Water Level Dynamics Research Articles

Combined Physical Process and Deep Learning for Daily Water Level Simulations across Multiple Sites in the Three Gorges Reservoir, China

Water level prediction in large dammed rivers is an important task for flood control, hydropower generation, and ecological protection. The variations of water levels in large rivers are traditionally simulated based on hydrological models. Recently, most studies have begun applying deep learning (DL) models as an alternative method for forecasting the dynamics of water levels. However, it is still challenging to directly apply DL to the simultaneous prediction of water levels across multiple sites. This study attempts to develop a hybrid framework by combining the Physical-based Hydrological model (PHM) and Long Short-Term Memory (LSTM). This study hypothesizes that our hybrid model can enhance the predictive accuracy of water levels in large rivers, because it considers the temporal-spatial information of mainstream-tributaries relationships. The effectiveness of the proposed model (PHM-BP-LSTM) is evaluated using the daily water levels from 2012 to 2018 in the Three Gorges Reservoir (TGR), China. Firstly, we use a hydrological model to produce a large amount of water level data to solve the limited training data set. Then, we use the Back Propagation (BP) neural network to capture the mainstream-tributaries relationship. The future changes in water levels in the different mainstream stations are simultaneously predicted by the LSTM model. We reveal that our hybrid model yields satisfactory accuracy for daily water level simulations at fourteen mainstream stations of the TGR. We further demonstrate the proposed model outperforms the traditional machine learning methods in different prediction scenarios (one-day-ahead, three-day-ahead, seven-day-ahead), with RMSE values ranging from 0.793 m to 1.918 m, MAE values ranging from 0.489 m to 1.321 m, and the average relative errors at each mainstream station are controlled below 4%. Overall, our PHM-BP-LSTM, combining physical process and deep learning, can be viewed as a potentially useful approach for water level prediction in the TGR, and possibly for the rapid forecast of changes in water levels in other large rivers.

Optimizing selective withdrawal strategies to mitigate hypoxia under water-level reduction in Germany's largest drinking water reservoir

Water-level reduction frequently occurs in deep reservoirs, but its effect on dissolved oxygen concentration is not well understood. In this study we used a well-established water quality model to illustrate effects of water level dynamics on oxygen concentration in Rappbode Reservoir, Germany. We then systematically elucidated the potential of selective withdrawal to control hypoxia under changing water levels. Our results documented a gradual decrease of hypolimnetic oxygen concentration under decreasing water level, and hypoxia occurred when the initial level was lower than 410 m a.s.l (71 m relative to the reservoir bottom). We also suggested that changes of hypoxic region, under increasing hypolimnetic withdrawal discharge, followed a unimodal trajectory with the maximum hypoxic area projected under the discharge between 3 m3/sec and 4 m3/sec. Besides, our results illustrated the extent of hypoxia was most effectively inhibited if the withdrawal strategy was applied at the end of stratification with the outlet elevation at the deepest part of the reservoir. Moreover, hypoxia can be totally avoided under a hybrid elevation withdrawal strategy using surface withdrawal during early and mid stratification, and deep withdrawal at the end of stratification. We further confirmed the decisive role of thermal structure in the formation of hypoxia under water-level reduction and withdrawal strategies. We believe the conclusions from this study can be applied to many deep waters in the temperate zone, and the results should guide stakeholders to mitigate negative impacts of hypoxia on aquatic ecosystems.

