Outer River Research Articles

Simulation Study on the Impact of Water Flow Regulation Based on the MIKE 21 Model in a River Water Environment

Inadequate hydrodynamics can cause deterioration of the water environment within rivers. Regulating water conservancy projects can effectively improve the state of the water environment of rivers and promote sustainable regional development. The river plain in Zhejiang Province, China, suffers from severe hydrodynamic deficiencies, which have a significant impact on the state of the regional water environment. To investigate the changing state of the water environment of the river plain under water conservancy project control, in this study we constructed a two-dimensional hydrodynamic–water quality model based on the AD and ECOLAB modules in MIKE 21 software 2014 Edition. Combined with conservative tracers, the changes in the water displacement rate, flow rate, and water environment quality of the river plain were simulated under different regulation schemes over 7 days. A quantitative analysis of the effects of improving the state of the water environment in the river plain was carried out using a cluster analysis and a cloud model. (1) The water replacement rate of the outer river reached 90% after 3 days and approached 100% after 7 days. The water replacement rates of the inner pond were 51.2, 49.6, and 55.8%. This indicated that the engineering control measures effectively improved the replacement capacity of the river. (2) The contents of DO and BOD5 in the river have increased from class V to above class 3. The overall water quality is in the range of classes 2 to 3, and in some parts it can reach class 1. This indicates that the regulatory plan played a certain role in improving the river water environment. (3) The water pollution in the study area showed a fluctuating and decreasing trend over 7 days. There was a positive correlation between the flow velocity, water replacement rate, DO, and BOD5.

Effects of heavy rainfall and outer river level on urban waterlogging in hilly areas of South China: a case study of Nanhu Port, Changsha City

Effects of heavy rainfall and outer river level on urban waterlogging in hilly areas of South China: a case study of Nanhu Port, Changsha City

Effect of ship-lock-induced surges on navigation safety in a branched lower approach channel system

Abstract Ships docking and traveling in a branched lower approach channel system are at risk from surges caused by multi-lane locks during emptying operations. For this reason, water-level variations in the lower approach channel in response to discharge, interval running time, and outlet location of lock operations were studied using a 2-D hydrodynamic model validated by physical model tests, and the impact of water level variation on navigation safety under extreme operation scenarios of a quadruple-lane lock group was identified. Results indicated that discharge and interval running time of lock emptying had the greatest impact on the water level variation at the lock head. Water level variation at the lower lock head of the ship lift exhibited a trend of first decreasing and then increasing with the increment of the discharge from the lock chamber into the outer river. Specifically, the surge height at the lock head of the ship lift reached the minimum when approximately 40% of the discharge generated by dual-lane locks during emptying operations was released into the outer river. Overall, the simultaneous operation of quadruple-lane lock group and unit load rejection should be avoided in engineering applications.

Finding the optimum groin layout for the Konaweha river banks protection via 2D numerical modeling

River bank erosion has become a critical issue, especially for river bends with an alluvial soil type. Mostly, river bank erosions have caused structural failures because many national roads in Indonesia are placed near the river bend areas. Groins can reduce flow velocity, thereby increasing riverbank stability. However, most groins were installed in the river without impacting the river flow due to the improper design. This paper analyzes the use of groins placed at the river bend of the Konaweha River to protect the river bank with a length of 250 m from erosion. The evaluation employs 2D numerical modeling using MIKE21 FM to observe the influence of the groin on the river velocity, flow distribution pattern, and water level. Sixteen model scenarios with four groin configurations were tested for 25-year discharge, 2-year discharge, normal discharge 600 m3/s, and low discharge 197 m3/s to achieve the most effective plan. Based on the simulation results, Scenarios with five groins are recommended to reduce the flow velocity along the outer river bank from 2 to 0.3 m/s, thus minimizing the erosion. In addition, the spacing of groins being twice the groin length is recommended.

