Sediment Delivery Rates Research Articles

Tank 모형을 이용한 동해안 오십천 하구의 유사량 평가에 관한 연구

본 연구에서는 유량 및 유사량 자료가 부족한 미계측 유역에 대해 Tank모형을 확장하여 궁극적으로 유사량을 평가하는 방법을 제시하였다. 적용 유역은 동해안 타 유역에 비해 유량자료가 확보되어 있는 오십천을 대상으로 집중호우기의 토사유출 특징과 하천의 토사유달률을 구하였다. 본 연구의 주요 결과는 다음과 같다. 1) 실측에 의한 유사량의 산정에 있어서는 먼저 유사량 관계식(sediment rating curve)의 개발이 선행되어야 한다. 본 연구에서는 유량 산정지점에 대해 유량과 병행하여 유사량 관계식을 다음과 같이 구하였다. 오십천 유량-유사량 관계식 : <TEX>$Q_s=6.017Q^{1.374}$</TEX> 2) Tank모형을 적용하여 2006년 강우유출량을 산정한 결과 관측값과 유사한 값(<TEX>$RMSE=1.26m^3/day$</TEX>)을 얻을 수 있었다. 3) 대상지역의 2006년과 2009년의 연평균 토사전달율 을 비교한 결과 태풍에 따른 집중강우가 있었던 2006년의 토사전달율이 평년의 2009년에 비해 현저하게 높았는데 이는 급격한 강우유출량의 증가에 따른 것이라 보인다. 4) 개량된 Tank모형에 의한 유량 및 토사유출량은 기존의 SRC방법과 비교했을 경우 유사한 경향을 보였으며 이는 향후 유량과 유사량 자료가 부족한 유역에 대해 효과적으로 적용할 수 있을 것으로 본다. BACKGROUND: A large scale of sediment load delivered from watershed causes substantial waterway damages and water quality degradation. Controlling sediment loading requires the knowledge of the soil erosion and sedimentation. The various factors such as watershed size, slope, climate, land use may affect sediment delivery processes. Traditionally sediment delivery ratio prediction equations have been developed by relating watershed characteristics to measured sediment yield divided by predicted gross erosion. However, sediment prediction equations have been developed for only a few regions because of limited sediment data. Besides, little research has been done on the prediction of sediment delivery ratio for asia monsoon period in mountainous watershed. METHODS AND RESULTS: In this study Tank model was expanded and applied for estimating sediment yield to Oship River of east coast. The rainfall-runoff in 2006 was verified using the Tank model and we derived good result between observed and calculated discharge in 2009 at the same conditions. In relation to sediment yield, the sediment delivery rate of 2006 was very high than 2009 regardless of methods for estimating sediment load. It was thought to be affected by heavy rainfall due to the typhoon. CONCLUSION(s): For estimating sediment volume from watershed, long-term monitoring data on discharge and sediment is needed. This model will be able to apply to predict discharge and sediment yield simultaneously in ungauged area. This approach is more effective and less expensive method than the traditional method which needs a lot of data collection.

Late Cenozoic erosion of the high-latitude southwestern Barents Sea shelf revisited

