Tons Of Sediment Research Articles

Using diamond-mined sediment discharges to test the paradigms of sandy-beach ecology

The prevailing view of sandy-shore ecosystems is that they are controlled largely by physical conditions, particularly particle size, slope and wave regime, but it is rarely possible to test this view by experimentally manipulating these attributes. We report a unique opportunity to accomplish this because large-scale alteration of these properties has taken place on the Namibian coast, associated with diamond mining. Elizabeth Bay diamond mine, near Lüderitz, started modern operations in 1991. Since then, 30.8 million tonnes of sediment with a particle size (<1.4 mm) coarser than the native beach sand have been discharged as slurry onto the beach as part of the treatment process. The physical and biological effects of this were monitored on seven occasions between 1993 and 2012, spanning three phases: (1) an initial pre-upgrade phase (1994–2004) with discharges of moderate intensity; (2) doubling of discharges during upgrade of the mine (2005–2008); (3) temporary cessation of mining (2009–2011). These vicissitudes resulted in both spatial and temporal physical changes, including massive beach accretion (350–620 m), overall increases in mean sand particle size and slope and decreases in Dean's Parameter, east-to-west gradients in beach slope, wave height and erosion, and changes in the beach state from dissipative towards reflective conditions. Alteration of physical conditions led to significant macrofaunal changes, with the community structure in the centre of the bay opposite the discharge points shifting from a state dominated by sand mussels to one dominated by peracarid crustaceans, accompanied by reductions in diversity, biomass and abundance. Grossebucht, which lies nearby and is not mined, provided comparative reference samples: physical conditions there changed little, and biotic communities were constant, significantly more diverse and had greater abundances and biomasses than at Elizabeth Bay. The changes in physical conditions and ensuing biological responses confirmed the prevailing paradigm that sandy beaches are physically driven, with diversity, abundance and biomass all declining at places and times where sediment particle size and beach slope increased due to sediment inputs.

Transport of the river load from the Błądzikowski stream to the puck lagoon (southern Baltic Sea, Poland)

Abstract The main aim of this study was to determine the size of the load carried by the Błądzikowski Stream and discharged into the Puck Lagoon, and the role of the river load in the formation of the sea bed deposits at the stream mouth. The Błądzikowski Stream, with the length of only 10 km, discharges about 610 tons of sediment into the Puck Lagoon per year, including 89.8% (548 tons) of the bed load and 10.2% (62 tons) of the suspended load. The amount is 4.9% of the river load discharged into the Puck Lagoon. Mineral particles are more common in the composition of the river load and account for 94.6% of the suspended load and 98.7% of the bed load. It is mainly the bed load deposited in the estuarine area that creates a contemporary underwater accumulation form in the Puck Lagoon, which is corroborated by the granulometric composition of the channel and surface sediments; the suspended load is carried further into the Lagoon.

