Sediment Production Processes Research Articles

A Review of the Sediment Production and Transport Processes of Forest Road Erosion

Forest roads are a common land use feature with a significant impact on sediment yield and the water sediment transport processes within a watershed, seriously disrupting the safety and stability of the watershed. Previous studies have focused on the sediment production processes within the road prism. However, there has been limited attention given to the transport processes of road-eroded sediment at various scales, which is crucial for understanding the off-site effects of road erosion. This paper reviews research conducted on forest road erosion over the past two decades. It summarizes the mechanisms of sediment production from road erosion and provides a detailed analysis of the transport mechanisms of eroded sediments from roads to streams at the watershed scale. The paper also examines the ecological and hydrological effects, research methods, and control measures related to sediment transport caused by forest road erosion. It identifies current research limitations and outlines future research directions. The findings of this review highlight several key points: (1) Most research on forest road erosion tends to be specific and unilateral, often neglecting the broader interaction between roads and the watershed in terms of water–sediment dynamics. (2) Various research methods are employed in the study of forest road erosion, including field monitoring, artificial simulation experiments, and road erosion prediction models. Each method has its advantages and disadvantages, but the integration of emerging technologies like laser scanning and fingerprint recognition remains underutilized, hindering the simultaneous achievement of convenience and accuracy. (3) The transport processes of forest road-eroded sediment, particularly on road–stream slopes, are influenced by numerous factors, including terrain, soil, and vegetation. These processes exhibit significant spatial and temporal variability, and the precise quantification of sediment transport efficiency to the stream remains challenging due to a lack of long-term and stable investigation and monitoring methods. The establishment and operation of runoff plots and sedimentation basins may help offer a solution to this challenge. (4) Both biological and engineering measures have proven effective in reducing and limiting sediment erosion and transport. However, the costs and economic benefits associated with these regulation measures require further investigation. This review provides a comprehensive summary of relevant research on sediment erosion and transport processes on unpaved forest roads, enhancing our understanding of sediment yield in watersheds and offering valuable insights for reducing sediment production and transport to streams.

Analysis of the Impact of Land Use Changes on Soil Erosion Intensity and Sediment Yield Using the IntErO Model in the Talar Watershed of Iran

Land use change is known as one of the main influencing factors on soil erosion and sediment production processes. The objective of the article is to study on how land use change impacts on soil erosion by using Intensity of Erosion and Outflow (IntErO) as a process-oriented soil erosion model. The study has been conducted under land use changes within the period of 1991–2014 in the Talar watershed located in northern Iran. The GIS environment was used to prepare the required maps including Digital Elevation Model (DEM), geology, land use, soil, and drainage network. The climatology data including average annual precipitation and air temperature as well as the volume of torrential rain were extracted from the data of meteorological stations located inside and around the study watershed. The results indicates that, within the period of 1991–2014, the forest area decreased by 12,478.04 ha (6%), while the other land uses including rainfed agriculture, rangeland, irrigated agriculture, and residential area increased by 7248.25, 4481.05, 476.00, and 273.95 ha, respectively. The estimated outflow with 100 year return interval was 432.14 m3 s−1 in 1991, which increased to 446.91 m3 s−1 in 2014. It can be concluded that the probability of larger and/or more frequent floods waves in the Talar River is expected to increase. In addition, the amount of production of erosion material (gross erosion) in the watershed increased from 1,918,186 to 2,183,558 m3 yr−1, and the real soil losses per year (sediment yield) of the watershed increased from 440,482.4 to 501,421.3 m3 yr−1. The results clearly emphasized how the lack of appropriate land management and planning leads to increase the maximum flow discharge and sediment yield of the watershed.

