flux and siltation rate of a rift valley lake basin (Lake Ziway, Ethiopia) was modeled using suspended sediment concentration (SSC) samples from four rivers and lake outlet stations. Both linear and non-linear least squares log–log regression methods were used to develop the model. The best-fit model was tested and evaluated qualitatively by time-series plots, quantitatively by using watershed model evaluation statistics, and validated by calculating the prediction error. Sediment yield (SY) of ungauged rivers were assessed by developing and using a model that includes catchment area, slope, and rainfall, whereas bedload was estimated. As a result, the gross annual SY transported into the lake was 2.081 Mton/year. Annually, 0.178 Mton/year of sediment is deposited in floodplains with a sediment trapping rate of 20.6%, and 41,340 ton/year of sediment leaves the lake through the Bulbula River. The annual sediment deposition in the lake is 2.039 Mton/year with a mean sediment trapping efficiency of 98%. Based on the established sediment budget with average rainfall, the lake will lose its volume by 0.106% annually and the lifetime of Lake Ziway will be 947 years. The results show that the approach used can be replicated at other similar ungauged watersheds. As one of the most important sources of water for irrigation in the country, the results can be used for planning and implementing a lake basin management program targeting upstream soil erosion control.

Extent and Causes of Siltation in a Headwater Stream Bed: Catchment Soil Erosion is Less Important than Internal Stream Processes

Abstract: The stream bed is a key habitat for many species, and its physicochemical properties govern important ecosystem functions. Stream bed colmation resulting from catchment erosion is considered a core problem of stream headwaters in which many species depending on coarse substrates are in decline. Here, we identify the origin of fine sediment and compare the contribution of external (i.e. catchment erosion) versus internal (i.e. in-stream carbonate precipitation and internal biomass production) sources of siltation using a case study of a pre-alpine river, the Moosach. The stream bed was dominated (51%) by fine sediment of mainly silt size. The average fine sediment thickness of 58 cm and a net deposition rate of 1.32 kg m−2 yr−1 confirmed siltation problems. Mineral analyses and mass balancing showed that still only less than 1% of the erosion input into the stream was deposited on the stream bed. Internal temperature-dependent calcite precipitation also removed less than 1% of the calcium from the water column. Thus, by far, most of the fine material from erosion and precipitation was transported and did not contribute to the deposition of fines. Since the colmation problem is governed by the sink, it cannot be solved by exclusively addressing the sources (erosion, precipitation). Despite the well-founded linkage between terrestrial and aquatic systems, this study suggests that restoration of stream bed quality must also focus on in-stream processes and flow regime management, while erosion control remains essential in its own right. Copyright © 2017 John Wiley & Sons, Ltd.

The impacts of land reclamation on suspended-sediment dynamics in Jiaozhou Bay, Qingdao, China

Abstract: A three-dimensional, high-resolution tidal model coupled with the UNSW sediment model (UNSW-Sed) based on Finite Volume Coastal Ocean Model (FVCOM) was set up to study the suspended-sediment dynamics and its change in Jiaozhou Bay (JZB) due to land reclamation over the period 1935 to 2008. During the past decades, a large amount of tidal flats were lost due to land reclamation. Other than modulating the tides, the tidal flats are a primary source for sediment resuspensions, leading to turbidity maxima nearshore. The tidal dynamics are dominant in controlling the suspended-sediment dynamics in JZB and have experienced significant changes with the loss of tidal flats due to the land reclamation. The sediment model coupled with the tide model was used to investigate the changes in suspended-sediment dynamics due to the land reclamation from 1935 to 2008, including suspended-sediment concentrations (SSC) and the horizontal suspended-sediment fluxes. This model can predict the general patterns of the spatial and temporal variation of SSC. The model was applied to investigate how the net transport of suspended sediments between JZB and its adjacent sea areas changed with land reclamation: in 1935 the net movement of suspended sediments was from JZB to the adjacent sea (erosion for JZB), primarily caused by horizontal advection associated with a horizontal gradient in the SSC; This seaward transport (erosion for JZB) had gradually declined from 1935 to 2008. If land reclamation on a large scale is continued in future, the net transport between JZB and the adjacent sea would turn landward and JZB would switch from erosion to siltation due to the impact of land reclamation on the horizontal advection of suspended sediments. We also evaluate the primary physical mechanisms including advection of suspended sediments, settling lag and tidal asymmetry, which control the suspended-sediment dynamics with the process of land reclamation.

