LINEAR RAINFALL–RUNOFF SYSTEM IDENTIFICATION WITH RAMIFICATIONS FOR MODELLING CATCHMENT PROCESSES

The convolution assumption between excess rainfall and runoff provides a framework in which catchment runoff can be predicted with reasonable accuracy and moderate computational cost. Associated with it, the deconvolution problem of estimating unitgraph ordinates from rainfall–runoff events involves a matrix with a particularly simple structure. This matrix structure is used here as a basis on which the ill-posed nature of deconvolution is analysed. As a result, based on a simple transform of the excess rainfall data, a very simple criterion is derived to test the degree to which deconvolution may yield a unit hydrograph estimate displaying spurious oscillations of large magnitude. This has practical implications as the solution to an ill-posed problem can be very sensitive to errors in the model and the data and therefore may need to be stabilized. Illustration of these issues is provided using published rainfall–runoff data.     

Statistical analysis of flash flood events for designing water harvesting systems in an extremely arid environment

A water harvesting system for research purposes has been established in the Lisan Peninsula of the Dead Sea in the middle of the Jordan Rift Valley, where no authorized guideline is available for designing water harvesting systems. Rainfall and runoff, which occurred as flash floods, were observed at the downstream end of a gorge with a 1.12 km² barren catchment area from October 2014 through July 2019. Due to the extremely arid environment, runoff from the catchment is ephemeral, and the flash flood events can be clearly distinguishable from each other. Thirteen flash flood events with a total runoff volume of more than 100 m³ were successfully recorded during the five rainy seasons. Pearson and Spearman correlations between duration, total rainfall depths at two points, total runoff volume, maximum runoff discharge, bulk runoff coefficient, total variation in runoff discharge and maximum variation in runoff discharge of each flash flood event were examined, revealing no straightforward relationship between rainfall and runoff. The performance of the conventional SCS runoff curve number method was also deficient in reproducing any rainfall–runoff relationship. Therefore, probability distribution fitting was performed for each random variable, focusing on the lognormal distribution with three parameters and the generalized extreme value distribution. The maximum goodness-of-fit estimation turns out to be a more rational and efficient method in obtaining the parameter values of those probability distributions rather than the standard maximum likelihood estimation, which has known disadvantages. Results support the design of the water harvesting system and provide quantitative information for designing and operating similar systems in the future.     

Assessment of transmission losses and groundwater recharge from runoff events in a wadi under shortage of data on lateral inflow,Negev, Israel

A hydrological–lithostratigraphical model was developed for assessment of transmission losses and groundwater recharge from runoff events in arid water courses where hydrological and meteorological records are incomplete. Water balance equations were established for reaches between hydrometric stations. Because rainfall and tributary flow data are scarce, lateral inflow, which is an essential component of the water balance equation, could not be estimated directly. The solution was obtained by developing a method which includes a hydrological–lithostratigraphical analogy. This is based on the following assumptions: (a) runoff resulting from a given rainfall event is related to the watershed surface lithology; (b) for a given event, the spatial distribution of runoff reflects the distribution of rainfall: and (c) transmission losses are uniquely related to the total inflow to the reach. The latter relationship, called the loss function, and the water balance equation comprise a model which simultaneously assesses lateral inflow and transmission losses for runoff events recorded at the terminal stations. The model was applied to three reaches of the arid Nahal Tsin in Israel. In this case study, the transmission losses were of the same order of magnitude as the flow at the major hydrometric stations. The losses were subdivided into channel moistening, which subsequently evaporates, and deep percolation, which recharges groundwater. For large runoff events, evaporation was substantially smaller than the losses. The mean annual recharge of groundwater from runoff events in the Tsin watershed was 4·1×10⁶ m³, while the mean annual flow volume at the major stations ranged from 0·6 to 1·5×10⁶ m³. Once in 100 years, the annual recharge may be seven times higher than the mean annual value, but the recharge during most years is very small. Copyright © 1999 John Wiley & Sons, Ltd.     