ANALYSIS OF INFILTRATION WATER INTAKES PRODUCTIVITY

Purpose. Construction of new and reconstruction of existing water supply systems, in order to increase water consumption, provides for the search and analysis of water supply new sources and water intake facilities. This issue acquires particular importance when looking for additional power sources for water supply systems with relatively low water consumption. To reduce the load on wastewater treatment plants that process water from open sources, infiltration intakes are used, which take water from underground aquifers. Infiltration water intakes can be vertical and consist of wells united by prefabricated pipelines or horizontal and have an underground horizontal water intake part − a drainage pipe. Therefore, the problem arises of determining the water intake that has the highest productivity under the same local conditions. Methodology. The productivity of water intakes is characterized by the influence of determining factors on the flow rate of water intakes with one-way feeding in a free-flow aquifer. The conditions of the location of the intake parts of the intakes in the aquifer and their sizes were considered as factors of influence. Results. The analysis of the existing methods for determining the productivity of underground infiltration water intake structures, depending on their location, the influence of water supply sources and design features. It has been determined that the greatest impact on the productivity of water intakes is the amount of water level decrease in the aquifer during water withdrawal, that is, the position of the dynamic water level relative to the static one. Also, the distance from the intake structure to the water's edge has a significant impact. Reducing the distance between the wells and the length of the drainage pipe, within the limits of the study conditions, has no effect on the results. As a result of the research, it has been established that, under the adopted hydrogeological and technical conditions, horizontal underground water intakes are distinguished by a large flow rate. Scientific novelty. The analysis of factors influencing the choice of infiltration water intake structures is carried out. The results of determining the productivity of structures under the same initial conditions are shown. Practical value. Using the results of the analysis allows you to most quickly and effectively solve the issues of choosing the option for powering water supply systems. The analysis has identified the most significant factors influencing the productivity of water intakes and makes it possible to vary them to achieve a result.

Características hidroquímicas y ambiente acuático de las aguas superficiales y subterráneas poco profundas en el norte del delta del río Amarillo, China

The present study envisaged the dynamic monitoring and study of the hydrochemistry of the surface water and shallow groundwater in the northern part of the Yellow River Delta, China. Analysis of the surface water and shallow groundwater revealed that the shallow groundwater exhibited in two forms: precipitation evaporation type and hydrological type, and the latter was obviously affected by the dynamic water level of the Yellow River. The surface water and shallow groundwater exhibited a higher degree of mineralization. Cations of Mg2+, Na+ and K+ and anions of Cl- and SO42- were the main ion components of the total dissolved solids. The hydro-chemical type of shallow groundwater was Cl-Na·K that was a typical seawater or brine form. The water chemical type of surface water changed to Cl·SO4-Na·K·Ca due to the industrial, agricultural and urban pollution. The overall quality of surface water was poor, and the main pollution indexes were found to be present, except for cyanide. The levels of COD and fluorine exceeded the standard values in the surface water. The groundwater quality was poor, since most of the pollutants were detected, except for cyanide and volatile phenol. Eight indexes exceeded the groundwater quality standard levels including Cl-, Na+, total hardness, COD, NH4+, Hg, As, NO3-, Cl- and Na+. The pollution of the surface water and shallow groundwater was mainly caused by the discharge of the wastewater from the petroleum; chemical industry and brine enterprises; agricultural non-point source pollution; leakage of septic tanks and sewage pipes in urban and rural areas, and rainwater leaching from the garbage piles. In order to improve the water quality, the sewage control and management needs be optimised, and the industrial layout should be reconsidered.

Study of the Instantaneous Water Level Measurement Method on Unsteady Flow Based on Single Camera and Fixed Scale Compensation in the Tunnel Model

The shape of instantaneous water surface profiles for the unsteady flow in the tunnel model can be determined by measuring the instantaneous water levels at multiple points synchronously. However, the measurement accuracy of the ultrasonic method is affected greatly because of the complex state of the water surface when water level changes rapidly. Using an optical method, multicamera synchronous measurement is difficult to control, and the cost is high. For single camera measurement, the reading of the steel ruler in the image cannot be clearly seen when the distance between the measuring point and single camera is far. When the distance is short, all steel rulers cannot be captured at the same time. Hence, in this paper, a single camera and fixed scale compensation method for instantaneous water level observation in unsteady flow is proposed. A series of fixed scales is placed with the same height and width near the water surface to be measured. In order to capture dynamic images of all fixed scales with a clear water surface, a single camera is set at a far position to continuously record the water level change process within the model range. According to the height of the fixed scale, the image accuracy is compensated and the effect of the wide-angle image distortion is automatically avoided. The water level elevation is obtained according to the relationship between the fixed scale and the water surface. In this paper, the unsteady flow model measuring test is applied to the Southern Main Tunnel and the Water Distribution Pool of the Huangchigou Water Diversion Project. The accuracy of this method in measuring the dynamic water level is 1–2 mm, which meets the accuracy requirement and greatly reduces the observation cost of the model test. The proposed method may also be suitable for measuring the instantaneous water level of the unsteady flow in other similar hydraulic model tests.