Combining field monitoring and aerial imagery to evaluate the role of gully erosion in a Mediterranean catchment (Tunisia)

Abstract: The objective of this study was to address the role of gully erosion on sediment delivery at the catchment scale by assessing the contribution of gullies to the total sediment yield at the outlet of the Kamech (Cape Bon, Tunisia), which is a small cultivated catchment in the Mediterranean environment. The methodology was based on the long-term analysis of the evolution of gully volume, and the total volume of sediment that reached the catchment outlet. The evolution of gully volume was assessed by field surveys and image analysis. The total volume of sediment was calculated using intensive field monitoring of the runoff and erosion in the reservoir at the catchment outlet. The contribution of gullies to the total flux of sediment that reached the catchment outlet was estimated to be less than 30%. This means that siltation of the reservoir was mainly due to erosion processes other than gully erosion, i.e., topsoil erosion processes such as rill and interrill erosion in cropland areas. This result was consistent with a previous independent estimation of the apportionment of gully and topsoil erosion sources conducted at the same site using the fingerprinting approach. Therefore, the study confirms that, even in a heavily eroded agricultural catchment area with a dense network of gullies, gully erosion nevertheless accounted for less than 30% of the total erosion balance. The results also showed that the cumulated gully length has decreased in the last fifty years, thus revealing the declining role of gullies. However, the decrease in gully activity could not be linked to an isolated factor. Complementary observations, such as the appearance of vegetation in the permanent gullies and the decrease in the percentage of active gullies, showed that the degree of hydro-sedimentary connectivity in the Kamech catchment has probably entered a decreasing phase. We also analysed the potential use of historical aerial images for studying gully erosion. We found that these images were useful for calculating accurate ortho-photography but failed to provide a DEM with the precision required to measure the historical volume of gullies.

Influence of land use changes on spatial erosion pattern, a time series analysis using RUSLE and GIS: the cases of Ambuliyar sub-basin, India

Abstract: Soil erosion and its impact on the land and surface water resources are posing both ecological and socioeconomic threats around the world. In South India, tank systems are quite ancient, supporting rural livelihood including their agricultural needs. But, in recent decades they have lost their significance. The aggravated catchment erosion and resultant siltation have significantly reduced their storage capacity and thereby their functionality. Ambuliyar sub-basin, encompassing 809 irrigation tanks, has once satisfied multifunctional needs of people but now becomes degraded due to siltation. Though desilting of tanks and feeder channels is practiced, the tanks often get silted owing to aggravate soil erosion. Hence, to sustain their life span, it is essential to minimize the erosion in the catchment. Thus, the present study intends to estimate the rate of erosion, analyze their spatial variation through a time series analysis, and ascertain the causative factor. Accordingly, the annual soil loss estimated using Revised Universal Soil Loss Equation method has shown an increase in the rate of erosion from 4084.40 (1996) to 4922.47 t ha−1 y−1 (2016). However, spatially, a non-uniform pattern is inferred, and hence based on the variations, the sub-basin is divided into five zones. In zones I, II, and V, there is an increase in erosion, and in zones III and IV, a decrease is witnessed. Variations studied in conjunction with RUSLE parameters reveal that the improper land use practice has modified the erosion rate and pattern. Further, it is presumed that the silted watercourses might have increased the overland flow, which in turn increased the erosion. Remedial measures such as afforestation, promotion of coconut plantation, and reduction in overland flow by desilting tanks are suggested; thereby, the surface and groundwater resources will be enhanced and in turn the agricultural productivity.