Simulation and design of joint distribution of rainfall and tide level in Wuchengxiyu Region,China

Flood control schemes and the scale of drainage facilities are closely related to the occurrence of rainstorms and the tide level of an outer river, so it is necessary to study the probability of the occurrence of rainstorms and the tide levels. Based on the daily rainfall and tide level data of Jiangyin station from 1956 to 2018 in the Wuchengxiyu region of Taihu Lake basin, copula functions were used to establish the joint distribution function of annual 1-day, 3-day, 7-day, and 15-day maximum rainfall and the highest tide level of the Yangtze River for different return periods. Based on this information, a risk probability model was constructed to evaluate the flood and tidal risks.It was found that when the design criteria of rainfall and tide level were similar, the probability of the simultaneous occurrence of rainfall and tide level greater than their respective magnitudes was significantly less than their respective design frequencies. The encounter combination analysis method proposed in this study has a wide application prospect for flood control and drainage design.

Numerical simulation of groyne placement in minimising Krueng Aceh river bank erosion

This paper presents the prediction of the flow velocity in a 575 meters-long reach of the Krueng Aceh river. It focused on the part of the riverbank where erosion occurred due to the pillars and bridge abutments. One alternative to reduce erosion is using groynes for regulation. The simulations were conducted using the Surface Water Modelling System program (SMS 11.2). The effects of the groynes on the flow changes causing erosion were determined by mathematical simulation of two-dimensional flow using RMA2. The calibration of RMA2 was undertaken by determining the Root-Mean-Square (RMS) error between the measured and mathematical model velocities. Nine scenarios of simulations have been done to investigate the effect of the groyne installation in reducing erosion in the river bend, in term of its length (L), and angle (α), according to river condition. From the simulation results, it can be concluded that the distribution of flow velocities towards the outer river bend for the perpendicular groyne of 9.0m long was smaller compared to the 7.0m one. The groyne with the angle of 10° and length of 7.0m was better in reducing the velocities at the outer riverbank than the 9.0m one. Whereas the groyne with 30° orientation and 9.0m long is better in reducing the eddy than that of the 7.0 m.

Efektivitas Krib Untuk Mengurangi Gerusan Di Tikungan Sungai Bengawan Solo

Sungai Bengawan Solo mempunyai karakteristik sungai berliku (meander). Hal ini berpotensi untuk memicu terjadinya gerusan lokal akibat tingginya kecepatan aliran di tikungan luar sungai. Fenomena gerusan lokal ini terjadi pada ruas pertemuan Sungai Bengawan Solo dan Kali Pepe, tebing sungai sudah bergeser 2 meter. Hal ini menunjukkan bahwa erosi dan gerusan lokal telah terjadi dan memerlukan penanganan khusus karena gerusan tebing tersebut semakin mendekati jalan raya dan kawasan pemukiman warga. Penanganan yang dapat dilakukan adalah memproteksi tebing sungai yang kritis tersebut dengan struktur krib untuk mengarahkan aliran yang datang dengan kecepatan tinggi ke arah palung sungai sehingga tidak membahayakan tebing tanggul sungai. Penelitian ini mengkaji efektivitas penempatan tata letak krib di tikungan luar sungai melalui uji model fisik 3 dimensi di Laboratorium Hidraulika dan diverifikasi oleh pemodelan numerik 2 dimensi. Berdasarkan hasil uji model hidraulik fisik, pemasangan krib dan riprap dengan jarak dan dimensi yang optimum dapat meredam energi dan kecepatan aliran sungai untuk mengamankan tebing dan tanggul sungai.