Runoff initiation in a preserved semiarid Caatinga small watershed,Northeastern Brazil

This study analyses some hydrological driving forces and their interrelation with surface‐flow initiation in a semiarid Caatinga basin (12 km²), Northeastern Brazil. During the analysis period (2005 – 2014), 118 events with precipitation higher than 10 mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on‐site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface‐water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60‐min rainfall intensity (I₆₀). Runoff always occurred when rainfall surpassed 31 mm, but it never occurred for rainfall below 14 mm or for I₆₀ below 12 mm h^?1. The fact that the duration of the critical intensity is similar to the basin concentration time (65 min) and that the infiltration threshold value approaches the river‐bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27% of the events. It is possible that surface‐flow initiation in the Caatinga biome is strongly influenced by the root‐system dynamics, which changes macro‐porosity status and, therefore, initial abstraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Influence of rainfall and soil properties spatial aggregation on extreme flash flood response modelling: An evaluation based on the Sesia river basin,North Western Italy

High resolution radar rainfall fields and a distributed hydrologic model are used to evaluate the sensitivity of flood and flash flood simulations to spatial aggregation of rainfall and soil properties at catchment scales ranging from 75 to 983 km². Hydrologic modeling is based on a Hortonian infiltration model and a network-based representation of hillslope and channel flow. The investigation focuses on three extreme flood and flash flood events occurred on the Sesia river basin, North Western Italy, which are analysed by using four aggregation lengths ranging from 1 to 16 km. The influence of rainfall spatial aggregation is examined by using the flow distance as a spatial coordinate, hence emphasising the role of river network in the averaging of space–time rainfall. The effects of reduced and distorted rainfall spatial variability on peak discharge have been found particularly severe for the flash flood events, with peak errors up to 35% for rainfall aggregation of 16 km and at 983 km² catchment size. Effects are particularly remarkable when significant structured rainfall variability combines with relatively important infiltration volumes due to dry initial conditions, as this emphasises the non-linear character of the rainfall–runoff relationship. In general, these results confirm that the correct estimate of rainfall volume is not enough for the accurate reproduction of flash flood events characterised by large and structured rainfall spatial variability, even at catchment scales around 250 km². However, accurate rainfall volume estimation may suffice for less spatially variable flood events. Increasing the soil properties aggregation length exerts similar effects on peak discharge errors as increasing the rainfall aggregation length, for the cases considered here and after rescaling to preserve the rainfall volume. Moreover, peak discharge errors are roughly proportional to runoff volume errors, which indicates that the shape of the flood wave is influenced in a limited way by modifying the detail of the soil property spatial representation. Conversely, rainfall aggregation may exert a pronounced influence on the discharge peak by reshaping the spatial organisation of the runoff volumes and without a comparable impact on the runoff volumes.     

Coupling the Xinanjiang model to a kinematic flow model based on digital drainage networks for flood forecasting

The Xinanjiang model, which is a conceptual rainfall‐runoff model and has been successfully and widely applied in humid and semi‐humid regions in China, is coupled by the physically based kinematic wave method based on a digital drainage network. The kinematic wave Xinanjiang model (KWXAJ) uses topography and land use data to simulate runoff and overland flow routing. For the modelling, the catchment is subdivided into numerous hillslopes and consists of a raster grid of flow vectors that define the water flow directions. The Xinanjiang model simulates the runoff yield in each grid cell, and the kinematic wave approach is then applied to a ranked raster network. The grid‐based rainfall‐runoff model was applied to simulate basin‐scale water discharge from an 805‐km² catchment of the Huaihe River, China. Rainfall and discharge records were available for the years 1984, 1985, 1987, 1998 and 1999. Eight flood events were used to calibrate the model's parameters and three other flood events were used to validate the grid‐based rainfall‐runoff model. A Manning's roughness via a linear flood depth relationship was suggested in this paper for improving flood forecasting. The calibration and validation results show that this model works well. A sensitivity analysis was further performed to evaluate the variation of topography (hillslopes) and land use parameters on catchment discharge. Copyright © 2009 John Wiley & Sons, Ltd.     

