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Runoff Response (runoff + response)
Selected AbstractsThe effect of soil type, meteorological forcing and slope gradient on the simulation of internal erosion processes at the local scaleHYDROLOGICAL PROCESSES, Issue 13 2010Guillaume Nord Abstract Numerical simulation experiments of water erosion at the local scale (20 × 5 m) using a process-based model [Plot Soil Erosion Model_2D (PSEM_2D)] were carried out to test the effects of various environmental factors (soil type, meteorological forcing and slope gradient) on the runoff and erosion response and to determine the dominant processes that control the sediment yield at various slope lengths. The selected environmental factors corresponded to conditions for which the model had been fully tested beforehand. The use of a Green and Ampt model for infiltration explained the dominant role played by rainfall intensity in the runoff response. Sediment yield at the outlet of the simulated area was correlated positively with rainfall intensity and slope gradient, but was less sensitive to soil type. The relationship between sediment yield (soil loss per unit area) and slope length was greatly influenced by all environmental factors, but there was a general tendency towards higher sediment yield when the slope was longer. Contribution of rainfall erosion to gross erosion was dominant for all surfaces with slope lengths ranging from 4 to 20 m. The highest sediment yields corresponded to cases where flow erosion was activated. An increase in slope gradient resulted in flow detachment starting upstream. Sediment exported at the outlet of the simulated area came predominantly from the zone located near the outlet. The microrelief helped in the development of a rill network that controlled both the ratio between rainfall and flow erosion and the relationship between sediment yield and slope length. Copyright © 2010 John Wiley & Sons, Ltd. [source] Effects of hillslope topography on hydrological responses in a weathered granite mountain, Japan: comparison of the runoff response between the valley-head and the side slopeHYDROLOGICAL PROCESSES, Issue 14 2008Masamitsu Fujimoto Abstract To evaluate the effects of hillslope topography on storm runoff in a weathered granite mountain, discharge rate, soil pore water pressures, and water chemistry were observed on two types of hillslope: a valley-head (a concave hillslope) and a side slope (a planar hillslope). Hydrological responses on the valley-head and side slope reflected their respective topographic characteristics and varied with the rainfall magnitude. During small rainfall events (<35 mm), runoff from the side slope occurred rapidly relative to the valley-head. The valley-head showed little response in storm runoff. As rainfall amounts increased (35,60 mm), the valley-head yielded a higher flow relative to the side slope. For large rainfall events (>60 mm), runoff from both hillslopes increased with rainfall, although that from the valley-head was larger than that from the side slope. The differences in the runoff responses were caused by differences in the roles of lower-slope soils and the convergence of the hillslope. During small rainfall events, the side slope could store little water; in contrast, all rainwater could be stored in the soils at the valley-head hollow. As the amount of rainfall increased, the subsurface saturated area of the valley-head extended from the bottom to the upper portion of the slope, with the contributions of transient groundwater via lateral preferential flowpaths due to the high concentration of subsurface water. Conversely, saturated subsurface flow did not contribute to runoff responses, and the subsurface saturated area at the side slope did not extend to the upper slope for the same storm size. During large rainfall events, expansion of the subsurface saturated area was observed in both hillslopes. Thus, differences in the concentration of subsurface water, reflecting hillslope topography, may create differences in the extension of the subsurface saturated area, as well as variability in runoff responses. Copyright © 2007 John Wiley & Sons, Ltd. [source] The influence of elevation error on the morphometrics of channel networks extracted from DEMs and the implications for hydrological modellingHYDROLOGICAL PROCESSES, Issue 11 2008John B. Lindsay Abstract Stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models. This is because channel network geometry partly controls the runoff response of a basin. Network indices are often measured from channels that are mapped from digital elevation models (DEMs) using automated procedures. Simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics, including stream order, the bifurcation, length, area and slope ratios, stream magnitude, network diameter, the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph (GIUH) and the network width function. DEMs of three UK basins, ranging from high to low relief, were used for the analyses. The findings showed that moderate elevation error (RMSE of 1·8 m) can result in significant uncertainty in DEM-mapped network morphometrics and that this uncertainty can be expressed in complex ways. For example, estimates of the bifurcation, length and area ratios and the flood magnitude and timing parameters of the GIUH each displayed multimodal frequency distributions, i.e. two or more estimated values were highly likely. Furthermore, these preferential estimates were wide ranging relative to the ranges typically observed for these