Dam Operation Research Articles

Total Mercury Mass Load from the Paglia-Tiber River System: The Contribution to Mediterranean Sea Hg Budget.

The Mediterranean Sea is characterized by a marked mercury (Hg) geochemical anomaly, arising in part from large Hg deposits. Mercury mass loads discharged from the Monte Amiata mining district (Central Italy) to the Mediterranean Sea through the Paglia–Tiber River system were estimated. Data from two seasons showed that up to 40 kg year−1 of Hg are drained to Tiber River and finally to the Mediterranean Sea. The mercury mass loads varied in different seasons, from 3 mg day−1 in the upper section of Paglia River in November to 42 g day−1 before the confluence with Tiber River in June. Along Tiber River, up to 15 ng L−1 of the total Hg found at a site after Rome showed that Hg can be discharged to the sea. The Alviano reservoir along Tiber River acts as a temporary trap for Hg-rich particulate, while dam operations may promote Hg release (up to 223 g day−1). The combination of hydrologic factors controlling Hg transport, the torrential regime in the upper catchment of Paglia River, the waterway steepness, together with Hg-contaminated legacy sediments in the Paglia River floodplain, make the Paglia–Tiber River system a long-lasting intermittent source of Hg to Tiber River and the Mediterranean Sea.

Seismic Safety Review of Gravity Dam Based on Finite Element Method

With the change of the seismic parameter zoning map of China (GB 18306-2015), the seismic grade of reservoir dams in some areas had changed. At the same time, the standard for seismic design of hydraulic structures (GB 51247-2018) also put forward new requirements for the seismic calculation of reservoir dams. In order to ensure the safe operation of reservoir dams, it is necessary to review the seismic safety based on the finite element numerical simulation technology. Taking the retaining dam section of a gravity dam as an example, a finite element model of the retaining dam section was established, the corresponding calculation and analysis of ground motion were carried out using the mode decomposition response spectrum method, and the seismic safety evaluation of the retaining dam section was carried out according to the calculation results. The results show the following: (1) after considering the effect of hydrodynamic pressure, the natural frequency of the dam body has been significantly reduced, and the first-order natural frequency has been reduced by about 10%; (2) in addition to the local tensile stress at the dam heel, the rest of the vertical stress on the foundation surface of the retaining dam section is compressive stress, and the length of the tensile stress is less than the distance from the dam heel to the curtain center line, which met the requirements; (3) the antisliding stability safety factor of the retaining dam section is greater than the design value in the specification and meets the safety requirements; and (4) the seismic safety of the retaining dam section meets the standard requirements, and the seismic grade is evaluated as grade A.

Land use and land cover changes resulting from the urban El Molinito reservoir in the drying Sonoran River Basin

ABSTRACT Although the impacts of dams on the environment and human populations have been widely documented, many developing countries continue constructing large dams. In Mexico, impact studies have neglected to analyze downstream effects of dams. Thus, we analyzed land use and land cover (LULC) changes downstream of El Molinito dam, constructed on the Sonora River in northwest Mexico. We used Landsat Thematic Mapper (TM) to generate classifications (for 1993, 2002 and 2011), from which an assessment is performed to identify the principal changes. In addition, we analyzed changes in photosynthetic activity using the simple but informative Normalized Difference Vegetation Index (NDVI). We found a drastic decline between 1993 and 2011 in agricultural LULC because of water diversions from El Molinito. This study demonstrates the need for agencies responsible for water management to better assess the negative effects of dam construction and operation, especially on the livelihoods of downstream rural communities.

