Infiltration Excess Mechanism Research Articles

A unified runoff generation scheme for applicability across different hydrometeorological zones

Runoff generation in humid and semi-arid regions are usually dominated by saturation-excess mechanism and infiltration-excess mechanism, respectively. However, both mechanisms can co-exist in semi-humid regions. Therefore, we proposed a unified runoff generation scheme to represent the single and mixed runoff generation processes, making it applicable for different hydrometeorological conditions. The saturation-excess runoff generation scheme of the Xin'anjiang model was integrated with a modified Horton infiltration scheme at the grid cell scale. By substituting the original runoff generation scheme of the grid-Xin'anjiang (GXAJ) with the integrated scheme, we developed a new distributed hydrological model called grid-Xin'anjiang-infiltration-excess (GXAJ-IE) model. GXAJ-IE was tested in four watersheds and compared with two benchmark models with single runoff generation mechanism. The results indicate that GXAJ-IE model has higher flexibility and robustness in reproducing flood hydrographs under different rainfall conditions in semi-humid watersheds and has comparable performances with the benchmark models in humid and semi-arid regions.

Hydrological modelling with an improved flexible hybrid runoff generation strategy

The saturation-excess mechanism, infiltration-excess mechanism and subsurface stormflow mechanism are the fundamental of the hybrid runoff generation models. Existing hybrid runoff generation methods pay much attention to the surface runoff and subsurface runoff, but less to the characterization of subsurface stormflow. Additionally, the subsurface stormflow was mostly separated from the saturated-excess. This kind of separation ignores subsurface stormflow in unsaturated areas, and therefore may result in significant errors sometimes. Therefore, a novel conceptual method for subsurface stormflow in unsaturated areas over the interface was proposed through a combination of the Green-Ampt equation with the parabolic infiltration capacity distribution curve. Then, the subsurface stormflow was considered as the sum of the infiltration excess over the unsaturated areas and the saturation excess over the saturated areas. On this basis, an improved flexible runoff generation strategy was developed to incorporate the spatial heterogeneity of underlying surface conditions and rainfall conditions based on the three single runoff generation mechanisms. Finally, the Xun River basin was selected as a case study. Performances of different runoff generation strategies were compared and discussed based on flood events and continues flow. And the sensitivity analysis of the parameters was carried out. Results show that the proposed strategy performed the best among the five strategies, and the accuracy of the simulation results was affected significantly by the infiltration-excess subsurface stormflow over the unsaturated areas. The proposed method can be used for the watersheds where there may be abundant subsurface stormflow.

A hybrid runoff generation modelling framework based on spatial combination of three runoff generation schemes for semi-humid and semi-arid watersheds

It is challenging to accurately differentiate and simulate different runoff components yielded under the saturation-excess and infiltration-excess mechanisms in semi-arid and semi-humid watersheds. Fixed model structures and runoff generation modes in most of the existing conventional hydrological models limit their ability to account for respective contributions of saturation-excess and infiltration-excess flows to flood processes. To conquer this limitation, this study developed a new flexible hybrid runoff generation modeling framework, which is named as spatial combination computing models (SCCMs) for runoff generation. SCCMs can determine the dominant runoff generation mode, either saturation-excess or infiltration-excess, on the sub-watershed level and then adopt one of the Xinanjiang (XAJ), Xinanjiang-Green Ampt (XAJG) and Green-Ampt (GA) runoff generation schemes to compute runoff generation at each sub-watershed. The logical combination of the above three runoff generation schemes led to six flavors of SCCMs. Curve number and topographic index are used for dividing a watershed into infiltration-excess dominated and saturation-excess dominated sub-watersheds. The proposed models were tested in two typical semi-humid (Dongwan) and semi-arid (Zhidan) watersheds. The multi-objective generalized likelihood uncertainty estimation method (GLUE) was used to analyze the parameter uncertainty of SCCMs. The results show that all two-scheme SCCMs outperform any of the single-scheme SCCMs. SCCM-2c (a combination model of XAJ and XAJG) achieves the best performance in the semi-humid Dongwan Watershed, while SCCM-5c (a combination model of XAJG and GA) performs best in the semi-arid Zhidan Watershed. The multi-objective GLUE-based uncertainty analysis shows that parameter uncertainties of the two-scheme SCCMs (SCCM-2c and SCCM-5c) are slightly lower than those of the single-scheme SCCMs (SCCM-1n, i.e., the XAJ model, and SCCM-6n, i.e., the GA model), indicating that increased model complexity in SCCMs does not cause increased model parameter uncertainty. Our results indicate that SCCMs with more realistic representation of spatial heterogeneity can achieve higher simulation accuracies and even lower uncertainties than the conventional single-scheme models.

