Water Level Dynamics Research Articles

Research on Water-Level Recognition Method Based on Image Processing and Convolutional Neural Networks

Water level dynamics in catchment-scale rivers is an important factor for surface water studies. Manual measurement is highly accurate but inefficient. Using automatic water level sensors has disadvantages such as high cost and difficult maintenance. In this study, a water level recognition method based on digital image processing technology and CNN is proposed. For achieving batch segmentation of source images, the coordinates of the water ruler region in the source image and characters’ region and the scale lines’ region on the ruler are obtained by using image processing algorithms such as grayscale processing, edge detection, and the tilt correction method based on Hough-transform and morphological operations. The CNN is then used to identify the value of digital characters. Finally, the water level value is calculated according to the mathematical relationship between the number of scale lines detected by pixel traversal in the binarized image and the value of digital characters. This method is used to identify the water levels of the water ruler images collected in the Hulu watershed of the Qilian Mountains in Northwest China. The results show that the accuracy compared with the actual measured water level reached 94.6% and improved nearly 24% compared to the template matching algorithm. With high accuracy, low cost, and easy deployment and maintenance, this method can be applied to water level monitoring in mountainous rivers, providing an effective tool for watershed hydrology research and water resources management.

Risk Analysis of Dynamic Water Level Setting of Reservoir in Flood Season Based on Multi-index

Long-term operation of the reservoir at the flood limit water level (FLWL) in the flood season is not conducive to the exertion of the comprehensive benefits of the reservoir, especially in the flood free period, causing a certain waste of resources. In order to make full use of water resources and avoid the risk of flooding due to extreme events, this paper proposes a dynamic water level decision-making model in flood free period, which considers the utmost of resources, effective response measures for possible catastrophic floods and the credible decision method, thus improving the operational benefit of hydropower station in the flood season and reducing flood control risk. The proposed model includes four modules. Firstly, historical data and the fuzzy statistical test method are used to divide the flood season into multiple stages. Secondly, the maximum inflow process in the effective forecast period of flood forecast in each stage is selected, and according to this inflow process, the operating limited water level (OLWL) in the flood free period of each stage is determined based on the reservoir discharge capacity, then the operating water level range and discharge ratio are discretized. Thirdly, multi-order Monte Carlo Markov Chain (MCMC) and Monte Carlo method are used to calculate the risk rate, and the scheme set is established by the three variables of power generation benefit, discharge ratio and risk rate. Finally, the weighted Topsis method, considering subjective and objective weighting method, is applied to determine the best scheme. This method has been verified in Youjiang reservoir in Yujiang River Basin. The main conclusions are as follows: (1) Combined with the discharge in the forecast period, the reservoir operating water level has a certain raising space in the flood free period. (2) The multi-order MCMC method effectively reflects the relationship between adjacent periods of runoff forecast error, and its simulation process is closer to the reality. (3) The Topsis method, which combines AHP with entropy weight method, can fully consider the characteristics of power generation efficiency, flow ratio and risk rate, and can effectively select satisfactory schemes from non-inferior schemes. This method provides a new idea for determining the operating water level of the reservoir in the flood season.

