Showing papers on "Siltation published in 2015"

Linking Stream Sediment Deposition and Aquatic Habitat Quality in Pearl Mussel Streams: Implications for Conservation

Abstract: The introduction of fine sediments into streams is considered to have a major effect on habitat quality affecting the reproduction of sensitive species such as unionid mussels and salmonid fishes. To date, there is a lack of information on the magnitude and spatio-temporal resolution of sediment introduction. This study aimed to quantify the spatio-temporal deposition of fine sediments in headwater streams in relation to the status of Margaritifera margaritifera and Salmo trutta. Fine sediment deposition was linked to physicochemical conditions of the adjacent streambed. The mean observed deposition of fine sediments over the study period was 3.4 kg m−2 month−1 with a high spatio-temporal variation ranging from <0.01 to 20.3 kg m−2 month−1. Discharge had the strongest influence on deposition rates. Mean differences in redox potential between free-flowing water and the interstitial zone were 90 mV. The spatio-temporal variability of physicochemical parameters increased with degree of degradation. High-quality reaches had more constant conditions. Our results indicate that monitoring of sediment quality and deposition in streams has to comprise several time points and study reaches, or should at least be conducted during periods with the most adverse habitat conditions, to allow valid assessments of habitat quality. In streams with increased fine sediment deposition, in-stream restoration measures are insufficient for the enhancement of pearl mussel habitats as a result of rapid clogging of interstitial pores. Only integrative catchment management based on detailed habitat analysis can ensure sufficient habitat quality for species sensitive to siltation. Copyright © 2014 John Wiley & Sons, Ltd.

Downstream Ecological Impacts of Controlled Sediment Flushing in an Alpine Valley River: A Case Study

Abstract: Sediment flushing may be effective to tackle the loss of reservoir storage as a result of siltation. When operationally possible, the impact of this practice on the downstream aquatic environment can be mitigated by limiting the sediment concentration of the discharged waters (controlled sediment flushing). However, this topic is poorly documented, and concerns arise when limits are discussed. We present the results of a 3-year field investigation concerning the controlled sediment flushing of a small reservoir on the Adda River, the main tributary of Lake Como—Italy. Two limits for suspended solid concentration (SSC) were adopted: 1.5 g L−1, as average value throughout the whole working day, and 3.0 g L−1, as alert threshold to adjust the ongoing activity. These constraints were essentially fulfilled in the course of the documented operations. The first year sediment flushing was more significant than the following year: 25 000 tons of fines below 2 mm in diameter were flushed in six non-consecutive days in summer 2010, while, one year earlier, 75 000 tons were flushed in 16 non-consecutive days. In the third year of investigation (2011), no sediment evacuation took place. The benthic macroinvertebrate and the fish communities were surveyed a short distance below the reservoir, that is, in the potentially more affected river reach. Clear pieces of evidence of environmental quality degradation were not detected; the adopted strategies can therefore be considered to be appropriate when planning sediment flushing management in comparable contexts. Copyright © 2014 John Wiley & Sons, Ltd.

Cost‐effectiveness of soil and water conservation measures on the catchment sediment budget–the laaba watershed case study, burkina faso

Abstract: In the Sahelian region, the high precipitation intensity and the daily rainfall extreme values are currently the main cause of soil erosion and land degradation. In addition, solid transport often leads to reservoir siltation and reduction of the amount of water available for agriculture. To cope with these issues, Soil and Water Conservation (SWC) measures have been regularly employed in the Sahelian area. However, a proper cost-effectiveness analysis of the impact of SWC interventions on the catchment sediment budget normally requires quantitative surveys on erosion and sedimentation processes. Where data for calibration and validation of models are scarce, an overall methodology to evaluate the economical sustainability of a proposed intervention can be of paramount importance. The study herein proposed aims to assess the monetary sustainability of SWC measures in limiting the reservoir siltation of the Laaba dam (Yatenga District, Northern Burkina Faso). In particular, the catchment sediment budget was estimated by means of morphological and pedologic parameters and dam sedimentation rates; a cost-effectiveness analysis was then performed to assess the economic sustainability of a possible SWC intervention. The proposed methodology showed interesting potentials for land and water management in Burkina Faso, particularly when data and financial resources are limited and where the application of detailed process-based models is not possible.

