Overland Flow Depth Research Articles

Impact-based classification of extreme rainfall events using a simplified overland flow model

ABSTRACT In this study, we present a new rainfall classification method based on the potential of individual rainstorm events to generate and sustain overland flow on a simplified urban model surface. Conventional rainfall classification approaches using peak intensities or rainfall sums can lead to misjudgements of the impact of rainfall events, as they do not explicitly consider the potential of rain to generate and sustain substantial amounts of overland flow on typical sealed urban surfaces. The new method of impact-based rainfall classification proposed here comprises three steps: Identification of rainfall events from high-resolution time series, computation of overland flow depths for each event, and impact-based classification of rainfall events as a function of the magnitude of overland flow. The accuracy of this approach was evaluated by its ability to describe seasonal and annual occurrences of and variations in rainstorm impacts for high-resolution series at three different urban stations in Germany.

Anomalous overland flow on hillslopes: A fractional kinematic wave model, its solutions and verification with data from laboratory observations

This paper analyses a fractional kinematic wave equation (fKWE) for overland flow and evaluates its solutions for applications using data from overland flow flumes with simulated rainfall in the laboratory. Solutions of fKWE presented have been derived for large time or when the Laplace transform variable s→0, which is one of the most important situations for overland flow. The solutions include expressions for the depth, velocity, and unit discharge, of overland flow. Fitting the approximate solution for the depth of overland flow to the data yields the values of the order of space-fractional derivatives, ρ, which is around ρ=1.5. It is found that ρ increases with the slope gradient and the rainfall intensity. The approximate order of ρ=1.5, which is about the average of order 1 for the advection equation and 2 for the diffusion equation, implies that diffusive mechanisms manifest in the overland flow. The findings mean that either an fKWE is used or a diffusion term is needed to account for dynamic forces in overland flow as the fKWE captures more physical mechanisms.

Field survey of the 30 October 2020 Samos (Aegean Sea) tsunami in the Greek islands.

On October 30th, 2020, a magnitude 7.0 earthquake offshore off the northern coast of Samos, Greece, generated a tsunami that impacted the nearshore Greek islands and the Aegean coastline of Turkey. Here, we describe detailed results from several post-event field surveys, and report first wave arrival timing and polarity information as well as tsunami height/runup measurements, from five islands. In Chios, wave runup reached 1.38 m, in Samos ~ 3 m, in Fourni 1.57 m, in Thimena 1.46 m, and in Ikaria 1.18 m. This event marks two milestones. One, the General Secretariat for Civil Protection of Greece, disseminated a message through Greece's 1–1-2 Emergency Communications Service to all cell phones in the eastern Aegean geographical region, warning recipients to stay away from coastal areas. According to eyewitnesses, the message was received ~ 3–5 min prior to the second and largest flood in Vathi, as the first flood had not sufficiently alarmed the local authorities to evacuate residents. Two, we were able to infer complete tsunami hydrographs from measurements for the first two floods in Vathi, which suggests that the water level rose to about one meter overland flow depth in one minute.

Improvement of Two-Dimensional Flow-Depth Prediction Based on Neural Network Models By Preprocessing Hydrological and Geomorphological Data

The stability and efficiency of a rainfall–runoff model are of concern for establishing a flood early warning system. To tackle any problems associated with the numerical instability or computational cost of conducting a real-time runoff prediction, the neural network (NN) method has emerged as an alternative to calculate the overland-flow depths in a watershed. Therefore, instead of developing a new algorithm of machine learning to improve the predicted accuracy, this study focuses on thoroughly exploring the influence of input data that are highly related to the flow responses in space, and then establishing a procedure to process all the input data for the NN training. The novelty of this study is as follows: (1) To improve the overall accuracy of the 2D flood prediction, geomorphological factors, such as the hydrologic length (L), the flow accumulation value (FAV), and the bed slope (S) at the location of each element extracted from the topographic dataset were considered together and were classified into multiple zones for separate trainings. (2) An optimal length of the effective rainfall condition (To) was proposed by conducting a correlation analysis to determine the most informative precipitation data. In this study, the outcomes of four types of NN models were examined and compared with one another. The results show that the simplest structure of the NN methods could achieve satisfactory predictions of flow depth, as long as the approaches of data preprocessing and model training proposed in this study were implemented.