Research Article| January 01, 2012 Late Cenozoic erosion of the high-latitude southwestern Barents Sea shelf revisited Jan Sverre Laberg; Jan Sverre Laberg † Department of Geology, University of Tromsø, N-9037 Tromsø, Norway †E-mail: jan.laberg@uit.no Search for other works by this author on: GSW Google Scholar Karin Andreassen; Karin Andreassen Department of Geology, University of Tromsø, N-9037 Tromsø, Norway Search for other works by this author on: GSW Google Scholar Tore O. Vorren Tore O. Vorren Department of Geology, University of Tromsø, N-9037 Tromsø, Norway Search for other works by this author on: GSW Google Scholar GSA Bulletin (2012) 124 (1-2): 77–88. https://doi.org/10.1130/B30340.1 Article history received: 22 May 2010 rev-recd: 31 Jan 2011 accepted: 20 Feb 2011 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jan Sverre Laberg, Karin Andreassen, Tore O. Vorren; Late Cenozoic erosion of the high-latitude southwestern Barents Sea shelf revisited. GSA Bulletin 2012;; 124 (1-2): 77–88. doi: https://doi.org/10.1130/B30340.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The southwestern Barents Sea has experienced profound erosion during the last ∼2.7 m.y. that has resulted in the development of a characteristic glacial morphology of the continental shelf and deposition of a several-kilometer-thick sediment fan along the western margin prograding into the deep sea. In the period from ca. 2.7 to 1.5 Ma, proglacial processes, including fluvial and glaciofluvial erosion, dominated. For this period, the total average erosion of the shelf was 170–230 m, the average erosion rate was 0.15–0.2 mm/yr, and the average sedimentation rates on the fan were 16–22 cm/k.y. Subglacial erosion affected an area of ∼575,000 km2 during the period from ca. 1.5 to 0.7 Ma. Total average erosion is estimated at 330–420 m for this interval, and the average erosion rate was 0.4–0.5 mm/yr. Average sedimentation rates were 50–64 cm/k.y. During the last ∼0.7 m.y., glacial erosion mainly has occurred beneath fast-flowing paleo–ice streams topographically confined to troughs (∼200,000 km2). The total average erosion is estimated at 440–530 m, average erosion rate is 0.6–0.8 mm/yr, and average sedimentation rate on the continental slope is 18–22 cm/k.y. The amount of erosion was mainly determined by the duration of the glaciations and the location, velocity, and basal properties of the ice streams. In total, glacial erosion of the troughs has been relatively high throughout the last ∼2.7 m.y. at ∼1000–1100 m. For the banks, erosion is inferred to have increased from ca. 2.7 Ma to a peak between 1.5 and 0.7 Ma. Subsequently, little erosion occurred in these areas, which implies a total of 500–650 m of erosion. Compared with other high-latitude areas, our rates are among the highest so far reported. This comparison also demonstrates that there have been large variations in the rate of sediment delivery to the glaciated continental margins. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Post-fire changes in sediment rating curves in a wet Eucalyptus forest in SE Australia

Summary Empirical power law sediment rating curves of the form C = aQb (where C is the sediment concentration, Q is the discharge rate, and the coefficient a and exponent b are fitted parameters), or the alternative form given by log(Qs) = log(a) + (b + 1)log(Q) (where Qs = CQ is the sediment delivery rate, and the natural logarithm is used) are widely used for characterising sediment transport across a broad range of spatial and temporal scales. Fire frequently has a large effect on erosion rates and sediment delivery. We investigate the temporal changes in the coefficient a and exponent b for 3 years following a wildfire between February 2003 and April 2006, for two South Eastern Australian Eucalyptus forested catchments (136 and 244 ha) with mean annual rainfall of 1900 mm. Storm-event integrated sediment loads and discharges were calculated for each of 596 storm events using stage-discharge control structures and in situ turbidity measurements at 15 min intervals. Measurements were converted to sediment concentrations using regression relationships developed from storm activated water auto-samplers. The analysis identified: (i) strong negative linear relationships between the rating coefficient log(a), and the rating exponent b, reflecting sediment rating curves that “pivot” around a common fulcrum point in log–log space, (ii) a systematic shift in this linear relationship between log(a) and b as a function of time since fire, (iii) maximum values of b of ca. 2.5 (i.e. maximum non-linearity in the relationship between discharge and sediment delivery, and therefore maximum sensitivity to high peak-discharge events) immediately following the fire, which decline rapidly and monotonically by a factor of 10 to ca. 0.25 in the first 8 months, attributed to a dominance of hillslope erosion processes and declining rill and interill erodibility, (iv) irregular patterns in the value of b during the vegetation recovery period, probably reflecting a shift from hillslope dominated erosion processes to a greater contribution from channel processes (8–24 months after the fire) and (v) annual cycles in the value of b in the recovered state (24–38 months after the fire) ranging from a minimum of ca. 0.5 in the dry season to a maximum of ca. 1.5 in the wet season. The physical cause of these cycles could not be isolated in this study. The results provide a robust quantitative perspective on the magnitude and temporal variability of the sensitivity of catchments recovering from wildfire.