Geoinformation modeling of antropogenic transformation of the basin geosystems (case study of Dnister right tributaries)

The purpose of the article is to analyze anthropogenic transformation of river-basin geosystems of the outer Subcarpathian region by geoinformational modeling tools using various methods of quantitative estimation of anthropogenic pressure; comparison of modeling results on the basis of administrative-territorial and natural units, selection of optimal structural units for the study of anthropogenic changes in basin geosystems. Research methods. The features of estimation methods of anthropogenic transformation level of territorial complexes, based on various conceptual approaches to the study of anthropogenic changes in the components of the environment were investigated. In particular, the article compares methods of F.M. Milkov, P.G. Shyshchenko, E. Klementova and V. Geinige, P.P. Borschevsky, M.V. Boyarin, I.P. Kovalchuk, N.M. Ridey and D.L. Shofolov, A.M. Tretyak and others and by the means of geoinformation modeling of river-basin geosystems (namely, the case study of the outer Subcarpathian Dniester tributaries) shows the degree of representativeness of the results produced by each of them. It is noted that the technique by P.G. Shyshchenko allows to more accurately reflect the state of anthropogenic transformation of the river-basin system’s natural conditions Results. A range of digital cartographic models was developed to evaluate and compare anthropogenic transformation level of the two Carpathian basin systems and to identify similar and distinctive features of the state and the transformation level of the basin systems’ natural environment andstability of agricultural and forest landscapes in the studied basin geosystems. In particular, the study has revealed that the anthropogenic transformation of the outer Carpathian river basins is rising downstream. In the upper parts of the basins, it manifests itself in deforestation, while in the lower parts agricultural influence dominates. In addition, the index of anthropogenic transformation is rising with an increase in the order of sub-basins. The worst conditions of agro-landscapes are observed in the reclaimed valleys of the main rivers and their tributaries (due to the considerable level of plowing in the plain parts of the basins due to low fertility of soils, high levels of their acidity, degradation processes and chemical pollution). Stable territories are inherent exclusively in sub-basins which remain in their natural state or bear only traces of human activity. Settlements, which influence adjacent areas, are characterized by unsustainable land use. As for anthropogenic transformation, in the basin geosystem of the Berezhnytsia river its indicators increase upwards due to an increase in the share of arable land. On the contrary, in the basin of Bystrica much more land is occupied by industrial facilities, which affect the components of the geosystem the hardest. In this regard, the largest values of nature anthropogenic transformation indicators are found in the northern part of the basin and upstream of the city of Nadvirna and the town of Bykiv. Scientific significance. Case study of the administrative regions and the river basin located within them reveals the advantages of studying the geoenvironmental state of the territories according to their natural geographic taxonomic units, which allows to determine the most strained areas in geosystems. Particular attention is paid to the choice of optimum sized geospatial objects during the study of diverse basin systems. River sub-basins of the third order (according to the classification scheme of A. Strahler) were chosen to this purpose. Their size corresponds to that of the combined territorial communities’ area. The importance of formation a database that reflects on the state of the geospatial entities under study is emphasized. For this purpose, it is appropriate to convey the structure of land use, represented by indices of different land cover and land use types (protected areas, forest covered areas, swamps and wetlands, meadows, gardens and vineyards), arable land, land under rural and urban development, natural objects modified by human activities (reservoirs , ponds, channels), land utilized by industry and transport in each investigated object. The article shows that the best solution to this problem is provided by the processing of high-resolution spatial (in panchromatic and multispectral) remote sensing data. The most appropriate in this case are QuickBird satellite imagery, designed to create and update topographic maps and plans, to make inventories of forests and agricultural lands and to assess their condition, therefore allowing mapping of land use types that are not identified in statistical inventories. Practical significance. The results of this work will be helpful in selecting the specific technique allowing the most complete representation of anthropogenic transformation of natural objects; in choosing the most optimal spatial units to carry out the analysis and, accordingly, to fill in the database. The developed models reveal the most anthropogenically loaded parts of river-basin geosystems of the outer Subcarpathian region, which is essential for the extrapolation of the obtained results to other right tributaries of the Dniester River.