Water quality changes in a short-rotation woody crop riparian buffer

Converting riparian buffers in agricultural areas from annual row crops to short rotation woody crops (SRWCs) grown for biofuel can provide both water quality benefits and a financial incentive for buffer adoption among agricultural producers. A randomized complete block design was used to determine water quality changes resulting from converting plots previously cultivated in corn to SRWC willow (Salix. spp) adjacent to a stream in Storrs, CT. Both overland flow and ground water samples were analyzed for total nitrogen (TN) and total phosphorus (TP). Additionally, overland flow was analyzed for suspended solids concentration (SSC) and ground water samples were analyzed for nitrate + nitrite (NO2+NO3-N). Lower (p = 0.05) concentrations of TN (41%) and TP (53%) were observed in overland flow from willow plots than from corn plots. Shallow ground water concentrations at the edge of willow plots were lower in TN (56%) and NO3+NO2-N (64%), but 35% higher in TP, than at the edge of corn plots. SSC was also lower (71%) in overland flow associated with willow compared to corn. The treatment had no effect on the depth or volume of overland flow or mass export. The changes in concentrations resulting from conversion of corn to SRWC in a riparian buffer are similar to those observed in restored and established buffers.

Water fluxes between inter-patches and vegetated mounds in flat semiarid landscapes

It has been assumed that bare soil (BS) inter-patches in semi arid spotted vegetation behave as sources of water to near vegetated soil (VS) patches. However, little evidence has been gained from direct measurements of overland and infiltration water fluxes between bare soil inter-patches and shrub mounds at a scale compatible with available high resolution imagery and hydrological modeling techniques. The objective of this study is to address the thin scale internal redistribution of water between BS inter-patches and vegetated mounds at relatively flat spotted semiarid landscapes. The relation between plant cover, topography and runoff was inspected with non-parametric association coefficients based on high resolution remotely sensed imagery, ground truth topographic elevation and spatial-explicit field data on potential runoff. Measurements of advective flows at the same spatial scale were carried out at micro-plots of BS and shrub mounds. Water fluxes between BS inter-patch and a shrub mound were simulated under varying typical Patagonian rainfall scenarios with an hydrological model. Results obtained revealed that the soil properties, infiltration and overland flow metrics at the mounds and inter-patches exhibit spatially and dynamic variable hydraulic properties. High micro-topographic roughness and depression storage thickened overland flow depth at VS patches. At BS inter-patches prevailing low slopes and depression storage were found to be important variables attenuating the surface runoff. At both rainfall scenarios simulated, the soil under the shrub mound accumulated more moisture (from direct rain) and reached saturation long before this occurred in BS nearby inter-patch area. Overland flow at the inter-patch was attenuated as it reached the border of the patch, diverging from the latter as it followed the (small) topographic gradient. The overland flow generated inside the vegetated mound was effectively retained at the typical Summer rainfall scenario; while several threads of runoff were routed outside the mound at the typical Winter rainfall scenario. The results here shown fail to detect: (a) enough runoff momentum that could route runon onto the vegetated mounds and (b) a contrast in infiltration rates between BS and the vegetated mound enough to lead to a free-surface gradient in ponded water that could inundate the mound.

An Approximately Semi-Analytical Model for Describing Surface Runoff of Rainwater Over Sloped Land

Accurate prediction of surface runoff is critical to watershed management. In this research a semi-analytical model was adopted to solve the kinematic wave equation based on the assumption that the rate of overland-flow depth change is proportional to the rainfall excess. Simulations were compared with the results from laboratory experiments at various rain intensities. Parameters of infiltration rate and Manning’s roughness coefficient were determined. The accuracy of the semi-analytical model was evaluated by numerical simulations. The predicted outflow rates from the numerical simulations agreed well with the observed data. Further, our study indicated that the ratio (c) of the overland-flow depth change to the rainfall excess was a power function of the rain intensity. The depth and velocity of water flow at any time and distance could be calculated with the semi-analytical model. Hydraulic parameters including Reynolds number, Froude number, hydraulic shear stress, stream power and Darcy-Weisbach friction factor characterizing the dynamic features of overland flow of rainwater were calculated based on calculated overland-flow depth and velocity. The proposed analytical method can provide a new way to predict infiltration and runoff over sloped land.