A method of constructing a dynamic chart depth model for coastal areas.

The depth is important for vessel navigation at sea. Currently, most vessels use electronic navigation charts to navigate at sea. In coastal areas, especially close to shallow water areas, the dynamic change of the water level is very important to safe navigation. Ships calculate the change of water level by using up-to-date tide tables, to obtain the dynamic water depth in the channels. However, the depth caused by the tide and non-tidal components may reach several meters in some seas, causing the dynamic depth below the safety depth, which can easily lead to grounding of vessels stranding accidents. The channel is regularly dredged to achieve navigational depth. Without regular dredging, the offshore non-channel area becomes the common area of ship grounding. The dynamic chart depth model studied in this article can provide real-time depth, which serves the ships navigation in the non-channel. The model incorporates the chart depth and the dynamic water levels on the same reference datum. The chart depth is from the electronic navigational chart depth. The dynamic water levels are constructed by the simulated tidal levels and continuous series of nontidal residual. We then designed a deviation correction method to reduce the discrepancy of the simulated tidal level with the actual water level, including datum offset correction and residual water level correction. Finally, by merging the revised dynamic water levels with the electronic navigational chart depth, we obtained the dynamic chart depth model of the study region.

ОЦІНКА РОЗВИТКУ ДЕФОРМАЦІЙ ЗЕМНОЇ ПОВЕРХНІ НА ШАХТНОМУ ПОЛІ СТЕБНИЦЬКОГО КАЛІЙНОГО РОДОВИЩА ЗА ДАНИМИ ГІДРОГЕОЛОГІЧНОГО МОНІТОРИНГУ

The paper presents the data generalization of the observations of hydrogeological monitoring of mining sites on the dynamics of groundwater level. The processing of hydro-regime studies conducted in 2009-2021 in the area of the mine bypass of the № 2 pit was carried out. Hydrogeological sections reflecting changes in water levels over time were prepared. The most important factor in the lowering of the ground surface is salt karst development. The evaluation of the intensity of karst collapse processes was based on the interpretation of the results of the dynamics of the subsurface water level. The site network consists of more than 30 observation wells drilled into suprasaline and Quaternary aquifers. The main causes of deformation of the salt rock massif and the earth's surface have been identified. These are a decrease in the geomechanical strength of the rock due to its hydration and subsequent subsidence under the geostatic load of the overlying rock, and subsidence of the clay layer covering the salt rock due to the karst process. Based on the observed data, hydrogeologically oriented spatial zoning of the mining concession was performed. As a result of the development of a complex depression in the area of influence of the karst drainage, a drop in the water level in the gypsum-clay horizons was observed over the entire area in 2009-2019. The depression funnel runs in a northwesterly direction, indicating the development of a karst channel in the salts. Significant inflow of suprasaline water in the southwestern and central parts of the mine field combined with intense karstification of the salt massif and gypsum-clay cap deposits within the depression funnel resulted in significant deformation of the earth's surface, formation of karst funnels, and technogenic and ecological threats to critical infrastructure objects. To prevent a man-made ecological catastrophe, it is urgent to develop a scientific rationale for the maximum permissible changes in the environmental parameters of the man-made geological system of the № 2 mine of the Stebnytsky potash deposit during the post-mining phase.

Water Level and Temperature as the Main Factors Responsible for the Formation of Conditions for Aboriginal Fish Fauna Effective Reproduction in the Kremenchuk Reservoir

Modern dynamics of the main abiotic environmental factors responsible for fish fauna effective reproduction in the Kremenchuk Reservoir are discussed in the paper. Annual dynamics of water level and temperature were analyzed. It has been found that the main factor responsible for the rate of breeding stock maturation in the Kremenchuk Reservoir is water temperature dynamics rather than spawning temperatures. It is underlined that the operation of hydroelectric facilities and the spawning campaign must be synchronized to ensure sustainable fisheries. The drainage of spawning grounds in low-water years results in the decrease in their area and, as a consequence, in the formation of low-yielding generations. It is recommended to optimize the annual dynamics of water level according to the needs of fisheries.