indices. The wide-ranging estimates of the two GIUH parameters represented significant uncertainty in the shape of the unit hydrograph. Stream magnitude, network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low-magnitude links. Uncertainties in the width function were found to increase with distance from outlet, implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph. In light of these findings, care should be exercised when interpreting the results of analyses based on DEM-mapped stream networks. Copyright © 2007 John Wiley & Sons, Ltd. [source] Incorporating variable source area hydrology into a curve-number-based watershed modelHYDROLOGICAL PROCESSES, Issue 25 2007Elliot M. Schneiderman Abstract Many water quality models use some form of the curve number (CN) equation developed by the Soil Conservation Service (SCS; U.S. Depart of Agriculture) to predict storm runoff from watersheds based on an infiltration-excess response to rainfall. However, in humid, well-vegetated areas with shallow soils, such as in the northeastern USA, the predominant runoff generating mechanism is saturation-excess on variable source areas (VSAs). We reconceptualized the SCS,CN equation for VSAs, and incorporated it into the General Watershed Loading Function (GWLF) model. The new version of GWLF, named the Variable Source Loading Function (VSLF) model, simulates the watershed runoff response to rainfall using the standard SCS,CN equation, but spatially distributes the runoff response according to a soil wetness index. We spatially validated VSLF runoff predictions and compared VSLF to GWLF for a subwatershed of the New York City Water Supply System. The spatial distribution of runoff from VSLF is more physically realistic than the estimates from GWLF. This has important consequences for water quality modeling, and for the use of models to evaluate and guide watershed management, because correctly predicting the coincidence of runoff generation and pollutant sources is critical to simulating non-point source (NPS) pollution transported by runoff. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrological importance of an unusual hazard in a mountainous basin: flood and landslideHYDROLOGICAL PROCESSES, Issue 14 2006Umesh K. Haritashya Abstract The Bhagirathi River, a proglacial melt water stream of the Gangotri Glacier, is the principal source of the Ganges river system. The upper part of the basin lies in the high altitude region of the Garhwal Himalayas and is extensively covered by glaciers. We provide hydro-meteorological insight into a severe storm that produced unusual high rains in June 2000 in the uppermost part of the Bhagirathi River. This storm was concentrated upstream of Gangotri town and triggered landslides/rockslides at several locations between the glacier snout and Gangotri town. One of the major rockslides blocked the Bhagirathi River at Bhujbas, about 3 km downstream of the Gangotri Glacier snout, creating an artificial lake at this location. High stream flow in the river, generated by rapid runoff response from mountain slopes along with melt runoff from the glacier, quickly increased the level of water stored in the artificial lake. Daily rainfall in this region rarely exceeds 10 mm, while total rainfall during this 6-day storm was 131·5 mm. This unusual rain event occurred during the tourist season in June, consequently trapping a large number of tourists and vendors in this area. Sudden release of stored water generated floods that created havoc downstream of the artificially created lake. This paper presents the hydrological and meteorological information related to such an unusual and devastating event observed in the high altitude region of the Himalayas. Copyright © 2006 John Wiley & Sons, Ltd. [source] Infiltration, runoff and sediment production in blanket peat catchments: implications of field rainfall simulation experimentsHYDROLOGICAL PROCESSES, Issue 13 2002J. Holden Abstract Blanket peat covers the headwaters of many major European rivers. Runoff production in upland blanket peat catchments is flashy with large flood peaks and short lag times; there is minimal baseflow. Little is known about the exact processes of infiltration and runoff generation within these upland headwaters. This paper presents results from a set of rainfall simulation experiments performed on the blanket peat moorland of the North Pennines, UK. Rainfall was simulated at low intensities (3,12 mm h,1), typical of natural rainfall, on bare and vegetated peat surfaces. Runoff response shows that infiltration rate increases with rainfall intensity; the use of low-intensity rainfall therefore allows a more realistic evaluation of infiltration rates and flow processes than previous studies. Overland flow is shown to be common on both vegetated and bare peat surfaces although surface cover does exert some control. Most runoff is produced within the top few centimetres of the peat and runoff response decreases rapidly with depth. Little vertical percolation takes place to depths greater than 10 cm owing to the saturation of the peat mass. This study provides evidence that the quickflow response of upland blanket peat catchments is a result of saturation-excess overland flow generation. Rainfall,runoff response from small plots varies with season. Following warm, dry weather, rainfall tends to infiltrate more readily into blanket peat, not just initially but to the extent that steady-state surface runoff rates are reduced and more flow takes place within the peat, albeit at shallow depth. Sediment