Sediment transport along the Cap de Creus Canyon flank during a mild, wet winter

Abstract. Cap de Creus Canyon (CCC) is known as a preferential conduit for particulate matter leaving the Gulf of Lion continental shelf towards the slope and the basin, particularly in winter when storms and dense shelf water cascading coalesce to enhance the seaward export of shelf waters. During the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) cruise in March 2011, deployments of recording instruments within the canyon and vertical profiling of the water column properties were conducted to study with high spatial-temporal resolution the impact of such processes on particulate matter fluxes. In the context of the mild and wet 2010–2011 winter, no remarkable dense shelf water formation was observed. On the other hand, the experimental setup allowed for the study of the impact of E-SE storms on the hydrographical structure and the particulate matter fluxes in the CCC. The most remarkable feature in terms of sediment transport was a period of dominant E-SE winds from 12 to 16 March, including two moderate storms (maximum significant wave heights = 4.1–4.6 m). During this period, a plume of freshened, relatively cold and turbid water flowed at high speeds along the southern flank of the CCC in an approximate depth range of 150–350 m. The density of this water mass was lighter than the ambient water in the canyon, indicating that it did not cascade off-shelf and that it merely downwelled into the canyon forced by the strong cyclonic circulation induced over the shelf during the storms and by the subsequent accumulation of seawater along the coast. Suspended sediment load in this turbid intrusion recorded along the southern canyon flank oscillated between 10 and 50 mg L−1, and maximum currents speeds reached values up to 90 cm s−1. A rough estimation of 105 tons of sediment was transported through the canyon along its southern wall during a 3-day-long period of storm-induced downwelling. Following the veering of the wind direction (from SE to NW) on 16 March, downwelling ceased, currents inside the canyon reversed from down- to up-canyon, and the turbid shelf plume was evacuated from the canyon, most probably flowing along the southern canyon flank and being entrained by the general SW circulation after leaving the canyon confinement. This study highlights that remarkable sediment transport occurs in the CCC, and particularly along its southern flank, even during mild and wet winters, in absence of cascading and under limited external forcing. The sediment transport associated with eastern storms like the ones described in this paper tends to enter the canyon by its downstream flank, partially affecting the canyon head region. Sediment transport during these events is not constrained near the seafloor but distributed in a depth range of 200–300 m above the bottom. Our paper broadens the understanding of the complex set of atmosphere-driven sediment transport processes acting in this highly dynamic area of the northwestern Mediterranean Sea.

Mountains on the Market: Industry, the Environment, and the South by Randal L. Hall (review)

Reviewed by: Mountains on the Market: Industry, the Environment, and the South by Randal L. Hall Robert Gudmestad (bio) Mountains on the Market: Industry, the Environment, and the South. By Randal L. Hall. Lexington: University Press of Kentucky, 2012. Pp. 322. $40. Randal Hall's new book "delves into the exploitation of natural resources along the upper New River over a 250-year period" (p. 3). In this section of southwestern Virginia, lead mines drew in entrepreneurs, and the resulting development led to a variety of industries, such as railroads and the processing of phosphates. The extractive industries also created an environmental disaster area, led to the displacement of Native Americans, and fueled the oppression of unskilled workers. While the activities along the New River took place in relative isolation, Hall argues that they were emblematic of the whole of American history. The first white explorers to the region immediately recognized the value of lead. Permanent settlers quickly set up mining companies that extracted lead, iron ore, and copper. The American Revolution and its demand for bullets fueled both great profits and significant risks. While lead commanded a high price and allowed a small group of capitalists to tighten its political and economic control, the mines were also magnets for Loyalist attacks. The environmental assault was so severe that even contemporaries noted how smelting operations consumed a large share of the region's timber. Technology for the various industries remained fairly stagnant during the nineteenth century, as Hall explains, because the steady supply of water tamped down calls for a switch to steam power. Also, the relatively low price of labor inhibited technological development. On these two points, readers of this journal will probably crave more explanation. Hall's discussion of technological stagnation lacks depth and familiarity with the rich literature surrounding technological diversification. The American Civil War had an uneven effect on the region. Iron thrived while copper and smelting struggled. What did stay the same, though, was industrial consolidation. Some of the faces changed between 1850 and 1870, but a small group of capitalists still held sway in the region. These proponents of the "New South" used northern capital to expand their operations. Particularly noteworthy was the development of cold-blast furnaces that produced durable steel. Hydroelectric power came to the region in the twentieth century, as did the production of sulfuric acid, carbide, and zinc. This economic diversification, which received significant boosts during both world wars, led to even more environmental degradation. For example, an Allied Chemical plant ended up on the EPA's superfund list. Although the mines are closed, "the pits still pour about seven tons of sediment into Chestnut Creek each year" (p. 109). [End Page 409] Perhaps the most interesting chapter deals with deindustrialization. As mills shuttered, the communities along the New River had to reinvent themselves. Interstate 77 provided easy access to the region and allowed a switch to tourism. Promoters stress the bucolic life and opportunities to explore the region's natural beauty. This last appeal is somewhat surprising, as the environmental hangover is still noticeable. Hall's book is an effective look at the environmental costs of industrialization in southwestern Virginia. He has included seven appendixes that trace the range of technological change in the region. Each entry is a lengthy quote about industrial practices and together they trace technological change in a fairly small area. For instance, Hall includes a description from 1790 of ironworks along Cripple Creek, an 1884 account of iron furnaces, and a report from 1928 that details mining operations. Another strength of the book is its time span; reading a history book that does not stop or start with the Civil War era is refreshing. Hall's book is limited, however, in its utility for those who study the importance of technology. He confines his analysis primarily to the environmental consequences and is less successful in studying human perceptions of technological change. It is really only in the final chapter where Hall has a sustained analysis of the influences of technology on the workers. And the writing, while adequate, hardly urges the reader to turn the page. That being said, the book will appeal to...