Water Level Fluctuations in the Middle and Late Holocene in the Curonian Lagoon, Southeastern Baltic: Results of the Macrofossil and Phytolith Analyses

This paper presents the results of a study on fluctuations in the water level of the Curonian Lagoon (in the Baltic Sea). To date, the genesis of this inland bay as part of the complex postglacial development of the southeastern Baltic is poorly understood. The data from lithological, geochronological, and phytolith analyses, as well as assessments of plant and animal macroremains from the lagoonal sediments, provide a reconstruction of local coastal biocenoses and water level dynamics in the Middle and Late Holocene time. This study reveals the fairly dynamic evolution of the coastal zone of the Curonian Lagoon over the past 7000 years, as indicated by the traced succession of plant communities from forest to near-shore, open-water biocenoses and the alternations of the drying out and inundation of the area under consideration. Thus far, a connection with two stages of the Baltic Sea water level fluctuations has been traced: the regressional stage, which took place approximately 5600 cal years BP, and the Late Subatlantic transgression, which started at approximately 1100 cal BP. This study demonstrates that phytolith (microbiomorphic) analysis is a promising method for the study of temperate-latitude lagoonal sediments, providing information not only on the local plant communities, but also on the changes in the hydrological regime of the area.

Dynamic water level changes in Qinghai Lake from integrating refined ICESat-2 and GEDI altimetry data (2018–2021)

The water levels of inland lakes on the Tibetan Plateau are extremely sensitive to global climate change and can objectively reflect the temporal and spatial changes in local water resources. However, monthly and seasonal variations in lake water levels are difficult to monitor due to the lack of sufficient in situ gauges across mountainous areas. Moreover, GEDI products exhibit large uncertainties in mountainous surroundings. In this paper, taking Qinghai Lake as an example, we first refined the raw data of the GEDI and ICESat-2 missions by implementing a quality control procedure involving outlier removal tailored to the characteristics of each mission; then, we analyzed the accuracy of each mission, especially targeting factors that affect the water level retrievals in the GEDI products. Third, the bias between the two missions was adjusted by selecting the overlapping or adjacent observation dates. Finally, we constructed dense temporal water-level data by integrating the refined ICESat-2 and GEDI data. Data from water level stations and the DAHITI and Hydroweb datasets were also utilized for validation. The results show that (1) very accurate results can be obtained from the ICESat-2 ATL13 product, and the standard deviations of most observed days are under 0.05 m; (2) the GEDI products derived from algorithm 2 can offer more effective footprints than those from algorithm 1, with an improvement of approximately 9.78 %. Moreover, large differences exist among the different GEDI beams, and beams 1 and 2 are recommended for further analysis. Overall, most beams overestimated the lake levels with a bias of 0.264 ± 0.357 m; (3) the long-time-series water levels showed a mean increasing trend of 0.243 m/yr from 2018 to 2021. The relatively high-water-level periods were distributed mostly in August and September, while the low-water-level periods were distributed mostly in February and March. The combined water levels were very correlated with the DAHITI and Hydroweb datasets, with R values larger than 0.8, and highly consistent with the observations from hydrological stations (the inter-year change range spanned from 0.015 m to 0.327 m, and the intra-year difference range varied from 0.03 m to 0.16 m); and (4) Integrating the GEDI and ICESat-2 missions allowed us to capture the monthly, seasonal and annual dynamics of the lake water level, and the results indicate that the combined dataset presents a valuable resource for hydrological and climatic change studies.

