Two-dimensional Hydraulic Simulation Research Articles

Real-time flood maps forecasting for dam-break scenarios with a transformer-based deep learning model

This paper presents a purely data-driven deep-learning approach for flood maps forecasting. For the first time in this context a Transformer-based algorithm is employed to address one of the main issues in early-warning systems for flood propagation, i.e., the long computational times required to forecast the inundation evolution in real time. The proposed model, named “FloodSformer”, is trained to extract the spatiotemporal information from a short sequence of water depth maps and predict the water depth map at one subsequent instant. Then, to forecast a sequence of future maps, we employ an autoregressive procedure based on the trained surrogate model. The method was applied to both synthetic dam-break scenarios and to a real case study, specifically the ideal failure of the Parma River dam (Italy). The training and testing datasets were generated numerically from two-dimensional hydraulic simulations. In the case of the real test case, the average Root Mean Square Error was found to be equal to 10.4 cm. The short computational time (e.g., the forecast of 90 maps, representing a lead time of 3 h, takes less than 1 min) makes the FloodSformer model a suitable tool for real-time emergency applications.

Effectiveness in storing and reducing floods of the red river upstream reservoirs under the incident of Lienmac dyke

The Red river and Thai Binh river’s dyke system includes 56 dikes classified from grade III to special grade with a total length of 2.207,75km which 37.709km of special grade, 553.70km of grade I, 502,43km of grade II and grade III. At the present, on the Red River and Thai Binh River systems, there are 230 existing weak locations, which have not been completely reinforced yet. It might cause unsafety situations of large flood flush and high water levels of rivers for a long time. Therefore, studying the solutions to support the response under unsafety situations of the dike system is a significant meaning topic. The present paper aims to evaluate the effectiveness of solutions using reservoirs at the Red river upstream in order to store and reduce floods in downstream. This also supports the effort to respond the urgent situations upstream such as huge floods, dyke failures in downstream and dyke failure at Lien Mac. In the scope of this paper, one and two-dimensional hydraulic simulation method was utilized, which describes the scenarios to regulate the upstream reservoir of the Red River and hydraulic calculation of the downstream river network. Then, the effectiveness of flood reduction in each scenario can be estimated. Simulation results show that depending on the calculation scenarios, the capacity of reservoirs can be 5.553 million m3 to cut and reduce flood for downstream. The flooded area might be decreased by 47.528 ha in case using a part of the capacity of the construction. The time when the reservoirs completely close the floodgates and do not discharge the flood into downstream is from 27 to 30 hours, this is an important time for the Lien Mac dike to be completely sealed within 24 hours. The time when the reservoirs completely close the floodgates and do not discharge the flood into downstream is from 27 to 30 hours, this is an important time for the Lien Mac dike to be completely closed within 24 hours.

Evaluation of Casualty Risk Index for Evacuating When Inundation Occurs on Excavation Construction Sites

Recently, inundation accidents occur repeatedly on underground excavation construction sites owing to frequent intensive rainfall events. In the case of the inundation of underground construction sites, injury and drowning accidents may occur on the evacuation route. However, no method or standard for calculating the risk of casualty while evacuating workers has been proposed. In this study, we defined the casualty risk index (CRI) and developed a method for estimating CRI. We adopted the “HV,” which is the product of height (water depth) and velocity (water velocity) recommended by previous researches. The “HV” indicates that humans can walk safely in water flow without stumbling. The proposed method was applied to a hypothetical underground construction site in the city of Yeosoo. ArcGIS Pro was used to model the hypothetical excavation site, and XPSWMM was used to simulate rainfall runoff and two-dimensional hydraulic simulation. While the runoff was flowing into an underground construction site, we simulated the water height and water velocity on the evacuation route to estimate the CRI. The results showed that CRIs from various rainfall scenarios remained in the safe criteria, indicating that workers could safely evacuate from the site in the rainfall scenarios. However, the CRI is influenced by site-based factors, and these factors are discussed.

