Post‐fire hydrological response and suspended sediment transport of a terraced Mediterranean catchment

In July 2013, a wildfire severely affected the western part of the island of Mallorca (Spain). During the first three post‐fire hydrological years, when the window of disturbance tends to be more open, the hydrological and sediment delivery processes and dynamics were assessed in a representative catchment intensively shaped by terracing that covered 37% of its surface area. A nested approach was applied with two gauging stations (covering 1.2 km² and 4.8 km²) built in September 2013 that took continuous measurements of rainfall, water and sediment yield. Average suspended sediment concentration (1503 mg L^?1) and the maximum peak (33 618 mg L^?1) were two orders of magnitude higher than those obtained in non‐burned terraced catchments of Mallorca. This factor may be related to changes in soils and the massive incorporation of ash into the suspended sediment flux during the most extreme post‐fire event; 50 mm of rainfall in 15 min, reaching an erosivity of 2886 MJ mm ha^?1 h^?1. Moreover, hysteretic counter‐clockwise loops were predominant (60%), probably related to the increased sensitivity of the landscape after wildfire perturbation. Though the study period was average in terms of total annual precipitation (even higher in intensities), minimal runoff (2%) and low sediment yield (6.3 t km^?2 y^?1) illustrated how the intrinsic characteristics of the catchment, i.e. calcareous soils, terraces and the application of post‐fire measures, limited the hydrosedimentary response despite the wildfire impact. Copyright © 2017 John Wiley & Sons, Ltd.     

Factors affecting connectivity and sediment yields following wildfire and post-fire salvage logging in California's Sierra Nevada

Sediment delivery following post-fire logging is a concern relative to water quality. While studies have assessed the effect of post-fire logging on sediment yields at different spatial scales, none have explicitly identified sediment sources. Our goal was to quantify post-fire and post-salvage logging sediment yields and use rill patterns to identify sediment sources. We measured the extent and type of logging disturbance, length of rills per unit area or “rill density”, ground cover, and sediment yields in nine logged and five control small catchments or “swales”, 0.09 to 0.81 ha, for 5 years after the 2013 Rim Fire in California's Sierra Nevada. The logged swales had a mean ground disturbance of 31%. After the first wet season following logging, there was no difference in either mean rill density (0.071 and 0.088 m m⁻², respectively) or mean transformed, normalized sediment yields between the control and logged swales. Untransformed mean sediment yields across three sites ranged from 0.11–11.8 and 1.1–3.2 Mg ha⁻¹ for the controls and salvage-logged swales, respectively. Rill density was strongly related to sediment yield and increased significantly with the amount of high-traffic skid trail disturbance in logged swales. Rill density was not significantly related to the amount of bare soil despite a significant relationship between sediment yields and bare soil. Rills usually initiated in bare soil and frequently connected high traffic skid trails to the drainage network after being diverted by waterbars. Rill connectivity and sediment yields decreased in control and logged swales where vegetation or other surface cover was high, suggesting this cover disconnected rills from the drainage network. Increasing ground cover on skid trails and between areas disturbed by post-fire logging and stream channels may reduce sediment yields as well as the hydrologic connectivity between hillslopes and the drainage network.     