Assessing soil loss using GIS based RUSLE methodology. Case of the Bou Namoussa watershed – North-East of Algeria

Abstract: Abstract This study aims to estimating annual soil erosion rate and its spatial distribution in the Bou Namoussa water-shed located in the North-East of Algeria by applying the revised universal soil loss equation (RUSLE) within a Geographical Information System environment (GIS). The application of the RUSLE model in different natural environments and on every scale takes into account five key factors namely: the rainfall erosivity, the soil erodibility, the steepness and length of slopes, the vegetation cover and the conservation support practices. Each of these factors was generated in GIS as a raster layer, their combination, resulted in the development of a soil loss map indicating an average erosion rate of 7.8 t·ha−1·y−1. The obtained soil loss map was classified into four erosion severity classes; low, moderate, high and very high severity representing respectively 40, 30.48, 22.59 and 6.89% of the total surface. The areas, showing moderate, high and very high erosion rates which represent more than half of the basin area were found generally located in regions having high erodibility soils, steep slopes and low vegetation cover. These areas should be considered as priorities in future erosion control programs in order to decrease the siltation rate in the Cheffia reservoir.

Soil Erosion Risk and Flood Behaviour Assessment of Sukhnag catchment, Kashmir Basin: Using GIS and Remote Sensing

Abstract: Kashmir Basin is surrounded on all sides by lofty mountains, there is only one outlet i.e., Jhelum River to drain water from the basin. The mountainous areas of Kashmir Basin have rugged topography and unstable slopes with highly shuttered rocks. Based on these factors, the evaluation of basin characteristics from the morphometric analysis and other associated factors will help to understand the physical behaviour of the area with respect to floods and soil erosion risk. Remote sensing and GIS techniques were applied to extract drainage network using Digital Elevation Model (DEM) to evaluate morphometric parameters for Sukhnag catchment. Lineament, slope and aspect maps were generated to support morphometric parameters to demarcate the soil erosion and flood prone areas during harsh weather conditions. In low lying areas with more habitation and construction on the river banks and flood plains have squeezed the rivers and minimized their water carrying capacity. Morphometry together with lineament density, slope distribution and flood plain conditions helps to classify the catchment into three categories, high, medium and low priority for conservation and management with respect to soil erosion and floods. Among 14 sub-watersheds SF1, 2, 5, 6 and 7 are more prone to landslides and SF10, 12, 13 and 14 are more prone to flood and siltation hazard. More chances of erosion risk in SF1, 2, 5, 6 and 7 can be due to lose upper layer, high altitude, unstable slope and high structural density. Conversely, the floods and siltation hazard are more in low lying subwatersheds as faced in Kashmir Valley (Sept. 2014 Flood). The present work emphasized that categorization of smaller hydrological unit’s i.e., sub-watersheds are ideally recommended for initiating soil conservation and flood mitigation measures in the area.

Assessment of Siltation Processes of the Koronowski Reservoir in the Northern Polish Lowland Based on Bathymetry and Empirical Formulas

Abstract: Artificial reservoirs have an important role in water management of river systems in terms of flood control, water supply and sediment budgeting. Therefore, it is important to maximize the time of their effective functioning. Sediment budgeting mainly depends on sediment transport dynamics. This article illustrates the impact of the Koronowski Reservoir on suspended sediments transported by the Brda River. The river system and the reservoir represent a typical lowland river environment. Our research is based on hydrological and sedimentological investigations on the reservoir and the river system. Field measurements were used to create the respective hydrological and sediment budgets. Moreover, we carried out bathymetric measurements to generate present day bathymetry and to calculate the reservoir’s capacity. We assessed the silting of the reservoir following the approaches proposed by Goncarov and Stonawski. We show that the size and dynamics of suspended sediments are mainly determined by the hydrological conditions. Moreover, we illustrate that the suspended sediment measurements made with the filtration method correlate with the nephelometric results. Generally, we show that the Koronowski Reservoir is mainly filled up by suspended sediments. We further illustrate that the level of siltation estimated with the empirical formulas deviates significantly from calculations made by bathymetric measurements.

Analyzing ecological restoration strategies for water and soil conservation.