Unraveling the Importance of the Yangtze River and Local Catchment on Water Level Variations of Poyang Lake (China) After the Three Gorges Dam Operation: Insights From Random Forest Modeling

Investigating the contributions of the factors influencing lake water level and their related changes with regard to hydraulic facilities is vital for understanding the driving mechanism of water level variations under the manifold pressures from anthropogenic activities and climate change. In this study, a random forest (RF) model was used to investigate the changes of the relationship between water level and discharge of the Yangtze River and local tributaries in Poyang Lake, China, based on daily hydrological data from 1980 to 2018. The results indicated that RF exhibited robust capability for water level prediction in Poyang Lake, with average R2 of 0.95, 0.88, 0.92, and 0.94 for the dry, rising, wet, and recession seasons, respectively. Predictor importance analysis showed that the discharge of the Yangtze River had greater influence on the water level than the discharge of local tributaries except for the dry season in Poyang Lake, where the influence on the water level was evident with discharge less than 5,000 m3/s. The influence of the Yangtze River also showed a clear attenuation pattern as the distance from the outlet of the lake increased, where the water level was constantly regulated by the Yangtze River. In addition, the partial dependence plots also indicated that the Yangtze River discharge changes after the TGD operation have resulted in remarkable water level decreases in the wet and recession seasons, especially for the recession period. Meanwhile, a slight increase in water level was predicted under identical discharge of local catchment in the dry season, which was only concentrated in the outlet of the lake. This study indicated the RF model as a robust technique for water level predictions and attribution analysis under multiple temporal and spatial scales. Moreover, this study confirmed the uneven influences of the Yangtze River and local tributaries on water level across different seasons, gauging stations, and phases.

Short-range reservoir inflow forecasting using hydrological and large-scale atmospheric circulation information

Short and long range reservoir inflow forecast is essential for efficient real time operational planning, scheduling of hydroelectric power system and management of water resources. Large-scale climate phenomenon indices have a strong influence on hydrological processes under complex weather conditions, and it should be considered to forecast reservoir inflow for efficient dam operation strategies. This study aims to explore the relevance of large-scale climate phenomenon indices in improving the reservoir inflow prediction at short-term time scales. This paper presents a simple and effective framework to combine various data-driven machine learning (ML) algorithms for short-range reservoir inflow forecasting. Random Forest (RF), Gradient Boosting Regressor (GBR), K-Nearest Neighbors Regressor (KNN), and Long Short-Term Memory (LSTM) were employed for predicting daily reservoir inflows considering various climate phenomenon indices (e.g., Arctic Oscillation, North Atlantic Oscillation, and Southern Oscillation Index) and hydroclimatic variables (precipitation), accounting for time-lag effects. After training the individual ML algorithm, a framework was developed to create an ensemble model using a robust weighted voting ensemble method to quantify forecasting uncertainty and to improve the model performance by combining the inflow results of the single ML model and the highest vote is chosen based on the weights assigned to the single ML model. The developed framework was examined in two distinct reservoirs located in India and California, USA. The ensemble model consistently outperformed the standalone RF, GBR, KNN, and LSTM in predicting high (flood control and monsoon seasons) and low flows (runoff and non-monsoon seasons) of both study reservoirs. The demonstrated short-term reservoir forecasting model allows reservoir operators to adapt and add regional hydrological and large-scale climate indices in real-time decision-making. The presented framework can be applied for any reservoir inflow forecasting.

Experimental reductions in subdaily flow fluctuations increased gross primary productivity for 425 river kilometers downstream.

Aquatic primary production is the foundation of many river food webs. Dams change the physical template of rivers, often driving food webs toward greater reliance on aquatic primary production. Nonetheless, the effects of regulated flow regimes on primary production are poorly understood. Load following is a common dam flow management strategy that involves subdaily changes in water releases proportional to fluctuations in electrical power demand. This flow regime causes an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production. In collaboration with dam operators, we designed an experimental flow regime whose goal was to mitigate negative effects of load following on ecosystem processes. The experimental flow contrasted steady-low flows on weekends with load following flows on weekdays. Here, we quantify the effect of this experimental flow on springtime gross primary production (GPP) 90-to-425km downstream of Glen Canyon Dam on the Colorado River, AZ, USA. GPP during steady-low flows was 41% higher than during load following flows, mostly owing to nonlinear reductions in sediment-driven turbidity. The experimental flow increased weekly GPP even after controlling for variation in weekly mean discharge, demonstrating a negative effect of load following on GPP. We estimate that this environmental flow increased springtime carbon fixation by 0.27g C m-2 d-1, which is ecologically meaningful considering median C fixation in 356US rivers of 0.44g C m-2 d-1 and the fact that native fish populations in this river are food-limited.