Mapping runoff generating areas using AGNPS-VSA model

ABSTRACT In humid regions, surface runoff is often generated by saturation-excess runoff mechanisms from relatively small variable source areas (VSAs). However, the majority of the current hydrologic models are based on infiltration-excess mechanisms. In this study, the AGricultural Non-Point Source Pollution (AGNPS) model was used to integrate the VSA concept using topographic wetness index (TWI). Both the original and AGNPS-VSA models were evaluated for a small agricultural field in Ontario, Canada. The results indicate that the AGNPS-VSA model performed better than original model. The AGNPS-VSA model predicted that only the saturated portion of the field with higher TWI values produced runoff, whereas the original AGNPS model showed uniform hydrologic response from the entire field. The results of this study are important for accurately mapping the locations of VSAs. This new model could be a powerful tool in identifying critical source areas for applying targeted best management practices to minimize pollutant loads to receiving waters.

Assessment of variable source area hydrological models in humid tropical watersheds

ABSTRACTThe objective of this study was to compare the performances of hydrological models that incorporate the Variable Source Area (VSA) mechanism of runoff generation with that of the Soil and Water Assessment Tool (SWAT), which uses the infiltration-excess mechanism. One of the VSA-based model used, SWAT–VSA, has been proposed as a re-conceptualization of the SWAT and uses a topography-based wetness index to identify source areas. In this study, the topography-based wetness index was replaced with a Modified Normalized Difference Water Index (MNDWI) derived from satellite imagery resulting in the SWAT–MNDWI model. Model performances were evaluated through their application in two humid tropical watersheds (Hemavathi – 2974 km2; Harangi – 538.8 km2) located in the Upper Cauvery River Basin, India. Using relevant data inputs, the three models were applied separately to both watersheds. Models were calibrated for the historical period 2000–2003 and validated for the period 2004–2006 using observed daily observed streamflow records at the watershed outlets. Overall, the SWAT–MNDWI model was the best one in simulating daily streamflow with Nash–Sutcliffe efficiency of 0.85, coefficient of determination of 0.88, percentage bias of 13.2% and root mean square error of 37.48 m3/s for the Hemavathi watershed and corresponding values of 0.88, 0.88, 1.09% and 16.67 m3/s for the Harangi watershed. The spatial patterns of surface runoff generation were similar for the SWAT–VSA and SWAT–MNDWI models, but completely different for the SWAT model. Overall results have demonstrated that models incorporating VSA hydrology, and in particular the proposed SWAT–MNDWI model, provide accurate and convenient tools for distributed hydrologic modelling in humid tropical watersheds.

Spatial Combination Modeling Framework of Saturation-Excess and Infiltration-Excess Runoff for Semihumid Watersheds

There exist two types of direct runoff generation mechanisms in semihumid watersheds: saturation-excess mechanism and infiltration-excess mechanism. It has always been a difficult problem for event hydrological simulation to distinguish the two types of runoff processes. Based on the concept of dominant runoff processes, combined with GIS and RS techniques, this paper proposed an event-based spatial combination modeling framework and built two spatial combination models (SCMs) accordingly. The CN parameter and topographic index, both of which are widely used in hydrological researches, are adopted by the SCM to divide the entire watershed into infiltration-excess dominated (IED) areas and saturation-excess dominated (SED) areas. Dongwan watershed was taken as an example to test the performances of infiltration-excess model, saturation-excess model, and SCM, respectively. The results of parameter optimization showed that the parameter values and state variables of SCM are much more realistic than those of infiltration-excess model and saturation-excess model. The more accurate the divisions of infiltration-excess and saturation-excess dominated areas, the more realistic the SCM parameter values. The simulation results showed that the performance of SCM was improved in both calibration and validation periods. The framework is useful for flood forecasting in semihumid watersheds.