Modelling of wildfire impacts on catchment hydrology applied to two case studies

We used a conceptual modelling approach on two western Canadian mountainous catchments that were burned in separate wildfires in 2003 to explore the potential of using modelling approaches to generalize post‐wildfire catchment hydrology in cases where pre‐wildfire hydrologic data were present or absent. The Fishtrap Creek case study (McLure fire, British Columbia) had a single gauged catchment with both pre‐fire and post‐fire data, whereas the Lost Creek case study (Lost Ck. fire, Alberta) had several instrumented burned and reference catchments providing streamflows and climate data only for the post‐wildfire period. Wildfire impacts on catchment hydrology were assessed by comparing pre‐wildfire and post‐wildfire model calibrated parameter sets for Fishtrap Creek (Fishtrap Ck.) and the calibrated parameters of two burned (South York Ck. and Lynx Ck.) and two unburned (Star Ck. and North York Ck.) catchments for Lost Ck. Model predicted streamflows for burned catchments were compared with unburned catchments (pre‐fire in the case of Fishtrap Ck. and unburned in the case of the Lost Ck.). Similarly, model predicted streamflows from unburned catchments were compared with burned catchments (post‐fire in the case of Fishtrap Ck. and burned in the case of the Lost Ck.). For Fishtrap Ck., different model parameters and streamflow behaviour were observed for pre‐wildfire and post‐wildfire conditions. However, the burned and unburned model results from the Lost Ck. wildfire did not show differing streamflow responses to the wildfire. We found that this hydrological modelling approach is suitable where pre‐wildfire and post‐wildfire data are available but may provide limited additional insights where pre‐disturbance hydrologic data are unavailable. This may in part be because the conceptual modelling approach does not represent the physical catchment processes, whereas a physically based model may still provide insights into catchment hydrological response in these situations. Copyright © 2015 John Wiley & Sons, Ltd.     

Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC_N-OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N-OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC ( $\overline{x}$= − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( $\overline{x}$= + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N-OUT at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N-OUT. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AIC_N-OUT. AIC_N-OUT proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.     

Suspended sediment transport in a small Mediterranean agricultural catchment

The aim of this study is to analyze suspended sediment transport in a Mediterranean agricultural catchment under traditional soil and water conservation practices. Field measurements were conducted in Can Revull, a small ephemeral catchment (1.03 km²) on the island of Mallorca. This study uses continuous turbidity records to analyse suspended sediment transport regimes, construct and interpret multiple regression models of total suspended sediment concentration (SSC) and of SSC related to stormflow discharge, and assess the sediment loads and yields of three hydrological years (2004–2005 to 2006–2007). An annual average SSC of 17.3 mg l^?1, with a maximum of 2270 mg l^?1, was recorded in the middle of the winter period when rainfall intensities are high and headwater slopes are ploughed and thus bare. Strong seasonal contrasts of baseflow dynamics associated with different degrees of dilution provide a large scatter in SSC and in the derived rating curves, reflecting that other factors control the supply of suspended sediment. Multiple regression models identify rainfall intensity as the most significant variable in sediment supply. However, under baseflow conditions, physical and biological processes generate sediment in the channel that is subsequently removed during high flow. In contrast, when baseflow is not present, rainfall intensity is the only process that supplies sediment to the channel, mostly from hillslopes. Considering the study period as average in terms of total annual rainfall and intensities, suspended sediment yields were an order of magnitude lower than those obtained in other Mediterranean catchments, a factor that can be related to the historical use of soil conservation practices. Copyright © 2009 John Wiley & Sons, Ltd.     

Hillslope sediment production after wildfire and post-fire forest management in northern California

High severity wildfires impact hillslope processes, including infiltration, runoff, erosion, and sediment delivery to streams. Wildfire effects on these processes can impair vegetation recovery, producing impacts on headwater and downstream water supplies. To promote forest regeneration and maintain forest and aquatic ecosystem functions, land managers often undertake active post-fire land management (e.g., salvage logging, sub-soiling, re-vegetation). The primary objective of our study was to quantify and compare sediment yields eroded from (a) burned, (b) burned and salvage logged, and (c) burned, salvage logged, and sub-soiled plots following the 2015 Valley Fire in the northern California Coast Range. We distributed 25 sediment fences (~75 m² contributing area) across four hillslopes burned at high severity and representative of the three management types. We collected eroded sediment from the fences after precipitation events for 5 years. We also quantified precipitation, canopy cover, ground cover, and soil properties to characterize the processes driving erosion across the three management types. Interestingly, during the second year after the fire, sediment yields were greater in the burned-only plots compared with both the salvage logged and sub-soiled plots. By the third year, there were no differences in sediment yields among the three management types. Sediment yields decreased over the 5 years of the study, which may have occurred due to site recovery or exhaustion of mobile sediment. As expected, sediment yields were positively related to precipitation depth, bulk density, and exposed bare soil, and negatively related to the presence of wood cover on the soil surface. Unexpectedly, we observed greater sediment yields on the burned-only plots with greater canopy closure, which we attributed to increased throughfall drop size and kinetic energy related to the residual canopy. While these results will aid post-fire management decisions in areas with Mediterranean climates prone to low intensity, long duration rainstorms, additional research is needed on the comparative effects of post-fire land management approaches to improve our understanding of the mechanisms driving post-fire erosion and sediment delivery.     

