River Sediment Load Research Articles

Forecasting suspended sediment load using regularized neural network: Case study of the Isser River (Algeria)

Abstract In the management of water resources in different hydro-systems it is important to evaluate and predict the sediment load in rivers. It is difficult to obtain an effective and fast estimation of sediment load by artificial neural network without avoiding over-fitting of the training data. The present paper comprises the comparison of a multi-layer perception network once with non-regularized network and the other with regularized network using the Early Stopping technique to estimate and forecast suspended sediment load in the Isser River, upstream of Beni Amran reservoir, northern Algeria. The study was carried out on daily sediment discharge and water discharge data of 30 years (1971–2001). The results of the Back Propagation based models were evaluated in terms of the coefficient of determination (R2) and the root mean square error (RMSE). Results of the comparison indicate that the regularizing ANN using the Early Stopping technique to avoid over-fitting performs better than non-regularized networks, and show that the overtraining in the back propagation occurs because of the complexity of the data introduced to the network.

Dynamic changes of sediment load and water discharge in the Weihe River, China

The abrupt reduction of the water discharge and sediment load in the Yellow River has attracted much attention during the past several decades. This paper investigates the temporal and spatial changes of annual sediment load and water discharge in the Weihe River basin, the largest tributary of the Yellow River, which contributes 40 % of the sediment and 26 % of the water to the Yellow River. The results suggest that sediment load and water discharge in the Weihe River basin from both mainstream and tributaries show significant decreasing trends (significance level of 0.05). The trends show the following three distinct stages: the fluctuating stage (1956–1969), the slowly decreasing stage (1970–1979) and the accelerated decreasing stage (1980–2010). Additionally, the water discharge decreases more quickly than sediment. Spatially, the greatest reduction in water discharge and sediment load occurs upstream of the river. Additionally, the decrease in water discharge and sediment load in the main stream is greater than in the tributary. The focal years of water discharge and sediment changes are the same for each station except for the Zhuangtou Station, which were approximately 1970 and during the 1990s. Human activities contribute much more to changes in the hydrological series, and the percentage of human activity impacts on the water discharge are much larger than the sediment load for most of the periods. The relationship between the average monthly water discharge and the sediment load shows a clockwise loop curve. The change points for the annual water discharge and the sediment load relationship occurred mainly in 1983 for most stations. The reduction in the water discharge and sediment load is caused mainly by human activities, especially soil and water conservation projects (such as afforestation, terraces, reservoirs and dams). In summary, the results in this study provide further evidence of the need for river basin management.

A geomorphic approach to the analysis of bedload and bed morphology of the Lower Mississippi River near the Old River Control Structure

The Mississippi River is the ultimate single-thread meandering river. Five hundred kilometers upstream from its mouth, about 25% of the river's discharge and sediment load is diverted into the Atchafalaya River. This diversion is controlled by the Old River Control Structure (ORCS), built by the U.S. Army Corps of Engineers (USACE) in stages since 1961, to stop the avulsion of the Mississippi River into the Atchafalaya. The effects of ORCS on sediment and water discharge and geomorphic change to the Lower Mississippi River (LMR) channel are not yet completely understood and require placing the river into a geomorphic context, first classifying the channel into similar categories before evaluating change. The objectives of this study are to estimate the LMR bedload, develop and apply a geomorphic classification of the LMR near the ORCS, and explore geomorphic change within the classified areas.We studied a 115-km-long stretch between ORCS and Baton Rouge that is highly impacted by engineering. We used six sets of bathymetric multibeam echosounder surveys conducted by the USACE, multitemporal cartographies, and a field survey supported by multibeam echosounder bathymetry, acoustic Doppler current profiler (ADCP) measurements, sediment samples collection, and geomorphic observations. A three-dimensional method for estimating bedload from time-elapsed bathymetric surveys was developed and applied on seven sets of time-elapsed surveys downstream from ORCS from 2010, 2011, and 2012. We estimate that the fraction of bedload as a percentage of total sand load between 2003 and 2011 was 13.2%. A bedform classification scheme, based on bedform height, was developed. The bed was almost completely mantled by sandy bedforms above the −24-m isoline.The studied reach was divided into ten zones according to four geomorphic types based on channel planform, geologic controls, presence of islands, and other morphometric parameters. These zones were shown to be physically distinct in terms of bedform location, depth to bedform size, channel sinuosity, channel width-to-depth ratios, and adjustments in the thalweg and channel width from 1948 to 2012.The 1948 to 1975 period displayed a relatively large amount of thalweg aggradation, with a spatial average of 1.8m and an average channel narrowing of 80m. The 1975 to 2012 period had much lower spatial aggradation of 0.5m and a lower average channel narrowing of 35m. Thalweg sinuosity did not adjust very much, with an average reduction of 0.02 from 1948 to 2012 and an average of zero adjustment between 1975 and 2012.The shape and spatial extent of a very large, anomalous bar near ORCS varied at seasonal and decadal timescales and may be influenced by the ORCS. Bed morphology was specific to geomorphic zones, which were shown to be physically significant, and should be employed in future studies of large rivers.