<sup>10</sup>Be systematics in the Tsangpo-Brahmaputra catchment: the cosmogenic nuclide legacy of the eastern Himalayan syntaxis

Abstract. The Tsangpo-Brahmaputra River drains the eastern part of the Himalayan range and flows from the Tibetan Plateau through the eastern Himalayan syntaxis downstream to the Indo-Gangetic floodplain and the Bay of Bengal. As such, it is a unique natural laboratory to study how denudation and sediment production processes are transferred to river detrital signals. In this study, we present a new 10Be data set to constrain denudation rates across the catchment and to quantify the impact of rapid erosion within the syntaxis region on cosmogenic nuclide budgets and signals. The measured 10Be denudation rates span around 2 orders of magnitude across individual catchments (ranging from 0.03 to > 4 mm yr−1) and sharply increase as the Tsangpo-Brahmaputra flows across the eastern Himalaya. The increase in denudation rates, however, occurs ∼ 150 km downstream of the Namche Barwa–Gyala Peri massif (NBGPm), an area which has been previously characterized by extremely high erosion and exhumation rates. We suggest that this downstream lag is mainly due to the physical abrasion of coarse-grained, low 10Be concentration, landslide material produced within the syntaxis that dilutes the upstream high-concentration 10Be flux from the Tibetan Plateau only after abrasion has transferred sediment to the studied sand fraction. A simple abrasion model produces typical lag distances of 50 to 150 km compatible with our observations. Abrasion effects reduce the spatial resolution over which denudation can be constrained in the eastern Himalayan syntaxis. In addition, we also highlight that denudation rate estimates are dependent on the sediment connectivity, storage, and quartz content of the upstream Tibetan Plateau part of the catchment, which tends to lead to an overestimation of downstream denudation rates. While no direct 10Be denudation measurements were made in the syntaxis, the dilution of the upstream 10Be signal, measured in Tsangpo-Brahmaputra sediments, provides constraints on the denudation rates in that region. These denudation estimates range from ca. 2 to 5 mm yr−1 for the entire syntaxis and ca. 4 to 28 mm yr−1 for the NBGPm, which is significantly higher than other large catchments. Overall, 10Be concentrations measured at the outlet of the Tsangpo-Brahmaputra in Bangladesh suggest a sediment flux between 780 and 1430 Mt yr−1 equivalent to a denudation rate between 0.7 and 1.2 mm yr−1 for the entire catchment.

Runoff and soil loss characteristics on loess slopes covered with aeolian sand layers of different thicknesses under simulated rainfall

In the Wind-Water Erosion Crisscross Region of the northern Loess Plateau, parts of loess slopes have been covered by layers of aeolian sand of different thicknesses. Knowledge of soil erosion processes and magnitudes on these slopes is essential to understanding the coupled water-wind erosion processes and to address the resulting downstream coarse sediment problems in the Yellow River. Simulated rainfall (intensity 90mmh−1) was performed to explore the effects of sand layer thickness on runoff and soil loss from loess slopes covered with different sand layer thicknesses (0, 0.5, 2, 5, 10, 15, 20, and 25cm). Initial runoff time increased with increasing sand layer thickness, with greater changes occurring for the increases in the thinner (0–5cm) than for the thicker layers (5–25cm). Total runoff yield from the sand-covered loess slopes was 18%–55% lower than from the uncovered loess slope and decreased with increasing sand layer thickness. In contrast, total sediment yield was up to 14times greater from the sand-covered loess slopes than from the uncovered loess slope and rapidly increased with increasing sand layer thickness. During the rainstorm, runoff and soil loss rates exhibited unimodal distributions, and they were related by a positive linear function, both before and after the maximum soil loss rate, that had a high determination coefficient (R2>0.8, p<0.05) on loess slopes with sand layer thicknesses greater than 5cm. The maximum runoff and soil loss rates tended to occur simultaneously and increased abruptly with increasing sand layer thickness. During the rainstorms, some runoff rates on the loess slopes with thicker sand layers were higher than the rainfall intensity due to rainwater combining with water emerging from the saturated sand, which could never occur on the uncovered loess slope. The critical sand layer thickness, which produced a qualitative change in runoff and sediment production modes, appeared to be in the range of 5–10cm. These results indicated that the thickness of the sand layer on the loess slope significantly influenced runoff and sediment production processes and mechanisms. These effects should be considered when assessing and predicting soil losses in this region and from similar slopes elsewhere.