erosion from bare peat plots tends to be supply limited. Seasonal weather conditions may affect this in that after a warm, dry spell, surface desiccation allows sediment erosion to become transport limited. Copyright © 2002 John Wiley & Sons, Ltd. [source] Runoff generation and routing on artificial slopes in a Mediterranean,continental environment: the Teruel coalfield, SpainHYDROLOGICAL PROCESSES, Issue 3 2002José-Manuel Nicolau Abstract The aim of this study was to identify the mechanisms of runoff generation and routing and their controlling factors at the hillslope scale, on artificial slopes derived from surface coal mining reclamation in a Mediterranean,continental area. Rainfall and runoff at interrill and microcatchment scales were recorded for a year on two slopes with different substrata: topsoil cover and overburden cover. Runoff coefficient and runoff routing from interrill areas to microcatchment outlets were higher in the overburden substratum than in topsoil, and greater in the most developed rill network. Rainfall volume is the major parameter responsible for runoff response on overburden, suggesting that this substratum is very impermeable,at least during the main rainfall periods of the year (late spring and autumn) when the soil surface is sealed. In such conditions, most rainfall input is converted into runoff, regardless of its intensity. Results from artificial rainfall experiments, conducted 3 and 7 years after seeding, confirm the low infiltration capacity of overburden when sealed. The hydrological response shows great seasonal variability on the overburden slope in accordance with soil surface changes over the year. Rainfall volume and intensities (I30, I60) explain runoff at the interrill scale on the topsoil slope, where rainfall experiments demonstrated a typical Hortonian infiltration curve. However, no correlation was found at the microcatchment level, probably because of the loss of functionality of the only rill as ecological succession proceeded. The runoff generation mechanism on the topsoil slope is more homogeneous throughout the year. Runoff connectivity, defined as the ratio between runoff rates recorded at the rill network scale and those recorded at the interrill area scale in every rainfall event, was also greater on the rilled overburden slope, and in the most developed rill network. The dense rill networks of the overburden slope guarantee very effective runoff drainage, regardless of rainfall magnitude. Rills drain overland flow from interrill-sealed areas, reducing the opportunity of reinfiltration in areas not affected by siltation. Runoff generation and routing on topsoil slopes are controlled by grass cover and soil moisture content, whereas on overburden slopes rill network density and soil moisture content are the main controlling factors. Copyright © 2002 John Wiley & Sons, Ltd. [source] Modeling Postfire Response and Recovery using the Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS),JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 3 2009Kristina Cydzik Abstract:, This paper investigates application of the Army Corps of Engineers' Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) to a burned watershed in San Bernardino County, California. We evaluate the HEC-HMS' ability to simulate discharge in prefire and postfire conditions in a semi arid watershed and the necessary parameterizations for modeling hydrologic response during the immediate, and subsequent recovery, period after a wildfire. The model is applied to City Creek watershed, which was 90% burned during the Old Fire of October 2003. An optimal spatial resolution for the HEC-HMS model was chosen based on an initial sensitivity analysis of subbasin configurations and related model performance. Five prefire storms were calibrated for the selected model resolution, defining a set of parameters that reasonably simulate prefire conditions. Six postfire storms, two from each of the following rainy (winter) seasons were then selected to simulate postfire response and evaluate relative changes in parameter values and model behavior. There were clear trends in the postfire parameters [initial abstractions (Ia), curve number (CN), and lag time] that reveal significant (and expected) changes in watershed behavior. CN returns to prefire (baseline) values by the end of Year 2, while Ia approaches baseline by the end of the third rainy season. However, lag time remains significantly lower than prefire values throughout the three-year study period. Our results indicate that recovery of soil conditions and related runoff response is not entirely evidenced by the end of the study period (three rainy seasons postfire). Understanding the evolution of the land surface and related hydrologic properties during the highly dynamic postfire period, and accounting for these changes in model parameterizations, will allow for more accurate and reliable discharge simulations in both the immediate, and subsequent, rainy seasons following fire. [source] Soil pipe distribution and hydrological functioning within the humid tropics: a synthesisHYDROLOGICAL PROCESSES, Issue 12 2010Nick A. Chappell Abstract Some of the most responsive runoff systems in the world are found within the humid tropics. These runoff responses are likely to be affected by the presence of natural pipes within the soil. This study provides a synthesis of the hydrological aspects of these phenomena within the humid tropics. Of the studies reporting the presence of soil piping within the humid tropics, most are associated with