Spatio‐temporal sedimentation patterns in beaver ponds along the Chevral river, Ardennes, Belgium

AbstractWith the recovery of the European beaver (Castor fiber) and their capacity to engineer fluvial landscapes, questions arise as to how they influence sediment transport, including the spatio‐temporal trends and patterns of sedimentation in beaver ponds. The Chevral river (Ardennes, Belgium) contains two beaver dam sequences, which appeared in 2004. Volumes of sediment deposited behind the dams were measured, and grain‐size distribution patterns were determined. Flow discharges and sediment fluxes were measured at the inflow and outflow of each dam sequence. Between 2004 and 2011, 1710.1 m3 of sediment was deposited behind the beaver dams, with an average sediment thickness of 25.1 cm. The thickness of the sediment layer was significantly (p &lt; 0.001) related to the area of the beaver ponds. Along the stream, beaver pond sediment thickness displayed a sinusoidal deposition pattern, in which ponds with thick sediment layers were preceded by a series of ponds with thinner sediment layers. A downstream textural coarsening in the dam sequences was also observed, probably because of dam failures subsequent to surges. Differences in sediment flux between the inflow and outflow at the beaver pond sequence were related to the river hydrograph, with deposition taking place during the rising limbs and slight erosion during the falling limbs. The 7‐year‐old sequences have filtered 190.19 ton of sediment out of the Chevral river, which is of the same order of magnitude as the 374.4 ton measured in pond deposits, with the difference between the values corresponding to beaver excavations (60.24 ton), inflow from small tributaries, and runoff from the valley flanks. Hydrogeomorphic effects of C. fiber and Castor canadensis activity are similar in magnitude. The detailed analysis of sedimentation in beaver pond sequences confirms the potential of beavers to contribute to river and wetland restoration, and catchment management. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The sediment budget of an alpine cirque