Developing policy for the Yellow River sediment sustainable control

The Yellow River of China is one exception where erosion and sediment delivery have successfully been reduced [1]. This riverwasonce theworld’s largest carrier of fluvial sediment load and peaked at about 1.6 Gt yr−1 in the middle of the last century [1–3]. The Yellow River is the birthplace of Chinese civilization, but throughout history it has produced frequent and catastrophic floods and droughts [3,4]. Over thousands of years, a diverse range of strategies and methods have been applied in attempts to control the sediment transport of the YellowRiver, but none have succeeded in completely eradicating this scourge [2]. Fortunately, since the 1970s, the sediment transport by the Yellow River has significantly declined [1–5]. Nearly 90% of the sediment load is originated and transported from the Loess Plateau in the middle reach [3]. The current input of sediment from the Loess Plateau is less than one quarter of what it was before 1980 [1], and the sediment export to the ocean at Lijin station is now only 10.7% of the 1950s’ level [6]. That is a reduction of 90% in sediment transport. This decline implies that the sediment load in this large river has been regulated to a near prehuman level, i.e. that prior to around 600 AD [7]. We argue that it is a time for the cessation of engineering constructions, more important is themaintenanceof a sustainable (i.e. little water consumption) vegetated ecosystem on the Loess Plateau for soil conservation, especially necessity is the establishment of an integrated basin-wide ecosystem and land-use management regime for sustainable water use and sediment regulation. DRIVING FORCES OF THE REDUCED SEDIMENT

Earthquake-triggered increase in biospheric carbon export from a mountain belt

On geological time scales, the erosion of carbon from the terrestrial biosphere and its burial in sediments can counter CO2 emissions from the solid Earth. Earthquakes may increase the erosion of this biospheric carbon and supply it to mountain rivers by triggering landslides, which rapidly strip hillslopes of vegetation and soil. Over the long term, elevated river sediment loads may promote more efficient carbon burial. However, riverine export of earthquake-mobilized carbon has remained poorly constrained. Here we quantify biospheric carbon discharge by the Zagunao River following a large earthquake with a unique set of samples collected before and after the A.D. 2008 M w 7.9 Wenchuan (China) earthquake. Radioactive and stable carbon isotopes are used to isolate the biospheric carbon, accounting for rock-derived organic carbon inputs. River discharge of biospheric carbon doubled in the downstream reaches, characterized by moderate landslide impact, following the earthquake. The rapid export of carbon from earthquake-triggered landslides appears to outpace its degradation on hillslopes while sediment loads are elevated. This means that enhanced river discharge of biospheric carbon following large earthquakes can link active tectonics to CO2 drawdown.