Rapid wetland expansion during European settlement and its implication for marsh survival under modern sediment delivery rates

Fluctuations in sea-level rise rates are thought to dominate the formation and evolution of coastal wetlands. Here we demonstrate a contrasting scenario in which land-use–related changes in sediment delivery rates drive the formation of expansive marshland, and vegetation feedbacks maintain their morphology despite recent sediment supply reduction. Stratigraphic analysis and radiocarbon dating in the Plum Island Estuary (Massachusetts, United States) suggest that salt marshes expanded rapidly during the eighteenth and nineteenth centuries due to increased rates of sediment delivery following deforestation associated with European settlement. Numerical modeling coupled with the stratigraphic observations suggests that existing marshland could survive, but not form under the low suspended sediment concentrations observed in the estuary today. These results suggest that many of the expansive marshes that characterize the modern North American coast are metastable relicts of high nineteenth century sediment delivery rates, and that recent observations of degradation may represent a slow return to pre-settlement marsh extent. In contrast to ecosystem management practices in which restoring pre-anthropogenic conditions is seen as a way to increase ecosystem services, our results suggest that widespread efforts to restore valuable coastal wetlands actually prevent some systems from returning to a natural state.

A Rangeland Hydrology and Erosion Model

Soil loss rates on rangelands are considered one of the few quantitative indicators for assessing rangeland health and conservation practice effectiveness. An erosion model to predict soil loss specific for rangeland applications is needed because existing erosion models were developed from croplands where the hydrologic and erosion processes are different, largely due to much higher levels of heterogeneity in soil and plant properties at the plot scale and the consolidated nature of the soils. The Rangeland Hydrology and Erosion Model (RHEM) was designed to fill that need. RHEM is an event-based derivation of the WEPP model made by removing relationships developed specifically for croplands and incorporating new equations derived from rangeland data. RHEM represents erosion processes under disturbed and undisturbed rangeland conditions, it adopts a new splash erosion and thin sheet-flow transport equation developed from rangeland data, and it links the model hydrologic and erosion parameters with rangeland plant communities by providing a new system of parameter estimation equations based on 204 plots at 49 rangeland sites distributed across 15 western U.S. states. RHEM estimates runoff, erosion, and sediment delivery rates and volumes at the spatial scale of the hillslope and the temporal scale of a single rainfall event. Experiments were conducted to generate independent data for model evaluation, and the coefficients of determination (r2) for runoff and erosion predictions were 0.87 and 0.50, respectively, which indicates the ability of RHEM to provide reasonable runoff and soil loss prediction capabilities for rangeland management and research needs.

The kinematics of ancient tidewater ice margins: criteria for recognition from grounding-line moraines

Abstract Modern studies indicate that the kinematic behaviour of tidewater glaciers is a crucial part of ice-sheet dynamics. A similar relationship may be expected for ancient ice sheets, but can the kinematics of ancient tidewater ice margins be recognized? The paper addresses this methodological issue by pointing to the high-resolution stratigraphic record of marine moraines, thus far little explored. On the basis of a series of case studies, a range of field criteria are proposed for the recognition of short-term grounding-line movement and possible oscillations in moraine outcrop sections. The method combines allostratigraphic mapping and architectural facies analysis of the moraine sedimentary units formed during glacier advance, subaqueous stillstand and eventual subaerial stillstand, with recognition of the successive ice-contact surfaces. The stacking architecture of the sedimentary units and their ice-contact bounding surfaces reveal the time–distance trajectory of the grounding-line positions. It is also possible to recognize changes in the mode and rate of subglacial sediment delivery, as well as fluctuations in the ice flux and meltwater discharge. This methodology invites detailed studies of marine moraines. Systematic case studies on a regional scale may provide new information on the behaviour of tidewater ice margins and lead to unprecedented insights into the dynamics of ancient ice sheets.

Rivers in Australia

As a continent, Australia is unusual. It has a long history of habitation by a relatively small population of Aboriginals with a low technology culture. Just over 200 years ago, in 1788, it was invaded by a technological society from the UK, and the settlers brought with them an understanding of rivers and the landscapes in which they were situated which was quite at odds with the reality of the Australian continent. Australia is a piece of old continental crust derived from the break-up of Gondwana that, unlike other Gondwana continents, has experienced little tectonic modification since the break-up. It is a low relief continent dominated by arid and semi arid climates. Australian river systems have poor slope-channel coupling and poor hydrological connectivity and are characterized by low rates of sediment delivery. The flow of Australian rivers has high interannual variability, two to three times that of comparable rivers elsewhere, and highly variable flood behavior. In this paper, examples are given of particular Australian rivers to illustrate the manner in which the morphological and climatic characteristics of the continent combine to produce some distinctive river systems.