Research Article| January 01, 2013 The sediment budget of an alpine cirque Johnny W. Sanders; Johnny W. Sanders † 1Department of Earth and Planetary Science, University of California, Berkeley, California 94720, USA †E-mail: jws@eps.berkeley.edu Search for other works by this author on: GSW Google Scholar Kurt M. Cuffey; Kurt M. Cuffey 2Department of Geography, University of California, Berkeley, California 94720, USA Search for other works by this author on: GSW Google Scholar Kelly R. MacGregor; Kelly R. MacGregor 3Geology Department, Macalester College, St. Paul, Minnesota 55105, USA Search for other works by this author on: GSW Google Scholar Brian D. Collins Brian D. Collins 4U.S. Geological Survey, MS-973 Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2013) 125 (1-2): 229–248. https://doi.org/10.1130/B30688.1 Article history received: 22 Feb 2012 rev-recd: 11 May 2012 accepted: 11 May 2012 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 Johnny W. Sanders, Kurt M. Cuffey, Kelly R. MacGregor, Brian D. Collins; The sediment budget of an alpine cirque. GSA Bulletin 2013;; 125 (1-2): 229–248. doi: https://doi.org/10.1130/B30688.1 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 Cirques form and evolve as glaciers attack the bed and subaerial processes dismantle the surrounding walls. Collectively, these processes—which can make a cirque longer, or deeper, or both—profoundly influence near-divide regions of glaciated mountains and yet are rarely studied in a systematic way. Toward this end, we developed a theoretical framework for the sediment budget of a cirque that includes sediment sources, transport pathways, and storage elements. We quantified each component of the sediment budget using field measurements and remote-sensing data of a glaciated alpine cirque in British Columbia, Canada. The cirque has a plan-view area of 1.64 km2 and relief of ∼780 m. Our budget values, which correspond to a period of substantial glacier retreat, are based on measurements reflecting time intervals ranging from 1 yr to 80 yr. We report errors as a range (enclosed in parentheses), analogous to 95% confidence bounds.On average, 1640 (250–7950) metric tons of rock are released by the headwall each year; nearly 90% of this debris leaves the wall as small rockfalls or in snow avalanches. Our field observations indicated that snow avalanches originating as cornice failures are currently the most important transport process on the headwall. We estimated the mass of debris transported annually by the glacier to the foreland using (1) the volume and age of the foreland ground moraine and (2) the product of rock mass per unit volume of ice and glacier velocity. Over the past several decades, the glacier delivered 6440 (1180–14930) tons/yr to the foreland via forward ice motion and margin retreat (mostly in subglacial till or sediment-rich basal layers). Less than 3% of the glacierborne sediment flux traveled as supraglacial debris (170 [50–320] tons/yr). At present, sediment evacuation from the cirque occurs in a single meltwater stream. We monitored water discharge and suspended sediment concentration in this stream between 29 June and 28 August 2007. By season’s end, 650 (80–1860) tons of sediment had passed our gauging station (equivalent to an erosion rate of 0.2 [0.03–0.70] mm/yr, when averaged over the glacier bed). Approximately one third of the total annual streamborne sediment transport occurred over a 2 d period during the first major melt event of the year.Using our budget relations and flux magnitudes, we estimate the glacier is removing between 1240 and 2470 tons of rock from its bed per year, a rate equivalent to 0.5–0.9 mm/yr of erosion glacierwide. The headwall, by comparison, is being worn away horizontally at ∼1.2 (0.2–5.9) mm/yr. Thus, our results suggest that the headwall is retreating at rates roughly equivalent to vertical incision by the glacier. Our sediment budget results demonstrate that the wide variety of sediment sources and transport processes active in cirques necessitates a holistic view of cirque formation, one that most morphometric, range-scale, and glacial erosion analyses ignore. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Dynamics of the ice cover and peculiarities of the ice transportation of the sediments at the tidal flats of the Kandalaksha Gulf of the White Sea

Ten years of semistationary studies of the interaction of the ice cover and the coastal relief of the Kandalakhsa Gulf in the White Sea allowed us to reveal the peculiarities of these processes in the warm and cold years and the mechanisms of the origination of ice forms, including ice tents, which govern the character of the tidal flats. Three dynamic fast ice zones are distinguished by their geomorphological location, morphology, and ice dynamics. The dependence of the mechanisms and volumes of the enrichment of the fast ice in the sediments on the coastal zone’s relief was established. At the coast of the Kindo Peninsula (Velikaya Salma Strait), the ice mostly contains fine-sandy sediments. Coarser sediments, including boulders, are occasional and frozen into the ice at the contact of the fast ice and the bottom. At the expense of the ice’s spreading by 4–6 times in the warm years and 2–4 times in the cold years, several thousand tons of sediments mostly from the tidal flat’s surface (100–700 m3 from 1 km of coast in the wide tidal flats and <50 m3 on the steep coasts) are delivered to the water area.

Assessing the potential of reservoir outflow management to reduce sedimentation using continuous turbidity monitoring and reservoir modelling