Spatial-Temporal Dynamics of Runoff Generation Areas in a Small Agricultural Watershed in Southern Ontario

The identification of runoff generating areas (RGAs) within a watershed is a difficult task because of their temporal and spatial behavior. A watershed was selected to investigate the RGAs to determine the factors affecting spatio-temporally in southern Ontario. The watershed was divided into 8 fields having a Wireless System Network (WSN) and a V-notch weir for flow and soil moisture measurements. The results show that surface runoff is generated by the infiltration excess mechanism in summer and fall, and the saturation excess mechanism in spring. The statistical analysis suggested that the amount of rainfall and rainfall intensity for summer (R2 = 0.63, 0.82) and fall (R2 = 0.74, 0.80), respectively, affected the RGAs. The analysis showed that 15% area generated 85% of surface runoff in summer, 100% of runoff in fall, and 40% of runoff in spring. The methodology developed has potential for identifying RGAs for protecting Ontario’s water resources.

Producción y transporte de sedimento en cárcavas desarrolladas en la Depresión Interior Altoaragonesa (Cuenca de Aragúas, Pirineo Central)

This study shows the analyses of suspended sediment transport from badland areas developed in the Inner Depression (Central Pyrenees). The importance of these morphologies is related to its frequency, and to the high impact that they produce on the drainage net, because of their intense geomorphological dynamics. The occurrence and development of these morphologies is associated to two main factors: the geological characteristics of the substratum constituted by marls, and the strong climatic seasonality of the submediterranean climate. The area has been studied since 2004, through the selection of a small basin, which was monitored with sensors and plots for observation of weathering and erosion processes (between January 2004 and December 2006). This instrumentation was completed with a gauging station (October 2005) on the main drainage (Rebullesa ravine) that facilitates the record of hydrological response and suspended sediment transport. This paper shows an analysis, based on 79 recorded events between October 2005 and April 2007. The results, that correspond to a short period of time, have allowed pointing out some general characteristics of hydro-sedimentological responses in these morphologies: very high hydrological response, even during the driest period; great capacity of sediment yield and exportation, with punctual concentrations than can reach more than 1000 g·l-1, and the strong sensibility against climatic seasonality. Likewise, it was observed that precipitation intensity is well correlated with sediment concentration, especially during the driest periods, which demonstrates that the main runoff generation process is associated to infiltration excess mechanisms (Hortonian flow).

A statistically based runoff‐yield model coupling infiltration excess and saturation excess mechanisms

AbstractA statistically based runoff‐yield model is proposed in this paper. The model considers spatial heterogeneities of rainfall, soil infiltration capacity and soil water storage capacity that are main factors controlling runoff‐yield process. It assumes that the spatial variation of rainfall intensity at each time step can be characterized by a probability density function, which is estimated by matching the hyetograph through goodness‐of‐fit measure, whereas the spatial heterogeneities of soil infiltration capacity and soil water storage capacity are described by parabola‐type functions. Surface runoff is calculated according to infiltration excess mechanism; the statistical distribution of surface runoff rate can be deduced with the joint distribution of rainfall intensity and soil infiltration rate, thus obtaining a quasi‐analytical solution for surface runoff. Based on saturation excess mechanism, the groundwater flow (flows below the ground are collectively referred to as groundwater flow) is calculated by infiltration and the probability distribution of soil water storage capacity. Consequently, the total runoff is composed of infiltration excess and saturation excess runoff components. As an example, this model is applied to flood event simulation in Dongwan catchment, a semi‐humid region and a tributary of Yellow River in China. It indicates that the proposed runoff‐yield model could achieve acceptable accuracy. Copyright © 2011 John Wiley & Sons, Ltd.