Channel variations of the different channel pattern reaches in the lower Yellow River from 1950 to 1999

The Yellow River is widely known as a “hanging river” due to its high sedimentation rate (the current channel bed is about 2.74 m higher than the overbank plains on average) in the lower reach. Understanding the variations in channel patterns and their influencing factors is crucial to regulate potential flooding risk in this critical region. Changes in discharge, suspended sediment delivery rate, median grain size, sedimentation rate, channel planform and cross-section, and channel width/depth ratio during 1950–1999 from gauging stations in Huayuankou, Gaocun-Sunkou and Lijin that represent the braided, meandering and straight channel sections, respectively, were compared. During this period, frequent internal channel variations dominated in the braided channel section. The channel bed was continuously raised as a whole, but experienced strong erosion in certain times, mainly influenced by the operation and closure of the Sanmenxia Dam. The straight channel section was relatively stable due to restricted lateral migration by the solid artificial levees in both banks. Instead, channel aggradation was the dominant process and erosion only happened when channel avulsions occurred in the river mouth. The meandering channel section between the upstream braided and downstream straight channel sections was formed as a result of stream self-adjustment. Rapid lateral migrations were observed during this period, but the extent of the migration was restricted by artificial levees. Sediment aggradation on the channel bed and floodplain was apparent. Since 1970, the channel shrank remarkably in all sections due to the increased use of water resources and the decreased precipitation in the Yellow River basin. Recently, migration of the channel is limited, and the lower portion of the braided section seems to be a meandering channel.

Holocene sediment accretion in the Trinity River delta, Texas, in relation to modern fluvial input

Purpose This study uses sediment cores to quantify Holocene sedimentation rates in the Trinity River delta, Texas. An important question is whether modern fluvial sediment input from the Trinity River is adequate to sustain sedimentation in the delta, thereby combating subsidence and further wetland loss. Our objective was to quantify sedimentation rates within the delta in order to assess whether the delta is in- or out-of-phase with modern sediment delivery rates.

Rates of sediment delivery from the Fennoscandian Ice Sheet through an ice age

Sediment delivery rates through an entire ice age are investigated using seismic records of glacial erosion products from the Fennoscandian Ice Sheet deposited offshore of mid-Norway in the 2.7 m.y. old Naust Formation (volume 100,000 km 3 ). The mean sedimentation rate over the ice age is ∼0.24 m k.y. −1 , with bedrock lowering of ∼520 m in the ice-sheet catchment. The mean sediment delivery is 2–3 times higher for the most recent 600 k.y. than for earlier Naust sequences. The hypothesis that glacial erosion is most rapid early in an ice age, when there was presumably much weathered bedrock and preglacial sediment available, is not accepted for our study area. More important are changing ice-sheet dimensions and dynamics, varying intensity of individual glacial cycles, and complex ice-sheet dynamics in single deglaciations. The mean rate of sediment delivery from ice sheets is an order of magnitude higher than from fluvial activity in the huge Amazon and Mississippi systems, implying that ice is a very effective agent of long-term denudation during cold periods of Earth history.

Balancing corn stover harvest for biofuels with soil and water conservation

The emerging cellulosic biofuel industry offers both challenges and opportunities for conserving soil and water resources in an agriculturally productive environment. Crop residues are North America9s most important soil and water conservation resource and concurrently will be the most important feedstock for the emerging cellulosic biofuels industry. This analysis of factors affecting water-induced soil erosion, soil carbon maintenance, and water quality in the emerging cellulosic bioenergy industry identifies a variety of critical issues likely to both directly and indirectly lead to greater degradation of these resources. Pressing issues are also identified for scientific research and for policy analysis. Research should determine more precisely the erosion rates and sediment delivery rates of different biomass cropping systems, determine the acceptable rates of residue removal for different crops and soils in the face of more frequent extreme rainfall events, describe how those removal rates vary spatially across the landscape, develop the harvest technology that removes residue at these rates, and develop a suite of conservation practices appropriate for use with crop residue harvest. Policy analysis should examine land ownership and management patterns to develop a policy environment in which conservation practices are encouraged, or at least not discouraged. A framework must be developed to oversee and insure that residue removal rates are not abusive to soil and water resources.