Identifying sediment sources by applying a fingerprinting mixing model in a Pyrenean drainage catchment

Abstract: Spanish Pyrenean reservoirs are under pressure from high sediment yields in their contributing catchments. Sediment fingerprinting approaches offer the potential to quantify the contribution of different sediment sources, evaluate catchment erosion dynamics and develop management plans to tackle, among other problems, reservoir siltation. Within this context, the objective of this study was to assess catchment source contribution changes both over a longitudinal river reach and to a reservoir delta deposit to improve our understanding of sediment supply dynamics. The catchment of the Isabena River (445 km2), located in the central Spanish Pyrenees, is an agroforest catchment supplying sediments, together with the Esera River, to the Barasona reservoir at an annual rate of ~350 t km2 with implications for reservoir longevity. The ability to discriminate between agricultural, forest, subsoil and scrubland sources based on geochemical, radionuclide and magnetic susceptibility fingerprint properties analysed in the 82 %. The channel bed sediments in the upper reach were dominated by subsoil sources (>80 %), and the lower reaches had a higher proportion of sediment coming from the agricultural source (>55 %). Contributions for delta sediments were dominated by agricultural, forest and subsoil sources but in varying proportions within the deposit. The switch in the sources of sediment between the headwaters and the catchment outlet was due to differences in the distribution of the land uses/land covers in the contributing areas. Differences between channel bed sediment and delta sediment source contributions were related to local sediment deposition conditions. The new unmixing approach is able to provide the optimal solution by a robust and integral Monte Carlo method guaranteeing a broader interpretation of the optimal solution including its dispersion in all unmixing cases. The results support the use of sediment fingerprinting approaches in this Spanish Pyrenees mountain catchment, which will enable us to better understand catchment sediment delivery to an important water supply reservoir.

Climatically induced levee break and flood risk management of the Gorakhpur region, Rapti River basin, Ganga Plain, India

Abstract: A densely populated city, Gorakhpur, located on the bank of Rapti river in the Ganga plain, is frequently affected by flooding. The Rapti river exhibits narrow channel within wide valley, channel bars, natural levee and river terraces. Artificial levees are constructed in the valley during low discharge period to mitigate the flood and also to provide the additional land to the society. These levees break during prolonged heavy rain and induce the catastrophic flood because it is not constructed by analyzing the capacity of the bracketed channel to accommodate the high discharge of the river. The precipitation, discharge, sediment load, and river water levels are correlated by making graphs between these parameters to analyze and identify the threshold limits and main reasons for flood. It explains that discharge and sediment load increases with precipitation during monsoon season, whereas the water storage capacity of the river decreases due to siltation and artificial levee. Hence, during heavy rain in this region, water rises in the channel, which either overtops the bank or breaks the levee and creates the flood. Flood inundation map was prepared using GIS techniques from 70 m base level to 81.5 m high level, which indicate the inundated area with every 1–2.5 m rise in the Rapti river water level. Rating curves and flood frequency curves have been prepared to identify the recurrence interval for major floods. It is concluded that prolong heavy precipitation, discharge variability of the river, siltation in the river bed, artificial levee, and anthropogenic impacts on younger river terraces and river valley leads to flood. Its affect is devastating when water level, discharge and sediment loads are above 77 m, 5000 m3/sec, and 5 metric tones respectively. The flood inundation map and recurrence interval are useful parameters for flood risk management, whereas the upland terrace is flood-free surface suitable for settlement. This study can be used as a model for other flood prone regions.