An Approach to Approximate Wave Height from Acoustic Tide Gauges

Abstract The demand for nearshore wave observations is increasing due to spatial gaps and the importance of observations for accurate models and better understanding of inundation processes. Here, we show how water level (WL) standard deviation (sigma, σ) measurements at three acoustic NOAA tide gauges that utilize an Aquatrak sensor [Duck, North Carolina, Bob Hall Pier (BHP) in Corpus Christi, Texas, and Lake Worth, Florida] can be used as a proxy for significant wave height (Hm0). Sigma-derived Hm0 is calibrated to best fit nearby wave observations and error is quantified through RMSE, normalized RMSE (NRMSE), bias, and a scatter index. At Duck and Lake Worth, a quadratic fit of sigma to nearby wave observations results in a R2 of 0.97 and 0.83, RMSE of 0.11 and 0.11 m, and NRMSE of 0.09 and 0.22, respectively. A linear fit between BHP sigma and Hm0 is best, resulting in R2 0.62, RMSE of 0.22, and NRMSE of 0.26. Regression fits deviate across NOAA stations and from the classic relationship of Hm0 = 4σ, indicating Hm0 cannot be accurately estimated with this approach at these Aquatrak sites. The dynamic water level (DWL = still WL ± 2σ) is calculated over the historic time series showing climatological and seasonal trends in the stations’ daily maximums. The historical DWL and sigma wave proxy could be calculated for many NOAA tide gauges dating back to 1996. These historical wave observations can be used to fill observational spatial gaps, validate models, and improve understanding of wave climates. Significance Statement There is a large spatial gap in nearshore real-time observational wave data that can provide critical information to researchers and resource managers regarding inundation and erosion, help validate coastal hydrodynamic models, and provide the maritime community with products that help ensure navigational safety. This study utilizes existing infrastructure to help fill the demand for nearshore wave observations by deriving a proxy for wave height at three sites. This work shows spatial variability in the regression fits across the sites, which should be explored at more stations in future work. Multidecadal length time series were also used at the sites to investigate climatological and seasonal trends that provide insight into wave climates and wave driven processes important for coastal flooding.

Global sensitivity analysis in hydrodynamic modeling and flood inundation mapping

Flood simulation with two-dimensional hydrodynamic models is subject to different sources of uncertainties in model configuration, boundary conditions, and model parametrization. HEC-RAS 2D is a widely used hydrodynamic model. Here, we assess the sensitivity of the HEC-RAS 2D to its configuration factors and parameters. We evaluate the impacts of different model configuration factors, including the floodplain and channel roughness coefficients, terrain and mesh size, as well as river boundary conditions on the dynamic of water levels, maximum water level, and flood extent, and determine the importance of these contributing factors for reliable flood inundation modeling using both variogram and variance-based analyses. For our case study, we found that depending on the perturbation scale, the performance measure, and the predicted output, the sensitivity to input factors changes. While for simulation of water level dynamics, the DEM and mesh resolutions are the most important factors, for flood extent mapping the floodplain roughness coefficient and the upstream boundary condition are the key factors. In addition, our analyses indicated that for a reliable simulation of maximum flood water level, modelers need to spend resources on the calibration of floodplain roughness coefficient while using fine DEM and mesh resolutions. Here, we also investigate the role of computational time interval and mesh resolution on the model's run time and accuracy. Our results suggested that reducing the computational time interval has minimum impact, as it increases the model run time without much improving the model accuracy.

Changes in Large Lake Water Level Dynamics in Response to Climate Change

Understanding impacts of climate change on water level fluctuations across Earth's large lakes has critical implications for commercial and recreational boating and navigation, coastal planning, and ecological function and management. A common approach to advancing this understanding is the propagation of climate change scenarios (often from global circulation models) through regional hydrological models. We find, however, that this approach does not always fully capture water supply spatiotemporal features evolving from complex relationships between hydrologic variables. Here, we present a statistical approach for projecting plausible climate-related regional water supply scenarios into localized net basin supply sequences utilizing a parametric vine copula. This approach preserves spatial and temporal correlations between hydrologic components and allows for explicit representation and manipulation of component marginal and conditional probability distributions. We demonstrate the capabilities of our new modeling framework on the Laurentian Great Lakes by coupling our copula-derived net basin supply simulations with a newly-formulated monthly lake-to-lake routing model. This coupled system projects monthly average water levels on Lake Superior, Michigan-Huron, and Erie (we omit Lake Ontario from our study due to complications associated with simulating strict regulatory controls on its outflow). We find that our new method faithfully replicates marginal and conditional probability distributions, as well as serial autocorrelation, within and among historical net basin supply sequences. We find that our new method also reproduces seasonal and interannual water level dynamics. Using readily-available climate change simulations for the Great Lakes region, we then identified two plausible, transient, water supply scenarios and propagated them through our model to understand potential impacts on future water levels. Both scenarios result in an average water level increase of <10 cm on Lake Superior and Erie, with slightly larger increases on Michigan-Huron, as well as elevated variability of monthly water levels and a shift in seasonal water level modality. Our study contributes new insights into plausible impacts of future climate change on Great Lakes water levels, and supports the application and advancement of statistical modeling tools to forecast water supplies and water levels on not just the Great Lakes, but on other large lakes around the world as well.