A modeling approach to assess the hydrological response of small mediterranean catchments to the variability of soil characteristics in a context of extreme events

Abstract. This paper presents a modeling study aiming at quantifying the possible impact of soil characteristics on the hydrological response of small ungauged catchments in a context of extreme events. The study focuses on the September 2002 event in the Gard region (South-Eastern France), which led to catastrophic flash-floods. The proposed modeling approach is able to take into account rainfall variability and soil profiles variability. Its spatial discretization is determined using Digital Elevation Model (DEM) and a soil map. The model computes infiltration, ponding and vertical soil water distribution, as well as river discharge. In order to be applicable to ungauged catchments, the model is set up without any calibration and the soil parameter specification is based on an existing soil database. The model verification is based on a regional evaluation using 17 estimated discharges obtained from an extensive post-flood investigation. Thus, this approach provides a spatial view of the hydrological response across a large range of scales. To perform the simulations, radar rainfall estimations are used at a 1 km2 and 5 min resolution. To specify the soil hydraulic properties, two types of pedotransfer function (PTF) are compared. It is shown that the PTF including information about soil structure reflects better the spatial variability that can be encountered in the field. The study is focused on four small ungauged catchments of less than 10 km2, which experienced casualties. Simulated specific peak discharges are found to be in agreement with estimations from a post-event in situ investigation. Examining the dynamics of simulated infiltration and saturation degrees, two different behaviors are shown which correspond to different runoff production mechanisms that could be encountered within catchments of less than 10 km2. They produce simulated runoff coefficients that evolve in time and highlight the variability of the infiltration capacity of the various soil types. Therefore, we propose a cartography distinguishing between areas prone to saturation excess and areas prone only to infiltration excess mechanisms. The questions raised by this modeling study will be useful to improve field observations, aiming at better understanding runoff generation for these extreme events and examine the possibility for early warning, even in very small ungauged catchments.

Comparison of Runoff Parameterization Schemes with Spatial Heterogeneity across Different Temporal Scales in Semihumid and Semiarid Regions

Due to the spatial variability of precipitation, topography, soil properties, and antecedent soil moisture, runoff is generated by more than one kind of mechanism. Based upon digital elevation model-derived subcatchments and river network, the Xinanjiang Model (XAJ, saturation excess mechanism of rainfall-runoff partitioning), the Shaanbei Model (SAB, infiltration excess mechanism), and the Hybrid Model (HYB, two mixed runoff mechanisms by combining spatial distribution curves of soil tension water storage capacity and infiltration capacity) were applied for streamflow modeling at four hydrological observational stations in the Laohahe River basin, and compared at different time intervals ranging from 1 to 24 h. The results show that the daily (24 h) HYB Model or XAJ Model performs better than the SAB Model over semihumid and semiarid areas. It is revealed that there is less possibility that rain intensity is larger than infiltration rate in semihumid and semiarid regions within a duration of 24 h. Uniform distribution of precipitation within a duration of 24 h makes the physical concept of infiltration excess fuzzy. In the event-based flood modeling at time intervals of 1, 2, 3, 4, 6, and 12 h, HYB is superior to XAJ and SAB in semiarid areas where the mean annual precipitation is less than 400 mm. It is concluded that it is more meaningful to use infiltration excess mechanisms for shorter-duration flood modeling than for daily streamflow simulation in semihumid and semiarid regions.