Application of MOMSA algorithm for optimal operation of Karun multi objective multi reservoir dams with the aim of increasing the energy generation

Multi-reservoir system operation is a challenging and complex task, because of the curse of uncertainties, nonlinearities, dimensionalities and conflicts among the various contradictory objectives. Contemporaneous optimization of such competing objectives needs improving the capability of existing optimization algorithms. This study reports the first application of the recently-introduced multi-objective moth swarm algorithm (MOMSA) in optimization of long-term operation of the large Karun multi-purpose multi-reservoir system. In this algorithm, the decision variables were defined in such a way that the algorithm synchronization capability has improved. Furthermore, a robust mechanism (crowding distance mechanism) with high exploratory capability was employed to select the most efficient solutions within the population. To evaluate the algorithm's efficiency, the results of MOMSA were compared with two well-known multi-objective algorithms of the non-dominated sorting genetic algorithm-II (NSGA-II) and the strength Pareto evolutionary algorithm-II (SPEA-II). To compare the capability of these algorithms, a set of statistical indices including the generational distance (GD), the spacing (S), the spread (Δ), and the maximum spread (MS), along with four reservoir's performance evaluation indicators of the reliability (Rel), the vulnerability (Vul), the resiliency (Res), and the sustainability index were employed. The results demonstrated the superior performance of the MOMSA in solving the Karun multi-reservoir system problem with GD = 259.64, S = 3574.69, Δ = 0.755 and MS = 18420.8. The MOMSA, with the optimized average annual energy production of 15669.7 GW, outperformed the NSGA-II (7569.1 GW) and SPEA-II (9026.3 GW) algorithms. Furthermore, the developed algorithm could supply the downstream demands with a sustainability index of 86.73%, while the corresponding values for the NSGA-II, the SPEA-II and the real operating conditions were 22.73%, 46.09% and 78.87%, respectively. In addition, among the utilized algorithms, the MOMSA demonstrated the best results for flood control purpose. The superior performance of MOMSA will ensure it as a robust algorithm in the optimization of complex and large-scale problems.

Effects of Fly Ash Dosage on Shrinkage, Crack Resistance and Fractal Characteristics of Face Slab Concrete

The crack resistance of face slab concretes to various shrinkages is crucial for the structural integrity and the normal operation of concrete-faced rockfill dams (CFRDs). In this work, the effects of fly ash with four dosages (i.e., 10%, 20%, 30% and 40%) on the drying shrinkage, autogenous shrinkage and the cracking resistance of face slab concrete were studied. Besides, the difference in shrinkage behavior due to fly ash addition was revealed from the viewpoint of the pore structure and fractal dimension of the pore surface (Ds). The findings demonstrate that (1) the incorporation of 10–40% fly ash could slightly reduce the drying shrinkage by about 2.2–13.5% before 14 days of hydration, and it could reduce the drying shrinkage at 180 days by about 5.1–23.2%. By contrast, the fly ash addition could markedly reduce the autogenous shrinkage at early, middle and long-term ages. (2) Increasing fly ash dosage from 0 to 40% considerably improves the crack resistance of concrete to plastic shrinkage. Nevertheless, the increase in fly ash dosage increases the drying-induced cracking risk under restrained conditions. (3) The pore structures of face slab concrete at 3 and 28 days become coarser with the increase in fly ash dosage up to 40%. At 180 days, the pore structures become more refined as the fly ash dosage increases to 30%; however, this refinement effect is not as appreciable as the fly ash dosage increases from 30% to 40%. (4) The Ds of face slab concrete is closely related with the concrete pore structures. The Ds of face slab concrete at a. late age increases from 2.902 to 2.946 with increasing of the fly ash dosage. The pore structure and Ds are closely correlated with the shrinkage of face slab concrete. (5) The fly ash dosage around 30% is optimal for face slab concretes in terms of lowering shrinkage and refining the pore structures, without compromising much mechanical property. However, the face slab concretes with a large fly ash dosage should be well cured under restrained and evaporation conditions at an initial hydration age.