Heat tracing of embankment dam leakage: Laboratory experiments and 2D numerical modelling

Recently, the use of heat as a tracer to evaluate the process of leakage in embankment dams has attracted wide attention. A more accurate flow-heat coupling model of embankment dams could help us to better understand the patterns of water flow and heat transfer in embankment dams and provide a scientific basis for the seepage prevention and repair of these dams. In this paper, combined with thermal conductivity empirical models (TCEMs), the saturated-unsaturated flow-heat coupling model of embankment dams was established. Through laboratory sand tank experiments of concentrated leakage in embankment dams, the accuracy of the flow-heat coupling model under 10 types of TCEMs were tested and compared. The results show that the performance of the flow-heat coupling model varies under different types of TCEMs, and the Chung and Horton (1987) model shows better simulation effects, with a coefficient of determination (R2), root mean square error (RMSE) and relative error (Re) ranging from 0.916 to 0.980, 0.266–0.467℃ and 1.370–2.442%, respectively. Therefore, this model could better reflect the dynamic temperature variations in embankment dams. Finally, the flow-heat coupling model was improved by modifying the COMSOL built-in equation, i.e. built-in COMSOL model was replaced by the Chung and Horton (1987) model, which further improved the accuracy of the flow-heat coupling model in the numerical simulation of seepage heat monitoring. Based on the improved model, the concentrated leakage of embankment dams under dynamic water levels was simulated numerically. Under the condition of a dynamic water level, the flow velocity and pressure at the leakage passage are positively correlated with the water level change, and the temperature field also shows the same change trend.

БИОЛОГИЧЕСКАЯ ХАРАКТЕРИСТИКА НЕРЕСТОВОГО СТАДА СТЕРЛЯДИ ACIPENSER RUTHENUS (LINNAEUS, 1758) Р. СЕВЕРНАЯ ДВИНА

According to results of ichthyological monitoring of the sterlet population in the middle part of the Severnaya Dvina river in the spring period 2018–2020 established a greater dependence of the value of catches in stationary traps on the dynamics of the water level in the river, compared with water temperature. On the spawn places located in the middle part of the Severnaya Dvina river in the catches of stationary traps, sterlet dominates both in quantity and in mass. Average catch per unit of fishing effort (CPUE) is more dependent on water level dynamics than on water temperature. Age and length composition of sterlet catches is represented by two-thirds by fish of the younger age classes (3–5+) and small sizes (30–45 cm and 0.2–0.6 kg). The sexual structure of spawning sterlet represented by about 80% of males. The sterlet in the Severnaya Dvina river is currently grow faster than 70 years ago – probably due to an increase in the average water temperature in the river. In pre-spawning and spawning parts of sterlet population proportion of maturing and sexually mature females and males is 90%. The number of past-spawners increases with increasing water temperature. Currently, sterlet grows more slowly than in the 50–60s of the 20th century. Sterlet is intensively fed in the Severnaya Dvina river during the spawning period. In the middle part of the river, the basis of spring nutrition is chironomids and caddis fly larvae. Secondary fed objects are bivalve mollusks and blackfly. Random objects characterizing the nutritional spectrum in the spring include larvae of flies, butterflies, hemipterous and fish eggs. There are no significant differences in fed of sterlet with an increase in its size in the Severnaya Dvina river.

Гідродинамічне функціонування водосховища річки Лобо в західно-центральному Кот-д’Івуарі

Built to improve water supply for the populations of the city of Daloa, the Lobo River reservoir is no longer functioning properly due to human activities near its reservoir. This study, based on a 2D hydrodynamic model, carried out with the Mike21 HD software, allowed the reconstruction of the flows in the Lobo River reservoir. The results of the simulation indicate that the hydrodynamic model could reproduce the variation of water levels at the free surface of the reservoir. Also, the results are very sensitive to the boundary conditions of the model but also to the initial conditions. The results of the influence of pumping on the dynamics of water levels in the Lobo River reservoir showed that water levels are not significantly modified by pumping (less than 1.3 mm). Therefore, pumping has little impact on the hydrodynamics of the Lobo River because the pumped flows are much less than the inflow to the reservoir.