Modelling the Potential of Integrated Vegetation Bands (IVB) to Retain Stormwater Runoff on Steep Hillslopes of Southeast Queensland, Australia

Rainfall intensity is predicted to increase under a changing climate, leading to increased risks of hillslope erosion, downstream sedimentation and flooding. For many catchments used for grazing and agricultural land uses, it will become increasingly important to maintain ecohydrological functioning despite climatic extremes. One means to achieve this is through strategic reforestation using locally endemic species, in spatial configurations that effectively intercept, retain or and redistribute overland flows. This paper adopts a modelling approach for investigating the potential of one such design termed “integrated vegetation bands” (IVB), to increase the retention of runoff across steep hillslopes, particularly in the sub-tropics where rainstorms are becoming increasingly intense. A spatially distributed simulation model (MIKE-SHE) was applied to a steep, grazed catchment (Maronghi Creek catchment, Southeast Queensland, Australia) to compare stormwater runoff characteristics between: (1) the existing pasture land cover; and (2) a series of hypothetical IVB added across this pasture land. The IVB were approximately 20 m wide, and configured at 5% gradient towards ridgelines. Results for estimates of overland flow depth and infiltration (spatial), and accumulative water balance (temporal), confirm that the area of hillslope retaining > 10 mm/day more runoff increased by 22% under IVB compared to the pasture land use. Excluding the IVB themselves, the area of hillslope where runoff retention increased was 11%. During the most intense rainfall, IVB held up to 25% greater water depth and had 10% greater infiltration at the hillslope scale. At the sub-catchment scale, discharge decreased by 7% and infiltration increased by 23%. The findings for sub-tropical landscapes presented here are consistent with studies conducted in temperate regions. Based on the results of this preliminary modelling work, the IVB concept has been established as a paired-catchment field trial in a high rainfall catchment in Southeast Queensland, Australia.

Low losses of a P and sediment in overland flow suggest that this tillage site and others like it may not be high risk for phosphorous pollution

This trial examined phosphorus (P) loss in overland flow (OLF) at a tillage farm in the southeast of Ireland. The soil was a grey-brown podzolic, and was representative of land covering 16% of the total agricultural area, with tillage practised on approximately one-third of this area. The object of the trial was to establish whether this site is a P-pollution risk to surface water. The productive tillage field was divided into three plots, each of approximately 1ha in size. Plots had low earth dams and open lined drains on the lower boundaries. A flow meter sampler with V-notch tank was connected to each of the three drains. Macro-pore flow (MPF) samplers were installed in the plots. Average depth of overland flow across the three plots was 5.4, 17.5 and 18.1mm y−1 for 2005, 2006 and 2007, respectively. Phosphorus concentration was 1.01, 0.64 and 0.6mg l−1, respectively, and P load was 0.04, 0.11 and 0.18kg ha−1 y−1. The median P concentration in MPF was 1.59mg l−1. Sediment yield (95kg ha−1 y−1) was low compared to that achieved in other studies. No pollution parameter measured represented a serious pollution threat. The results of this study suggest that a large proportion of tillage land in Ireland might be classified as low risk for P loss through the overland flow pathway.

Low losses of a P and sediment in overland flow suggest that this tillage site and others like it may not be high risk for phosphorous pollution

This trial examined phosphorus (P) loss in overland flow (OLF) at a tillage farm in the southeast of Ireland. The soil was a grey-brown podzolic, and was representative of land covering 16% of the total agricultural area, with tillage practised on approximately one-third of this area. The object of the trial was to establish whether this site is a P-pollution risk to surface water. The productive tillage field was divided into three plots, each of approximately 1ha in size. Plots had low earth dams and open lined drains on the lower boundaries. A flow meter sampler with V-notch tank was connected to each of the three drains. Macro-pore flow (MPF) samplers were installed in the plots. Average depth of overland flow across the three plots was 5.4, 17.5 and 18.1mm y 1 for 2005, 2006 and 2007, respectively. Phosphorus concentration was 1.01, 0.64 and 0.6mg l , respectively, and P load was 0.04, 0.11 and 0.18kg ha 1 y . The median P concentration in MPF was 1.59mg l . Sediment yield (95kg ha 1 y ) was low compared to that achieved in other studies. No pollution parameter measured represented a serious pollution threat. The results of this study suggest that a large proportion of tillage land in Ireland might be classified as low risk for P loss through the overland flow pathway.