AbstractIn‐stream sensors are increasingly deployed as part of ambient water quality‐monitoring networks. Temporally dense data from these networks can be used to better understand the transport of constituents through streams, lakes or reservoirs. Data from existing, continuously recording in‐stream flow and water quality monitoring stations were coupled with the two‐dimensional hydrodynamic CE‐QUAL‐W2 model to assess the potential of altered reservoir outflow management to reduce sediment trapping in John Redmond Reservoir, located in east‐central Kansas. Monitoring stations upstream and downstream from the reservoir were used to estimate 5.6 million metric tons of sediment transported to John Redmond Reservoir from 2007 through 2010, 88% of which was trapped within the reservoir. The two‐dimensional model was used to estimate the residence time of 55 equal‐volume releases from the reservoir; sediment trapping for these releases varied from 48% to 97%. Smaller trapping efficiencies were observed when the reservoir was maintained near the normal operating capacity (relative to higher flood pool levels) and when average residence times were relatively short. An idealized, alternative outflow management scenario was constructed, which minimized reservoir elevations and the length of time water was in the reservoir, while continuing to meet downstream flood control end points identified in the reservoir water control manual. The alternative scenario is projected to reduce sediment trapping in the reservoir by approximately 3%, preventing approximately 45 000 metric tons of sediment from being deposited within the reservoir annually. This article presents an approach to quantify the potential of reservoir management using existing in‐stream data; actual management decisions need to consider the effects on other reservoir benefits, such as downstream flood control and aquatic life. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Dynamics of suspended sediment delivery to the Eastern Mediterranean continental shelf

AbstractThis study provides data on the fluvial sediment transport at the Eastern Mediterranean, an area in which the regional importance for comparative study has often been raised by investigators but the data are rather scarce. We analysed long‐ and short‐term hydrologic and sedimentological data from one of the largest coastal streams of Israel, Qishon River (1100 km2), and its estuarine environment. The results indicate that during 65 years (1944–2009), a total 140 floods have contributed to the sea an amount of approximately 2.58 × 106 tons of sediment. During this period, (i) the number of floods with a return period of more than 10 years has almost doubled during the last 30 years, and (ii) the mean annual discharge during last 10 years increased by approximately 175%. The analysis of the short (2 years) hydrological and sediment data revealed that approximately 30% of the upstream channel loads do not reach the river mouth and are deposited along the channel bed, even during major flood events. This observation was attributed largely to the facts that the lower river bed is incised below sea level, to the very low slopes and to the correspondingly low stream power and transport capacity. The results of this study highlight the effect of interchannel dynamics as well as the constraints of interaction between fluvial system and estuarine processes on sediment transport. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Salt marsh sediment and metal fluxes in response to rainfall

Lay AbstractWe hypothesize that rainfall during low tide is an important process that affects the cycling of materials (nutrients and metals) in estuaries. We simulated a 45‐min rainfall event in a salt marsh to examine the effects of a low‐tide summer storm on the sediment surface. Surface runoff (sediment concentration (SC), discharge, and rainfall rate) at the downslope end of a 1‐ × 2‐m plot was collected and analyzed chemically in the laboratory. SC peaked at 6100 mg L–1 after 3 min and remained elevated for 15 min before declining. The metal content of the sediments varied considerably with time but was consistently higher than the average background content by a factor of 4–4000. Based on these experimental results, we estimated that 4.8–8.4 tonnes of sediment per square kilometer per minute can be entrained by rainfall during low tide, or up to 96–168 tonnes per year. We also estimated the annual loading of heavy metals that occurs in larger subtidal channels fed by intertidal creeks draining the salt marsh in response to rainfall. Our results demonstrate that rainfall‐entrained sediment during low tides is an important process affecting the cycling of materials in estuarine ecosystems.

The transport and distribution of the river load from the Kacza River into the Gulf of Gdańsk (Southern Baltic Sea, Poland)

Abstract The results of measurements of suspended sediment and bed load carried by the Kacza River into the Gulf of Gdańsk are discussed. The investigations were conducted in the years 2009–2010 at the Orłowo transect and at the mouth of the Kacza River in the Gulf of Gdańsk. The research has shown that the Kacza River discharged about 673 tons of sediment annually to the Gulf of Gdańsk, with 77% being transported as bed load. The granulometric composition of the river load is dominated by coarse-grained sand fractions.