СТАТИСТИЧЕСКИЙ АНАЛИЗ ВОДНОГО РЕЖИМА РЕКИ АМУР ДЛЯ ЦЕЛЕЙ ПРОГНОЗА

The Amur is navigable along its entire length, and it has a great transport importance for the Far East region. In years with spring-summer-autumn periods of low water level, the Amur River navigation suffers great economic losses. In such years, the volume of cargo transportation and the movement of passenger ships are disrupted, the work of water intakes deteriorates, and water supply to the population and enterprises is hampered. In the Khabarovsk Territory, material damage is sometimes commensurate with the damage from floods. More than a century of observations of the Amur regime near Khabarovsk made it possible to carry out a statistical analysis of the characteristic water level dynamics in three water phases: spring flood, summer low-water period and rain floods. The territory climate with cold dry winters and warm humid summers determines a dual maximum runoff in the Amur regime, reduced in spring and high in summer. It is noteworthy that both maximum runoffs have a steady downward trend in the dynamics of the highest water levels for 1896–2021. However, the height of the spring flood wave, in contrast to the annual maximums, decreases in dynamics more intensively (at a rate of 10–12 cm / 10 years and 5–7 cm / 10 years, respectively). The lowest water levels observed after the flood wave (summer low water period) have a long-term trend in dynamics, parallel to the spring trend. A similar trend in the Amur regime is associated with the variability of the regional climate and is synchronous with global warming characterized by an increase in surface air temperature, which contributes to an increase in evaporation from the water surface, and therefore, to a decrease in river runoff. The performed assessment of the Amur water regime during the navigation period makes it possible, by means of trend components, to orient the hydrologist-forecaster on the distribution of the Amur water content in in the coming season.

Возможности ГИС-технологий для изучения гидрологических характеристик водного объекта и экологических параметров его водосборной площади

This work summarizes literary and cartographic material that characterizes the Morskoy Glaz Lake and its catchment area. The levels of aquifers and the catchment area of the lake were determined along with development of digital models of the terrain and relief of the lake basin, which were developed on the basis of multi-temporal microdrone photo-shooting with usage of geodetic referencing of basepoints using the tools of Agisoft Metashape and GIS “Panorama”. The catchment area of the lake doesn’t exceed more than 1.3 km², while the main supply of water nourishment of the lake forms as a surface runoff and groundwater flow on an area of about 0.6 km². This area contains 45 residential building connected by local sewerage and many private water wells. The lands of rural settlements and agricultural lands make up 26 % and 64 % of main catchment area, respectively. With the usage of photographic materials of the lake provided by users of social medias and usage of digital terrain models of Agisoft Metashape, a reconstruction of the dynamics of the lake water levels for 2013–2022 was carried out, which made it possible to calculate volumes of lake waters for specific calendar dates along with possibility of estimation of the rate of change of water volumes in the lake, which was achieved through the usage of tools of GIS “Panorama”. Long-term level of water’s edge of the lake is 121.5 meters, the total volume of the lake is 53,185 m³. Since 2014, there have been significant fluctuations in the level of the water’s edge in the lake. Meanwhile, the rate of water volume change varied from 3.9 to −3.6 dm³ per second. The reason for the negative water balance in March 2022 is formation of a ponor at the end of the winter of 2014, which subsequent expansion along with periodic overlapping by screes and microlandslides have led to complete disappearance of the lake. The proposed algorithm based on the usage of the Citizen science technologies (collection of amateur photo- and video- data), combined with usage of GIS-tools can be used for providing monitoring for water bodies.