Testing the Effects of Detachment Limits and Transport Capacity Formulation on Sediment Runoff Predictions Using the U.S. Army Corps of Engineers GSSHA Model

The physics-based Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model was developed by the U.S. Army Corps of Engineers for hydrologic, sediment transport, and water quality analyses. GSSHA simulates erosion and transport of sediments on the overland flow plain based on rainfall intensity and overland flow depth and velocity. The original sediment transport capabilities in GSSHA were taken from the GSSHA predecessor, CASC2D-SED. Independent testing of the sediment transport methods in CASC2D-SED by researchers identified several deficiencies in the formulation that caused significant overestimation of sediment yield during hydrologic events that were much larger than a calibration event. Sediment detachment limits and a variety of overland sediment transport equations were incorporated into the GSSHA model to address these deficiencies. This paper presents an evaluation of these modifications in terms of GSSHA sediment yield predictions of both single-event and summer growing season sediment yields. Simulation results are compared with research-quality sediment discharge data set from the USDA Goodwin Creek Experimental Watershed (GCEW). Results show that the reformulated GSSHA sediment transport model predicts event-total sediment discharge volume within (±) 50% over hydrologic events that vary by three orders of magnitude. The transport capacity method selected for use in the simulation had a large effect on the model results.

Enabling high-resolution forecasting of severe weather and flooding events in Rio de Janeiro

Safe operation of many cities is affected by relative extremes in weather conditions. With precipitation events, local topography and weather influence water runoff and infiltration, which directly affect flooding. Hence, the availability of highly focused predictions has the potential to mitigate the impact of severe weather on a city. Often, such information is simply unavailable. The initial step to address this gap is the application of state-of-the-art weather models at an urban scale calibrated to address this mismatch. The generation of operational forecasts at such a scale for the Rio de Janeiro metropolitan area suggests a horizontal resolution of approximately 1 km and a vertical resolution in the lower boundary layer of tens of meters. Forecasting impacts from storm-driven flooding events requires the development of a coupled hydrological model that operates at a street scale with resolution of approximately 1 m, capturing local terrain effects and simulating surface flow and water accumulation, especially for overland flow and ponding depth. This coupled approach has enabled operational prediction of storm impacts on local infrastructure, as well as measurement of the model error associated with such forecasts.

Application of a finite difference computational model to the simulation of earthquake generated tsunamis

Tsunamis are long waves and commonly modeled with the shallow-water wave approximation of the equations of motion. The calculation of tsunami inundation remains after two decades of progress a vexing and temperamental computation exquisitely dependent on ad-hoc algorithms. We present computed results using, a splitting method in space to reduce this hyperbolic system in two successive hyperbolic systems, one for each primitive variable. Then, we use dispersive, Godunov type finite difference method and solve the equations in characteristic form. We use the methodology implemented in the code MOST to calculate inundation from four different earthquake scenarios for Heraklion, Greece. MOST has been repeatedly benchmarked. The scenarios are geophysical estimates of the source mechanisms of the 365 AD event, the largest known earthquake in the Eastern Mediterranean in the last two millenia. The earthquake scenarios used allow for defining the seafloor deformation resulting from the parent seismic motions and, after translating them to the water surface, they constitute the initial conditions for computations. We use high resolution bathymetric and topographic data to generate fine resolution grids used in the computations. Our practice allows for a precise identification of the onland inundation and the overland flow depths and currents during tsunami flooding in Heraklion. This is the first time such a quantitative study has been undertaken for Eastern Crete. We conclude that there is substantial hazard, and there is little difference among the four different seismic interpretations of the 365 AD earthquake.

Rainfall Energy Loss: An Empirical Model

Kinetic energy of a rainfall event is determined by its intensity. However, the effective kinetic energy reaching a soil surface that is responsible for detachment and transportation of soil particles is often less than the total kinetic energy of the rainfall event. This is because of the cushioning effect a film of water provides. Therefore it is essential to account for the loss in kinetic energy of a rainfall event and incorporate it in simulation models to accurately estimate soil erosion. This paper proposes a logarithmic energy loss model to estimate kinetic energy of rainfall reaching the soil surface. The model accounts for the depth of shallow overland flow and rainfall intensity. The empirical model was established through the set of data obtained from a rainfall simulation experimental setup consisting of a laboratory-scale tilting hydraulic flume, rainfall simulator and a series of sensitive piezoelectric force transducers. Slope variations were simulated by mechanically tilting the flume between 0° and 15°. Responses captured by the transducers in the form of voltage and pulses were analysed to establish the empirical model. The high Nash-Sutcliffe efficiency (Ε = 0.90) suggests the reliability of the empirical model and its potential for applications in soil erosion modelling.