Test Study on Influence of a Sluice on Navigation of Ships

The navigation influenced by extension project of a sluice was researched in this paper. This sluice connected the inland river and outer river, and the hydraulic characteristics beside it were significant for ships’ passages. The test in this paper was conducted for simulating the flow patterns and hydraulic characteristics around this sluice. According to the test results, the flow velocities and flow patterns around approach channels of the inland river and the outer river in various conditions are given in this paper, including the maximum lateral flow velocity and the maximum reserved flow velocity. These data provided scientific bases for safe operation of the sluice and navigation channels. In addition, a guide wall was proposed to effectively reduce the lateral flow velocity.

Sedimentology of Late Holocene fluvial levee and point-bar deposits from the Cambodian tract of the Mekong River

The study of channel margin deposits is crucial to better understand fluvial systems and has significant social and economic implications. This paper describes sedimentological features of Late Holocene levee and point-bar deposits from five excellent outcrop exposures along the Cambodian tract of the Mekong River. Point-bar deposits show a typical fining-upward trend with low-angle inclined bedding and consist of gravelly sand, sand and mud beds. Levee deposits show a typical coarsening-upward or no clear vertical grain-size trend and consist of mud and very fine sand beds. Channel margin deposits formed in the outer river bend show a simple levee element, whereas inner bend deposits show more complex architecture with combinations of point-bar and levee elements. Water-level fluctuations play a fundamental role in the construction of point-bar and levee architecture; the resulting deposits show evidence of strong river currents with rapid sedimentation alternating with evidence of subaerial exposure with no sedimentation. This combination of sedimentary features can also form in other environments, but is distinctive of channel margin deposits forming in climates with a pronounced seasonality, including large and perennial rivers in tropical savannah climate areas.

Ten-year change of total phosphorous pollution in the Min River, an upstream tributary of the Three Gorges Reservoir

Understanding the spatial and temporal variation of nutrient concentrations, loads and their distribution from upstream tributaries is important for management of large lakes and reservoirs. The Min River is an important tributary of the upper reaches of the Three Gorges Reservoir (TGR) that contributes about 20 % of the inflow water from the Yangtze River to the TGR. It is also one of the main phosphorous sources of the TGR. In this study, total phosphorous (TP) concentrations and hydrological data from 2004 through 2014 for 13 sites in Min River and its tributaries were analyzed. The result suggested that the concentration of TP was comparatively lower in the upstream of the Min River and Dadu River, but tended to increase in recent years. Additionally, the TP pollution status in the Min River basin has gradually evolved from local pollution to whole-basin pollution. The concentration of TP in the Min River main stream increased, decreased and then increased again along the waterway. Pollution from nonpoint sources was the main contribution in the upstream portion and Outer River basin of Min River. Pollution from point sources was more serious than that from nonpoint sources in Chengdu, Meishan and Leshan segment. Specifically, TP pollution in Min River of Chengdu segment (Huanglongxi, Inner River) was primarily affected by urbanization, while Leshan segment (Yuebo) was mainly affected by glyphosate production. Controlling pollution from nonpoint sources and improving the sewage collection rate to reduce TP loads will be the primary task in the upstream portion and Outer River basin. Point source pollution controlling will still be the primary task associated with water quality management in the Inner River (Chengdu segment) and the downstream (Leshan segment) basin of Min River for the foreseeable future. Pollution from both point sources and nonpoint sources should be cared in the other area of Min River basin.

Nitrate drawdown and its unexpected isotope effect in the Danube estuarine transition zone