Calibrating 1D hydrodynamic river models in the absence of cross-section geometry using satellite observations of water surface elevation and river width

Abstract. Hydrodynamic modeling has been increasingly used to simulate water surface elevation which is important for flood prediction and risk assessment. Scarcity and inaccessibility of in situ bathymetric information have hindered hydrodynamic model development at continental-to-global scales. Therefore, river cross-section geometry is commonly approximated by highly simplified generic shapes. Hydrodynamic river models require both bed geometry and roughness as input parameters. Simultaneous calibration of shape parameters and roughness is difficult, because often there are trade-offs between them. Instead of parameterizing cross-section geometry and hydraulic roughness separately, this study introduces a parameterization of 1D hydrodynamic models by combining cross-section geometry and roughness into one conveyance parameter. Flow area and conveyance are expressed as power laws of flow depth, and they are found to be linearly related in log–log space at reach scale. Data from a wide range of river systems show that the linearity approximation is globally applicable. Because the two are expressed as power laws of flow depth, no further assumptions about channel geometry are needed. Therefore, the hydraulic inversion approach allows for calibrating flow area and conveyance curves in the absence of direct observations of bathymetry and hydraulic roughness. The feasibility and performance of the hydraulic inversion workflow are illustrated using satellite observations of river width and water surface elevation in the Songhua river, China. Results show that this approach is able to reproduce water level dynamics with root-mean-square error values of 0.44 and 0.50 m at two gauging stations, which is comparable to that achieved using a standard calibration approach. In summary, this study puts forward an alternative method to parameterize and calibrate river models using satellite observations of river width and water surface elevation.

Performance of nearest neighbour metrics for pluvial flood nowcasts in urban catchments

Urban flood warning systems need fast response times between the rainfall forecast and the flood alarm. Flood forecasts from physically based numerical models usually need much computation time. Flood forecasts based on databases from previous events or pre-simulated events can speed up the process of decision making. This work introduces and compares four distance metrics for temporal rainfall patterns used in a nearest neighbour based forecast system for dynamic water levels and velocities during pluvial floods. The system uses a database of 960 pre-calculated flood events. The performance of each metric is evaluated by analysis of time-series of flow variables. For the error quantification,a procedure to find a small number of representative locations in an urban catchment is described. A new approach to quantify the similarity of dynamic flow fields is introduced, which makes use of particle transport tracking. The four distance metrics are tested on forecast for four exemplary pluvial flood events resulting from rainfall of durations between 15 and 50 min and return-periods between 10 and 100 years. The best metric is based on the temporal precipitation pattern and takes the response time of the drainage system into account. If the pattern has a very short duration, a simpler characterisation-metric can be used, which takes the total volume, peak intensity and peak position into account.

Stochastic Model and Method of Optimization of Operation Modes of a Group of Artesian Wells in Water Supply Systems

Groups of spatially distributed wells interconnected by sections of pipelines (a common collector) supplying water to a clean water reservoir are used in water supply systems in order to provide drinking water to settlements. A group of wells together with a clean water reservoir is called a water intake facility of the water supply system. Further, water is supplied from the clean water reservoir to consumers in settlements by means of second stage pumping stations. In terms of each well the operating mode of the submersible pumping unit, i.e. the position of its operating point at a fixed moment in time, depends on the actual values ​​of many internal and external factors: dynamic water level in the well; the actual characteristics of the pumping unit; the position of the final control elements (drive speed, opening degree of the regulating valve); hydraulic resistances of pipeline sections of the water intake facility; the water level in the clean water reservoir; the number and operating modes of pumping units in other wells of the water intake facility.
 The paper describes a deterministic model of a water intake well. At the same time, the processes of water consumption are random processes, since they depend on many uncontrolled and unmanageable factors. The parameters of the technological equipment of the water intake facility are also random values, since they are estimated from experimental data of finite length.
 Therefore, a stochastic model of a water intake well is also proposed. A model of a quasi-stationary operation mode of a water intake facility, which is used to optimize the operation of a group of artesian wells operating on a common collector, is considered.