Abstract: The choice of areas for nature conservation involves the attempt to maximize the benefits, whether by carrying out an economic activity or by the provision of Ecosystem Services. Studies are needed to improve the understanding of the effect of the extent and position along the watershed of restored areas on soil and water conservation. This study aimed to understand how different restoration strategies might reflect in soil conservation and sediment retention. Using InVEST tool, sediment transport was simulated in a small 12 km2 watershed (Posses River, in Southeast Brazil), where one of first Brazilian Payment for Ecosystem Services (PES) projects is being carried out, comparing different hypothetical restoration strategies. With 25% of restoration, sediment export decreased by 78% for riparian restoration, and 27% for the steepest slopes restoration. On the other hand, the decrease in soil loss was lower for riparian restoration, with a 16% decrease, while the steepest slopes restoration reduced it by 21%. This mismatch between the reduction of sediment export and soil loss was explained by the fact that forest not only reduces soil loss locally but also traps sediment arriving from the upper parts of the watershed. While the first mechanism is important to provide soil stability, decreasing the risk of landslip, and to maintain agricultural productivity, the second can improve water quality and decrease the risk of silting, with positive effects on the water reservoirs at the outlet of the watershed. This suggests that Riparian and the Steepest Slopes restoration strategies are complementary in the sense of preventing sediments from reaching the water bodies as well as protecting them at their origin (with the reduction of erosion), so it will be advisable to consider the two types of restoration.

Coastal erosion and shore protection: A brief historical analysis

Abstract: Since the Neolithic, humans have gathered along coastal plains, where they had to face sea level rise and subsidence without the technology to oppose these processes. When sea level stabilized, approx. 6.000 yr. B.P., coastal colonization was allowed, but where mountain deforestation was carried out river sediment input increased tremendously: settlements were disconnected from the shore and harbour siltation occurred. Shore erosion was a limited process at the time and local solutions were adopted: clay dikes, wood piles, fascinates and rock revetments. Along the Mediterranean, in China and Japan the construction of more complex structures has been documented since the Middle Ages. Further human development, with river bed quarrying, wetland reclamation, dam construction and mountain re-afforestation, favoured a coastal erosion that nowadays threatens most world coasts. From the Venetian “Murazzi” to the recent 114-km-long concrete element defence at the Yellow river delta, shore protection structures evolved following the different needs (protect coastal communication routes, urban and industrial settlements, tourist resorts). Beach nourishment, previously performed with inland quarried materials, is now intensively carried out with marine aggregates. The vernacular solution, left to undeveloped countries, has been recently revaluated by “green engineering”. However, with Sea Level Rise, the debate of whether to defend, accommodate or retreat is open.

Suspended sediment dynamics in a well-mixed estuary: The role of high suspended sediment concentration (SSC) from the adjacent sea area

Abstract: Understanding the sediment transport processes, especially the formation and maintenance of the estuarine turbidity maximum (ETM) in estuaries is essential for dealing with harbour siltation and the related estuarine environmental issues. To gain insight into the mechanism of sediment dynamics and ETM formation in the Yongjiang estuary (YE), which is well-mixed and features abundant suspended sediment sourced from the adjacent sea area, field observations were conducted in June 2015. The flow velocity, salinity, and suspended sediment concentration (SSC) were synchronously measured over a 25-h tidal cycle along the YE and its adjacent sea area. Observations showed that there was abundant suspended sediment exchanging between the YE and its adjacent sea area. In particular, there existed an obvious difference in the single or twin peak SSC signals in different stations during a semi-diurnal tidal cycle, especially between the inner-estuary and outer-estuary regions. Detailed analyses on the processes of sediment transport showed that, in the outer sea area, the tidal-driven advection of suspended sediment was dominant to the temporal distribution of SSC, which was featured by a single peak signal in a semi-diurnal tidal cycle. For the estuarine channel, the landward transport of high-concentration suspended sediment by the flood current from the sea region was the major inducement of peak SSC signals in the lower reach of the YE, while the effect of bed sediment resuspension was mainly responsible for the peak signals during the ebb period. Unlike the formation of ETM in highly stratified or partially mixed estuaries, the ETM in the YE, which is located approximately 7 km upstream from the estuary mouth, was mainly controlled by the effect of tidal asymmetry, together with the contributions made by local resuspension of bed sediment and possible fluid mud. Some other possible factors, such as deflocculation, may also impact the formation and maintenance of the ETM in the YE, but further study is needed in the future.