Computation of Time of Concentration Based on Two-Dimensional Hydraulic Simulation

Time of concentration (TC) is a parameter in runoff estimation, used to study and design different types of projects in watersheds. Any error in TC calculation leads to an inaccurate estimation of the design flow, which can lead to over-sizing or under-sizing of designed facilities that can have great economic and environmental consequences. Therefore, choosing the correct method to estimate TC is of great importance. Due to the diversity of estimation methods in the literature, the obtained TC values are different. This study aims to present a new method to calculate TC, based on its main concept, i.e., the time required for a water parcel to reach its outlet from the farthest hydrological point of a watershed. A two-dimensional hydraulic simulation was used to model the water parcel travel. A watershed was selected as a case study, and its time of concentration was determined by salt solution tracing. The field measurement results were used for calibration of the numerical simulation model. Meanwhile, 31 empirical relations in the literature were reviewed to determine the most accurate ones. Estimated TC values were compared with the measured ones, and the relative error percentage was used to evaluate the accuracy of the result. In the empirical TC methods, the maximum error was above 300%, and the minimum error was 6.7% for the field studied area. The relative errors of hydraulic simulation outputs were between 3 and 27%. The results showed that only three empirical methods, namely Simas and Hawkins, SCSlag, and Yen and Chow, had the least errors respectively equal to 6.7%, 8.660%, and 13.5%, which can be recommended for the studied area and those with similar hydrological characteristics. On the other hand, hydraulic simulation is also introduced as an efficient method to determine TC which can be used in any desired watershed.

One and Two-Dimensional Hydraulic Simulation of a Reach in Al-Gharraf River


 One and two-dimensional hydraulic models simulations are important to specify the hydraulic characteristics of unsteady flow in Al-Gharraf River in order to define the locations that facing problems and suggesting the necessary treatments. The reach in the present study is 58200m long and lies between Kut and Hai Cities. Both numerical models were simulated using HEC-RAS software, 5.0.4, with flow rates ranging from 100 to 350 m3/s. Multi-scenarios of gates openings of Hai Regulator were applied. While the openings of Al-Gharraf Head Regulator were ranged between 60cm to fully opened. The suitable manning roughness for the unsteady state was 0.025. The obtained results show that the average velocities for the one-dimensional model were ranged between 0.36 and 0.5 m/s, and the average water surface elevations range between 15.14 m and 17.84 m. While these values ranged between 0.25 and 0.44 m/s and 14.125 and 18.82 m respectively for the two-dimensional model. The simulation results of the two-dimensional model were more accurate than their corresponding one-dimensional model, due to more agreement of these values with measured values, which achieved minimum values of the root mean square error and the determination coefficient.

Green sturgeon habitat suitability varies in response to drought related flow regimes

A series of habitat suitability models were created based upon 2-dimensional tracking of Green Sturgeon and hydraulic simulations. This is an effort to better understand the relationship between the population decline, habitat suitability, and knowledge of the remaining post-dam era habitat available to Green Sturgeon. Records of the movements of Green Sturgeon were collected using a refined acoustic telemetry system (Vemco Ltd., Vemco Positioning System [VPS]) in three pools, the first at rkm 377.0 at the confluence with the Sacramento River of Antelope Creek, the second at rkm 407.5 at the confluence with Inks Creek, and the third at rkm 426.0 at the confluence with Paynes Creek near Red Bluff over a period of two years. The Flow and Sediment Transport with Morphologic Evolution of Channels (FaSTMECH) model was used to simulate depth and velocity. Previously developed habitat suitability curves for spawning Green Sturgeon within the study area were coupled to two-dimensional hydraulic simulations to estimate Weighted Usable Area (WUA), a metric of suitable habitat area within each of the studied reaches. The effect of changing river discharges on suitable spawning habitat for Green Sturgeon was examined over a six-year period, the first of which had normal rain conditions and the following years drought conditions. The peak amounts of spawning habitat in the pool on the Sacramento River at the rkm 377 was the same for all six years, roughly 8000 square meters. The constancy in the amount of WUA, in the face of decreasing rates of discharge may explain why these sites are occupied from year to year. The amount of spawning habitat in the pool at rkm 426, decreased during the four-year drought period, from 2012 to 2015. This may make it less favorable for occupation by Green Sturgeon.

Moving to 3-D flood hazard maps for enhancing risk communication

3-D representations of flood inundation through emerging formats in virtual and augmented realities may be a powerful tool with which to interact with political decision-makers and to engage people with flood hazards. Despite that, environmental scientists are far from fully harnessing these techniques when interacting with non-scientists. Integrations with computer graphic science is considered necessary to such an extent that a distinct and emerging field of research related to the visualization in assisting environmental scientists can be detected in the literature.A key issue could be represented by the implementation of a simple visualization product that can be used by hydraulic engineers as a reasonable balance between the intrinsic informatics complexity of virtual reality and the practical need to represent flooding events in 3-D environments for risk communication purposes. Therefore, this paper aims at defining a suitable path that starts from the river model set-up and, passing through 2-D flood simulations obtained by means of shallow water equations, arrives at 3-D visualizations of the results. In particular, this paper is focused on developing an intentionally simple workflow for the representation of two-dimensional hydraulic simulations within a 3-D virtual reality environment. The level of detail as well as the pro and cons associated with the use of this procedure are discussed and the appropriateness of visualization outputs of the proposed procedure are analysed. These issues are discussed with reference to a case study located in the old town of Cosenza (Calabria, Italy).