Spatial–temporal variability and hydrologic connectivity of runoff generation areas in a North Alabama pasture—implications for phosphorus transport

This study delineated spatially and temporally variable runoff generation areas in the Sand Mountain region pasture of North Alabama under natural rainfall conditions, and demonstrated that hydrologic connectivity is important for generating hillslope response when infiltration‐excess (IE) runoff mechanism dominates. Data from six rainfall events (13·7–32·3 mm) on an intensively instrumented pasture hillslope (0·12 ha) were analysed. Analysis of data from surface runoff sensors, tipping bucket rain gauge and HS‐flume demonstrated spatial and temporal variability in runoff generation areas. Results showed that the maximum runoff generation area, which contributed to runoff at the outlet of the hillslope, varied between 67 and 100%. Furthermore, because IE was the main runoff generation mechanism on the hillslope, the data showed that as the rainfall intensity changed during a rainfall event, the runoff generation areas expanded or contracted. During rainfall events with high‐intensity short‐ to medium‐duration, 4–8% of total rainfall was converted to runoff at the outlet. Rainfall events with medium‐ to low‐intensity, medium‐duration were found less likely to generate runoff at the outlet. In situ soil hydraulic conductivity (k) was measured across the hillslope, which confirmed its effect on hydrologic connectivity of runoff generation areas. Combined surface runoff sensor and k‐interpolated data clearly showed that during a rainfall event, lower k areas generate runoff first, and then, depending on rainfall intensity, runoff at the outlet is generated by hydrologically connected areas. It was concluded that in IE‐runoff‐dominated areas, rainfall intensity and k can explain hydrologic response. The study demonstrated that only connected areas of low k values generate surface runoff during high‐intensity rainfall events. Identification of these areas would serve as an important foundation for controlling nonpoint source pollutant transport, especially phosphorus. The best management practices can be developed and implemented to reduce transport of phosphorus from these hydrologically connected areas. Copyright © 2009 John Wiley & Sons, Ltd.     

The quantity of stormwater runoff from ten stretches of road,a car park and eight roofs in Hertfordshire,England during 1983

Rainfall and runoff were monitored simultaneously for one year from a residential road, a car park, nine sections of road draining to individual gullies, two house roofs, two garage roofs, and three types of factory roof. The sites, which included an automatic weather station, were in Redbourn, Hertfordshire on Flood Studies Report Soil Type 1. The 2906 quality controlled ‘station-storms’ represented 193 rain storms and involved 57.2 per cent of the annual rainfall. 1732 storms were of less than 1.4mm of rain, whilst 77 had over 10mm. The percentage runoff averaged 11.4 per cent for roads and 56.9 per cent for roofs (28.3 per cent and 90.4 per cent respectively for rainfalls >5mm). Percentage runoff from the roads was cyclic with a peak during the summer months but there was a marked variation in monthly percentage runoff within and between sites. Regression analysis to explain percentage runoff was undertaken with various subsets of data for: each site; roads; and roofs. The regression analysis considered all storms; >1 percent runoff events; >5mm rainfalls; and events with > = 4 mm rain and > = 5 per cent runoff. The variable values in percentage runoff could not be explained satisfactorily with statistical methods. Only eight of the 72 equations explained more than 57 per cent of the variance. The most important explanatory variables for roads were short term rainfall intensity and rainfall amount, the former was the most important for roofs. ‘Seasonal’ variables had a positive relation ship for roads which shows that the percentage runoff from roads is higher in summer than winter. The antecedent variables showed that percentage runoff from roads and roofs is increased by antecedent rainfall. Seasonal factors and evaporation were unimportant for the percentage runoff from roofs. Depression storage, assessed by examining rainfalls that did and did not produce runoff, showed a diversity of monthly values. The depression storages derived by the regression intercept method were usually smaller. There were no relationships between depression storage and catchment or roof slope. The mean values for roofs and roads respectively were 0.52 mm and 1.23 mm for the classification method and 0.42 mm and 0.6mm with the regression approach. Peak runoff from the roads showed an attenuation to 12.8 per cent for 1 minute rainfall intensities and 24.2 per cent for 5 minute intensities. For roofs the attenuation averaged 36.8 per cent for 1 minute intensities and 92.6 for 5 minute intensities. Regression for peak runoff coefficients from roofs and roads explained negligible amounts of the variance except when events with 1 minute rainfall intensities of over 30 mm hr^?1 over the roads were analysed. Total rainfall was an important explanatory variable as was the slope of the road. There was evidence that peak coefficients for roads are greater during the summer.     