Rethinking Spatial and Temporal Variability of Erosion in Badlands

Abstract: This chapter reviews the most significant aspects of erosion in badlands, one of the most impressive erosion landforms on Earth. Badlands occur in arid, semiarid and humid areas, are characterized by intense erosion processes and generally have extremely high sediment yields. They lead to sedimentation in pediments, high sediment load in fluvial channels and sediment silting in reservoirs. The present study examines the factors that most affect erosion in badlands: lithology, seasonal contrasts in climate, rainfall intensity, and low plant cover, weathering and erosion processes, spatial and temporal variability of erosion processes and the complex spatial and temporal connections at the catchment scale. Two sections examine critical future issues: the relationship between conservation and reclamation in badlands and the future evolution of badland erosion in the context of global change. In many cases, badland initiation and development occurred due to interactions between climate changes and human activities, particularly the use of fire and cultivation on steep slopes of soft bedrock material. The largest badlands should be preserved as geomorphological monuments because of their importance to education, research and tourism.

The siltation of debris flow behind check dam in the midstream of Bailong River.

Abstract: Siltation gradient and siltation length are important parameters for designing gravity check dams for debris flows, which directly affect the accuracy of estimates of interception capacity. At present, siltation gradient calculations are based primarily on empirical values, and range from 0.4 to 0.95 times the channel slope coefficient. The middle reaches of the Bailong River are one of the four areas in China that are most severely affected by debris flow hazards. Gravity dams are widely employed in this mountainous area. However, field studies of their capacity are lacking. In this paper, the operations of check dams were investigated. Based on field investigation results and theoretical analysis, calculations for siltation gradient, siltation length, and dam storage capacity are established. The impact of debris flow density, channel slope, and particle size weight percentages are discussed. The calculations show that the theoretical values for siltation gradient are consistent with measured values with 83.6% accuracy; and theoretical values of siltation length are consistent with measured values with 91.6% accuracy. The results of this research are an important reference for optimal height and spacing of dams, estimation of dam storage capacity, and disaster prevention.

Analysis of sedimentation at the fishing harbor entrance: case study of El-Burullus, Egypt

Abstract: Sedimentation in artificial ports and harbors is a common issue throughout the world. Based on an assessment of the coastal fishing harbors in Egypt, the El-Burullus fishing harbor has been found to suffer severely from siltation. Sediment deposits are concentrated at the harbor entrance, which threatens navigation through this area. Although the harbor authority has constructed a perpendicular extension on the main breakwater to mitigate these siltation issues, fishing boats are still suffering from the siltation at the harbor entrance. Dredging is required every year to maintain continuity of navigation through the harbor; the cost of dredging is a critical element which impacts the economic feasibility of the harbor. Therefore, the need to investigate new solutions for the siltation issue is critical. In this study, a two-dimensional calibrated and validated model using the Coastal Modeling System package is used to understand the coastal processes within the study area. It is also used to investigate the effects of the proposed breakwater extension on the siltation at the harbor outlet. Field data such as hydrographic surveys, waves, tides, and lake outlet discharge data were collected and included in the model. The results obtained for the current breakwater conditions confirmed the claims of the fishermen that the sedimentation problem still occurs at the entrance. Thus, five possible solutions to mitigate the problem were proposed and simulated considering the following parameters: sediment deposition rate to the west of the main breakwater, the erosion rate in front of the seawall in the eastern part of the harbor, and the morphological changes within the El-Burullus lake outlet. According to the simulation results, reducing the length of the upper edge of the middle jetty by 90 m improves the stability of the harbor entrance. Alternatively, replacing the perpendicular extension by an inclined extension of 60 m in length and shortening the middle jetty by 60 m reduces the accretion and erosion rates around the harbor which promotes the long-term stability for the coastal area in addition to favorable conditions to the El-Burullus harbor entrance.