Development of a Revised Multi-Layer Perceptron Model for Dam Inflow Prediction

It is necessary to predict dam inflow in advance for flood prevention and stable dam operations. Although predictive models using deep learning are increasingly studied, these existing studies have merely applied the models or adapted the model structure. In this study, data preprocessing and machine learning algorithms were improved to increase the accuracy of the predictive model. Data preprocessing was divided into two types: The learning method, which distinguishes between peak and off seasons, and the data normalization method. To search for a global solution, the model algorithm was improved by adding a random search algorithm to the gradient descent of the Multi-Layer Perceptron (MLP) method. This revised model was applied to the Soyang Dam Basin in South Korea, and deep learning-based discharge prediction was performed using historical data from 2004 to 2021. Data preprocessing improved the accuracy by up to 61.5%, and the revised model improved the accuracy by up to 40.3%. With the improved algorithm, the accuracy of dam inflow predictions increased to 89.4%. Based on these results, stable dam operation is possible through more accurate inflow predictions.

Sensitive indicators of soil nutrients from reservoir effects in the hot-dry valleys of China

The construction of giant reservoirs can affect the hydroclimatic cycles and related soil nutrient recycling. The current understanding of variations in soil nutrients driven by reservoir impoundment is limited because soil often reacts slowly to changes and the impoundment effects can be masked by various factors, making detection difficult. The soils in the hot-dry valleys suffer from a savanna-like hot and dry climate, making it an ideal area for studying the effect of reservoir impoundment on the soil. Here we collected 138 soil samples in April and November along the cascading reservoirs located in the hot-dry valleys of China, including Xiangjiaba, Xiluodu, Baihetan, and Wudongde reservoirs. Results showed that (1) the reservoir impoundment does alter the soil nutrients. The contribution of the impoundment to the variation of soil nutrients was 3.82% in April and 6.44% in November. (2) Compared to April, a relatively dry and cold November is preferred for revealing the reservoir impact on soil nutrients in the hot-dry valleys. (3) Available nitrogen and available phosphorus, followed by soil organic matter, are potential sensitive indicators that can be used to reflect the reservoir impoundment effects. Additionally, pH may be a potential indicator, particularly in the head reservoir area. It is important to note that the effect of reservoir impoundment on soil nutrients is easily masked. This study encourages dam operating agencies, policymakers, and researchers to regard reservoirs as integral parts of the forcings that modify soil nutrients and is an essential step in gaining an insight into the impact of hydropower development on surrounding terrestrial ecosystem services related to soil nutrients.

Spatial and temporal changes in nutrients associated with dam regulation of the Yellow River