Ultisol soils, and, locally, most pipe outlets are observed on the lower sections of hillslopes. While the drainage role of pipes has been observed (providing faster and slower components of stream hydrographs), the mechanism of their recharge remains less clear. In part, this is because their spatial extent is poorly mapped within the hillslopes of the humid tropics. Further studies quantifying the length and recharge of soil pipe networks within the humid tropics are needed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Effects of hillslope topography on hydrological responses in a weathered granite mountain, Japan: comparison of the runoff response between the valley-head and the side slopeHYDROLOGICAL PROCESSES, Issue 14 2008Masamitsu Fujimoto Abstract To evaluate the effects of hillslope topography on storm runoff in a weathered granite mountain, discharge rate, soil pore water pressures, and water chemistry were observed on two types of hillslope: a valley-head (a concave hillslope) and a side slope (a planar hillslope). Hydrological responses on the valley-head and side slope reflected their respective topographic characteristics and varied with the rainfall magnitude. During small rainfall events (<35 mm), runoff from the side slope occurred rapidly relative to the valley-head. The valley-head showed little response in storm runoff. As rainfall amounts increased (35,60 mm), the valley-head yielded a higher flow relative to the side slope. For large rainfall events (>60 mm), runoff from both hillslopes increased with rainfall, although that from the valley-head was larger than that from the side slope. The differences in the runoff responses were caused by differences in the roles of lower-slope soils and the convergence of the hillslope. During small rainfall events, the side slope could store little water; in contrast, all rainwater could be stored in the soils at the valley-head hollow. As the amount of rainfall increased, the subsurface saturated area of the valley-head extended from the bottom to the upper portion of the slope, with the contributions of transient groundwater via lateral preferential flowpaths due to the high concentration of subsurface water. Conversely, saturated subsurface flow did not contribute to runoff responses, and the subsurface saturated area at the side slope did not extend to the upper slope for the same storm size. During large rainfall events, expansion of the subsurface saturated area was observed in both hillslopes. Thus, differences in the concentration of subsurface water, reflecting hillslope topography, may create differences in the extension of the subsurface saturated area, as well as variability in runoff responses. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hillslope hydrology and wetland response of two small zero-order boreal catchments on the Precambrian ShieldHYDROLOGICAL PROCESSES, Issue 22 2007M. D. Frisbee Abstract Two Precambrian Shield zero-order catchments were monitored from January 2003 to July 2004 to characterize their hydrological and biogeochemical characteristics prior to a forest management experiment. Hydrometric observations were used to examine temporal trends in hillslope-wetland connectivity and the hillslope runoff processes that control wetland event response. The hillslope groundwater flux from the longer transect (E1) was continuous throughout the study period. Groundwater fluxes from a shorter and steeper hillslope (E0) were intermittent during the study period. Large depression storage elements (termed micro-basins) located on the upper hillslope of the E1 catchment appeared to be at least partly responsible for the observed rapid wetland runoff responses. These micro-basins were hydrologically connected to a downslope wetland by a subsurface channel of glacial cobbles that functioned as a macropore channel during episodic runoff events. The runoff response from the hilltop micro-basins is controlled by antecedent water table position and water is quickly piped to the wetland fringe through the cobble channel during high water table conditions. During periods of low water table position, seepage along the bedrock,soil interface from the hilltop micro-basin and other hillslopes maintained hillslope,wetland connectivity. The micro-basins create a dynamic variable source-area runoff system where the contributing area expands downslope during episodic runoff events. The micro-basins occupied 30% of the E1 catchment and are a common feature on the Precambrian Shield. Copyright © 2007 John Wiley & Sons, Ltd. [source] Comparison of stormflow responses of surface-mined and forested watersheds in the Appalachian Mountains, USAHYDROLOGICAL PROCESSES, Issue 16 2006Timothy L. Negley Abstract The results of a hydrological analysis that was conducted as part of a larger, multifaceted, collaborative effort to quantify ecosystem functions in watersheds subjected to land-use and land-cover change are presented. The primary goal of the study was to determine whether a small watershed in the Appalachian region (USA) that was recently subjected to surface mining and reclamation practices produces stormflow responses to rain events that are different from those produced by a nearby reference watershed covered by young, second-growth forest. Water balances indicated that runoff yields did not vary significantly between the two watersheds on an annual basis. Statistically significant differences (p,0·05) in runoff responses were observed on an event basis, however, with the mined/reclaimed watershed producing, on