Analytical solutions on non-Darcy seepage of grouted and lined subsea tunnels under dynamic water levels

For the grouted and lined subsea tunnels, the fluid in the low permeability media follows non-Darcy's law rather than Darcy's law. To address this, we provide analytical solutions for the grouted and lined subsea tunnel with dynamic water levels. Our method uses complex variable functions and Hansbo non-Darcy seepage model. The analytical solutions divide into three cases according to the critical water inflow and can degenerate into the traditional method following Darcy's law. The numerical simulation, experimental data, in-situ data, and other analytical solutions are adopted to verify our proposed method. The calculated results subjected to non-Darcy seepage are close to the in-situ data compared with other analytical solutions. When degenerating into the traditional method, the results agree well with those of previous methods following Darcy's law. It reveals that our method is suitable and universal. The parametric analyses of the non-linear flow index m, the critical hydraulic gradient il, the dynamic water level ξci, the thickness of lining zone tl, and the relative permeability coefficient ratio of the grouting zone and lining zone kg/kl are carried out. The results show that non-linear seepage parameters and dynamic water levels significantly affect the water inflow and water head. The denser grouting material can apportion more water heads and make the lining apportion fewer water heads to protect the lining from fluctuation influencing of dynamic water levels.

Численное моделирование самосогласованной динамики поверхностных вод, влекомых и взвешенных наносов: II. Исследование поперечных деформаций русла и перераспределения расходов воды по рукавам р. Волги при промышленной добыче песка

The dynamics of water levels, transverse channel deformations, and redistribution of water discharges along the branches of the Volga River, both during planned industrial sand mining and during extreme transformation of the bottom topography in the area of the quarry, have been studied. A real quarry of non-metallic building materials was considered, located at the mouth of the Volozhka Partridge of the Volga — Akhtuba floodplain (VAF) in the section 2549–2550 km of the Volga River. Mathematical modeling of the joint dynamics of shallow waters, traction and suspended sediments is carried out, which takes into account the nonlinear dynamics of the liquid and bottom deformations. For the numerical solution of the Saint-Venant and Exner equations, the CSPH-TVD method was used, the parallel CUDA algorithm of which is adapted for highperformance computing on supercomputers with graphics coprocessors (GPUs). It is shown that the conditions of quarry development, both during planned mining and under extreme bottom deformation, do not significantly affect the structure of channel flows along shipping routes.

Integrated machine learning and GIS-based bathtub models to assess the future flood risk in the Kapuas River Delta, Indonesia

AbstractAs more and more people live near the sea, future flood risk must be properly assessed for sustainable urban planning and coastal protection. However, this is rarely the case in developing countries where there is a lack of both in-situ data collection and forecasting tools. Here, we consider the case of the Kapuas River Delta (KRD), a data-scarce delta on the west coast of Borneo Island, Indonesia. We assessed future flood risk under three climate change scenarios (RCP2.6, RCP4.5, and RCP8.5). We combined the multiple linear regression and the GIS-based bathtub inundation models to assess the future flood risk. The former model was implemented to model the river's water-level dynamics in the KRD, particularly in Pontianak, under the influence of rainfall changes, surface wind changes, and sea-level rise. The later model created flood maps with inundated areas under a 100-year flood scenario, representing Pontianak's current and future flood extent. We found that about 6.4%–11.9% more buildings and about 6.8%–12.7% more roads will be impacted by a 100-year flood in 2100. Our assessment guides the local water manager in preparing adequate flood mitigation strategies.

Quantifying the impacts of the Three Gorges Dam on the spatial–temporal water level dynamics in the upper Yangtze River estuary

Abstract. Understanding the alterations in spatial–temporal water level dynamics caused by natural and anthropogenic changes is essential for water resources management in estuaries, as this can directly impact the estuarine morphology, sediment transport, salinity intrusion, navigation conditions, and other factors. Here, we propose a simple triple linear regression model linking the water level variation on a daily timescale to the hydrodynamics at both ends of an estuary. The model was applied to the upper Yangtze River estuary (YRE) to examine the influence of the world's largest dam, the Three Gorges Dam (TGD), on the spatial–temporal water level dynamics within the estuary. It is shown that the regression model can accurately reproduce the water level dynamics in the upper YRE, with a root mean squared error (RMSE) of 0.061–0.150 m seen at five gauging stations for both the pre- and post-TGD periods. This confirms the hypothesis that the response of water level dynamics to hydrodynamics at both ends is mostly linear in the upper YRE. The regression model calibrated during the pre-TGD period was used to reconstruct the water level dynamics that would have occurred in the absence of the TGD's freshwater regulation. Results show that the spatial–temporal alterations in water levels during the post-TGD period are mainly driven by the variation in freshwater discharge due to the regulation of the TGD, which results in increased discharge during the dry season (from December to March) and a dramatic reduction in discharge during the wet-to-dry transitional period. The presented method to quantify the separate contributions made by changes in boundary conditions and geometry to spatial–temporal water level dynamics is particularly useful for determining scientific strategies for sustainable water resources management in dam-controlled or climate-driven estuaries worldwide.