Quantifying drivers of the sediment load reduction in the Yellow River Basin

Human activities have significantly changed the transport and fluxes of terrestrial sediment of global rivers, trapping over 100 billion metric tons of sediment in reservoirs worldwide, reducing the sediment delivery to coastal areas, and affecting the environmental quality and economic vitality of coastal regions [1–3]. The impacts of reducing sediment loads of the global rivers include increasing coastal recession rate, threatening the safety of the coastal residents, changing the benthic environment of coastal estuaries, and productivity of coastal fisheries [1–3]. To tackle such impacts, it is essential to identify, understand, and quantify the drivers and their interactions that produce such sediment reduction. TheYellowRiverwas once theworld’s largest carrier of fluvial sediment load, withnearly 90%of it originated and transported from theLoess Plateau in themiddle reach (Fig. 1a) [2,3]. However, the sediment load has dramatically reduced, from∼1.6 billion tons/year in the 1970s to∼0.3 billion tons/year at present, a reduction of over 81% [2,3]. Such reduction not only resulted in significant improvement in ecosystem services such as ecosystem net primary productivity, soil carbon storage, and net ecosystem productivity over the Loess Plateau [2–5], but also led to decreasing water yield of both the lower reach and the delta of the Yellow River particularly in dry years [2–5]. Many studies have investigated the effects of coupled climate change and anthropogenic activities on sediment P1-P3 P1-P2 P2-P3 Periods

Sediment deposition patterns in a tropical floodplain, Tana River, Kenya

Floodplains exert strong controls on downstream sediment transport and are as such important in material budgets of river systems. To understand sediment budgets in the Tana River, we investigated sediment storage along a 380 km floodplain reach (Garissa-Garsen) in the lower Tana River (Kenya), using a combination of approaches: (i) measurements of sediment deposition after an important flood event and, (ii) quantification of sediment storage using fallout radionuclide activities (137Cs and 210Pbex). Event-based sediment deposition ranged between 2-15 mm vertical accretion, corresponding to an average of 0.58±0.42 g cm-2 (dry weight). Average annual sediment storage based on fallout radionuclide activities were at a 50 yr mean of 1.15-1.21 g cm-2 yr-1 and a 100 yr mean of 1.01 g cm-2 yr-1 (using 137Cs and 210Pbex, respectively). Sediment deposition rates were mainly dependent on distance relative to the main river, flood height and microtopography. The deposited sediments originated from various sources including deeply mobilized, radionuclide-poor sediments. Shallow overbank deposits (< 2 m depth), dominated by silty-clay sediment fractions were observed in most depositional areas. Floodplain sediment stocks are controlled by annual overbank flooding, with a 73 yr flooding frequency of 1.05 flood yr-1. On average ca. 1-2 Mt (15-30%) of the river sediment load is deposited in the Garissa-Garsen floodplain reach. However, the overall channel dynamics including channel sediment storage and reworking are important and may have a very high impact on short-term sediment storage and release.

Prediction of suspended sediment load using ANN GA conjunction model with Markov chain approach at flood conditions

Development of cities, destruction of forests and pastures, population growth and other factors have increased suspended sediment load in rivers of developing countries. Measurement of suspended sediment load is a challenging issue for engineers at flood conditions. The case study of this research is Idenak hydrometric station on the Marun River in the south west of Iran. The used data consists of 42 years (1968 to 2009) flood discharge. A perceptron artificial neural network is trained and validated by observed data. For training of Artificial Neural Network (ANN), momentum and Levenberg-Marquardt training methods are applied. For decreasing of Normalized Mean Square Error (NMSE) and increasing of correlation coefficient (R), parameters of ANN are optimized by Genetic Algorithm (GA) method. GA method optimizes the number of nodes of hidden layers of ANN that is trained by Levenberg-Marquardt training method while it optimizes the number of nodes and momentum of ANN that is trained by momentum training method. GA method can reduce NMSE to 80% while GA method doesn't increase R significantly. In order to predict flood condition, the Markov chain method is applied. The results show that suspended sediment load may be increased almost from 400000 ton/day to 800000 ton/day at future.