Integrated Duflow-Drainmod model for planning of water management operation in tidal lowland reclamation areas

The research objective was to develop field operational model to control water table level at reclaimed area of tidal lowland for food crop cultivation. DUFLOW computer model was used to evaluate the perfomance of water management network at secondary and tertiary levels, whereas DRAINMOD computer model is used to evaluate soil water status at tertiary block. Results of DUFLOW model simulation can be used to improve water management by passing the Secondary Irrigation Chanel (SPD) and Secondary Drainage Chanel (SDU) through tertiary channels, water gate installation of stop-log type and weir construction in Drainage Secondary Channel (SDU). The weir construction has function as long storage and capable to control or maintain soil water level in land not quickly drawdown. Drainmod simulation model is acceptable, this is indicated by the results of statistical analysis where the correlation coefficient value reaches 0.89. Analysis of DUFLOW-DRAINMOD computer model software showed mutually supportive results in which DUFLOW simulation results can provide water potential information in channel for supply purpose. This water level condition is an important part in DRAINMOD model because it has effect on soil water level dynamics as targeted on tertiary block as well as on capacity to applied drainage operation system.

Monitoring of Water Level Variations of Bosten Lake based on Ice Cloud and Land Elevation satellite-1/2 Altimetry Data

Bosten Lake is located in the arid area of China, it has experienced drastic change on water level due to the climate environment changes and human activities. Based on ICESat-1/2 satellite altimetry data, this paper extracted the water level data of Bosten Lake from 2003 to 2020, and analysed the multistage dynamics of water level. The result shows that: the overall water level of Bosten Lake appeared an upward trend from 2003 to 2020, and the annual rate of change was 0.06 m/a. From an annual perspective, the lake’s water level gradually declined from 2003 to 2009, and then continued to rise until 2020. The lake water level fluctuates in a bimodal shape during the year, and March and October are the peak water level months. The research results can provide reference for the comprehensive management of water resources utilization in arid areas.

Stochastic programming for floodwater utilization of a complex multi-reservoir system considering risk constraints

Floodwater utilization through dynamic operating flood limited water levels (FLWLs) of reservoirs plays an important role in flood control and water conservation. This study proposes a risk-based aggregation-decomposition method for floodwater utilization of a complex multi-reservoir system. The original system is decomposed into four basic configurations. For the subsystem with hydraulic connections, the upper bound of FLWL of each reservoir is identified based on a given risk level for the subsystem and risk hedging between reservoirs. A stochastic programming model to maximize hydropower generation is then established for joint operation of the multi-reservoir system to find and update the optimal operation strategy during flood seasons. The mixed cascade reservoirs in the Pi River Basin are selected as a case study. The application results are compared with those of the original design model and deterministic operation model without considering risk, which shows that joint operation and dynamic control of FLWLs: 1) significantly increases the power generation and improves the utilization rate of floodwaters compared to those of the original design model; 2) power production rate increases with the acceptable risk but the increasing rate between them decreases with higher levels of risk; 3) results in lower utilization rate of floodwaters compared to that of the deterministic model, but the difference is not significant. The proposed method provides a framework for risk-based decision-making in floodwater utilization to enhance the comprehensive benefits of a multi-reservoir system.

Constructed wetland management in urban catchments for mitigating floods

Wetlands in urban ecosystems provide significant environmental benefits. In the present study, the concept of urban constructed wetland development is studied from the viewpoint of urban planning with dynamic water level orifice setting controller. A two-step modelling procedure is carried out: (1) development of a hybrid model, by coupling a well-established two-dimensional hydrodynamic model (International River Interface Cooperative, iRIC) with a one-dimensional physically-based, distributed-parameter model (Storm Water Management Model, SWMM), to compute and map flood scenarios and to identify the flood-prone areas; and (2) use of SWMM to simulate the water inflow to the proposed constructed wetland, which acts as a cushion for storing excess flood water. The proposed methodology is implemented on the Jahangirpuri drain catchment located in Delhi, India. Results show that the hybrid model is effective, and the simulations are observed to be in good agreement with the recorded data, which assist in detecting the flood-prone areas. Further, an estimation of the impact of the proposed constructed wetland on catchment hydrology indicates an overall reduction of 23% in flooding adjacent to the channel with a significant reduction in backflow as well as water depth in the drain. The flapgate at the outlet of the wetland helps in maintaining the desired water depth in the wetland. The outcomes of this study will assist the hydrologists and administrators in urban stormwater management and planning to mitigate the impact of floods in urban watersheds.