Temporal variability in hydrological response within a small catchment with badland areas,central Pyrenees

Abstract

The lower Araguás catchment, central Pyrenees, is characterized by extensive badlands (25% of the total catchment), whereas the upper catchment is covered by dense plantation forest. The catchment (45 ha) has been monitored since October 2005 with the aim of studying its hydrological response. The 44 floods recorded over this period were analysed to identify the factors that control the rainfall—runoff relationship. The first relevant feature of the catchment was its responsiveness. The catchment reacted to all rainfall events, but the irregular nature of the hydrological response was the most characteristic feature of the response. No single variable could explain the response of the Araguás catchment. It was found that stormflow coefficients mainly depend on the combination of rainfall volume and antecedent baseflow. A significant correlation was observed between maximum rainfall intensity and peak flow values. The shapes of the different hydrographs are very similar, regardless of the peak flow magnitude; they show a short time lag, relatively narrow peak flow, and steep recession limb. This indicates a large contribution by overland flow, resulting mainly from the generation of infiltration excess runoff in badland areas.     

Soil cracking effects on hydrological and erosive processes: a study case in Mediterranean cultivated vertisols

Shrink–swell soils, such as those in a Mediterranean climate regime, can cause changes in terms of hydrological and erosive responses because of the changing soil water storage conditions. Only a limited number of long‐term studies have focused on the impacts on both hydrological and erosive responses and their interactions in an agricultural environment. In this context, this study aims to document the dynamics of cracks, runoff and soil erosion within a small Mediterranean cultivated catchment and to quantify the influence of crack processes on the water and sediment supplied to a reservoir located at the catchment outlet using water and sediment measurements at a cultivated field outlet as baseline. Detailed monitoring of the presence of topsoil cracks was conducted within the Kamech catchment (ORE OMERE, Tunisia), and runoff and suspended sediment loads were continuously measured over a long period of time (2005–2012) at the outlets of a field (1.32 ha) and a catchment (263 ha). Analysis of the data showed that topsoil cracks were open approximately half of the year and that the rainfall regime and water table level conditions locally control the seasonal cracking dynamics. Topsoil cracks appeared to seriously affect the generation of runoff and sediment concentrations and, consequently, sediment yields, with similar dynamics observed at the field and catchment outlets. A similar time lag in the seasonality between water and sediment delivery was observed at these two scales: although the runoff rates were globally low during the presence of topsoil cracks, most sediment transport occurred during this period associated with very high sediment concentrations. This study underlines the importance of a good prediction of runoff during the presence of cracks for reservoir siltation considerations. In this context, the prediction of cracking effects on runoff and soil erosion is a key factor for the development of effective soil and water management strategies and downstream reservoir preservation. Copyright © 2016 John Wiley & Sons, Ltd.     