Online Interactive U.S. Reservoir Sedimentation Survey Database

In April 2009, the U.S. Geological Survey and the Natural Resources Conservation Service (prior to 1994, the Soil Conservation Service) created the Reservoir Sedimentation Survey Database (RESSED) and Web site, the most comprehensive compilation of data from reservoir bathymetric and dry basin surveys in the United States. RESSED data can be useful for a number of purposes, including calculating changes in reservoir storage characteristics, quantifying rates of sediment delivery to reservoirs, and estimating erosion rates in a reservoir's watershed.

Holocene sediment budgets for upland catchments: The problem of soilscape model and data availability

Abstract This study presents a Holocene sediment budget for the upland catchment of the Speyerbach in the Palatinate Forest, southwestern Germany. The influences of both, data availability and the choice of an appropriate soilscape model on the sediment budget calculations are investigated. For budget calculations the spatial distribution of soils was derived from the soil map 1:50,000. Thickness values of soil truncation and colluvial burial were extracted from two soil data sets with varying information content. Data processing contained a disaggregation of the soil map with the help of land use data. In order to model the sediment budget a reference soil thickness (a so-called soilscape model), which represents the initial conditions is necessary. As upland soils are developed in periglacial solifluction sheets, the main solifluction sheet (MSS, “Hauptlage”) showing a constant thickness and being affected by soil forming processes was chosen. Determining the initial thickness of the MSS is a crucial point, as a comparison of reference values shows. The literature values are actual thicknesses and differ significantly between 30 and 100 cm among various studies. Therefore a statistical model using the local profile descriptions of the soil database for the Speyerbach catchment was set up. We found that the 95 percentile worked best to extract the depths of pristine soils. Hence, a pristine soil profile depth of 60 or 70 cm could be extracted for the Speyerbach catchment. Calculating the sediment budget for 60 cm returns a sediment delivery rate (SDR) of 64.8%. With a soilscape model of 70 cm a catchment SDR of 83.2% can be derived, which is 18.4% higher than the first one. The computed SDR is twice as high as the SDR determined by Houben et al. [Houben, P., Burggraaf, P., Hoffmann, T., Kleefeld, K., Zimmermann, A., Dikau, R., 2007. Reconstructing Holocene land-use change and sediment budgets in the Rhine system. PAGES News 15 (1), 17–18.] and Rommens et al. [Rommens, T., Verstraeten, G., Poesen, J., Govers, G., Van Rompaey, A.J.J., Peeters, I., Lang, A., 2005. Soil erosion and sediment deposition in the Belgian loess belt during the Holocene: establishing a sediment budget for a small agricultural catchment. The Holocene 15 (7), 1032–1043.]. This may reflect differences in physio-geographical settings and settlement history between a loess covered basin catchment and a deeply furrowed upland catchment. Since no datings or proxy data are available, the classification to individual settlement periods and furthermore an estimation of human impact is not possible yet. Future work will address the estimation of human impact by the analysis of historical data and datings of colluvial layers as well as a field validation of the computed sediment budgets.

Radiocarbon-derived sedimentation rates in the Gulf of Mexico

Abstract Sedimentation rates were determined for the northern Gulf of Mexico margin sediments at water depths ranging from 770 to 3560 m, using radiocarbon determinations of organic matter. Resulting sedimentation rates ranged from 3 to 15 cm/kyr, decreasing with increasing water depth. These rates agree with long-term sedimentation rates estimated previously using stratigraphic methods, and with estimates of sediment delivery rates by the Mississippi River to the northern Gulf of Mexico, but are generally higher by 1–2 orders of magnitude than those estimated by 210Pbxs methods. Near-surface slope sediments from 2737 m water depth in the Mississippi River fan were much older than the rest. They had minimum 14C ages of 16–27 kyr and δ13C values ranging from −24‰ to −26.5‰, indicating a terrestrial origin of organic matter. The sediments from this site were thus likely deposited by episodic mass wasting of slope sediment through the canyon, delineating the previously suggested main pathway of sediment and clay movement to abyssal Gulf sediments.