On the prediction of the Toce alpine basin floods with distributed hydrologic models

AbstractWith the objective of improving flood predictions, in recent years sophisticated continuous hydrologic models that include complex land‐surface sub‐models have been developed. This has produced a significant increase in parameterization; consequently, applications of distributed models to ungauged basins lacking specific data from field campaigns may become redundant.The objective of this paper is to produce a parsimonious and robust distributed hydrologic model for flood predictions in Italian alpine basins. Application is made to the Toce basin (area 1534 km2). The Toce basin was a case study of the RAPHAEL European Union research project, during which a comprehensive set of hydrologic, meteorological and physiographic data were collected, including the hydrologic analysis of the 1996–1997 period. Two major floods occurred during this period. We compare the FEST04 event model (which computes rainfall abstraction and antecedent soil moisture conditions through the simple Soil Conservation Service curve number method) and two continuous hydrologic models, SDM and TDM (which differ in soil water balance scheme, and base flow and runoff generation computations).The simple FEST04 event model demonstrated good performance in the prediction of the 1997 flood, but shows limits in the prediction of the long and moderate 1996 flood. More robust predictions are obtained with the parsimonious SDM continuous hydrologic model, which uses a simple one‐layer soil water balance model and an infiltration excess mechanism for runoff generation, and demonstrates good performance in both long‐term runoff modelling and flood predictions. Instead, the use of a more sophisticated continuous hydrologic model, the TDM, that simulates soil moisture dynamics in two layers of soil, and computes runoff and base flow using some TOPMODEL concepts, does not seem to be advantageous for this alpine basin. Copyright © 2006 John Wiley & Sons, Ltd.

The impact of parameter lumping and geometric simplification in modelling runoff and erosion in the shrublands of southeast Arizona

There have been many studies of hydrologic processes and scale. However, some researchers have found that predictions from hydrologic models may not be improved by attempting to incorporate the understanding of these processes into hydrologic models. This paper quantifies the effect of simplifying watershed geometry and averaging the parameter values on simulations generated using the KINEROS2 model. Furthermore, it examines how these changes in model input effect model output. The model was applied on a small semiarid rangeland watershed in which runoff is generated by the infiltration excess mechanism. The study concludes that averaging input parameter values has little effect on runoff volume and peak in simulating runoff. However, geometric simplification does have an effect on runoff peak and volume, but it is not statistically significant. In contrast, both averaging input parameter values and geometric simplification have an effect on model-predicted sediment yield. Copyright © 2005 John Wiley & Sons, Ltd.

Rainfall-runoff modelling in a catchment with a complex groundwater flow system: application of the Representative Elementary Watershed (REW) approach

Abstract. Based on the Representative Elementary Watershed (REW) approach, the modelling tool REWASH (Representative Elementary WAterShed Hydrology) has been developed and applied to the Geer river basin. REWASH is deterministic, semi-distributed, physically based and can be directly applied to the watershed scale. In applying REWASH, the river basin is divided into a number of sub-watersheds, so called REWs, according to the Strahler order of the river network. REWASH describes the dominant hydrological processes, i.e. subsurface flow in the unsaturated and saturated domains, and overland flow by the saturation-excess and infiltration-excess mechanisms. The coupling of surface and subsurface flow processes in the numerical model is realised by simultaneous computation of flux exchanges between surface and subsurface domains for each REW. REWASH is a parsimonious tool for modelling watershed hydrological response. However, it can be modified to include more components to simulate specific processes when applied to a specific river basin where such processes are observed or considered to be dominant. In this study, we have added a new component to simulate interception using a simple parametric approach. Interception plays an important role in the water balance of a watershed although it is often disregarded. In addition, a refinement for the transpiration in the unsaturated zone has been made. Finally, an improved approach for simulating saturation overland flow by relating the variable source area to both the topography and the groundwater level is presented. The model has been calibrated and verified using a 4-year data set, which has been split into two for calibration and validation. The model performance has been assessed by multi-criteria evaluation. This work represents a complete application of the REW approach to watershed rainfall-runoff modelling in a real watershed. The results demonstrate that the REW approach provides an alternative blueprint for physically based hydrological modelling.