Changes in water clarity in response to river discharges on the Great Barrier Reef continental shelf: 2002–2013

Water clarity is a key factor for the health of marine ecosystems. The Australian Great Barrier Reef (GBR) is located on a continental shelf, with >35 major seasonal rivers discharging into this 344,000 km2 tropical to subtropical ecosystem. This work investigates how river discharges affect water clarity in different zones along and across the GBR. For each day over 11 years (2002–2013) we calculated ‘photic depth’ as a proxy measure of water clarity (calibrated to be equivalent to Secchi depth), for each 1 km2 pixel from MODIS-Aqua remote sensing data. Long-term and seasonal changes in photic depth were related to the daily discharge volumes of the nearest rivers, after statistically removing the effects of waves and tides on photic depth. The relationships between photic depths and rivers differed across and along the GBR. They typically declined from the coastal to offshore zones, and were strongest in proximity to rivers in agriculturally modified catchments. In most southern inner zones, photic depth declined consistently throughout the 11-year observation period; such long-term trend was not observed offshore nor in the northern regions. Averaged across the GBR, photic depths declined to 47% of local maximum values soon after the onset of river floods, and recovery to 95% of maximum values took on average 6 months (range: 150–260 days). The river effects were strongest at latitude 14.5°–19.0°S, where river loads are high and the continental shelf is narrow. Here, even offshore zones showed a >40% seasonal decline in photic depth, and 17–24% reductions in annual mean photic depth in years with large river nutrients and sediment loads. Our methodology is based on freely available data and tools and may be applied to other shelf systems, providing valuable insights in support of ecosystem management.

Analyses of suspended sediment loads in Slovenian rivers

ABSTRACTSuspended solids are present in every river, but high quantities can worsen the ecological conditions of streams; therefore, effective monitoring and analysis of this hydrological variable are necessary. Frequency, seasonality, inter-correlation, extreme events, trends and lag analyses were carried out for peaks of suspended sediment concentration (SSC) and discharge (Q) data from Slovenian streams using officially monitored data from 1955 to 2006 that were made available by the Slovenian Environment Agency. In total more than 500 station-years of daily Q and SSC data were used. No uniform (positive or negative) trend was found in the SSC series; however, all the statistically significant trends were decreasing. No generalization is possible for the best fit distribution function. A seasonality analysis showed that most of the SSC peaks occurred in the summer (short-term intense convective precipitation produced by thunderstorms) and in the autumn (prolonged frontal precipitation). Correlations between Q and SSC values were generally relatively small (Pearson correlation coefficient values from 0.05 to 0.59), which means that the often applied Q–SSC curves should be used with caution when estimating annual suspended sediment loads. On average, flood peak Q occurred after the corresponding SSC peak (clockwise-positive hysteresis loops), but the average lag time was rather small (less than 1 day).Editor M.C. Acreman; Associate editor Y. Gyasi-Agyei

A Hybrid Double Feedforward Neural Network for Suspended Sediment Load Estimation

Estimation of suspended sediment loads (SSL) in rivers is an important issue in water resources management and planning. This study proposes a hybrid double feedforward neural network (HDFNN) model for daily SSL estimation, by combining fuzzy pattern-recognition and continuity equation into a structure of double neural networks. A comparison is performed between HDFNN, multi-layer feedforward neural network (MFNN), double parallel feedforward neural network (DPFNN) and hybrid feedforward neural network (HFNN) models. Based on a case study on the Muddy Creek in Montana of USA, it is found that the HDFNN model is strongly superior to the other three benchmarking models in terms of root mean squared error (RMSE) and Nash-Sutcliffe efficiency coefficient (NSEC). HDFNN model demonstrates the best generalization and estimation ability due to its configuration and capability of physically dealing with different inputs. The peak value of SSL is closely estimated by the HDFNN model as well. The performances of HDFNN model in low and medium loads are satisfactory when investigated by partitioning analysis. Thus, the HDFNN is appropriate for modeling the sediment transport process with nonlinear, fuzzy and time-varying characteristics. It explores a practical alternative for use and can be recommended as an efficient estimation model for SSL.