Changes to sediment sources following wildfire in a forested upland catchment,southeastern Australia

Few investigations link post‐fire changes to sediment sources and erosion processes with sediment yield response at the catchment scale. This linkage is essential if downstream impacts on sediment transport after fire are to be understood in the context of fire effects across different forest environments. In this study, we quantify changing source contributions to fine sediment (<63 µm) exported from a eucalypt forest catchment (136 ha) burnt by wildfire. The study catchment is one of a pair of research catchments located in the East Kiewa River valley in southeastern Australia that have been the subject of a research program investigating wildfire effects on runoff, erosion, and catchment sediment/nutrient exports. This previous research provided the opportunity to couple insights gained from a range of measurement techniques with the application of fallout radionuclides ¹³⁷Cs and ²¹⁰Pb_ex to trace sediment sources. It was found that hillslope surface erosion dominated exports throughout the 3·5‐year post‐fire measurement period. During this time there was a pronounced decline in the proportional surface contribution from close to 100% in the first six months to 58% in the fourth year after fire. Over the study period, hillslope surface sources accounted for 93% of the fine sediment yield from the burnt catchment. The largest decline in the hillslope contribution occurred between the first and second years after fire, which corresponded with the previously reported large decline in sediment yield, breakdown of water repellency in burnt soils, substantial reduction in hillslope erodibility, and rapid surface vegetation recovery. Coupling the information on sediment sources with hillslope process measurements indicated that only a small proportion of slopes contributed sediment to the catchment outlet, with material derived from near‐channel areas dominating the post‐fire catchment sediment yield response. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrological response of a humid agroforestry catchment at different time scales

Using data collected at the Mero catchment during three hydrological years (2005/06–2007/08), an analysis of rainfall–runoff relationships was performed at annual, seasonal, monthly, and event scales. At annual scale, the catchment showed low runoff coefficients (23–35%), due to high water storage capacity soils as well as high runoff inter‐annual variability. Rainfall variability was the main responsible for the differences in the inter‐annual runoff. At seasonal and monthly scales, there was no simple relationship between rainfall and runoff. Seasonal dynamics of rainfall and potential evapotranspiration in conjunction with different rainfall distribution during the study years could be the key factors explaining the complex relationship between rainfall and runoff at monthly and seasonal scale. At the event scale, the results revealed that the hydrological response was highly dependent on initial conditions and, to a lesser extent, on rainfall amount. The shapes of the different hydrographs, regardless of the magnitude, presented similar characteristics: a moderate rise and a prolonged recession, suggesting that subsurface flow was the dominant process in direct runoff. Moreover, all rainfall–runoff events had a higher proportion of baseflow than of direct runoff. A cluster‐type analysis discriminated three types of events differentiated mainly by rainfall amount and antecedent rainfall conditions. The study highlights the role of the antecedent rainfall and the need for caution in extrapolating relationships between rainfall amount and hydrological response of the catchment. Copyright © 2013 John Wiley & Sons, Ltd.     

Sources and sediment yield from a rural catchment in humid temperate environment,northwest Spain

A study was carried out on a rural catchment located in northwest Spain to examine the sediment yield from the catchment by measuring suspended sediments during rainfall events. Within the catchment regular surveys were conducted to obtain data on the suspended sediment sources. Important variations in sediment load were detected at event scale (0·3–21·0 Mg); some of these can be explained in terms of event size, antecedent conditions, rainfall distribution and soil surface erosion. To study the variables controlling suspended sediment yield during the events in the catchment, several event and pre‐event variables were calculated for all events. The sediment load is strongly influenced by discharge variables. During the events discharge–suspended sediments were also analysed. When the soil surface was unprotected, the formation of rills and ephemeral gullies on agricultural land at the catchment head was an important source of suspended sediments in the catchment. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of hydrological processes on the chemical composition of riverine suspended sediment in the Zhujiang River,China