Dynamic Regulation of Reservoir Drought Limit Water Level

Drought limit water level has been presented to guide reservoir drought resistance for years. However, current static drought limit water levels neglected the water transfer relationship among different periods. In this study, the Yuqiao Reservoir located in Tianjin, China, was taken as the study area. To avoid the excessive subjectivity brought by the conventional typical drought-year selection method, six indicators were used to analyse inflow intra-drought-season distribution characteristics, and a hierarchical agglomeration cluster method was used to propose a classification of the dry season inflow “shape.” To associate with the reservoir inter-month water transfer relationship, a number pair “early warning period/drought limit water level” format was proposed to represent the limit water level. The early warning period turned out to be related to initial water storage, inflow process in dry season and water supply rules. To overcome the uncertainty in inflow process during the dry season, a rolling computation mechanism was applied in determining the drought limit water level, thus dynamic regulation was realized. Finally, the dynamic reservoir drought limit water level was compared with the conventional method. The results suggest that drought limit water level has broad development potential in improving reservoir drought resistance guidance practices.

A Forecast-Skill-Based Dynamic Pre-Storm Level Control for Reservoir Flood-Control Operation

The design and operation of reservoirs based on conventional flood-limited water levels (FLWL) implicitly adopts the assumption of hydrological stationarity. As such, historical-record-based FLWL may not be the best choice for flood-control operations due to the inherent non-stationarity of rainfall inputs. With maturing flood forecasts, this study focuses on establishing linkage between FLWL and skill of forecast, thus developing a “dynamic pre-storm level” approach for reservoir flood-control operations. The approach utilizes forecast flood magnitude, forecast skill and exceedance probability of forecast error to determine the pre-storm reservoir storage for each flood event. The exceedance probability of forecast error for each incoming flood is used as the reservoir flood control standard instead of the probability of a static return interval flood. This approach is demonstrated in a hypothetical situation in the Three Gorges Reservoir in China. The results show that under zero-forecast-skill conditions, the proposed dynamic pre-storm level matches well with the Three Gorges Reservoir-designed FLWL; and, as the forecast accuracy/skill increase, the proposed approach can make better use of the increased forecast accuracy, thereby maximizing floodwater utilization and reservoir storage. In this way, coupling the new approach with FLWL allows for more efficient and economic day-to-day reservoir operations without adding any flood risk. This study validates the usefulness of dynamic water level control during flood season, considering the improvement of flood forecast accuracy.

Flood Pulse and Aquatic Habitat Dynamics of The Sentarum Floodplain Lakes Area

The Lake Sentarum is a complex of floodplain lakes in the middle part of the Kapuas River system in West Kalimantan, Indonesia. The area has a great ecological and economic importance, however, the Sentarum lakes complex and its catchment area are generally threatened by deforestation, fire, monoculture agroindustry, and pollution.The objective of this research is to establish the hydrological characteristics of the Sentarum lakes area and to reveal the dynamics of aquatic habitat resulted from changing water levels. Data were collected during our field campaigns of 2013-2017 representing the seasons. The water level was measured using a pressure sensor placed at the Lake Sentarum National Park resort, while rainfall data were obtained from the data portal of the Tropical Rainfall Measuring Mission. Inundation monitoring was carried out using a time-lapse camera. A hydrological model is used to simulate water levels beyond measurement period. Water quality and fish sampling were carried out at the lake area. Vegetation observation was carried out at the selected riparian zone of the lake area using the line transect method. Water level records show that the Sentarum floodplain lakes have two peaks of inundation period following the bimodal pattern of rainfall in the equatorial Kapuas catchment. This water level dynamics induced changes in water quality, nutrient availability, vegetation cover, and fish diversity found in the Sentarum lakes area. Despite its seasonal changes, water quality of Sentarum lakes is generally good and suitable for aquatic biota. Fish diversity of the Sentarum lakes is relatively higher during high water periods.