Coupling freshwater mussel ecology and river dynamics using a simplified dynamic interaction model

AbstractFreshwater faunal diversity and abundance have declined dramatically worldwide, concurrent with changes in streamflow and sediment loads in rivers. Cumulative effects and interdependencies of chronic covarying environmental stressors can obscure causal linkages that may be controlling the population dynamics of longer-lived freshwater fauna, such as mussels. To understand changes in long-term mussel population density, we developed a dynamic, process-based interaction model that couples streamflow, suspended sediment, phytoplankton, and mussel abundance under the hypothesis that chronic exposure to increased suspended sediment and food limitation are the primary factors controlling native mussel population density in a midwestern USA agricultural river basin. We calibrated and validated the model with extensive survey data from multiple time periods and used it to evaluate changes in mussel abundance at a subbasin scale over decades. We evaluated sensitivity of simulated mussel densities across a ...

Modeling of soil loss and its impact factors in the Guijiang Karst River Basin in Southern China

The Guijiang Karst River Basin (GKRB) is a typical karst river basin in southern China and one of the major tributaries to the Xijiang River in the Pearl River Basin. A portion of the main stem in the upper reach of GKRB is called the Li River known for its most scenic karst landforms in the world. Soil erosion has resulted in rocky desertification in karst areas of the basin. Excessive sediment load in rivers would affect tourism navigation in the Li River and the aquatic systems in the basin. This study employed the Revised Universal Soil Loss Equation Version 2(RUSLE2) model to estimate soil loss and to evaluate the impact factors for the spatial and temporal variation of soil erosion in the basin. The GKRB RUSLE2 model was calibrated with sediment yields from nine gaging stations with the Nash–Sutcliffe efficiency coefficient (NSE) as high as 0.69. This study showed that soil erosion occurred on 54.9 % of the land areas that are primarily forest and cropland and in low hills with elevations ranging from 30 to 600 m. It also showed that the soil erosion rate is higher in areas where the degree of rocky desertification is more severe, indicating area with high soil erosion intensity often has high risk of rocky desertification. Impacted by monsoons, soil erosion in the study basin showed clear seasonal variation. The second quarter of the year had highest erosion rate, mostly due to the intensive late spring and early summer rainstorms. This study has shown that the RUSLE2 model can be used for karst river basin with reasonable accuracy. Findings from this study may help in identifying locations for flow and sediment control structures to reduce the risk of soil erosion and subsequently rocky desertification.

Empirical Formula for Estimation the Sediment Load in Shat AL-Gharaf River

In this research, the sediment load in Shat AlGharaf River lies in the south of Iraq, has been studied.Two empirical formulas those have been presented by ;Bagnold and Van Rijn were adopted as a deterministicequations for computing the sediment discharge in selectedreaches of the river . The application of these equations requiresto do different hydraulic, sediment, and geometricmeasurements for the selected reaches. Accordingly ,thirteen sections along the river within a study area havebeen adopted. After analyzing the available data, a newthe formula for estimating the suspended sediment load in ShatAl-Gharaf was developed, depending on the data for tensections of this river and by using SPSS program, thedetermination coefficient of the new formula was (R2=0.94).The validity of the established formula has been verifiedusing some well related (i.e., nearly the same hydraulics andgeometrical circumstances) of field data over the world wasselected from published literatures [8] these are: Coloradoriver data of the U.S.B.R.(1958), River data from Leopold(1969) , and India canal data of Chaudry et.al.(1970). As wellAs those observed in the remaining three sections of presentRiver, the verification shows a good agreement.The results of the adopted two formulas and the new formulawere compared with field measurements using DiscrepancyRatio (bais) method. The suggested new formula gave thebest results where 50% of data located within a discrepancya ratio close to one and 30% of data located within an error±20%, that is referred to suitability adoption this formula as athe deterministic equation to estimate the sediment load in ShatAl-Garaf river within a study reach.