The chemical composition of riverine suspended sediment is the integration of the weathering crust minerals, soil organic matter and erosion agency within a specific drainage basin, which has been largely disturbed by the human activities. Selected metal elements of the riverine suspended sediment in the Zhujiang River were analysed using inductively coupled plasma–atomic emission spectrometry (ICP–AES) in three different hydrological phases from 1997 to 1998 at Makou and Sanshui hydrographic gauge stations, located at the lower reaches of the two main tributaries of the Zhujiang River, i.e. the Xijiang and the Beijing Rivers respectively. Organic carbon and nitrogen were also analysed using a conventional element analyser. The results demonstrate that the chemical composition of the riverine suspended sediment show obvious variability in different hydrological phases, which closely correlate to the organic matter content in suspended sediment. Intensified erosion in the flood phase results in lower concentration of the organic matter than that in the lower water level phase. The riverine suspended sediment with rich organic matter in the lower water level phase adsorbs some metal elements from the river water. Copyright © 2003 John Wiley & Sons, Ltd.     

Observational uncertainties in hypothesis testing: investigating the hydrological functioning of a tropical catchment

Hypothesis testing about catchment functioning with conceptual hydrological models is affected by uncertainties in the model representation of reality as well as in the observed data used to drive and evaluate the model. We formulated a learning framework to investigate the role of observational uncertainties in hypothesis testing using conceptual models and applied it to the relatively data‐scarce tropical Sarapiqui catchment in Costa Rica. Observational uncertainties were accounted for throughout the framework that incorporated different choices of model structures to test process hypotheses, analyses of parametric uncertainties and effects of likelihood choice, a posterior performance analysis and (iteratively) formulation of new hypotheses. Estimated uncertainties in precipitation and discharge were linked to likely non‐linear near‐surface runoff generation and the potentially important role of soils in mediating the hydrological response. Some model‐structural inadequacies could be identified in the posterior analyses (supporting the need for an explicit soil‐moisture routine to match streamflow dynamics), but the available information about the observational uncertainties prevented conclusions about other process representations. The importance of epistemic data errors, the difficulty in quantifying them and their effect on model simulations was illustrated by an inconsistent event with long‐term effects. Finally we discuss the need for new data, new process hypotheses related to deep groundwater losses, and conclude that observational uncertainties need to be accounted for in hypothesis testing to reduce the risk of drawing incorrect conclusions. Copyright © 2015 John Wiley & Sons, Ltd.     

Estimation of suspended sediment loads and delivery in an incised upland headwater catchment,south‐eastern Australia

Historically upland headwater catchments in south‐eastern Australia have undergone extensive gully erosion that has removed large amounts of sediment to lowlands. Recent research suggests these upland areas may continue to dominate fine sediment loads in lowland rivers. Improved understanding of sediment transfer through upland headwater catchments may have implications for interpreting downstream sediment supply. In this study a nested catchment design was utilized to examine suspended sediment yields and delivery from a small tributary sub‐catchment (1·64 km²) to the study catchment outlet (53·5 km²). Monitoring of suspended sediment concentration and discharge was undertaken for a period of nearly two years and used to estimate suspended sediment loads. Estimated total suspended sediment exports over the period of monitoring were 24·16 t from the sub‐catchment and 550·3 t from the catchment, which are generally less than previous reported small catchment yields in south‐eastern Australia. The extent of sediment delivery was examined using between‐site ratios of specific sediment yield per unit area and incised channel length. Sediment delivery was high under average rainfall conditions, but seasonally dependent. Both suspended sediment yields and the extent of delivery peaked over spring months, supplemented by remobilization of sediment stored during summer months in the main catchment channel. The findings of this study suggest much of the suspended sediment exported from small incised upland sub‐catchments (1–2 km²) may be delivered to downstream reaches under average rainfall conditions, which, in conjunction with the findings of previous research supports the potential importance of contributions from these areas to suspended sediment loads in lowland rivers during high flow periods. Copyright © 2007 John Wiley & Sons, Ltd.     