Sediment regulation via manipulating dam operations is an effective solution for dealing with reservoir siltation and downstream channel incision. Large amounts of sediment and thereby nutrients can be discharged within a short period of time. To ascertain the concentration of and transformation between dissolved and particulate nutrients during such periods, we conducted field observations in the Xiaolangdi Reservoir and its downstream reach during the sediment regulation stage of the Water-Sediment Regulation Scheme (WSRS) in 2018. We found that water and sediment characteristics differed significantly pre- and post-WSRS period. Nutrient concentrations varied significantly among the dissolved, suspended, and deposited phases, while no significant differences were observed between the reservoir and downstream reach, except for dissolved total carbon, particulate ammonium nitrogen, and calcium-bound phosphorus. Total nitrogen (TN) and total phosphorus (TP) concentrations of the dissolved phase were significantly positively correlated with suspended sediment concentration (SSC) and electrical conductivity (EC) (p < 0.05). Total organic carbon (TOC) concentration of the suspended phase was significantly negatively correlated with EC and median particle size (D50) (p < 0.05). Nutrient concentration during the deposited phase was less correlated to selected hydrological and physical parameters. Nutrient transformation between the deposited phase and the suspended and dissolved phases were higher than those between suspended and dissolved phases. TP transformation was closely related to hydrological parameters (SSC and D50), while TN transformation was predominantly related to physical parameters (EC and DO). The concentration and transformation of nutrients during the transport process from the reservoir to downstream were likely driven by different factors. In conclusion, reservoir management practices like WSRS could mitigate nutrients retention in reservoir, however, leading to higher nutrients transformation downstream.

Inferring the joint operation of high Aswan dam and Toshka depression using multi-sensor satellite approach

Remote sensing observations with high spatial and temporal resolutions have been successful in overcoming the challenge of data availability in ungauged basins. In this study, we applied a Multi-Sensor Satellite (MSS) approach to understand the reservoir operation in the Nile river basin (NRB) with the focus on the joint operation of High Aswan Dam (HAD) and Toshka depression, located in the southwestern part of HAD. The MSS data, which integrates Landsat (5-8), Sentinel-2A, MODIS with hydrological model outputs, are used in a water balance model to derive the operation of HAD reservoir and Toshka depression. The results show that the MSS approach has a reasonable skill when modelling the Toshka inflow (i.e. HAD spillway outflow) with a Relative Error and R2 of −19.14% and 0.79, respectively (for the period 1998–2002). Overall, our study provides a framework that harnesses free available sensors to infer the operation of lakes and reservoirs in the NRB.

Theoretical Foundations for Calculating the Erosion of Soil Dams during Overflow of Water over the Ridge

Large-scale hydraulic engineering construction associated with the erection and operation of large dams and reservoirs has an impact on the ecosystem and physical and geographical characteristics of the construction area. In addition, during the passage of catastrophic floods and high waters, the danger of a hydrodynamic accident increases, i. e. overflow of reservoirs, overflow of masses over the ridge of an earthen dam and its destruction, accompanied by the formation of a closure channel and the outflow of an unsteady water flow through it into the lower reaches in the form of a breakthrough wave. The process of erosion of an underground dam due to the overflow of water over the ridge can be divided into two stages. During the first one, the lower slope is eroded, along which the water moves as if by a rapid current. The profile of the dam, initially trapezoidal, by the end of the erosion takes a shape close to triangular, and the ridge mark on the side of the upper slope remains constant. The second stage is characterized by an intensive reduction of the ridge; the dam quickly takes the form of a practical profile spillway, which persists until the end of erosion. At the same time, there is an intensive expansion of the closure channel. As the analysis showed, the existing mathematical models used to calculate the dynamics of the erosion of the dam, especially its first stage before the expansion of the closure channel, are not perfect. The article presents a refined methodology developed by the authors for modeling the process of erosion of ground dams during water overflow over the ridge. The calculations made in accordance with this methodology make it possible to construct a flow hydrograph in the location of the eroded dam. The methodology can be used in the development of project documentation at the first stage of dam design, as well as in determining the forecast quantitative and qualitative characteristics of the water regime of reservoirs.