Factors Controlling the Suspended Sediment Yield During Rainfall Events of Dry and Wet Weather Conditions in A Tropical Urban Catchment

Abstract: The catchments of the Klang and Ampang Rivers are two sub-catchments that drain into the main Klang River, Selangor, Malaysia. Due to the development and siltation processes, the current capacity of the Klang River in the city centre is insufficient for accommodating the excess flood flow during major events, and, therefore overflows the riverbanks causing flash floods to occur in the Kuala Lumpur city centre. This study investigates the relationship between the rainfall, discharge and suspended sediment transport and its variations during the dry and wet periods in tropical sub-catchments; identifies the different hysteresis types of single flood events in the suspended sediment concentration/discharge relationships in the dry and wet periods, and determines the relationship between the types of single event hysteresis loops and the hydrological and sediment responses. Principal component analysis was performed to examine factors that have a major influence on the suspended sediment yields during both the dry and wet periods. The clockwise and counter-clockwise hysteresis loops occurring mostly during the dry period, can be described as events with moderate total rainfall, rainfall intensity (less than 10 mmh−1), average discharge and suspended sediment load. Counter-clockwise events occurring during the wet period are associated with low total rainfall, rainfall intensity, average discharge and suspended sediment load. The clockwise and counter-clockwise events that occurred in the wet period are related to events with a relatively high and low moisture condition, respectively. The figure-eight and complex hysteresis loop events occur predominantly during the wet period. The complex loop events occurred mostly during the wet period generates the highest suspended sediment load. The complex loop events occur mostly during the wet period generated the highest suspended sediment load.

Vulnerability assessment of soil erosion using geospatial techniques- a pilot study of upper catchment of markanda river

Abstract: Soil erosion remains a major threat to the Shivalik region of sub Himalayan mountainous environment The time required for data collection and high cost of research, is the difficulty in identification of area sensitive to water induced soil erosion by conventional methods However, these problems can be solved by the use of GIS based predictive models both at local and regional scale The main objective of the study is to assess the sites vulnerable to soil erosion based on multi-criteria evaluation (MCE) in the upper catchment of Markanda River The scope of present study is limited to identification of soil erosion sensitive sites GIS is used for derivation, integration, and spatial analysis of geographic layers of each theme Analytical Hierarchy Process (AHP) is used to calculate the weights of soil erosion influencing factors such as rainfall, vegetation, slope, soils, drainage density and land use Using AHP the weights derived for the factors are Rainfall (3193%), Drainage network (2308%), Soil (1772%), Slope (1414%), Drainage Density (745%) and Land use (568 %) It is observed that about 8 per cent of the total area of watershed is under severe risk of erosion, around 60 per cent of watershed lies in high to very high risk of erosion and 33 per cent of area shows slight to moderate risk of soil erosion The modeling result is validated by field survey and interpretation of high resolution satellite imagery Ground verification of resulted sites revealed that there are various visual indicators of erosional and depositional geomorphic features like sand point bars, cut bank erosion, abandoned channel and siltation in agriculture fields and the ponds Thus, the model’s result based on multi-criteria evaluation in GIS proves that identification of sites vulnerable to soil erosion is pre-requisite Such models based soil erosion scenario maps are important in planning conservation and control measures for soil erosion to prioritize the area according to severity of erosion

Dynamics of Land Cover and Impact on Stream flow in the Modder River Basin of South Africa: Case Study of a Quaternary Catchment

Abstract: Understanding how dynamics in individual land use types influence changes in streamflow is vital. Most hydrological studies are based on paired catchment and modelling approaches. These are data intensive and require a long period of monitoring. To determine the hydrological effects of tropical vegetation conversion over large areas, it is manageable to study the same basin over different time periods. The study analysed changes in historical stream flow patterns with reference to dynamics in land cover in C52A quaternary catchment of South Africa. Landsat images for years 1993, 2004 and 2013 were used for the development of land cover maps. Subsequently, step-change (median point change, Mann-Whitney and Kruskall Willis) and trend detection tests (Spearman’s rho and Kindall’s tau) were applied to average annual discharge and rainfall data for the catchment between 1984 and 2013.Tukey’s honestly significant difference (HSD) test was also used to compare the means. Results revealed that huge land cover changes coincided with significant (p<0.05) changes in streamflow although rainfall remained homogenous over the same period. This suggests that land cover change is intricately coupled to increases in streamflow. In addition, increased runoff is usually accompanied by increased rates of erosion and siltation. To ensure sustainable management of the catchment, therefore, soil and water conservation measures are critical within the broader context of integrated water resources management.