Reassessing the tsunami risk in major ports and harbors of California I: San Diego

We assess tsunami hazards in San Diego Bay, California, using newly identified offshore tsunami sources and recently available high resolution bathymetric/topographic data. Using MOST (Titov and Synolakis, J Waterways Port Coastal Ocean Eng ASCE 124(4):57–171, 1998), we simulate locally, regionally and distant-generated tsunamis. Local tsunami source models use more realistic fault and landslide data than previous efforts. With the exception of the Alaska-Aleutian Trench, modeling results suggest that local sources are responsible for the largest waves within the San Diego Bay and Mission Bay. Because San Diego Bay is relatively well protected by North Island and the Silver Strand, the wave heights predicted are consistently smaller inside the harbor than outside. However, historical accounts, recent tsunamis and our predictions show that San Diego Bay is vulnerable to strong tsunami induced currents. More specifically, large currents are expected inside the harbor for various distant and local tsunami sources with estimated flow velocities exceeding 100 cm/s. Such currents have been damaging to harbor facilities, such as wharves and piers, and may cause boats to break from moorings and ram into adjacent harbor structures, as observed in recent historic tsunamis. More recently, following the Mw 8.8 February 27, 2010 Chile earthquake, tsunami-currents damaged docks/piers in Shelter Island confirming our findings. We note that the first generation of inundation maps in use in San Diego County by emergency management was based on much larger “worst case but realistic scenarios” (Synolakis et al. 2002a), which reflected the understanding of offshore hazards pervasive ten years ago. Large inundation and overland flow depths were observed primarily in local tsunami source simulations. In particular, locally induced tsunamis appear capable to overtop the Silver Strand. The results suggest that further work needs to be carried out with respect to local tsunami sources as they seem to have worse impact in the San Diego region than previously thought but probably low probability of occurrence. We also predict that a coastal community can be devastated simultaneously by large waves inundating shores and large currents in locations with small flow depths.

Analysis of the development of a hydrological balance for future decades in the Senianska depression in the Eastern Slovak lowland

Analysis of the development of a hydrological balance for future decades in the Senianska depression in the Eastern Slovak lowlandThe goal of the article was to analyze the hydrological balance for future decades in a pilot area in the Eastern Slovak lowland. The aim was to set up the physically-based Mike SHE hydrological model for the modeling hydrological balance in the selected wetland ecosystem in the Eastern Slovak Lowland. The pilot area - the Senianska depression is located near the village of Senne, between the Laborec and Uh Rivers. Specifically, it is a traditional landscape of meadows, marshes, cultivated soil, small water control structures and forests. To get a complete model set up for simulating elements of the hydrologic balance in the pilot area, it was necessary to devise a model for a larger area, which includes the pilot area - the Senianska depression. Therefore, both the Mike SHE model was set up for the Laborec River basin (a model domain of 500 × 500 m) and the Čierna voda River basin (a model domain of 100 × 100 m), for the simulation period of 1981-2007, is order to get the boundary conditions (overland flow depth, water levels, discharges and groundwater table) for the model of the pilot area. The Mike SHE model constructed for the pilot area - the Senianska depression (a model domain of 1 × 1 m) -was used to simulate the elements of the hydrological balance for the existing conditions during the simulation period of 1983-2007 and for climate scenarios for the simulation period of 1983-2100. The results of the simulated elements of the hydrological balance for the existing conditions were used for a comparison of the evolution of the hydrologic conditions in the past, for identifying wet and flooded areas and for identifying the spatial distribution of the actual evapotranspiration in the pilot area. The built-up model with setting values was used for modeling the hydrological balance in changed conditions - climate change.