Following the curve? Reviewing the physical basis of the SCS curve number method for estimating storm runoff

Less attention has been paid to runoff generation from semi-arid than from humid-temperate catchments. The SCS curve number approach is simple to apply and widely used, but lacks physical underpinning. Here output from a runoff generation models is compared with data from field measurements, making use of 11 years data from rainfall and runoff events at the Sierra de Enguera Soil Erosion Experimental Station in Eastern Spain. Runoff from natural rainfall events was monitored for 10 years on bare plots of 1–16 m length. The largest storm event was of 142 mm, generating runoff of up to 115 mm on the smallest plots. The model presented simulates overland storm flow on a sloping rough and unvegetated surface, representing an area of 320 × 320 m. Green-Ampt infiltration constants are randomly assigned to each cell in a 128 × 128 grid, and rectangular storms applied at a range of total amounts and intensities to simulate runoff at each transect across the area. A simple algebraic expression is developed to estimate total runoff and storage in terms of storm size and duration, and plot length, with parameters that reflect infiltration behaviour, and this expression is compared with the SCS curve number approach. For the very largest storms, both expressions converge asymptotically towards 100% runoff, but the revised expression greatly improves estimates of runoff from smaller events. Output of these simulations is compared with measured storm runoff data on bare runoff plots at the Sierra de Enguera experimental Station in SE Spain and gives further support to the proposed expression for storm runoff.     

Modeling scale-dependent runoff generation in a small semi-arid watershed accounting for rainfall intensity and water depth

Observed scale effects of runoff on hillslopes and small watersheds derive from complex interactions of time-varying rainfall rates with runoff, infiltration and macro- and microtopographic structures. A little studied aspect of scale effects is the concept of water depth-dependent infiltration. For semi-arid rangeland it has been demonstrated that mounds underneath shrubs have a high infiltrability and lower lying compacted or stony inter-shrub areas have a lower infiltrability. It is hypothesized that runoff accumulation further downslope leads to increased water depth, inundating high infiltrability areas, which increases the area-averaged infiltration rate. A model was developed that combines the concepts of water depth-dependent infiltration, partial contributing area under variable rainfall intensity, and the Green–Ampt theory for point-scale infiltration. The model was applied to rainfall simulation data and natural rainfall–runoff data from a small sub-watershed (0.4 ha) of the Walnut Gulch Experimental Watershed in the semi-arid US Southwest. Its performance to reproduce observed hydrographs was compared to that of a conventional Green–Ampt model assuming complete inundation sheet flow, with runon infiltration, which is infiltration of runoff onto pervious downstream areas. Parameters were derived from rainfall simulations and from watershed-scale calibration directly from the rainfall–runoff events. The performance of the water depth-dependent model was better than that of the conventional model on the scale of a rainfall simulator plot, but on the scale of a small watershed the performance of both model types was similar. We believe that the proposed model contributes to a less scale-dependent way of modeling runoff and erosion on the hillslope-scale.     

A modification to the Soil Conservation Service curve number method for steep slopes in the Loess Plateau of China

The Soil Conservation Service curve number (CN) method is widely used for predicting direct runoff from rainfall. However, despite the extent of cultivation on hillslope areas, very few attempts have been made to incorporate a slope factor into the CN method. The objectives of this study were (1) to evaluate existing approaches integrating slope in the CN method, and (2) to develop an equation incorporating a slope factor into the CN method for application in the steep slope areas of the Loess Plateau of China. The dataset consisted of 11 years of rainfall and runoff measurements from two experimental sites with slopes ranging from 14 to 140%. The results indicated that the standard CN method underestimated large runoff events and overestimated small events. For our experimental conditions, the optimized and non‐optimized forms of the slope‐modified CN method of the Erosion Productivity Impact Calculator model improved runoff prediction for steep slopes, but large runoff events were still underestimated and small ones overpredicted. Based on relationships between slope and the observed and theoretical CN values, an equation was developed that better predicted runoff depths with an R² of 0·822 and a linear regression slope of 0·807. This slope‐adjusted CN equation appears to be the most appropriate for runoff prediction in the steep areas of the Loess Plateau of China. Copyright © 2005 John Wiley & Sons, Ltd.     