Quantification et evaluation de l’erosion hydrique en utilisant le modèle rusle et déposition intégrés dans un sig. application dans le bassin versant n'fis dans le haut atlas de marrakech (maroc)

Abstract: Located in the High Atlas central-western, N'Fis basin shows a dissected topography, frequent and violent floods, and its characterization by a litho-stratigraphic succession from the Precambrian to the current that engender significant erosion, and cause reservoirs siltation. This study aims to map areas vulnerable to erosion in the N'Fis Basin, developed a Geographic Information System (GIS) into account soil types, networks of drainage and traffic direction integrating remote sensing and spatial data. The results highlight the hydrographic phenomena and their effects on water resources. To achieve the objective of calculating the RUSLE equation Factor, it was based on annual and monthly climate data, field missions, the digital elevation model and satellite imagery. The result indicates a change in the rate of erosion and the values are between 7t / ha / year downstream of the wadi N'fis and a maximum value 1221t / ha / year to non-arable areas and areas with strong slope values.

Enhanced lakebed sediment erosion in Dongting Lake induced by the operation of the Three Gorges Reservoir

Abstract: Based on field-survey hydrological series in the Dongting Lake watershed from 1951 to 2011, the variations of lakebed sediment siltation/erosion (S/E) regimes of the Dongting Lake after the operation of the Three Gorges Reservoir (TGR) were analyzed. Significantly positive correlations were found between the flow rate from Zhicheng and the Three Outlets (r2=0.859, p<0.0001), and between the flow rate and sediment delivery rate at the Three Outlets (r2=0.895, p<0.0001). This indicated that the flow rate and sediment delivery rate at the Three Outlets were largely determined by the flow rate from the upstream Yangtze River. Sediment deposition amount in the Dongting Lake basin dropped from +4796.4×104 t during the period before the operation of TGR (1999–2002) to +684.1×104 t, +449.8×104 t and −559.6×104 t during the impoundment Phases I, II and III of TGR. The S/E regimes changed from a siltation-dominant to an erosion-dominant state under the pre-discharge, water-storage and water-supplement dispatch over the impoundment from Phase I to III. The sediment deposition amount decreased dramatically under the flood-storage dispatch over the impoundment Phase I to III. The estimated annual mean flow rate, sediment delivery rate and sediment concentration thresholds were respectively 970.81 m3/s, 466.82 kg/s and 0.481 kg/m3 for the upstream Three Outlets to maintain an erosion-dominant state in the downstream linked the Dongting Lake.

Investigation of the temporal relation of remotely sensed coastal water quality with GIS modelled upstream soil erosion

Abstract: Hydrological processes at the river basin influence the quality of downstream water bodies by controlling the loads of nutrients and suspended solids. Although their monitoring is important for social, economic and environmental reasons, in-situ measurements are too expensive and thus too sparse to describe their relations. The aim of this study is to investigate the temporal relations of soil erosion in the upstream part of river basins with water quality characteristics in the downstream coastal zone, using satellite remote sensing and GIS modelling. Data from satellite missions of MODIS, SRTM and TRMM were used to describe the soil erosion factors of the Universal Soil Loss Equation in three river basins, and MERIS satellite data was used to estimate chlorophyll-a and total suspended matter concentrations in the coastal zone of northwest Aegean Sea in Greece, where the rivers discharge. The resulting time series showed an average correlation of upstream rainfall with downstream water quality, which increased when soil erosion was introduced. Higher correlations were observed with the use of a time lag, revealing a variable delay between the three test sites. Lower correlation coefficients were observed for chlorophyll-a, due to the sensitivity of algae to environmental conditions. The use of free of charge satellite data and easy to operate GIS models renders the findings of this work useful for coastal zone management bodies, in order to help increase aquaculture productivity, predict algal blooms and predict siltation of ports. Copyright © 2014 John Wiley & Sons, Ltd.