AbstractThe northwestern Black Sea Shelf region suffered from severe eutrophication in recent decades, mainly due to the Danube River's increased nutrient loads, as well as nutrient remineralization in sediments. During two cruises (spring 2012 and summer 2013) in the Danube River Delta–Black Sea transition zone, we analyzed dissolved nutrients, dual isotope signatures of nitrate, and δ15N of suspended particulate matter across the salinity gradient, and two pore water nutrient profiles (only 2013) in the outer river plume. We aimed to investigate nitrogen turnover and nutrient dynamics in the present Black Sea Shelf region in order to elucidate the contemporary role of nitrogen inputs of the River Danube in the light of the past, severely eutrophic, situation in the Delta region. Data indicate intense drawdown of river‐borne nitrate, phosphate, and dissolved silica in the river plume. Isotopic patterns of nitrate and suspended N illustrate exceptionally clearly the dominance of nitrate assimilation over the entire salinity gradient. An unusual 1.9 : 1 enrichment of δ18ONO3 to δ15NNO3 questions the usually uniform enrichment that is attributed to phytoplankton. Accordingly, we investigated the potential effects of nitrate regeneration and uptake by heterotrophic plankton on the isotopic composition of nitrate in the Delta. Overall, our data suggest that today, the nitrogen input from the Danube River is taken up within the salinity gradient in large quantities, and its immediate effects on the eutrophication status of the Black Sea shelf are relatively limited.

Discussion of “Hydraulic Principles of the 2,268-Year-Old Dujiangyan Project in China” by Shanghong Zhang, Yujun Yi, Yan Liu, and Xingkui Wang

Discussion of “Hydraulic Principles of the 2,268-Year-Old Dujiangyan Project in China” by Shanghong Zhang, Yujun Yi, Yan Liu, and Xingkui Wang

Closure to “Hydraulic Principles of the 2,268-Year-Old Dujiangyan Project in China” by Shanghong Zhang, Yujun Yi, Yan Liu, and Xingkui Wang

Closure to “Hydraulic Principles of the 2,268-Year-Old Dujiangyan Project in China” by Shanghong Zhang, Yujun Yi, Yan Liu, and Xingkui Wang

Experimental Studies on Regressive Erosion of Piping in Double-Layer Levee Foundation

Seepage piping seriously threatens the safety of levee, but study on mechanism of regressive erosion is not in-depth. According to the characteristics of piping channel upstream movement, we designed a set of experiment equipment. In given experiment condition, we did the experiments with 2 kinds of overburden and 2 different position of piping channel, and measured the value of each piezometric tube. As the experiment results shows, the tip hydraulic gradient can better reflect the problems of regressive erosion, comparing with average hydraulic gradient between piping exit and outer river. The development of the regressive erosion is determined by the tip hydraulic gradient. It will stop expanding when the tip hydraulic gradient decreases after large-scale upstream movement. This paper lays a foundation for further theoretical study.

Area-Based Approach for Mapping and Monitoring Riverine Vegetation Using Mobile Laser Scanning

Vegetation plays an important role in stabilizing the soil and decreasing fluvial erosion. In certain cases, vegetation increases the accumulation of fine sediments. Efficient and accurate methods are required for mapping and monitoring changes in the fluvial environment. Here, we develop an area-based approach for mapping and monitoring the vegetation structure along a river channel. First, a 2 × 2 m grid was placed over the study area. Metrics describing vegetation density and height were derived from mobile laser-scanning (MLS) data and used to predict the variables in the nearest-neighbor (NN) estimations. The training data were obtained from aerial images. The vegetation cover type was classified into the following four classes: bare ground, field layer, shrub layer, and canopy layer. Multi-temporal MLS data sets were applied to the change detection of riverine vegetation. This approach successfully classified vegetation cover with an overall classification accuracy of 72.6%; classification accuracies for bare ground, field layer, shrub layer, and canopy layer were 79.5%, 35.0%, 45.2% and 100.0%, respectively. Vegetation changes were detected primarily in outer river bends. These results proved that our approach was suitable for mapping riverine vegetation.