Dynamics of stormflow generation—A hillslope‐scale field study in east‐central Pennsylvania,USA

A 40 m × 20 m mowed, grass hillslope adjacent to a headwater stream within a 26‐ha watershed in east‐central Pennsylvania, USA, was instrumented to identify and map the extent and dynamics of surface saturation (areas with the water table at the surface) and surface runoff source areas. Rainfall, stream flow and surface runoff from the hillslope were recorded at 5‐min intervals from 11 August to 22 November 1998, and 13 April to 12 November 1999. The dynamics of the water table (0 to 45 cm depth from the soil surface) and the occurrence of surface runoff source areas across the hillslope were recorded using specially designed subsurface saturation and surface runoff sensors, respectively. Detailed data analyses for two rainfall events that occurred in August (57·7 mm in 150 min) and September (83·6 mm in 1265 min) 1999, illustrated the spatial and temporal dynamics of surface saturation and surface runoff source areas. Temporal data analyses showed the necessity to measure the hillslope dynamics at time intervals comparable to that of rainfall measurements. Both infiltration excess surface runoff (runoff caused when rainfall intensity exceeds soil infiltration capacity) and saturation excess surface runoff (runoff caused when soil moisture storage capacity is exceeded) source areas were recorded during these rainfall events. The August rainfall event was primarily an infiltration excess surface runoff event, whereas the September rainfall event produced both infiltration excess and saturation excess surface runoff. Occurrence and disappearance of infiltration excess surface runoff source areas during the rainfall events appeared scattered across the hillslope. Analysis of surface saturation and surface runoff data showed that not all surface saturation areas produced surface runoff that reached the stream. Emergence of subsurface flow to the surface during the post‐rainfall periods appeared to be a major flow process dominating the hillslope after the August rainfall event. Copyright © 2002 John Wiley & Sons, Ltd.     

Seasonal evolution of runoff generation on agricultural land in the Belgian loess belt and implications for muddy flood triggering

Muddy floods due to agricultural runoff are a widespread and frequent phenomenon in the European loess belt, and particularly in central Belgium. These floods are triggered when high quantities of runoff are generated on cropland and cause severe erosion. Three soil surface characteristics are relevant to determine the runoff potential of cultivated soils: soil cover by crops and residues, soil surface crusting and roughness. These characteristics have been observed on 65 cultivated fields throughout 2005. A heavy rainfall event representative for events triggering muddy floods in the region (60 mm h^?1 during 30 minutes) has been simulated using a 0·5 m² simulator on fields with the 17 most observed combinations of soil surface characteristics in central Belgium. Runoff is not observed in the case of (ploughed) bare uncrusted soils, nor in the case of soils covered by crops showing a transitional crust and a moderate roughness (1–2 cm). In the cases where runoff has been observed, mean runoff coefficients ranged from 13% (wheat in July) to 58% (sugar beet or maize in May and June). Grassed buffer strips (GBSs) and grassed waterways (GWWs) show a higher runoff coefficient (62% for GBSs and 73% for GWWs) than most cultivated soils (13–58%). Furthermore, it is demonstrated that small plot measurements can be used to estimate runoff generation at the field scale. A classification of runoff generation risk based on the surveys of soil surface characteristics has been applied to common crops of central Belgium. February as well as the period between May and September are the most critical for runoff at the field scale. However, it appears from monitoring of a 16 ha catchment that the highest runoff volumes and peak discharges are recorded between May and August after heavy rainfall, explaining why 85% of muddy floods are recorded during this period in central Belgium. Copyright © 2007 John Wiley & Sons, Ltd.     

Storm runoff response to rainfall pattern,magnitude and urbanization in a developing urban catchment

This study explored the hydrological impacts of urbanization, rainfall pattern and magnitude in a developing catchment. The Stormwater Management Model was parameterized, calibrated and validated in three development phases, which had the same catchment area (12.3 ha) but different land use intensities. The model calibration and validation by using sub‐hourly hydro‐meteorological data demonstrated a good performance of the model in predicting stormwater runoff in the different development phases. Based on the results, a threshold between minor and major rainfall events was identified and conservatively determined to be about 17.5 mm in depth. Direct runoff for minor storm events has a linear relationship with rainfall; however, events with a rainfall depth greater than the threshold yield a rainfall–runoff regression line with a clearly steeper slope. The difference in urban runoff generation between minor and major rainfall events diminishes with the increase of imperviousness. Urbanization leads to an increase in the production of stormwater runoff, but during infrequent major storms, the runoff contribution from pervious surfaces reduces the runoff changes owing to urbanization. Rainfall pattern exerts an important effect on urban runoff, which is reflected in pervious runoff. With the same magnitude, prolonged rainfall events with unvarying low intensity yield the smallest peak flow and the smallest total runoff, yet rainfall events with high peak intensity produce the largest runoff volume. These results demonstrate the different roles of impervious and pervious surfaces in runoff generation, and how runoff responds to rainstorms in urban catchments depends on hyetograph and event magnitude. Furthermore, the study provides a scientific basis of the design guideline sustainable urban drainage systems, which are still arbitrary in many countries. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of urbanization on runoff characteristics of the On-Cheon Stream watershed in Pusan,Korea