Using three different approaches of OSL for the study of young fluvial sediments at the coastal plain of the Usumacinta–Grijalva River Basin, southern Mexico

AbstractWe use three different approaches of optically stimulated luminescence (OSL) to study young fluvial sediments located at the main channels of one of the largest fluvial systems of North America: the Usumacinta–Grijalva. We use the pulsed photo‐stimulated luminescence (PPSL) system also known as portable OSL reader, full OSL dating and profiling OSL dating in samples extracted from vertical sediment profiles (n = 9) of riverbanks to detect changes in depositional rates of sediments and to obtain the age of the deposits. The results of the PPSL system show that the luminescence signals of vertical sediment profiles highly scattered from the top to the bottom contrast with the luminescence pattern observed on well‐reset sequences of fluvial deposits where luminescence increase from the top to the bottom of the profile. The profiling and full OSL ages yielded large uncertainty values on their ages. Based on the inconsistencies observed in both ages and luminescence patterns of profiles we suggest that these fluvial deposits were not fully reset during their transport. As an explanation, we propose that in the Usumacinta and Grijalva rivers the cyclonic storms during the wet season promote the entrainment of large volumes of sediments due to high‐erosional episodes around the basin resulting from hyper‐concentrated and turbid flows. We conclude that the PPSL, profiling and full OSL dating of sediments are useful tools to quantify and to assess the depositional patterns in fluvial settings during the Holocene. These techniques also can yield information about sites where increases in the sediment load of rivers may produce poorly resetting of grains affecting the results of OSL dating. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Cambios globales en los manglares del golfo de Urabá (Colombia): entre la cambiante línea costera y la frontera agropecuaria en expansión

Accelerated mean sea level rise and deforestation are two global changes severely impacting mangroves along the Colombian Caribbean coast, but little has been discussed about them for the Gulf of Uraba. The objective of this review is to synthesize the published literature on such topics available to date for this area. This gulf holds extensive areas, structurally different from the rest of the Caribbean, which are shrinking and degrading as a consequence of: a) coastal erosion and sea level rise; b) selective logging and agricultural expansion; and c) watershed deforestation and sediment exports to the estuaries. The Atrato River delta, and several microdeltas located along the eastern coast have expanded, while the Rionegro Cove has remained relatively unchanged, at least during the 20th century. The eastern coast, with the smalles mangrove patches, have eroded at a rate of various meters per year due to the littoral drift currents. In the vicinity of the Turbo municipality, selective logging for different purposes has reduced the mean tree-diameter in Rhizophora mangle and has increased the importance value of Laguncularia racemosa, thus altering above ground biomass and carbon reservoirs. Agricultural expansion has been responsible for shrinking inland Avicennia germinans-stands. High deforestation rates in the coastal plains and watersheds in the banana agricultural district have increased river sediment load that has accumulated in the deltas. Mangroves in these areas trap significant amounts of sediments, with likely negative effects on colonization and survival of seedlings and benthic macroinvertebrates. In conclusion, in the Gulf of Uraba significant global changes, both natural and anthropogenic, currently occur within the littoral zone as well as within the coastal watersheds, and they require an urgent implementation of adaptive measures within the management plans for mangrove ecosystems and the coastal zone.

Modeling Typhoon‐Induced Alterations on River Sediment Transport and Turbidity Based on Dynamic Landslide Inventories: Gaoping River Basin, Taiwan

This study examines the impacts of storm‐triggered landslides on downstream sediment and turbidity responses in the Gaoping River Basin, Taiwan using the Soil and Water Assessment Tool (SWAT). Attention is given to analyzing the increased and altered baseline of suspended sediment load and turbidity after the disturbances caused by the rainfall and landslides associated with Typhoon Morakot in 2009. SWAT parameters were calibrated by the observed hydrometric data from 1999 to 2003 using the log‐scale root‐mean‐square error (log‐RMSE) and Nash‐Sutcliffe Model Efficiency. Both parameter sets were applied for the simulation of suspended sediment yield and turbidity with annual updated landslide inventories for the period 2004–2012. The landslide updating mirrors the physical land‐cover changes and has slightly improved the model performance, yet landslides alone cannot explain the difference between Morakot‐induced and SWAT‐simulated sediment discharge. The set of parameters calibrated by log‐RMSE can better approximate the increased baseline and typhoon induced alterations. The results show alterations in sediment erosion and transport: (1) drastically increased the turbidity baseline and occurrence of high‐turbidity; (2) altered coefficient and exponent values of the sediment rating curve; and (3) altered relationship between rainfall and induced turbidity during major rainfall events. The research in this study provides an improved modeling approach to typhoon‐induced alterations on river sediment loads and turbidity.