Impacts of dike systems on hydrological regime in Vietnamese Mekong Delta

Abstract This paper examines the impact of the dike systems on river flows in the Vietnamese Mekong Delta (VMD). The study combined a hydrological change index method and the Mann–Kendall test to assess the temporal dynamics of both discharge and water levels along the main rivers of the VMD. Results highlight that the system of rivers and canals helps facilitate waterway traffic and drainage during the flood season. However, the low elevation of the delta has created conditions suitable for saline water to increasingly penetrate upstream during the dry season. Observed changes in the hydrological indicators at the upstream stations of Tan Chau (Mekong River) and Chau Doc (Bassac River) are not only due to the dike system but also upstream alterations to the flow regime. More research is needed to consider the various drivers of flow-regime change associated with natural and human activities both inside and outside of the study area.

Optimization of the Operation of Groundwater Intakes Using Two-Column Wells

The average number of wells at a typical water intake is 30–40; while the power of the submersible pump is usually 32–40 kW; which means that only at one well water intake the power consumption of electric pumping equipment during the hours of greatest water consumption can reach 900–1600 kW. In the structure of operating costs of well water intakes; the share of electricity costs reaches 85 %. Taking into account the requirements for reducing costs and water tariffs of housing and communal services enterprises as well as of water utilities; energy saving is an urgent task. The article considers the optimization of the operation of groundwater intakes with uneven water supply due to the use of two-column water intake wells instead of typical single-column ones. It is shown that the use of powerful pumps in single-column wells of such water intakes causes a sharp decrease in the dynamic water level in the borehole. On the one hand; this provokes the formation of colmating deposits in the filters due to their aeration; reduces the specific flow rate of the well and shortens the intervals between regenerations. On the other hand; this increases the geometric pressure of submersible pumps and energy consumption for lifting water. The theoretical foundations of determining the supply of pumps installed in single- and two-column water intake wells supplying water to the pressure filter of the water treatment plant are considered. An example of a comparative analysis of the operation of one working well with one powerful pump as part of a water intake of two single-column wells (working and reserve) to cover the entire water supply schedule and two two-column working wells containing one less powerful pump in each column is given. The energy efficiency of these pumping systems is investigated. As a result of calculations; it was found that when combining the operation of pumps of two-column wells during periods of peak; main and partial loads; the annual energy savings will amount to 33 %.

Prediction of the flooding area of the northeastern Caspian Sea from satellite images

Studying the dynamic changes in the coastline of the northeastern Caspian Sea is significant since the level of the Caspian is unstable, and the coastline change can cause enormous damage to the ecology, economy, and population of the coastal part of Kazakhstan. In this work, we use remote sensing and Geographic Information System (GIS) technologies to study the changes in the coastline of the northeastern Caspian Sea and predict the extent of flooding with increasing water levels. The proposed methodology for creating dynamic maps can be used to monitor the coastline and forecast the extent of flooding in the area. As a result of this work, the main factors affecting changes in the coastline were identified. After analyzing the water level data from 1988 to 2019, it was revealed that the rise in water level was observed from 1980 to 1995. The maximum sea level rise was recorded at −26.04 m. After that, the sea level began to fall, and between 1996 and 2009, there were no significant changes; the water level fluctuated with an average of −27.18 m. Then, a map of the water level dynamics in the Caspian Sea from 1988 to 2019 was compiled. According to the dynamics map, water level rise and significant coastal retreat were revealed, especially in the northern part of the Caspian Sea and the northern and southern parts of Sora Kaydak. The method for predicting the estimated flooding area was described. As a result, based on a single map, the flooding area of the northeast coast was predicted. A comparative analysis of Landsat and SRTM data is presented.