Evaluating a reservoir parametrization in the vector-based global routing model mizuRoute (v2.0.1) for Earth system model coupling

Abstract. Human-controlled reservoirs have a large influence on the global water cycle. While global hydrological models use generic parameterizations to model dam operations, the representation of reservoir regulation is still lacking in many Earth system models. Here we implement and evaluate a widely used reservoir parametrization in the global river-routing model mizuRoute, which operates on a vector-based river network resolving individual lakes and reservoirs and is currently being coupled to an Earth system model. We develop an approach to determine the downstream area over which to aggregate irrigation water demand per reservoir. The implementation of managed reservoirs is evaluated by comparing them to simulations ignoring inland waters and simulations with reservoirs represented as natural lakes using (i) local simulations for 26 individual reservoirs driven by observed inflows and (ii) global-domain simulations driven by runoff from the Community Land Model. The local simulations show the clear added value of the reservoir parametrization, especially for simulating storage for large reservoirs with a multi-year storage capacity. In the global-domain application, the implementation of reservoirs shows an improvement in outflow and storage compared to the no-reservoir simulation, but a similar performance is found compared to the natural lake parametrization. The limited impact of reservoirs on skill statistics could be attributed to biases in simulated river discharge, mainly originating from biases in simulated runoff from the Community Land Model. Finally, the comparison of modelled monthly streamflow indices against observations highlights that including dam operations improves the streamflow simulation compared to ignoring lakes and reservoirs. This study overall underlines the need to further develop and test runoff simulations and water management parameterizations in order to improve the representation of anthropogenic interference of the terrestrial water cycle in Earth system models.

A study of Environmental and Ecological impacts due to Construction and Operation of Tehri-Polavaram Dam

Any water resources project has both a positive and a negative impact on the environment. Sometimes these environmental losses are unavoidable, so it is most important to minimize the environmental losses and their social-ecological and geopolitical impact. Environmental impact assessment plays an important role in identifying, predicting, and mitigating the various impacts on the environment. This paper presents the details of the construction of Tehri and Polavaram dam projects and their various impacts on the environment and ecological aspects. Any water resource expansion that fulfills minimum needs without endangering future generations’ ability to fulfils their own will be considered sustainable. There are a number of factors to consider when it comes to the long-term effects of dams on the surrounding environment, including redevelopment and relocation of people and businesses, socioeconomic influence on the surrounding area, and environmental concerns such as sedimentation, among others. Sustainable development also means that, in addition to minimizing the dam’s negative effects on the environment, making sure that the benefits of the dam outweigh the negative ones. As a result, it is recognized that water resource projects must be intended, implemented, and managed to meet future population demands while reducing disturbance to the existing eco-system and incorporating effective control measures at various phases to ameliorate any adverse effects.

Evaluation of hydrological regime alteration and ecological effects in the middle and lower of the Yangtze River, China

Abstract The flow regime is regarded as the key driver of the structure and function of riverine ecosystems. This study uses an ecologically meaningful indicator (range of variability approach method) to assess the dynamic runoff process in the middle and lower reaches of the Yangtze River, whose changes negatively affect the ecosystems in the study area. In addition, the study quantitatively analyzed the contribution rate of human activities and climate change to flow change. The effects of ecological index changes on four famous major carp species (FFMC) resources in the middle and lower reaches of the Yangtze River were studied. The results show that after the Three Gorges Dam (TGD) operation, the hydrological changes of Yichang Station, Hankou Station, and Datong Station were 65, 58, and 46%, respectively. The weight of the impact of human activities on runoff is smaller the farther away from the TGD. The impact weights of human activities at the three hydrological stations in the middle and lower reaches of the Yangtze River are 73.69, 67.98, and 56.84%, respectively. The operation of the Three Gorges Project caused changes in the hydrological regime of the Yangtze River, which adversely affected the structure and quantity of FFMC populations.