Tropical storms and the flood hydrology of the central Appalachians

Flooding from Hurricane Fran is examined as a prototype for central Appalachian flood events that dominate the upper tail of flood peak distributions at basin scales between 100 and 10,000 km2. Hurricane Fran, which resulted in 34 deaths and more than $3.2 billion in damages, made land fall on the North Carolina coast at 0000 UTC, September 6, 1996. By 1200 UTC on September 6, Fran had weakened to a tropical storm, and the center of circulation was located at the North Carolina–Virginia border. Rain bands surrounding the tropical depression produced extreme rainfall and flooding in Virginia and West Virginia, with the most intense rainfall concentrated near ridge tops in the Blue Ridge and Valley and Ridge physiographic provinces. The most severe flooding occurred in the Shenandoah River watershed of Virginia, where peak discharges exceeded the 100‐year magnitude at 11 of 19 U.S. Geological Survey stream‐gaging stations. The availability of high‐resolution discharge and rainfall data sets provides the opportunity to study the hydrologic and hydrometeorological mechanisms associated with extreme floods produced by tropical storms. Analyses indicate that orographie enhancement of tropical storm precipitation plays a central role in the hydrology of extreme floods in the central Appalachian region. The relationships between drainage network structure and storm motion also play a major role in Appalachian flood hydrology. Runoff processes for Hurricane Fran reflected a mixture of saturation excess and infiltration excess mechanisms. Antecedent soil moisture played a significant role in the hydrology of extreme flooding from Hurricane Fran. Land use, in particular, the presence of forest cover, was of secondary importance to the terrain‐based distribution of precipitation in determining extreme flood response.

Topographic Influence on the Seasonal and Interannual Variation of Water and Energy Balance of Basins in North America

A large area basin-scale (LABs) hydrologic model is developed for regional, continental, and global hydrologic studies. The heterogeneity in the soil-moisture distribution within a basin is parameterized through the statistical moments of the probability distribution function of the topographic (wetness) index. The statistical moments are derived using GTOPO30 (30 arc sec; 1-km resolution) digital elevation model data for North America. River basins and drainage network extracted using this dataset are overlaid on computed topographic indices for the continent and statistics are extracted for each basin. A total of 5020 basins with an average size of 3255 square kilometers, obtained from the United States Geological Survey HYDRO1K data, is used over the continent. The model predicts runoff generation due to both saturation and infiltration excess mechanisms along with the baseflow and snowmelt. Simulation studies are performed for 1987 and 1988 using the International Satellite Land Surface Climatology Project data. Improvement in the terrestrial water balance and streamflow is observed due to improvements in the surface runoff and baseflow components achieved by incorporating the topographic influences. It is found that subsurface redistribution of soil moisture, and anisotropy in hydraulic conductivities in the vertical and horizontal directions play an important role in determining the streamflow and its seasonal variability. These enhancements also impact the surface energy balance. It is shown that the dynamics of several hydrologic parameters such as basin mean water table depth and saturated fraction play an important role in determining the total streamflow response and show realistic seasonal and interannual variations. Observed streamflow of the Mississippi River and its subbasins (Ohio, Arkansas, Missouri, and Upper Mississippi) are used for validation. It is observed that model baseflow has a significant contribution to the streamflow and is important in realistically capturing the seasonal and annual cycles.

On hydrologic similarity: 2. A scaled model of storm runoff production

The paper describes a simple physically based conceptual model of runoff production based on catchment topography and the spatial variablity of rainfall and soil properties. Both infiltration excess (Horton type) and saturation excess (Dunne type) runoff production mechanisms are considered. The effect of topography is modeled using the In (α/tan β)‐topographic index method of Beven and Kirkby (1979). The effects of the spatial variability of soil properties and rainfall on areal average infiltration rates are handled using a quasi‐analytical approach. The interaction between the two mechanisms of runoff production and the effect of a finite water table on the infiltration excess mechanism are explicitly considered. The model equations are cast in a dimensionless form to clarify the interrelationships involved in hydrological responses and to identify measures of similarity between different heterogeneous catchments. The dimensionless formulation has led to the identification of five similarity parameters and three dimensionless variables representing initial conditions and storm characteristics. Finally, a number of experiments were performed to study the sensitivity of the runoff production response to some of these similarity parameters.