Land susceptibility to soil erosion in Orashi Catchment, Nnewi South, Anambra State, Nigeria

Abstract: . Soil erosion is one of the most critical environmental hazards that causes land degradation and water quality challenges. Specifically, this phenomenon has been linked, among other problems, to river sedimentation, groundwater pollution and flooding. This paper assesses the susceptibility of Orashi River Basin (ORB) to soil erosion for the purpose of erosion control measures. Located in the South Eastern part of Nigeria, the ORB which covers approximately 413.61 km2 is currently experiencing one of the fastest population growth rate in the region. Analysis of the soil erosion susceptibility of the basin was based on four factors including; rainfall, Land use/Land cover change (LULC), slope and soil erodibility factor ( k ). The rainfall was assumed to be a constant and independent variable, slope and soil types were categorised into ten (10) classes each while the landuse was categorised into five classes. Weight was assigned to the classes based on the degree of susceptibility to erosion. An overlay of the four variables in a GIS environment was used to produce the basin susceptibility to soil erosion. This was based on the weight index of each factors. The LULC analysis revealed that built-up land use increased from 26.49 km2 (6.4 %) in year 1980 to 79.24 km2 (19.16 %) in 2015 at an average growth rate of 1.51 km2 per annum while the light forest decreased from 336.41 km2 (81.33 %) in 1980 to 280.82 km2 (67.89 %) in 2015 at an average rate 1.59 km2 per annum. The light forest was adjudged to have the highest land cover soil erosion susceptibility. The steepest slope ranges between 70 and 82 ∘ (14.34 % of the total land area) and was adjudged to have the highest soil susceptibility to erosion. The total area covered of the loamy soil is 112.37 km2 (27.07 %) with erodibility of 0.7. In all, the overlay of all the variables revealed that 106.66 km2 (25.70 %) and 164.80 km2 (39.7 %) of the basin has a high and very high susceptibility to soil erosion. The over 50 % high susceptibility of catchment has serious negative implications on the surface water in terms of water quality and downstream siltation with great consequences on biodiversity and ecosystem services including domestic and industrial usage.

Influence of the sediment delivery ratio index on the analysis of silting and break risk in the Plasencia reservoir (Central System, Spain)

Abstract: Erosion and the production of sediments effect the siltation of reservoirs and create large environmental problems. This work calculates the volume of sediments caused by erosion in a hydrological basin using the Revised Universal Soil Loss Equation 2 (USLE–RUSLE2), applying, or not, the sediment delivery ratio, and is compared with the volume of sediments transported using the Lawrence method. The USLE–RUSLE2 method is validated in the study area, the Jerte Valley, using the geographic information systems. The result obtained showed an erosion of 7 Tm/ha year and low risk of siltation, which suggest that the Plasencia reservoir has a long life expectancy.

Modelisation Du Risque D’érosion Hydrique Par L’équation Universelle Des Pertes En Terre Dans Le Rif Occidental: Cas Du Bassin Versant De Moulay Bouchta (Maroc)

Abstract: Soil erosion causes many environmental and socio-economic problems: loss of biodiversity, decrease in the productivity of agricultural land, siltation of dams and increased risk of flooding It is therefore essential to establish a detailed evaluation of this process before any spatial planning To evaluate the effects of soil erosion spatially and quantitatively in order to face this phenomenon, and propose the best conservation and land development strategies, the Universal Soil Loss Equation (USLE) coupled with a geographic information system (GIS) is applied This model is a multiplication of the five erosion factors: the erosivity of the rain, the erodibility of the soil, the inclination and the slope length, the vegetation cover and the anti-erosion practices The study area is the Moulay Bouchta watershed (7 889 ha), which is located in the western part of the Rif Mountains, is characterized by a complex and contrasting landscape The resulting soil loss map shows an average erosion rate of 395 (t/ha/yr), 87% of the basin has an erosion rate above the tolerance threshold for soil loss (7 (t/ha/yr)) Soil losses per subbasin range from 162 to 814 (t/ha/yr) The amount of eroded soil is estimated at 311,591 (t/yr), corresponding to a specific degradation of 121 (t/ha/yr) In the absence of any erosion control, 25% of the soil losses would reach the new dam located a little upstream of the basin outlet, reducing its water mobilization capacity to 59,625 (m3/yr) The application of Principal Component Analysis (PCA) to soil erosion factors shows a significant influence of topographic factor (LS) on soil erosion process, followed by the effect of support practices (P), then by soil erodibility (K)