average (a) higher storm runoff coefficients (2·5×), (b) greater total storm runoff (3×), and (c) higher peak hourly runoff rates (2×) when compared with the reference watershed. Results of a unit hydrograph analysis also showed, unexpectedly, that the modelled unit responses of the two watersheds to effective rainfall pulses were similar, despite the noted differences in land cover. Differences in stormflow responses were thus largely explained by dramatic reductions in cumulative rates of rainfall abstraction (measured using infiltrometers) attributable to soil compaction during land reclamation. Additional field hydrological measurements on other mined watersheds will be needed to generalize our results, as well as to understand and predict the cumulative hydrological impacts of widespread surface mining in larger watersheds and river basins. Copyright © 2006 John Wiley & Sons, Ltd. [source] Modelling stream flow for use in ecological studies in a large, arid zone river, central AustraliaHYDROLOGICAL PROCESSES, Issue 6 2005Justin F. Costelloe Abstract Australian arid zone ephemeral rivers are typically unregulated and maintain a high level of biodiversity and ecological health. Understanding the ecosystem functions of these rivers requires an understanding of their hydrology. These rivers are typified by highly variable hydrological regimes and a paucity, often a complete absence, of hydrological data to describe these flow regimes. A daily time-step, grid-based, conceptual rainfall,runoff model was developed for the previously uninstrumented Neales River in the arid zone of northern South Australia. Hourly, logged stage data provided a record of stream-flow events in the river system. In conjunction with opportunistic gaugings of stream-flow events, these data were used in the calibration of the model. The poorly constrained spatial variability of rainfall distribution and catchment characteristics (e.g. storage depths) limited the accuracy of the model in replicating the absolute magnitudes and volumes of stream-flow events. In particular, small but ecologically important flow events were poorly modelled. Model performance was improved by the application of catchment-wide processes replicating quick runoff from high intensity rainfall and improving the area inundated versus discharge relationship in the channel sections of the model. Representing areas of high and low soil moisture storage depths in the hillslope areas of the catchment also improved the model performance. The need for some explicit representation of the spatial variability of catchment characteristics (e.g. channel/floodplain, low storage hillslope and high storage hillslope) to effectively model the range of stream-flow events makes the development of relatively complex rainfall,runoff models necessary for multisite ecological studies in large, ungauged arid zone catchments. Grid-based conceptual models provide a good balance between providing the capacity to easily define land types with differing rainfall,runoff responses, flexibility in defining data output points and a parsimonious water-balance,routing model. Copyright © 2004 John Wiley & Sons, Ltd. [source] Controls on runoff from a partially harvested aspen-forested headwater catchment, Boreal Plain, CanadaHYDROLOGICAL PROCESSES, Issue 1 2005K. J. Devito Abstract The water balance and runoff regime of a 55 ha aspen-forested headwater catchment located on the Boreal Plain, Alberta, Canada (55·1°N, 113·8°W) were determined for 5 years following a partial timber harvest. Variability in precipitation provided the opportunity to contrast catchment water balances in relatively dry (<350 mm year,1), wet (>500 mm year,1), and average precipitation years. In most years, the catchment water balance was dominated by soil water storage, evapotranspiration losses, and vertical recharge. In 1997, despite near-average annual precipitation (486 mm), there was significant runoff (250 mm year,1) with a runoff coefficient of 52%. A wet summer and autumn in the preceding year (1996) and large snow accumulation in the spring (1997) reduced the soil water storage potential, and large runoff occurred in response to a substantial July rainfall event. Maps of the surface saturated areas indicated that runoff was generated from the uplands, ephemeral draws, and valley-bottom wetlands. Following 1997, evapotranspiration exceeded precipitation and large soil water storage potentials developed, resulting in a reduction in surface runoff to 11 mm in 1998, and <2 mm in 1999,2001. During this time, the uplands were hydrologically disconnected from ephemeral draws and valley-bottom wetlands. Interannual variability was influenced by the degree of saturation and connectivity of ephemeral draws and valley wetlands. Variability in runoff from tributaries within the catchment was influenced by the soil water storage capacity as defined by the depth to the confining layer. An analysis of the regional water balance over the past 30 years indicated that the potential to exceed upland soil water storage capacity, to connect uplands to low-lying areas, and to generate significant runoff may only occur about once every 20 years. The spatial and temporal variability of soil water storage capacity in relation to evaporation and precipitation deficits complicates interpretation of forest harvesting studies, and low runoff responses may mask the impacts of harvesting of aspen headwater areas on surface runoff in subhumid climates of the Boreal Plain. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||