Clastic sediment flux to tropical Andean lakes: records of glaciation and soil erosion

We developed records of clastic sediment flux to 13 alpine lakes in Peru, Ecuador, and Bolivia, and compared these with independently dated records of regional glaciation. Our objectives are to determine whether a strong relationship exists between the extent of ice cover in the region and the rate of clastic sediment delivery to alpine lakes, and thus whether clastic sediment records serve as reliable proxies for glaciation during the late Pleistocene. We isolated the clastic component in lake sediment cores by removing the majority of the biogenic and authigenic components from the bulk sediment record, and we dated cores by a combination of radiocarbon and tephrochronology. In order to partially account for intra-basin differences in sediment focusing, bedrock erosivity, and sediment availability, we normalized each record to the weighted mean value of clastic sediment flux for each respective core. This enabled the stacking of all 13 lake records to produce a composite record that is generally representative of the tropical Andes. There is a striking similarity between the composite record of clastic sediment flux and the distribution of ∼100 cosmogenic radionuclide (CRN) exposure ages for erratics on moraine crests in the central Peruvian and northern Bolivian Andes. The extent of ice cover thus appears to be the primary variable controlling the delivery of clastic sediment to alpine lakes in the region, which bolsters the increasing use of clastic sediment flux as a proxy for the extent of ice cover in the region. The CRN moraine record and the stacked lake core composite record together indicate that the expansion of ice cover and concomitant increase in clastic sediment flux began at least 40 ka, and the local last glacial maximum (LLGM) culminated between 30 and 20 ka. A decline in clastic sediment flux that began ∼20 ka appears to mark the onset of deglaciation from the LLGM, at least one millennium prior to significant warming in high latitude regions. The interval between 20 and 18 ka was marked by near-Holocene levels of clastic sediment flux, and appears to have been an interval of much reduced ice extent. An abrupt increase in clastic sediment flux 18 ka heralded the onset of an interval of expanded ice cover that lasted until ∼14 ka. Clastic sediment flux declined thereafter to reach the lowest levels of the entire length of record during the early–middle Holocene. A middle Holocene climatic transition is apparent in nearly all records and likely reflects the onset of Neoglaciation and/or enhanced soil erosion in the tropical Andes.

Trapping Efficiencies of Cultivated and Natural Riparian Vegetation of Northern Laos

In northern Laos, intensification of cultivation on sloping land leads to accelerated erosion processes. Management of riparian land may counteract the negative impacts of higher sediment delivery rates on water quality. This study assessed water and sediment concentration trapping efficiencies of riparian vegetation in northern Laos and the effect of cultivation of riparian land on water quality. Runoff flowing in and out of selected riparian sites was monitored by means of open troughs. In 2005, two native grass, two bamboo, and two banana sites were monitored. In 2006, adjacent to steep banana, bamboo, and native grass sites, three upland rice sites were established and monitored. Water trapping efficiency (WTE) and sediment concentration trapping efficiency (SCTE) were calculated on an event basis; means and 95% confidence intervals (CIs) were estimated with a bootstrapping approach. Confidence intervals were large and overlapping among sites. Seepage conditions severely limited trapping efficiency. Native grass resulted in the highest WTE (95% CI, -0.10 to 0.23), which was not significantly different from zero. Banana resulted in the highest SCTE (95% CI, 0.06-0.40). Bamboo had negative WTE and SCTE. Median outflow runoff from rice sites was nine times the inflow. Median outflow sediment concentration from rice sites was two to five times that of their adjacent sites and two to five times the inflow sediment concentration. Although low-tillage banana plantation may reduce sediment concentration of runoff, cultivation of annual crops in riparian land leads to delivery of turbid runoff into the stream, thus severely affecting stream water quality.

A major trough-mouth fan on the continental margin of the Bellingshausen Sea, West Antarctica: The Belgica Fan

A 330-km length of the little known continental shelf edge and slope of the Bellingshausen Sea, West Antarctica, is investigated using multibeam swath-bathymetric and sub-bottom profiler evidence. The shelf break is at 650–700 m across the 150-km wide Belgica Trough, and to either side is about 500 m. When full-glacial ice advanced across the shelf to reach the shelf break, it was partitioned into fast- and slow-flowing elements, with an ice stream filling the trough. This had important consequences for the nature and rate of sediment delivery to the adjacent continental slope. Off Belgica Trough, the upper continental slope has convex-outward contours indicating a major sedimentary depocentre of gradient 1–2°. Acoustic profiles and cores from the depocentre show a series of diamictic glacigenic debris flows. The depocentre is interpreted as a trough-mouth fan, built largely by debris delivered from the ice stream. The slope is steeper beyond the trough margins at up to 6°. The main morphological features on the Bellingshausen Sea slope are gully systems and channels. Major canyons and Late Quaternary slides are absent. Most gullies and channels are found on the fan. Gullies are about 15–25 m deep, a few hundred metres wide and some are > 25 km long. The largest channel is over 60 km long, about a kilometre wide and 10 to 15 m deep. The channels provide pathways for sediment by-passing of the upper slope and transfer to the continental rise and beyond by turbidity currents. Gullies on the Bellingshausen Sea margin cut through debris flows on the slope. Assuming the debris flows are linked mainly to downslope transport of diamictic debris when ice was at the shelf edge under full-glacial conditions, then those gullies cut into them formed during deglaciation. Belgica Fan is > 22,000 km 2 in area and about 60,000 km 3 in volume. It is the largest depocentre identified to date on the continental margin of the West Antarctic Ice Sheet, fed by an interior ice-sheet basin of approximately 200,000 km 2.