Toward floodplain rejuvenation in the middle Ebro River (Spain): From history to action

The Mediterranean region is recognized as one of Earth's biodiversity hotspots, but disconnection of habitats and fluxes of energy and nutrients have made them particularly vulnerable to external perturbations in the current context of global warming. This paper presents a multitemporal approach to understand how past human impacts have led to present deficits in fluvial dynamics and to propose and assess possible future restoration scenarios. First, biogeomorphic regression and progression dynamics of the middle Ebro River (Spain) were studied at the reach scale over a period of 90 years (1927–2014). River bank fixations, flood defenses, and incision have caused a disconnection between the river and its floodplain leading to a remarkable tendency for stabilization and vegetation progression to forest. Restoration of processes is necessary for those rivers where rejuvenation is no longer occurring. Second, the selected restoration target for the studied middle Ebro River section focuses on the improvement of lateral hydrological connectivity and partial recovery of regression processes (bank erosion and riverbank vegetation succession disruption). Besides the base scenario (situation in 2014), three more restoration scenarios include levee opening, levee complete removal, and side channel reactivation. Finally, results from two-dimensional hydraulic simulations allow for sensitivity analysis, comparing the current situation with the proposed scenarios. The study of shear stress is used as a proxy for the initiation of side erosion and vegetation succession disruption. Outcomes indicate that scenarios would create conditions for mobilization of habitat patches in formerly stable floodplain areas, especially with the scenario of levee removal. The possibility of regaining channel mobility and floodplain connection would allow the fluvial system to increase its water retention capacity and, thus, to adapt to floods and droughts associated to climate change.

A habitat suitability model for Chinese sturgeon determined using the generalized additive method

Summary The Chinese sturgeon is a type of large anadromous fish that migrates between the ocean and rivers. Because of the construction of dams, this sturgeon’s migration path has been cut off, and this species currently is on the verge of extinction. Simulating suitable environmental conditions for spawning followed by repairing or rebuilding its spawning grounds are effective ways to protect this species. Various habitat suitability models based on expert knowledge have been used to evaluate the suitability of spawning habitat. In this study, a two-dimensional hydraulic simulation is used to inform a habitat suitability model based on the generalized additive method (GAM). The GAM is based on real data. The values of water depth and velocity are calculated first via the hydrodynamic model and later applied in the GAM. The final habitat suitability model is validated using the catch per unit effort (CPUE d ) data of 1999 and 2003. The model results show that a velocity of 1.06–1.56 m/s and a depth of 13.33–20.33 m are highly suitable ranges for the Chinese sturgeon to spawn. The hydraulic habitat suitability indexes (HHSI) for seven discharges (4000; 9000; 12,000; 16,000; 20,000; 30,000; and 40,000 m 3 /s) are calculated to evaluate integrated habitat suitability. The results show that the integrated habitat suitability reaches its highest value at a discharge of 16,000 m 3 /s. This study is the first to apply a GAM to evaluate the suitability of spawning grounds for the Chinese sturgeon. The study provides a reference for the identification of potential spawning grounds in the entire basin.

Seasonal invasion dynamics in a spatially heterogeneous river with fluctuating flows.

A key problem in environmental flow assessment is the explicit linking of the flow regime with ecological dynamics. We present a hybrid modeling approach to couple hydrodynamic and biological processes, focusing on the combined impact of spatial heterogeneity and temporal variability on population dynamics. Studying periodically alternating pool-riffle rivers that are subjected to seasonally varying flows, we obtain an invasion ratchet mechanism. We analyze the ratchet process for a caricature model and a hybrid physical-biological model. The water depth and current are derived from a hydrodynamic equation for variable stream bed water flows and these quantities feed into a reaction-diffusion-advection model that governs population dynamics of a river species. We establish the existence of spreading speeds and the invasion ratchet phenomenon, using a mixture of mathematical approximations and numerical computations. Finally, we illustrate the invasion ratchet phenomenon in a spatially two-dimensional hydraulic simulation model of a meandering river structure. Our hybrid modeling approach strengthens the ecological component of stream hydraulics and allows us to gain a mechanistic understanding as to how flow patterns affect population survival.