Integrated hydrodynamic and machine learning models for compound flooding prediction in a data-scarce estuarine delta

Abstract. Flood forecasting based on hydrodynamic modeling is an essential non-structural measure against compound flooding across the globe. With the risk increasing under climate change, all coastal areas are now in need of flood risk management strategies. Unfortunately, for local water management agencies in developing countries, building such a model is challenging due to the limited computational resources and the scarcity of observational data. We attempt to solve this issue by proposing an integrated hydrodynamic and machine learning (ML) approach to predict water level dynamics as a proxy for the risk of compound flooding in a data-scarce delta. As a case study, this integrated approach is implemented in Pontianak, the densest coastal urban area over the Kapuas River delta, Indonesia. Firstly, we build a hydrodynamic model to simulate several compound flooding scenarios. The outputs are then used to train the ML model. To obtain a robust ML model, we consider three ML algorithms, i.e., random forest (RF), multiple linear regression (MLR), and support vector machine (SVM). Our results show that the integrated scheme works well. The RF is the most accurate algorithm to model water level dynamics in the study area. Meanwhile, the ML model using the RF algorithm can predict 11 out of 17 compound flooding events during the implementation phase. It could be concluded that RF is the most appropriate algorithm to build a reliable ML model capable of estimating the river's water level dynamics within Pontianak, whose output can be used as a proxy for predicting compound flooding events in the city.

Evaluating irrigation status in the Mekong Delta through polarimetric L-band SAR data assimilation

For sustainable food production in the Mekong Delta, local information on irrigation status is essential for allocating water resources efficiently at the community level. ALOS-2 PALSAR-2 L-band SAR can be used to detect submerged and nonsubmerged soil covered by rice plants at a spatial resolution compatible with field observation but a low temporal resolution. In this study, a new multiscale data assimilation technique is developed to estimate the spatiotemporal dynamics of field water levels at a temporal resolution appropriate to inform decision-making on when to initiate irrigation. The method employs an irrigation model based on parameters representing farmers' irrigation practices. ALOS-2 PALSAR-2 data are used to derive the hydrological parameters of the model, including an irrigation parameter representing how deep the field water level dropped until the next round of irrigation was initiated. We developed observation operators for the soil submersion status under vegetation and spatial submersion percentages instead of assimilating soil moisture products. The study uses ALOS-2 PALSAR-2 data (25–100 m spatial resolution, approximately every 42 days) over the Mekong Delta and experimental data collected in situ for model initialization and validation. The estimated irrigation parameter controlling the maximum depth of field water level showed spatio-temporal consistency with the ground-observed value (RMSE = 4.24 cm). The values of the parameters also showed spatial consistency with respect to DEM data; he paddies with low irrigation model parameter values were prone to be located in low-elevation zones (<2 m), whereas high model parameters values tended to be located in paddies in the high-elevation zones (>3 m).The results show promising applications using L-band SAR observations for monitoring paddy field water level, for irrigation practices and for estimation of the water consumption and of methane emissions.

Spatial and seasonal water level dynamics in dryland grabens along the Rift Valley of northern Ethiopia

ABSTRACT We investigated water levels in semi-closed grabens of northern Ethiopia. Springs (n = 79), streamflows (n = 48), wetlands (n = 3), endorheic lakes (n = 3), hand-dug wells (n = 48) and boreholes in unconfined aquifers (n = 25) were monitored (2015–2017). Spring discharge fluctuates between wet (2.75 ± 1.5 L/s) and dry seasons (0.87 ± 0.21 L/s) (n = 68, p < .0001). Spring discharge and streamflow were larger at the foot of the escarpment than at the horst (p < .001). The water level of wells varied between horsts and escarpments in the grabens (p < .02). A water level depletion of up to 2.23 m/year occurred in response to withdrawals in the irrigated plains. Importantly, water level fluctuation was faster in streams, springs and hand-dug wells than in boreholes. Striking water level variations in the grabens were linked to rainfall deficit and management scarcity. An integration of surface water and groundwater management responses will bring the water table nearer to the surface; this could mitigate water storage in the fertile and productive grabens.