This study investigated the effect of urbanization on runoff from the On-Cheon Stream watershed in Pusan, Korea. This watershed has been experiencing considerable urbanization since the 1960s. There are two gauging stations in the watershed. For one of the stations there are recent flow data and for the other flow data were observed in the past. A linear reservoir model was chosen and runoff was analysed for several flood events. The linear reservoir model has been found to generate flood hydrographs accurately for both gauging stations, and its applicability to the study area has also been established. Using two methods of computing effective rainfall or rainfall excess (ϕ-index and constant percentage method), the results of runoff analyses were investigated. The ϕ-index method yielded better results than the constant percentage method. A comparison of hydrographs observed in the past with the simulation results at the Ie-Sup bridge site revealed that the peak discharge increased and the mean lag time of the study area decreased owing to urbanization over the past two decades. It is also possible to evaluate the effect of urbanization quantitatively. © 1998 John Wiley & Sons, Ltd.     

The Runoff Declining Process and Water Quality in Songhuajiang River Catchment,China under Global Climatic Change

The runoff in Songhuajiang River catchment has experienced a decreasing trend during the second half of the 20th century. Serially complete daily rainfall data of 42 rainfall stations from 1959 to 2002 and daily runoff data of five meteorological stations from 1953 to 2005 were obtained. The Mann–Kendall trend test and the sequential version of Mann–Kendall test were employed in this study to test the monthly and annual trends for both rainfall and runoff, to determine the start point of abrupt runoff declining, and to identify the main driving factors of runoff decline. The results showed an insignificant increasing trend in rainfall but a significant decreasing trend in runoff in the catchment. For the five meteorological stations, abrupt runoff decline occurred during 1957–1963 and the middle 1990s. Through Mann–Kendall comparisons for the area‐rainfall and runoff for the two decreasing periods, human activity, rather than climatic change, is identified as the main driving factor of runoff decline. Analysis of land use/cover shows that farmland is most related with runoff decline among all the land use/cover change in Nenjiang catchment. From 1986 to 1995, the area of farmland increased rapidly from 6.99 to 7.61 million hm². Hydraulic engineering has a significant influence on the runoff decline in the second Songhuajiang catchment. Many large‐scale reservoirs and hydropower stations have been built in the upstream of the Second Songhuajiang and lead to the runoff decline. Nenjiang and the Second Songhuajiang are the two sources of mainstream of Songhuajiang. Decreased runoff in these two sub‐catchments then results in runoff decrease in mainstream of Songhuajiang catchment. It is, therefore, concluded that high percent agricultural land and hydraulic engineering are the most probable driving factors of runoff decline in Songhuajiang River catchment, China.     

Large-scale physical facility and experimental dataset for the validation of urban drainage models

Numerical models are currently the main tool used to simulate the effects of urban flooding. The validation of these models requires thorough and accurate observed data in order to test their performance. The current study presents a series of laboratory experiments in a large-scale urban drainage physical facility of approximately 100 m² that includes roofs, streets, inlets, manholes and sewers. The facility is equipped with a rainfall simulator as well as a surface runoff and pipe inflows generators. The experiments were divided in two sets. In Set 1 the surface runoff was generated exclusively by the rainfall input, while in Set 2 the rainfall simulator was used in combination with the runoff generators. In all the tests the water discharge was measured at points on the inlets, roofs, and outfall. The water depth at different locations of the facility was also measured. The experimental tests were replicated numerically using the urban drainage model Iber-SWMM. Experimental results show that, even in a relatively small catchment the peaks in the hydrographs generated at each element of the facility during intermittent rainfalls are significantly attenuated at the catchment outlet. The agreement between the experimental and numerical results show that there are some differences in the hydrographs generated at each element, but that these differences compensate each other and disappear at the outfall. The results generated provide the research community with a thorough and high-resolution dataset obtained under controlled laboratory conditions in a large-scale urban drainage facility, something which has not previously been available.     