Studying solute and particulate sediment transfer in a small Mediterranean mountainous catchment subject to land abandonment

The sediment budget of the small research catchment of Cal Parisa (Vallcebre, Eastern Pyrenees) was studied by hydrological monitoring and assessment of the erosion rates in the major sediment sources. This area is characterized by clayey mudrock prone to landsliding and badland erosion, but the catchment was selected in an area free of major badland features, as a representative of middle mountain regions where a system of terraces and drainage ditches had been built for agricultural use but is now abandoned. Streamwater chemistry is dominated by Ca²⁺ and HCO₃⁻ at concentrations close to calcite saturation. Total dissolved solids show dilution during runoff peaks and positive hysteresis loops that support a slow contribution of subsurface water. Relative dissolved ion concentrations are different for each event analysed. Particulate sediment yield is very low and represents only about 1 per cent of gross erosion in the catchment. Mineralogical analysis of suspended sediments shows an enrichment in calcite because of precipitation. Chemical analysis of suspended sediments, using common one-litre water samples, shows higher contents of Ca, P and Mn in transported sediment than in sediment source areas, attributed to the precipitation of calcite, and enrichment in organic particulate matter during events respectively for the two first elements, whereas enrichment in Mn remains uncertain. Solid matter yield is therefore clearly dominated by dissolved transport as a result of both high calcium bicarbonate concentrations in runoff waters and strong suspended sediment conveyance discontinuities. Land conservation structures are very effective because they are in good condition whereas the soil is covered by dense permanent vegetation. Nevertheless, this state is unstable because the network of drainage ditches needs maintenance; its spontaneous breakdown after abandonment may result in the rearrangement of the elementary stream network and gullying of old fields in hollows. © 1997 John Wiley & Sons, Ltd.     

Delineation of flood generating processes and their hydrological response

Knowledge about flood generating processes can be beneficial for numerous applications. Especially in the context of climate change impact assessment, daily patterns of meteorological and catchment state conditions leading to flood events (i.e., storylines) may be of value. Here, we propose an approach to identify storylines of flood generation using daily weather and snow cover observations. The approach is tested for and applied to a typical pre‐Alpine catchment in the period between 1961 and 2014. Five precipitation parameters were determined that describe temporal and spatial characteristics of the flood associated precipitation events. The catchment's snow coverage was derived using statistical relationships between a satellite‐derived snow cover climatology and station snow measurements. Moreover, (pre‐) event snow melt sums were estimated using a temperature‐index model. Based on the precipitation and catchment state parameters, 5 storylines were identified with a cluster analysis: These are (a) long duration, low intensity precipitation events with high precipitation depths, (b) long duration precipitation events with high precipitation depths and episodes of high intensities, (c) shorter duration events with high or (d) low precipitation intensity, respectively, and (e) rain‐on‐snow events. The event groups have distinct hydrological characteristics that can largely be explained by the storylines' respective properties. The long duration, high intensity storyline leads to the most adverse hydrological response, namely, a combination of high peak magnitudes, high volumes, and long durations of threshold exceedance. The results show that flood generating processes in mesoscale catchments can be distinguished on the basis of daily meteorological and catchment state parameters and that these process types can explain the hydrological flood properties in a qualitative way. Hydrological simulations of daily resolution can thus be analysed with respect to flood generating processes.     

Effectivity of dissolved SF6 tracer for clarification of rainfall–runoff processes in a forested headwater catchment