Cyclone Gonu storm surge in Oman

Super Cyclone Gonu is the strongest tropical cyclone on record in the Arabian Sea. Gonu caused coastal damage due to storm surge and storm wave impact as well as wadi flooding. High water marks, overland flow depths, and inundation distances were measured in the coastal flood zones along the Gulf of Oman from 1 to 4 August 2007. The high water marks peaked at Ras al-Hadd at the eastern tip of Oman exceeding 5 m. The storm surge of Gonu is modeled using the Advanced Circulation Model (ADCIRC). The multi-hazard aspect is analyzed by comparing observations from Cyclone Gonu with the 2004 Indian Ocean Tsunami.

Modeling changes in rill erodibility and critical shear stress on native surface roads

AbstractThis study investigated the effect of cumulative overland flow on rill erodibility and critical shear stress on native surface roads in central Idaho. Rill erodibility decreased exponentially with increasing cumulative overland flow depth; however, critical shear stress did not change. The study demonstrated that road erodibility on the studied road changes over the course of one or more consecutive overland flow events. Therefore, model simulations that fail to take into consideration this change will probably over‐estimate sediment yields. An exponential function describing the relationship between rill erodibility and cumulative overland flow depth is presented as a basis for future model development for simulating erosion on native surface roads. Copyright © 2008 John Wiley & Sons, Ltd.

Hurricane Katrina Storm Surge Reconnaissance

Hurricane Katrina (August 23–30, 2005) was one of the costliest and deadliest hurricanes to ever strike the United States, impacting low-lying coastal plains particularly vulnerable to storm surge flooding. Maximum storm surges, overland flow depths, and inundation distances were measured along the Gulf Coast of Florida, Alabama, Mississippi, and Louisiana. The vehicle-based survey was complemented by inspections with the reconnaissance boat along the Gulf Coast and the Mississippi Barrier Islands. The survey covered both the impact on the built and the natural environments. The storm surge peaked to the east of Katrina’s path exceeding 10m in several locations along the Mississippi coastline. The storm surge measurements show that the lower floors of specially designed buildings were damaged by the surge of seawater and associated wave action, while the upper floors sustained minimal wind damage. The storm surge measurements along New Orleans Lakeshore allowed the investigators to exclude overtopping as failure mechanism for the 17th Street outfall canal levee. Hurricane Katrina’s storm surge distribution (Category 3 at landfall) is compared against Hurricane Camille’s storm surge distribution (Category 5 at landfall). The land loss on the barrier islands and the increased vulnerability of the US Gulf Coast to future hurricane storm surges is discussed.

Investigation of groundwater response to overland flow and topography using a coupled MIKE SHE/MIKE 11 modeling system for an arid watershed

Summary The distribution of groundwater and dynamic fluctuations in groundwater levels have direct impacts on the eco-environment of arid areas. Investigations of groundwater recharge in arid areas are typically limited by a lack of adequate meteorological and hydrogeological records. This study focuses on groundwater recharge in a seasonally flooded arid area within the Tarim Basin, China, with the aim of analyzing the influence of groundwater and topography on the response characteristics of overland flow. We conducted a simulation using a coupled MIKE SHE/MIKE 11 model over 112 days of the flood season and calculated the average water balance. Based on the properties of the multi-scale recognition of wavelets and the self-comparability of fractals in analyzing the detailed characteristics of groundwater diffusion and fluctuations in groundwater levels, a hybrid fractal–wavelet method was used to explain the recharge response associated with overland flow, distance from midstream, topography, and flooding depth. The results of the model simulations are generally consistent with observed data, indicating that the hybrid fractal–wavelet method is able to recognize the detailed characteristics of the groundwater response. Furthermore, the groundwater levels show a significant relationship with the orientation of the riverway prior to flooding. When flooding occurred, the groundwater levels showed a rapid response to changes in the depth of long-term overland flow. A total of 71.31% of the study area showed a strong correlation between groundwater level and the distance from midstream. The results demonstrate that the relationship exists for fluctuations in groundwater levels of more than 1.4 m. Variations in the height of the water table were significantly influenced by topographic elevation; in contrast, slope and aspect had little effect. In conclusion, the above results indicate that the proposed methodology is applicable for the management of water resources in arid regions. The modeling and hybrid fractal–wavelet method study allowed quantification of the processes affecting groundwater levels and provided an insight into their implications in exploring groundwater level management.