Simulation of sedimentary dynamics in a small-scale estuary: the role of human activities

Abstract: Human activities, such as tidal sluice gate construction and reclamation, are prevalent along northern coastline of China and influence significantly sedimentary environments. The Sheyang River estuary is a small estuary situated on the Jiangsu coast. For the objective of storing fresh water, maintaining river channel depth and managing the land resource, a tidal sluice gate was constructed. At the same time, estuarine wetlands have been reclaimed extremely in recent decades. A numerical model based upon Delft3D was developed to quantify the impact of these human activities, and four simulation schemes were designed (a) tidal sluice gate present, but always closed; (b) tidal sluice gate not present; (c) tidal sluice gate present, but closed during flood and open during the ebb; and (d) intertidal area reclamation taking place in the estuary. A bathymetric survey confirmed the erosion and deposition results of the simulation. The rate of sediment deposition increased significantly after the gate was closed. However, during the third scheme, the sediment deposition rate reduced considerably; that was because the ebb current increased the scouring force when the gate was open, especially within the channel area close to the gate. Meanwhile, reclamation lessened erosion behind the gates and may have been enhanced by siltation. The coastline shifted seaward as the siltation area increased; it extended farther because of reclamation. Appropriate coastal management planning strategies must be developed to reduce negative effects of the channel siltation, resulting from the various forms of human activity. The results of this study can provide input to governmental recommendations on more effective tidal gate management strategies.

Impact of sediment transport of the Chellif River on silting of the Boughezoul reservoir (Algeria)

Abstract: Abstract In this article, we discussed the effect of sediment transport in the Chellif catchment on the silting of Boughezoul reservoir. Since 1934, when the impoundment of the dam, nine bathymetric surveys were carried out by hydraulic services. Based on the last two bathymetric surveys (1986 and 2005), we assessed the average annual rate of silting 0.67 million m3·year−1. Is a filling rate of 70% of the total capacity of the reservoir in 2011. Storage capacity has decreased from 55 million m3 in 1934 to 15 million m3 in 2011. Concentrations exceeding 300 g·l−1, recorded in the river upstream of Boughezoul reservoir, caused formation of density currents.

Mapping the risk of water erosion in the watershed of the Ningxia-Inner Mongolia reach of the Yellow River, China

Abstract: Mapping and assessing soil-erosion risk can address the likelihood of occurrence of erosion as well as its consequences. This in turn provides precautionary and relevant suggestions to assist in disaster reduction. Because soil erosion by water in the watershed of the Ningxia-Inner Mongolia reach of the Yellow River is closely related to silting of the upper reaches of the Yellow River, it is necessary to assess erosion risk in this watershed. This study aims to identify the soil-erosion risk caused by water in the watershed of the Ningxia-Inner Mongolia reach of the Yellow River from 2001 to 2010. Empirical models called Chinese Soil Loss Equation (CSLE) and Modified Universal Soil Loss Equation (MUSLE) were used to predict the erosion modulus in slope surfaces and gullies. Then the soil erosion risk in this watershed was assessed according to the classification criteria of soil erosion intensities (SL190-2007). The study results showed that the range of values of the erosion modulus in this watershed was 0–44,733 t/km2/a. More than 20% of the total watershed area was found to present an erosion risk, with the regions at risk mainly located in channels and their upper reaches, and in mountainous areas. To determine the regression coefficients of the erosion factors with respect to erosion modulus, a GWR (geographically weighted regression) was carried out using the ArcGIS software. It was found that the topographic factor has the highest contribution rate to the soil erosion modulus, while the highest contribution rate of the erosion factors to the erosion modulus and the largest values of the factors were not located in the same places. Based on this result, the authors propose that slope management is the most important task in preventing soil loss in this watershed, and the soil-conservation projects should be built according to the contribution rate of the erosion factors.