Morphodynamic characteristics of the dextral diversion of the Yangtze River mouth, China: tidal and the Coriolis Force controls

AbstractThis paper examines the morphological development of the Yangtze River mouth, which has been diverting southeasterly (dextrally), according to historical (150 years) chart‐based digital evolution model and on‐site measured tidal flow data. We reveal a significantly narrowing of the northern river mouth branch from formerly >30 km wide to presently 10 km wide due to rapid siltation. Net siltation there, however, decreases gradually, which largely contrasts with the fact that the siltation has shifted to the southern river mouth area, as shown by many newly‐emerged estuarine islands, sandy shoals and bifurcated branches. Our data have further demonstrated that the ebb flow that dominates in the study area changes its direction gradually from east to southeast from the inner to outer river mouth area, and its duration is much longer than the flood flow in the inner river mouth area, but nearly equal at the river mouth area. Accordingly, the sediment transport pathway has been diverted from east to southeast. We examine whether the Coriolis Force could explain the dextral diversion of the ebb flow and the altered morphodynamical processes. Although too weak to strengthen the tidal flows, the Coriolis Force can drag the ebb flow southeasterly, and so influence sediment transport paths at the estuarine scale. The Coriolis Force is limited in the inner river mouth, but substantial at and in the outer river mouth area when gradually free of estuarine topographic constraints. The Coriolis Force causes an offset in propagation of in‐out flow directions at the river mouth area to form a slack water setting prone to estuarine siltation. Using the present approach also enables explanation of the morphological development of the Holocene Yangtze delta‐coast that extends to the southeast. Copyright © 2010 John Wiley & Sons, Ltd.

Overview of Dujiangyan Irrigation Scheme of ancient China with current theory

AbstractThe Dujiangyan Irrigation Scheme is located in the middle reach of the Mingjiang River in Sichuan Province. It was initiated by Li Bing, the governor of Shu Prefecture, in the Qin Dynasty in 256 BC. It is a great scheme with a long history of 2260 years in ancient China, and has been very well operated until today.The headworks of the Dujiangyan Irrigation Scheme are composed of three major parts, i.e. Dujiang Yuzui (fish mouth), Feishayan, and Baopingkou. Dujiang Yuzui is a diversion dam, dividing the Mingjiang River water into two rivers, the Outer River and the Inner River. Feishayan is a spillway used for removing sand and excess water from the Inner River into the Outer River during flood. Baopingkou is an intake of the irrigation system, which automatically controls for a steady flow. These three parts are combined as an organic and complete whole with multiple functions of diverting water, spilling flood, releasing sediment, silt sedimentation, and automatic control of irrigation water. The whole headworks are reasonably planned and ingeniously coordinated with obvious effectiveness. In particular, this scheme has successfully treated the silt problem, therefore the possibility of being damaged by silt sedimentation is to a great extent avoided, and thus it can continue to flourish. In addition, the system of yearly maintenance also has its specialty: the construction technique is easily mastered by farmers, and all the construction materials came from local places. Therefore, the Dujiangyan Irrigation Scheme can normally be operated generation after generation. The Dujiangyan Irrigation Scheme encapsulates the scientific intelligence and civilization of Chinese nationality, and it still plays a vital role in the economic, social, ecological and environmental benefits for Sichun Province nowadays. It is a model of harmonious coexistence between mankind and nature, and is also included as a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization (UNESCO) as the first water project in the world. Copyright © 2006 John Wiley & Sons, Ltd.

EVALUATION OF THE CONSEQUENCES OF VARIOUS RESPONSE OPTIONS USING MODELING OF FATE, EFFECTS AND NRDA COSTS OF OIL SPILLS INTO WASHINGTON WATERS