Restoring a Dynamic Ecosystem to Sustain Biodiversity

Over three decades, Tijuana Estuary became highly modified by frequent storms and runoff events that acted synergistically with intensifying land use to deliver tons of sediment to the salt marsh and its tidal channels. The marsh plain became higher, drier, and more hypersaline, with fewer microtopographic features. The result was reduced biodiversity. Because an endangered sparrow continued to use the marsh plain, it was not permissible to remove sediment or recontour the site. Thus, restoration took on new meaning, and efforts shifted to excavation of disturbed uplands and the creation of novel conditions. When subsequent excavations also accumulated sediment, planning expanded to larger areas to be restored in modules over decades. Sedimentation will likely recur during future stormy periods due to the Pacific Decadal Oscillation and global climate change. Thus, biodiversity will best be sustained within an adaptive restoration framework involving large field experiments that show how to sustain all of the native species somewhere in the estuary, even if no single module can provide all essential habitats.

GIS-Based Characteristic Analysis of Shoals Evolution Around Alluvial Islands in the Changjiang Estuary

Abstract Seven pieces of charts of the Changjiang estuary from 1879 to 2000 are digitized and digital elevation model (DEM) of the Changjiang estuary in different periods is established supported by GIS, based on which, the shoals around Changxing-Hengsha Island and Jiuduansha is visualized, the change of area, volume, the amount and thickness of erosion-accretion and horizontal transposition rate of depth contour are calculated. The results show that: the trend of the second and third generation of the shoals around alluvial islands in the Changjiang estuary in the past 150 years is that deposition is as a whole and progradation seaward along southeast with deposition rates is faster than that of previous time; there are a total of 1.948 billion tons of sediment from 1879 to 2000, with the average annual deposition of 16.1millin tons, nearly accounting for 3.72% of sediment flux in Datong, and with the average annual sediment thickness of 0.83 cm. The deposition rates differ in different periods, and some time there is even a certain degree of erosion; erosion-accretion status differs in different shoals, shoals of Changxing-Hengsha Island are in washed status, east of Hengsha Island and Jiuduansha are in siltation status; the natural evolution of shoals is an important part in the growth development of the Changjiang estuary and constrained by the amount of sediment in the Changjiang stream; with the increasing intensity of development in stream and the increasing number of coastal engineering in the estuary, the impact of human activities on the shoals around alluvial islands is becoming more and more intense, and the natural evolution process of shoals would even change.

Fine sediments as a granular source for civil engineering

ABSTRACT Across the world, every year, several millions of tons of sediments are dredged in harbours. These sediments, which are sometimes polluted, represent an interesting granular resource for the civil engineering. For this study, fine sediments are chosen because of the difficulties to evacuate them after dredging, in comparison to sands, induced by their high water content, the presence of organic matters, their mechanical behaviour and, in some cases, the presence of pollutants. The paper shows the study carried out with fine sediments from harbours of the north of France. The authors propose recommendations to optimize the re-use of these sediments in considering technical, environmental and economical criteria. A re-use process has been studied in laboratory and tested on field site.

Estimating sediment and caesium-137 fluxes in the Ribble Estuary through time-series airborne remote sensing

High spatial and temporal resolution airborne imagery were acquired for the Ribble Estuary, North West England in 1997 and 2003, to assess the application of time-series airborne remote sensing to quantify total suspended sediment and radionuclide fluxes during a flood and ebb tide sequence. Concomitant measurements of suspended particulate matter (SPM) and water column turbidity were obtained during the time-series image acquisition for the flood and ebb tide sequence on the 17th July 2003 to verify the assumption of a vertically well mixed estuary and thus justifying the vertical extrapolation of spatially integrated estimate of surface SPM. The 137Cs activity concentrations were calculated from a relatively stable relationship between SPM and 137Cs for the Ribble Estuary. Total estuary wide budgets of sediment and 137Cs were obtained by combining the image-derived estimates of surface SPM and 137Cs with estimates of water volume from a two-dimensional hydrodynamic model (VERSE) developed for the Ribble Estuary. These indicate that around 10,000 tonnes of sediment and 2.72 GBq of 137Cs were deposited over the tidal sequence monitored in July 2003. This compared favourably with bed height elevation change estimated from field work. An uncertainty analysis on the total sediment and 137Cs flux yielded a total budget of the order of 40% on the final estimate. The results represent a novel approach to providing a spatially integrated estimate of the total net sediment and radionuclide flux in an intertidal environment over a flood and ebb tide sequence.