喀斯特裸坡产流产沙过程试验研究

喀斯特裸坡产流产沙过程试验研究

Simulation of the reduction of runoff and sediment load resulting from the Gain for Green Program in the Jialingjiang catchment, upper region of the Yangtze River, China

A distributed catchment hydrologic model (Hydrological Simulation Program – FORTRAN; HSPF) with improved sediment production processes was used to evaluate the effect of restoration of cultivated land to forest on the reduction of runoff and sediment load in the Jialingjiang basin, which forms part of the Yangtze River basin, China. The simulation results showed that restoration to forest reduced sediment production even in the case of minimum restoration at a threshold catchment slope of 25°, as advocated in the “Gain for Green Program ” planned by the Chinese government, even though reduction of the peak flow rate in the river channel was small. The increase in forest area resulting from lowering of the threshold catchment slope reduced sediment production further.

Sediment generation in modern glacial settings: Grain-size and source-rock control on sediment composition

Clastic sediment generation is controlled by physical and chemical processes acting in concert in most geological settings. In glacial settings, however, it is possible investigating the sole impact of mechanical processes such as comminution on sediment composition, as chemical processes are thought to be negligible in this environment. Comminution is a selective process in the sense that minerals behave differently under mechanical forcing and has yet not been thoroughly investigated under strict grain-size control. We sampled sediment from modern front and side moraines from six retreating glaciers in the Alps, that drain and erode either pure felsic crystalline rocks (granites, granodiorites, orthogneisses) or largely pure metamafic rocks (amphibolites and hornblende-rich gneisses). Samples were split in up to eleven grain-size fractions from very coarse sand to clay. Grain-size fractions were analysed for major and trace elements using X-ray fluorescence. Mineralogical composition was determined by X-ray diffraction and endmember modelling of geochemical data.Results reveal in general strong grain-size control on sediment composition and strikingly similar patterns for both source lithologies. Significant influence of chemical weathering and hydrodynamic sorting is ruled out. Zr/Zn ratio is found as a valuable proxy for grain size while Cr/Rb constitutes one of the rare discriminants between the two cases over the entire grain-size range. Most trace elements, however, are not suitable for source rock discrimination across grain size grades even in glacial environment and extreme proximity to the source. Consequently, bulk sediment geochemistry has only limited benefit in provenance studies unless the samples were analysed under strict grain-size control.The data can be modelled by linear regression with two components: (i) a linear trend describing preferential enrichment of phyllosilicates at the expense of quartz and feldspar towards finer fractions, and (ii) some breaks at certain grain-size thresholds. Due to the observed step functions the model describes a four-step enrichment-depletion pattern that is largely similar for the two source-rock cases: feldspar is highest in the very coarse to medium sand fraction; quartz is highest in very fine sand; epidote, garnet, hornblende, apatite are highest and plagioclase is relatively high in the silt range; sheet silicates (chlorite, biotite, muscovite) are highest in the clay fraction. The observed pattern describes the process of comminution, i.e. the impact of mechanical forces on minerals with contrasting durability: the most durable minerals like quartz are concentrated close to their inherited grain-sizes while less durable minerals are enriched in silt fractions, and least durable minerals (i.e. sheet silicates) are enriched in the very fine silt to clay fractions. The latter, not chemical weathering causes an increase in chemical index of alteration (CIA) values up to ~63 at the finest grain-size grades. The model provides a quantitative description of the composition to grain-size relations and is thought to form a valuable module for building comprehensive sediment generation models that describe the entire network of sediment production processes from source to sink.