Understanding rainfall‐runoff processes is crucial for prevention and prediction of water‐related natural disasters. Sulfur hexafluoride (SF₆) is a potential tracer, but few researches have applied it for rainfall‐runoff process studies. We observed multiple tracers including SF₆ in spring water at 1‐ to 2‐hr intervals during rainstorm events to investigate the effectivity of SF₆ tracer in rainfall–runoff studies through the clarification of rainfall–runoff process. The target spring is a perennial spring in a forested headwater catchment with an area of 0.045 km² in Fukushima, Japan. The relationship between the SF₆ concentration in spring water and the spring discharge volume was negative trend; the SF₆ concentration in spring water becomes low as the spring discharge volume increases especially during rainstorms. The hydrograph separation using SF₆ and chloride ion tracers was applied for determining the contribution of principal sources on rainfall–runoff water. It suggested more than 60% contribution of bedrock groundwater at the rainfall peak and high percentage contribution continued even in the hydrograph recession phase. Based on observed low SF₆ concentration in groundwater after heavy rainfall, the replacement of groundwater near the spring with bedrock groundwater is indicated as a mechanism for water discharge with low SF₆ concentration during rainfall events. Consequently, rainstorm events play an important role as triggers in discharging water stored in the deeper subsurface area. In addition, SF₆ tracer is concluded as one of the strongest tracers for examining rainfall–runoff process studies. And, therefore, this study provided new insights into the dynamics of groundwater and its responses to rainfall in terms of SF₆ concentration variance in water in headwater regions.     

Evaluation of the WEPP model and digital elevation grid size,for simulation of streamflow and sediment yield in a heterogeneous catchment

The paper presents the result of an application of the GeoWEPP model in a heterogeneous semi‐agricultural catchment located in the northern Italian Apennines mountain range. The objectives were: (a) to evaluate the GeoWEPP model in a heterogeneous catchment in a Mediterranean climate and (b) to examine the effect of digital elevation model grid size on hydrological and sediment yield simulations. The catchment is characterized by large heterogeneity in geology, soil type, vegetation cover and topography. In addition, 10% of its area is occupied by calanchi (badlands), characterized by steep, bare soil and accentuated erosion. Experimental streamflow data were compared with those simulated by GeoWEPP for a period of eight years and the results were evaluated by means of statistical indices, with the analysis of the flow duration curve. Simulated sediment yields were compared with experimental data for one year. The streamflow cumulative annual results were satisfactory with NSE oscillating between 0.40 and 0.83 and RMSE between 1.1 and 2.9 mm. Also, the performance of the model with daily streamflow data was positive (NSE = 0.68 and RMSE = 1.9 mm). The flow duration curve indicated that GeoWEPP could represent the experimental streamflow for fluxes over 1 mm d^?1. The model performance for simulation of sediment yield was satisfactory with both digital elevation models of different grid sizes (NSE = 0.84 and 0.87). Indeed, the sensitivity analysis tests of the model showed that there was no statistically significant improvement in the accuracy of the digital elevation model between 10 and 2 m resolution. These results were confirmed for both streamflow as well as sediment yield. Additional sensitivity analysis of other model parameters performed on the entire catchment and badlands hillslopes showed that bedrock hydraulic conductivity primarily affected the model in both settings. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrological control of dissolved organic carbon dynamics in a forested headwater catchment,Kiryu Experimental Watershed,Japan

To evaluate the influence of hydrological processes on dissolved organic carbon (DOC) dynamics in a forested headwater catchment, DOC concentration was observed along the flow path from rainfall to stream water via throughfall, soil water, groundwater, and spring water for 4 years, and DOC flux through the catchment was calculated. The spatial and temporal variations in DOC concentration and flux were compared with physical hydrological observations and the mean residence time of water. In the upslope soil layer, DOC concentrations were not significantly correlated with water fluxes, suggesting that DOC concentrations were not strictly controlled by water fluxes. In the upslope perennial groundwater, DOC concentration was affected by the change in the amount of microbial degradation of DOC produced by changes in the mean residence time of water. In stream water, the temporal variation in DOC concentration was usually affected by changes in DOC concentration of the inflow component via vertical infiltration from above the perennial groundwater. During dry periods, however, the component from inflow via vertical infiltration was negligible and DOC in the upslope perennial groundwater became the major component of stream water DOC. The temporal variation in stream water DOC concentration during baseflow was affected by rainfall patterns over several preceding months. Therefore, records of rainfall over several preceding months are one of the most important factors for predicting changes in DOC concentration on a catchment scale. Copyright © 2007 John Wiley & Sons, Ltd.