The impact of the Tropical Water Project on the operation of Darbandikhan dam

In addition to global warming and population growth, the Turkish and Iranian water projects have negatively affected the water resources in Iraq. Recently, Iran has implemented its largest water project (The Tropical Water Project – TWP). This project aims to store the flowing water in the Sirwan and Zmkan rivers (i.e., tributaries of the Diyala River) to provide irrigation, domestic, and industrial water for areas inside and outside the Diyala River Basin. The Darbandikhan dam and Halabja water supply project are located on the Diyala River. In this study, the impact of the TWP on the operation of the Darbandikhan dam and Halabja water supply project was investigated. The monthly inflow data of the Darbandikhan dam from September 1991 to December 2017 were used to simulate the operation of the dam using the HEC-ResSim 3.1 package. Two scenarios were adopted for the operation of the Darbandikhan dam. In the first scenario, the Darbandikhan dam operation was simulated without considering the effects of the TWP project.In contrast, in the second scenario, the full operation of the TWP project was considered. The results revealed that about 48.4% of the power generation capacity would be lost, and the water surface elevation in the reservoir would be affected significantly due to the TWP project. The water surface elevation would be at or below 443 m for long periods, which will affect the operation of the Halabja water supply project.

Evaluasi Kinerja Embung Kecil di Kabupaten Kupang

The construction of a small dam in the Kupang District aims to help supply water needs for the agricultural sector, livestock sector, and human needs during the dry season. This study aimed to evaluate the performance of 30 small dams built in Kupang Regency through three aspects, namely physical aspects, utilization aspects, and operation and maintenance aspects. The method used is the Survey Method, Descriptive Analysis and the Likert Scale Method. The results showed that the performance of the small dam's physical aspects in Kupang Regency was in bad condition, with a bad percentage value of 73.23%. The minor dam utilization aspects in Kupang Regency were in good condition with a good percentage value of 55.75%. The operation and maintenance aspects of the small dam in Kupang Regency were in bad condition, with a bad percentage value of 63.74%. Overall, the percentage of small dams studied in the Kupang Regency that experienced a decline in function was 69.63%, and the percentage of small reservoirs that were still functioning was 31.37%.

A comparison of machine learning models for suspended sediment load classification

The suspended sediment load (SSL) is one of the major hydrological processes affecting the sustainability of river planning and management. Moreover, sediments have a significant impact on dam operation and reservoir capacity. To this end, reliable and applicable models are required to compute and classify the SSL in rivers. The application of machine learning models has become common to solve complex problems such as SSL modeling. The present research investigated the ability of several models to classify the SSL data. This investigation aims to explore a new version of machine learning classifiers for SSL classification at Johor River, Malaysia. Extreme gradient boosting, random forest, support vector machine, multi-layer perceptron and k-nearest neighbors classifiers have been used to classify the SSL data. The sediment values are divided into multiple discrete ranges, where each range can be considered as one category or class. This study illustrates two different scenarios related to the number of categories, which are five and 10 categories, with two time scales, daily and weekly. The performance of the proposed models was evaluated by several statistical indicators. Overall, the proposed models achieved excellent classification of the SSL data under various scenarios.

Dam operations, local rainfall, changing settlement growth pattern and flooding in the Niger Delta, Nigeria

Since 1968 when the Kainji dam was built on the R. Niger in Nigeria, many other large dams, and more than 10 formal, large-scale irrigation schemes have been constructed in the R. Niger drainage basin. By the early 1990s, a perception had developed in the Niger Delta, the floodplain and tidal region comprising the terminal distributaries of the R. Niger, that the operations of these dams and upstream land use have caused a marked reduction in river discharges in the Delta. Concurrently with the dam construction era (1964–1995), there was a 30-year (1968–1998) drought particularly in the Sudan-Sahel Zone of West Africa, a significant section of the R. Niger drainage basin. This negatively impacted the flow regime in the Delta. The long-term low flow regime appears to have influenced the direction of settlement growth in the region. Rainfall started reverting to pre-drought levels circa 1995, promoting spate flows on the R. Niger, its tributaries and the Delta. The consequence has been debilitating quasi-annual flooding also perceived in the Niger Delta as another result of dam operations. This study attempts to elucidate the cause of flooding in the Niger Delta, and particularly the roles of dam operations, local rainfall, and direction of settlement growth on the flooding phenomena. Flooding and flood impact mitigating solutions are proffered.