Dynamics and morpho-sedimentary interactions in the lower mesotidal estuary of Villaviciosa (NW Spain): A management proposal

Abstract: The accumulation of sediment in the mouth of Villaviciosa estuary (NW Spain) is becoming an obstaclefor the safe navigation in this estuary. One sector of its outer inlet is characterised by a broad shoal linkedwith a longshore bar of a beach, whose erosion is causing the silting of this area. On this basis, this paperaims to describe the processes that occurred in the lower part of the estuary due to the anthropogenicactivities in the channel and inlet. For this purpose, several measurements were made in the watercolumn and in the sedimentary bottoms to characterise the processes that occur in this area. Based onthese results, a dynamic and morpho-sedimentary model was developed to examine the interactionsbetween the lower estuary and the exposed part of the confining barrier beach, which allows to establishthe evolutionary trends of sedimentary bottoms linked to the marina of El Puntal. Different managementmeasures are carried out to reduce the impact of the sediment accumulation on the navigability, such asperiodically dredging in the inlet of the estuary, and the subsequent dumping of the sediments in areasnear to the closure depth. Consequently, future retreat of narrow inlet and sandy shoal can be avoided,maintaining the sedimentary volume in the system.

The Application of the Universal Soil Loss Equation by Using Free and Available Softwares

Abstract: Erosion is one of most serious form of soil degradation. In addition to reducing the productive potential of the soil, it can cause serious environmental damage such as pollution of the water resources, modifying the ecology of aquatic ecosystems and silting of watercourses. The Universal Soil Loss Equation (USLE) which estimates erosion under a variety of conditions like soil usage and soil coverage, slope, slope length, soil and rain types through the elaboration of thematic maps, is an important research tool on the erosion process and allows the partitioning of landscape instability levels. When applied through free software and free images, the costs for the study execution are reduced considerably. This study sought to map and to perform a qualitative analysis of the erosive susceptibility of the Paraiso das Aguas city – Mato Grosso do Sul state, Brazil, in 2013. The USLE mathematical model was applying by QGIS, gvSIG and LS-TOOLS softwares. The city obtained an average annual soil loss ranging from 0 to 1,307.32 ton/ha.year. Most part of the land, 91.94%, was classified as a low to moderate erosion since it has an erosive rate lower than 15 ton/ha.year. It was shown that the erosive dynamic was influenced mainly by land characteristics demonstrated through the topographical factor (LS).

Equilibrium sediment transport in lower Yellow River during later sediment-retaining period of Xiaolangdi Reservoir

Abstract: The Xiaolangdi Reservoir has entered the later sediment-retaining period, and new sediment transport phenomena and channel re-establishing behaviors are appearing. A physical model test was used to forecast the scouring and silting trends of the lower Yellow River. Based on water and sediment data from the lower Yellow River during the period from 1960 to 2012, and using a statistical method, this paper analyzed the sediment transport in sediment-laden flows with different discharges and sediment concentrations in the lower Yellow River. The results show that rational water-sediment regulation is necessary to avoid silting in the later sediment-retaining period. The combination of 3 000 m 3 /s Q 3 /s and 20 kg/m 3 S 3 (where Q is the discharge and S is the sediment concentration) at the Huayuankou section is considered an optimal combination for equilibrium sediment transport in the lower Yellow River over a long period of time.

The self-regulation process and its mechanism of channels’ bed changes in the Changjiang (Yangtze) Estuary in China

Abstract: Recent bathymetric changes in the Changjiang Estuary under the influence of artificial regulation engineerings and basin reservoirs have been analyzed based on the maritime charts since 1997 and recent fieldworks. The results indicate a slight erosion of the channels in the upper and middle estuary, continuing deposition and seaward move of the mouth bar crest and intensifying erosion at the nearshore seabed. It is noteworthy that the morphological evolution caused by intensive human activities dominates over the changes from nature process. First, the riverbes are eroded overall in the South Branch (SB), the South Channel (SC) and the upper and middle reaches of the North Channel (NC). The nearshore seabed outside the river mouth is being eroded slightly, which is attributed to the declining sediment supply from the Changjiang Basin due to the construction of the Three Gorges Dam upstream. The sediment above the seabed is very active and coarsened, meanwhile, sand waves are becoming more distinct. Second, a deposition occurs in the North Brach (NB), the mouth of the NC, the mouth bars of the North Passage (NP) and the South Passage (SP) and especially the main channel of the NP, where it shows a massive siltation after the deep waterway project. The reasons for the recent changes are not only the dynamic structure in estuarine mouth bars, but also the supply of sediment resuspension in a local and offshore area. Meanwhile, the severe erosion and siltation in some reaches is related to the construction of estuarine engineerings. It is indicated that the Changjiang Estuary is gradually self-adjusted and adapting to the varying natural factors and intensive human activities. The study on the mechanism of self-regulation of the recent bathymetric changes in the Changjiang Estuary has important and practical significance.