Chapter 8 - Assessing Badland Sediment Sources Using Unmanned Aerial Vehicles

Abstract: Badland erosion is a major sediment source for river systems in drylands (Poesen et al., 2002). Identifying their relevance as sediment sources is critical for measures aimed at reducing reservoir siltation. However, the spatial resolution of commonly available data products on topography is usually not sufficient to calculate sediment losses accurately. Unmanned aerial vehicles (UAVs) can help to overcome the gap between traditional, expensive, time-consuming ground-based assessment and insufficient data availability or quality at aerial photography or satellite imagery scale levels. This study investigates the use of UAVs for generating high-resolution digital terrain models (DTMs) of badlands in a remote catchment in the Karoo highveld in South Africa, which is affected by severe soil erosion and reservoir siltation, but where the relevance of badlands as sediment source is unclear. The chapter describes UAV hardware, image capture, DTM and orthomosaic generation and a workflow for badland erosion estimation with the acquired imagery. The results show that erosion volumes in badlands accounted for only 17.2% of the reservoir storage capacity in the study area, which indicates that there are additional sediment sources within the catchment.

A New Modeling Approach To Prioritize Riparian Restoration To Reduce Sediment Loading in Two Virginia River Basins.

Abstract: Human impact, particularly land cover changes (e.g., agriculture, construction) increase erosion and sediment loading into streams. Benthic species are negatively affected by silt deposition that coats and embeds stream substrate. Given that riparian buffers are effective sediment filters, riparian restoration is increasingly implemented by conservation groups to protect stream habitats. Limited funding and a multitude of impaired streams warrant the need for cost-effective prioritization of potential restoration actions. We created a decision-support framework for conservation agencies and aquatic resource managers to prioritize riparian restoration efforts. Our framework integrates GIS data and field surveys into a statistical model to predict instream silt from estimates of upland soil loss and riparian filtration capacity. We focus specifically on prioritizing sites in upper sections of the Roanoke and Nottoway river basins (Virginia, US) based on observed records of Roanoke logperch (Percina rex), an imperiled sediment-sensitive species. Our statistical approach examines soil characteristics, land cover, precipitation, topography, and annual soil loss estimates from the empirically derived Revised Universal Soil Loss Equation, combined with land cover-based riparian filtration capacity as potential stream habitat predictors. We found riparian filtration capacity to be a significant predictor of silt cover, while precipitation was a significant predictor of embeddedness. Spatial scale was also a factor, in that spatial variance in silt cover and embeddedness was more accurately predicted at smaller spatial extents. Ultimately, our model can be used as a prioritization tool for mitigating high siltation areas, or for protecting low soil erosion areas.

Restoration increases transient storages in boreal headwater streams

Abstract: Bed siltation can drastically alter the physical conditions of headwater streams and is therefore a stressor for stream ecosystems. We studied 32 headwater streams that represented near‐natural (reference; N = 11), sediment‐impacted (N = 12), or wood‐ (N = 4) or stone‐restored (N = 5) streams to quantify how extensive siltation and restoration with either large woody debris (LWD) or boulder structures influence transient storage conditions. We carried out repeated stream tracer experiments, field measurements of habitat characteristics, and numerical simulations to determine the effects of siltation and restoration on total transient storage. Compared with reference streams, impacted streams had a smaller storage zone cross‐sectional area (Aₛ/A) ratio and fraction of median travel time due to transient storage (F₂₀₀), whereas restored streams had transient storage conditions similar to near‐natural conditions. Both of the two restoration methods had positive but differing impacts on bed sediment and transient storage properties. The LWD restoration created diverse total transient storage conditions, whereas boulder restoration decreased fine sediment cover. Addition of both LWD and boulders could thus aid the recovery of headwater streams from excessive sediment input and increase transient storage and in‐stream habitat complexity.