Rapid assessment of gully sidewall erosion rates in data-poor catchments: A case study in Australia

Knowledge of erosion rates and sediment yields from gullies is critical for the effective prioritisation of management efforts aimed at reducing the impact of gully-derived sediments on water quality. This paper describes a rapid assessment method for estimating sidewall gully erosion rates for already established gully networks. It combines a conceptual-empirical model of the cycle of gully initiation and stabilisation with an easy-to-apply technique for assessing gully extent and dimensions. The method is illustrated using a case study of the Avon-Richardson Catchment of north-central Victoria, Australia. It is estimated that a total of 4.6 × 10 6 tonnes of sediment have been generated in that catchment from gully erosion since the latest major phase of gullying in the mid 1800s. This is equivalent to 8.9 t ha − 1 y − 1 if sediment generation was evenly distributed spatially and temporally across the 3300 km 2 catchment over 160 years prior to 2010. Current rates of gully erosion are estimated to be 4700 t y − 1 (equivalent to 1.4 t ha − 1 y − 1 ). The results are comparable with observed rates of sidewall erosion in the Avon-Richardson Catchment. Further testing is required to build confidence in its applicability to assess sediment yields and for assisting regional authorities to plan remediation efforts.

Late Holocene Evolution of the Mekong Subaqueous Delta, Southern Vietnam

As Asia's third largest river, with regard to sediment load, the Mekong River delivers approximately 160 million tons of sediment per year to the South China Sea. High-resolution seismic profiling and coring during 2006 and 2007 cruises revealed a low gradient, subaqueous delta system, up to 20 m thick, surrounding the modern Mekong River Delta (MRD) in the west of the South China Sea. Based on clinoform structure, grain size, 210Pb, AMS 14C, and δ 13C results, the subaqueous delta is divided into four zones defined by different sedimentary processes and depositional features. Over the past 3000 yr, the evolution of the MRD has shown a morphological asymmetry indicated by a large down-drift area and a rapid progradation around Cape Camau, ∼ 200 km downstream from the river mouth. This asymmetric feature is consistent with increased wave influence. The strong southwestward coastal current, strengthened by the strong NE monsoon, plays an important role locally in longshore transport of resuspended sediments into the Gulf of Thailand. A late Holocene sediment budget for the MRD has been determined, based on the area and thickness of deltaic sediment. Approximately 80% of Mekong delivered sediment has been trapped within the delta area, which, together with a falling sea-level, resulted in a rapidly prograding MRD over the past 3000 yr.