Soil loss risk and habitat quality in streams of a meso-scale river basin

Soil loss expectation and possible relationships among soil erosion, riparian vegetation and water quality were studied in the São José dos Dourados River basin, State of São Paulo, Brazil. Through Geographic Information System (GIS) resources and technology, Soil Loss Expectation (SLE) data obtained using the Universal Soil Loss Equation (USLE) model were analyzed. For the whole catchment area and for the 30 m buffer strips of the streams of 22 randomly selected catchments, the predominant land use and habitat quality were studied. Owing mainly to the high soil erodibility, the river basin is highly susceptible to erosive processes. Habitat quality analyses revealed that the superficial water from the catchments is not chemically impacted but suffers physical damage. A high chemical purity is observed since there are no urban areas along the catchments. The water is physically poor because of high rates of sediment delivery and the almost nonexistence of riparian vegetation.

River Enhancement in the Upper Mississippi River Basin: Approaches Based on River Uses, Alterations, and Management Agencies

Abstract The Upper Mississippi River is characterized by a series of locks and dams, shallow impoundments, and thousands of river channelization structures that facilitate commercial navigation between Minneapolis, Minnesota, and Cairo, Illinois. Agriculture and urban development over the past 200 years have degraded water quality and increased the rate of sediment and nutrient delivery to surface waters. River enhancement has become an important management tool employed to address causes and effects of surface water degradation and river modification in the Upper Mississippi River Basin. We report information on individual river enhancement projects and contrast project densities, goals, activities, monitoring, and cost between commercially non‐navigated and navigated rivers (Non‐navigated and Navigated Rivers, respectively). The total number of river enhancement projects collected during this effort was 62,108. Cost of all projects reporting spending between 1972 and 2006 was about US$1.6 billion. Water quality management was the most cited project goal within the basin. Other important goals in Navigated Rivers included in‐stream habitat improvement and flow modification. Most projects collected for Non‐navigated Rivers and their watersheds originated from the U.S. Department of Agriculture (USDA). The U.S. Army Corps of Engineers and the USDA were important sources for projects in Navigated Rivers. Collaborative efforts between agencies that implement projects in Non‐navigated and Navigated Rivers may be needed to more effectively address river impairment. However, the current state of data sources tracking river enhancement projects deters efficient and broad‐scale integration.

Reconceptualising coarse sediment delivery problems in rivers as catchment-scale and diffuse

This paper assesses river channel management activities in the context of the interaction between coarse sediment delivery, climate change, river channel response and flood risk. It uses two main sources of evidence: (1) an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods; and (2) a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network. The field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself. Extreme events, that could occur at any time in the year (i.e. they are not dependent on wet antecedent conditions), were crucial for sediment delivery. However, sustained high river flows were responsible for the majority of transfer within the river itself. Application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s, regardless of the climate downscaling scenario used. First approximations suggested that this would translate into annual bed level aggradation rates of between 0.10 and 0.20 m per year in the downstream main channel reaches. Second, the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in-channel simulation with river flows scaled for climate change to the 2050s and 2080s. Short-term sedimentation could result in similar magnitude increases in inundated area for 1 in 0.5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude. Finally, we were able to develop an alternative approach to river management in relation to coarse sediment delivery, based upon reducing the rates of coarse sediment delivery through highly localised woodland planting, under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem. Thus, the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process, with a much more explicit focus on the catchment scale, if our river systems are to become more insulated from the impacts of future climate changes.