ABSTRACT Oil spill fate and effects modeling and analysis were performed to evaluate the implications of spill response options being considered by the Washington State Department of Ecology in their rulemaking related to oil spill preparedness (WA State Contingency Plan Rule). The impacts of potential spills in Washington's outer coast, sound and river environments were modeled varying response options and operational timing, including use of conventional mechanical containment and recovery operations; dispersant application with concurrent mechanical containment and recovery; and in-situ burning with concurrent mechanical containment and recovery. US Coast Guard federal response capability standards, current Washington State standards, and potential theoretical higher response capability standards were simulated for scenarios involving spills of crude oil, bunker fuel and diesel into Washington waters (in the Strait of Georgia, Strait of Juan de Fuca, outer coast, and lower and upper Columbia River). The modeling was performed in probabilistic mode, i.e., by randomly varying location along tanker routes, spill date, and time, and so environmental conditions during and after the release among potential conditions that would occur. The model results were analyzed to estimate mean, standard deviation (SD), and 5th, 50th and 95th percentile results for surface water and shoreline oiling, water column and sediment contamination, biological impacts, and natural resource damages (NRD). NRD costs were based on the Washington Compensation Schedule and Oil Pollution Act (OPA) NRD procedures involving compensatory restoration scaling and associated costs. Response costs and socioeconomic damages were evaluated in a companion study by D.S. Etkin (Environmental Research Consulting). The fates, impacts and NRD cost results for two scenarios are presented here: those for the outer coast spills assuming (1) only protective booming and (2) protective booming plus the mechanical removal up to Washington State standards. The results of these and other scenarios are being incorporated into a rulemaking process and cost-benefit analysis by the Department of Ecology.

Seasonal benthic organic matter mineralisation measured by oxygen uptake and denitrification along a transect of the inner and outer River Thames estuary, UK

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 197:103-119 (2000) - doi:10.3354/meps197103 Seasonal benthic organic matter mineralisation measured by oxygen uptake and denitrification along a transect of the inner and outer River Thames estuary, UK M. Trimmer1, D. B. Nedwell1,*, D. B. Sivyer2, S. J. Malcolm2 1Department of Biological Sciences, University of Essex, Colchester CO4 3SQ, United Kingdom 2Centre for Environment Fisheries and Aquaculture Sciences, Lowestoft NR33 OHT, United Kingdom *Corresponding author. E-mail: nedwd@essex.ac.uk ABSTRACT: Seasonal measurements of organic matter mineralisation by oxygen uptake and denitrification were carried out from July 1996 to March 1998 along a ~200 km transect of the River Thames estuary, UK. There was a distinct gradient of decreasing rates of organic matter mineralisation seaward, which was related to the concentration of suspended solids and sedimentary organic carbon (C) at each site. There was clear seasonality and highest rates of oxygen uptake (10056 µmol O2 m-2 h-1) at the muddy sites, but lower rates and non-temperature-dependent oxygen uptake at the sandier sites. Denitrification, both that driven by nitrate from the overlying water (Dw) and that coupled to nitrification in the sediment (Dn), followed a similar trend to oxygen uptake, from negligible rates of approximately 1 µmol N m-2 h-1 for both Dw and Dn at the furthest offshore site, Site 12, to 11407 and 8209 µmol N m-2 h-1, respectively, at the inner muddy Site 1. The Thames estuary is heterotrophic and a very efficient organic C filter, trapping and remineralising 77% of its organic C input. Attenuation of fluvial nitrate loads was regulated by freshwater flow. Minimal attenuation (3%) occurred during peak flows (i.e. during periods of shortest freshwater flushing time) and >100% attenuation during periods of lowest freshwater flow (longest flushing times). Including the sewage treatment works (STWs) nitrate load in this calculation reduced the degree of attenuation of the nitrate load to, on average, 11%. Annual rates of Dw and Dn for an inner area of 125 km2 were 112 and 85 Mmol N yr-1, respectively, with a total rate of 196 Mmol N yr-1 (2744 t), which was equivalent to 9% of the total dissolved inorganic nitrogen (DIN) load for 1995-96. A mean denitrification rate (Dw) of 0.64 mol N m-2 yr-1, based on measurements in 4 east coast estuaries, was used to estimate a total rate of denitrification for the entire area of UK east coast estuaries. The total rate of 0.81 Gmol N yr-1 represented 16% attenuation of the total fluvial discharge of nitrate (~6 Gmol N yr-1) to the UK¹s east coast estuaries (1995-96) and hence a 16% reduction in the UK nitrate load to the North Sea. KEY WORDS: Organic mineralisation · Oxygen uptake · Denitrification · Nutrient attenuation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 197. Publication date: May 12, 2000 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 2000 Inter-Research.