Reduced sediment transport in the Yellow River due to anthropogenic changes

The erosion, transport and redeposition of sediments shape the Earth's surface, and affect the structure and function of ecosystems and society(1,2). The Yellow River was once the world's largest carrier of fluvial sediment, but its sediment load has decreased by approximately 90% over the past 60 years(3). The decline in sediment load is due to changes in water discharge and sediment concentration, which are both influenced by regional climate change and human activities. Here we use an attribution approach to analyse 60 years of runoff and sediment load observations from the traverse of the Yellow River over China's Loess Plateau - the source of nearly 90% of its sediment load. We find that landscape engineering, terracing and the construction of check dams and reservoirs were the primary factors driving reduction in sediment load from the 1970s to 1990s, but large-scale vegetation restoration projects have also reduced soil erosion from the 1990s onwards. We suggest that, as the ability of existing dams and reservoirs to trap sediments declines in the future, erosion rates on the Loess Plateau will increasingly control the Yellow River's sediment load.

Sediment yield of the lower Tana River, Kenya, is insensitive to dam construction: sediment mobilization processes in a semi‐arid tropical river system

AbstractDam construction in the 1960s to 1980s significantly modified sediment supply from the Kenyan uplands to the lower Tana River. To assess the effect on suspended sediment fluxes of the Tana River, we monitored the sediment load at high temporal resolution for 1 year and complemented our data with historical information. The relationship between sediment concentration and water discharge was complex: at the onset of the wet season, discharge peaks resulted in high sediment concentrations and counterclockwise hysteresis, while towards the end of the wet season, a sediment exhaustion effect led to low concentrations despite the high discharge. The total sediment flux at Garissa (c. 250 km downstream of the lowermost dam) between June 2012 and June 2013 was 8.8 Mt yr‐1. Comparison of current with historical fluxes indicated that dam construction had not greatly affected the annual sediment flux. We suggest that autogenic processes, namely river bed dynamics and bank erosion, mobilized large quantities of sediments stored in the alluvial plain downstream of the dams. Observations supporting the importance of autogenic processes included the absence of measurable activities of the fall‐out radionuclides 7Be and 137Cs in the suspended sediment, the rapid lateral migration of the river course, and the seasonal changes in river cross‐section. Given the large stock of sediment in the alluvial valley of the Tana River, it may take centuries before the effect of damming shows up as a quantitative reduction in the sediment flux at Garissa. Many models relate the sediment load of rivers to catchment characteristics, thereby implicitly assuming that alterations in the catchment induce changes in the sediment load. Our research confirms that the response of an alluvial river to external disturbances such as land use or climate change is often indirect or non‐existent as autogenic processes overwhelm the changes in the input signal. Copyright © 2015 John Wiley &amp; Sons, Ltd.

DYNAMICS OF SEDIMENTATION AND USE OF GENETIC ALGORITHMS FOR ESTIMATING SEDIMENT YIELDS IN A RIVER: A CRITICAL REVIEW

ABSTRACTThe presence of sediments in a river is one of the major factors that characterize the river. The presence of sediment in any water resource is detrimental to its design purpose and it scratches any structure such as bridge foundations, conduit pipes, and turbine blades it comes into contact with while in motion and this leads to their eventual failure under load. The correct estimation of sediment yield transported by a river is indispensable in water resources engineering as sediment affects its hydraulic structure. The use of mathematical modeling algorithms such as genetic algorithms (GA) has proved to be very accurate in predicting sediment load in a river. The analogy behind GA is that genes in DNA functions are manipulated in specific ways through specific transcription operations. Therefore, applying the same logical operators to selected parameters relevant to sediment loads in rivers leads to mathematical prediction of the sediment load. This review article discusses the dynamic of sedimentation and analyses the use of GA as a hydrological model for accurately predicting sediment yield in a river, its potentials and shortcomings while recommending its modification.