Reinventing the Dutch Delta: Complexity and Conflicts

Delta areas have been extremely attractive for urbanisation and economic development throughout history because of the fertility of the land and the strategic position for shipping networks. Moreover, nowadays the most rapid processes of urbanization occur in delta-areas [46].Urbanized deltas can be considered as areas with a double complexity: they have to deal with the complexity of the delta, as the meeting point of rivers and sea, and with the complexity of urban patterns, as a condition and result of economic, cultural and social life. Since the 1990s, delta-areas are facing new challenges related to this double complexity. Climate-change, rising sea-level and increasing peak-discharges of rivers force planners to reconsider flood-defence strategies. At the same time, globalisation and neo-liberalism created new conditions for urbanization processes. The vulnerable position of urbanized deltas has become clear with the disastrous effects of hurricane Katrina in the Mississippi-delta in 2005. In search of sustainable strategies, authorities and planners of different delta-areas are looking to the Netherlands as a benchmark, which seemed to deal with the double complexity in a successful and sustainable way. However, instead of considering the Netherlands as an example which can be copied in other urbanized deltas, it is important to understand the Dutch delta as a result of two specific conditions: first, the specific condition of the natural dynamics of the delta itself, and second, the coincidence of the Dutch delta with the territory of the Dutch nation-state. Moreover, fundamental discussions and reconsiderations are taking place concerning future policies and strategies for flood-defence, water-management and urban development in the Netherlands. Instead of the adage ‘fighting against the water’, a new adage ‘working with nature’ is arising. This change is not only important for future safety and urban development in the Netherlands itself, but might be relevant for other urbanized deltas as well. KEY-WORDS hydraulic engineering, urban design, land of cities, nation-state, metropolitan water-landscapes, cross-disciplinary approach 1 This article has been first published in Built Environment VOL 35 NO 4. THE NATURAL FORM OF THE DELTA A delta can be defined as the area where two different systems river and sea both with important influences on the morphology of the land, meet and influence each other. Processes of sedimentation, alluvium deposits and land-loss are contingent upon which system, the river or the sea, dominates. The Dutch delta is a sea-dominated delta, as a result of the meeting of a number of relatively small and medium-size rivers (Rhine, Meuse and Scheldt) and a coastal area with strong tidal currents and tidal differences, as well as formidable south-west winds and ocean currents. The importance of these special conditions is clear when we compare the Dutch delta with a river-dominated delta like the Mississippi-delta, which has a very different topography. In many respects, the Mississippi river represents a multiple of the river Rhine: in length, depth discharges, etcetera. However, the most astonishing contrast between these two rivers concerns sediment-transport: the Mississippi carries 400 times more sediment than the Rhine and deposits, each year, roughly 170 million tons of sediment in the Gulf of Mexico. Length 6,275 km 1,320 km Depth average New Orleans: 60 m Arnhem: 8 m Discharge average 16,000 m3/sec 2000 (summer) m3/sec Discharge – extreme 48,000 m3/sec 12,000 m3/sec Sediment transport 170 million ton/yr 0.4 million ton/yr

Rapid channel response to variability in sediment supply: Cutting and filling of the Tarndale Fan, Waipaoa catchment, New Zealand

In the headwaters of the Waipaoa catchment, fluvio-mass movement gully complexes are currently significant contributors of sediment, delivery of which is buffered by fans which have developed in the small tributaries that lead from the gully complexes. Biannual channel cross-section surveys made since 1983 show seasonal aggradation / incision cycles; channels generally incise in summer and infill during the winter months. This seasonal pattern of cutting and filling is driven by variations in sediment supply from the gully complexes. In this paper, to better understand patterns and processes of sediment delivery at the top of the sediment cascade, we examine cut and fill cycles on the ~ 11 ha Tarndale Fan over a two and a half year period. Analysis of sequential DEMs compiled from survey data obtained between December 2004 and August 2007 indicates cutting and filling may involve up to 47,000 tonnes of sediment over as little as three months. During discrete severe rainstorm and/or wet weather periods, mass movements in the gully complex are enhanced and contribute large quantities of sediment to the fan, via debris flows and landslides, which infill channels. During drier periods, mass movement activity is inhibited and runoff incises the feeder channels.

Only a River

NATURE'S RIVER Nature's Mississippi River is made of gravity and the dynamic interaction of water and earth and life. Before there were people living along its edge it was running, big and muddy, downhill to the sea. About 15,000 years ago melting glaciers sent a torrent of water down the center of the North American continent in an enormous braided stream, depositing millions of tons of sediment on the val ley floor. Dirt accumulated and eventually blocked the streams, forc ing them to take new paths across older sedimentary deposits and cutting out great fluvial terraces that remain prominent features of the topography. This process of building and cutting continued until glacial runoff at last diminished and the river slowed, becom ing the single wide, meandering stream we know. It carried much more silt than before, in part because it moved more slowly, in part because retreating ice fields exposed more of the continent to ero sion. The river also dropped more sediment along the way, rather than rushing so much of it to the gulf. A giant fan of Pleistocene dirt the size of the state of Louisiana still rests far out on the bottom of the Gulf of Mexico, a remnant of a lower sea level and the original, faster river. But over the last 10,000 years sediment has piled on the floodplain and the coast near its mouth. The Mississippi Valley is older than the river that runs through it. Two million years ago the American, European, and African continents smashed together, for a geological moment squeezing