Influence of Wind Force on a Silt-Muddy Coast: Huanghua Harbor Coast, China

Abstract: Huanghua Harbor, a semiclosed harbor with three 13.32–23.4 km-long breakwaters forming a coal port and a general port, is located on the silt-muddy coast of the Bohai Sea in China. Frequent gales cause thick sedimentation at the entrance and in the outer waterway. In this study, a two-dimensional depth-averaged horizontal version of the Delft3D software is used to formulate a hydrodynamic suspended sediment transport and bed evolution model. This model is validated by field data, including the tidal level, the tidal current, and the concentration of suspended sediment. The validated model is applied to predict the suspended sediment transport for three different wind scenarios and the short-term morphological evolution from a gale and a wave. The suspended sediment concentrations largely increase from gale-induced currents and waves. The predictions from the gale and its induced wave in 2003 and in 2012 indicate that suspended sediments are driven by the current along the jetties and can be easily...

Intervention of Naraj Barrage: Its effects on sediment inflows into Chilika Lake, India

Abstract: Chilika Lake, Asia's largest brackish water lagoon, is located in the state of Odisha on the east coast of India. It was designated as a Ramsar site in 1981, being the first Indian wetland of international importance under the Ramsar convention. Siltation of the lake is become a major concern, because it is leading to various geomorphic changes that are affecting the shape and size of the lagoon, which receives a major silt load through the Daya and Bhargovi rivers (both being branches of the Mahanadi river) via the Kathajodi and Kuakhai rivers. The Naraj barrage was constructed at the mouth of the Kathajodi river to regulate its inflow, and also its silt load, into the lagoon. Two observatories are established in the Daya and Bhargovi rivers to determine the quantity of silt entering Chilika Lake through the rivers, with the bed load and suspended (total solids) being measured. Various effects of siltation in the lagoon because of the barrage are analysed in this study, to include the pre- and postconstruction situation. By considering different flood situations in the Mahanadi river, various alternate strategies for operation of the Naraj barrage were studied, with the goal of minimizing the siltation in Chilika Lake. These alternate operation strategies, and their potential effects on the inflow into the lagoon, are analysed and discussed in this report.

Combination of Satellite Images and Numerical Model for the State Followed the Coast of the Bay of Bejaia-Jijel

Abstract: Bay of Bejaia-Jijel extends over a length of 100 km with the presence of the ports, the beaches of rivers that discharge of the bay. This area characterized by strong economic activity, namely tourism and fisheries. However, severe erosion, high hydrodynamic activity and significant silting of ports affect this bay. Hence, the interest of this study, which tries to explain these phenomena, based on multisource data with multitasking models. First, we developed an algorithm that can convert satellite images in coastline vector. This technique applied to three images LANDSAT TM and OLI sensed in 1987, 2011; 2015. The multi-temporal monitoring coastlines show that the region suffered severe erosion. This erosion is 4.6 m / year for the period of 1987/2011 and 1.5 m / year for the period 2011/2015. To explain this phenomenon we interested to do a study of hydrodynamics using the SWAN software. We used a long time series of wind speed and direction to discern extreme cases in the region. For maximum wind, the significant wave height recorded very high values and a very active orbital current with a speed that exceeds 0.7 m / s. Numerical modelling has allowed us to explain the erosion but does not explain the speed difference coastline. To find the explanation of erosion speed difference between the two periods we consulted the administrative archive of the region. In the archive, the number of authorized hourglasses is, 12 in the 90s, but 36 quarries operate haphazardly. In this period the balance of suspended matter is completely unbalanced which promotes erosion. After 2008, these quarries were closed therefore the balance of the suspended material has improved and consequently coastal erosion has decreased.