Sediment export from French rivers to the sea

ABSTRACTKnowledge of sediment exports from continental areas is essential for estimating denudation rates and biogeochemical cycles. However, the estimation of current sediment fluxes to the sea is often limited by the availability and quality of sediment discharge data. This study aims to quantify the relative contributions of French rivers to the sediment discharge to the ocean. Sediment fluxes were assessed using the French river quality database, which is characterized by a low temporal resolution but long‐term measurement periods. An improved rating curve approach (IRCA) using daily discharge data, which allows the estimation of mean annual sediment loads from infrequent sediment concentration data, was used to calculate sediment fluxes. The resulting mean annual sediment loads show that French rivers export c. 16.21 Mt yr‐1 of sediments to the sea. Among the 88 defined French rivers flowing to the sea, the four largest basins (Loire, Rhone, Garonne and Seine) export 13.2 Mt yr‐1, which corresponds to 81.3% of total exports. No relationship was found between the mass of exported sediment and the size of the drainage basins. This is due to the variety of river basin typologies among these rivers, including lowland rivers in temperate climates, such as the Seine on the one hand and rivers draining mountainous areas in Alpine/Mediterranean areas on the other hand, such as the Rhone. The latter contributes 60% to the total sediment export for France while its drainage area is only 19% of the total area considered. Differences between the river basins considered are also shown by temporal indicators describing the duration of the exports, which may be linked with sediment production processes over drained areas. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Preliminary modelling of sediment production and delivery in the Xihanshui River basin, Gansu, China

Abstract This paper outlines an analysis of the spatial distribution of sediment production, delivery and yield in the Xihanshui River basin, South Gansu, China, using the modelling tools of SedNet (Prosser et al., 2001). This model can assess the delivery efficiency to downstream locations, as well as identifying locations with high rates of sediment production. Preliminary model experiments assist understanding of the spatial dynamics of these sediment processes and evaluation of the effectiveness of soil conservation practices since the mid-1980s. Three scenario years (dry, average and wet) from the 1983–2005 record are identified and modelled, and land use and management are represented in the model to reflect known changes since the 1980s. Results show hillslope erosion to be a dominant source of sediment supply, causing the latter to decrease ten-fold between 1984 and 1997/2000. Estimated bank erosion and floodplain deposition rates are sensitive to parameter values, but bank erosion appears less sensitive than hillslope supply to rainfall. The model can be used to assess net changes in floodplain storage; for default parameters, floodplain deposition rates are 25–200 times the rates of bank erosion depending on the climate scenario. Comparing simulation results with measured sediment yields at the three gauging stations indicates encouraging agreement in 2000. In 1984 (the wet year), the model under-predicts, suggesting that additional unmodelled sediment production processes, especially mass movement and gully erosion, may be important in wet years. Mass movement inventory data could close the gap between the high yields measured in the wet scenario year and the estimated yield due to hillslope erosion alone. In 1997 (the dry year), the model over-predicts; this suggests that the land use change parameters required to reflect the effects of conservation may not have been sufficient, implying that conservation has been generally effective, and that evidence of declining sediment yield is not simply a reflection of drier conditions.

Erosion caused by hyperconcentrated flow on the Loess Plateau of China

Hyperconcentrated flows are widely observed in the middle Yellow River basin. They occur as a result of erosion, but once they form on slopes, they operate as a strong eroding and sediment-carrying force and play an important role in drainage basin erosion and sediment production processes. Since the energy expenditure is less and sediment-carrying capacity is greater, hyperconcentrated flows have very high eroding and transporting abilities. There exists a strong coupling relation between hyperconcentrated flow transport and gravitational erosion, which ensures a rapid removal of mass-wasted materials. Hyperconcentrated flows are an important factor responsible for the high-intensity erosion and sediment yield in the middle Yellow River basin. Many previous studies have indicated that the sediment delivery ratio on the Loess Plateau approaches 1. This can be explained by the action of hyperconcentrated flows. As hyperconcentrated flows exhibit some particular behaviors in erosion and sediment production processes, the present study suggests that the erosion by hyperconcentrated flows be regarded as a special type of erosion. Accordingly, some countermeasures are proposed to control hyperconcentrated flows and the resulting erosion.