A new magnitude category disaggregation approach for temporal high‐resolution rainfall intensities

Simulation of quick runoff components such as surface runoff and associated soil erosion requires temporal high‐resolution rainfall intensities. However, these data are often not available because such measurements are costly and time consuming. Current rainfall disaggregation methods have shortcomings, especially in generating the distribution of storm events. The objectives of this study were to improve point rainfall disaggregation using a new magnitude category rainfall disaggregation approach. The procedure is introduced using a coupled disaggregation approach (Hyetos and cascade) for multisite rainfall disaggregation. The new procedure was tested with ten long‐term precipitation data sets of central Germany using summer and winter precipitation to determine seasonal variability. Results showed that dividing the rainfall amount into four daily rainfall magnitude categories (1–10, 11–25, 26–50, >50 mm) improves the simulation of high rainfall intensity (convective rainfall). The Hyetos model category approach (Hyetos_Cat) with seasonal variation performs representative to observed hourly rainfall compared with without categories on each month. The mean absolute percentage accuracy of standard deviation for hourly rainfall is 89.7% in winter and 95.6% in summer. The proposed magnitude category method applied with the coupled Hyetos_Cat–cascade approach reproduces successfully the statistical behaviour of local 10‐min rainfall intensities in terms of intermittency as well as variability. The root mean square error performance statistics for disaggregated 10‐min rainfall depth ranges from 0.20 to 2.38 mm for summer and from 0.12 to 2.82 mm for the winter season in all categories. The coupled stochastic approach preserves the statistical self‐similarity and intermittency at each magnitude category with a relatively low computational burden. Copyright © 2014 John Wiley & Sons, Ltd.     

Rainfall–runoff response and event-based runoff coefficients in a humid area (northwest Spain)

Abstract

The hydrological response of a small agroforestry catchment in northwest Spain (Corbeira catchment, 16 km²) is analysed, with particular focus on rainfall events. Fifty-four rainfall–runoff events, from December 2004 to September 2007, were used to analyse the principal hydrological patterns and show which factors best explain the hydrological response. The nonlinearity between rainfall and runoff showed that the variability in the hydrological response of the catchment was linked to the seasonal dynamics of the rainfall and, to a lesser extent, to evapotranspiration. The runoff coefficient, estimated as the ratio between direct runoff and rainfall volume, on an event basis, was analysed as a function of rainfall characteristics (amount and intensity) and the initial catchment state conditions prior to an event, such as pre-event baseflow and antecedent rainfall index. The results revealed that the hydrological response depends both on the soil humidity conditions at the start of the event and on rainfall amount, whereas rainfall intensity presented only a significant correlation with discharge increment. The antecedent conditions seem to be a key point in runoff production, and they explain much of the response. The hydrographs are characterized by a steep rising limb, a relatively narrow peak discharge and slow recession limb. These data and the observations suggest that the subsurface flow is the dominant runoff process.

Editor Z.W. Kundzewicz; Associate editor T. Wagener

Citation Rodríguez-Blanco, M.L., Taboada-Castro, M.M. and Taboada-Castro, M.T., 2012. Rainfall–runoff response and event-based runoff coefficients in a humid area (northwest Spain). Hydrological Sciences Journal, 57 (3), 445–459.     

Reservoir rainfall–runoff geomorphological model. I: application and parameter analysis

This article describes and formulates a model designed to simulate runoff in wet weather events, called reservoir rainfall–runoff geomorphological model (R³GeM). In these wetlands, soil saturation is the main mechanism for the generation of surface runoff. To determine the saturated areas, the model applies a relationship based on the topographic index, between watershed storage and saturated surface. Precipitation is separated into surface runoff by saturation, subsurface runoff and losses; then, the flow of surface and subsurface runoff is performed. This hydrological model has five parameters and has been implemented in 37 events in Aixola watershed and 15 in Oiartzun watershed, both located on the Cantabrian coast of Spain. We analysed the influence of these five parameters in their behaviour, and we have proven, noting the efficiency gains, that the proposed model is valid to simulate the rainfall–runoff process. Copyright © 2012 John Wiley & Sons, Ltd.