Overland Flow Velocity Research Articles

Effects of grass coverage and distribution patterns on erosion and overland flow hydraulic characteristics

Grass coverage and its spatial distribution patterns have crucial influences on erosion. The laboratory scouring experiments were conducted to research the influence of grass cover on runoff, erosion rates, and overland flow hydraulic characteristics in the plots with differing grass coverage rates (30, 50, 70, and 90 %), grass distribution patterns (where US, MS, and DS stand for the grass laid on up-slope, middle-slope and down-slope, respectively) and with a bare soil plot (CK) at a slope gradient of 20. The results illustrate that the grassplots had a 2.06–10.94 % runoff reduction and 28.57–75.4 % sediment decreases, respectively, as compared with CK plot. There was no significant difference in the runoff rate among the three grass distribution patterns for the same grass coverage, while DS had the lowest sediment yield rate and greatest sediment yield reduction in comparison with US and MS. The sediment yield rates were found to have a significantly negative exponential relationship with the grass coverage (p < 0.01), while the sediment concentration had a significantly negative linear relationship with the grass coverage (p < 0.01). The overland flow velocity (V) increased with increasing inflow discharges and deceased with increasing grass cover, and it was negatively correlated with the grass coverage following a linear trend (p < 0.01). The mean Froude number (Fr) holds to a similar variation law with the changes in the V. There was no significant relationship found to exist between the grass coverage and Reynolds number (Re). The average Darcy–Weisbach resistance coefficient (f) of the whole slope for grass plots was 2.2–25.6 times of that for CK plot, and f was found to be an exponent correlated with the coverage rate (p < 0.01). In addition, f was negatively correlated with the erosion rate following a power function (p < 0.01); however V, Fr, and Re were positively correlated with the erosion rate (p < 0.01). The sediment yield rate itself was a function of the runoff rate for each treatment, and their relationships could be well described by the linear equation (p < 0.01). These results indicate that both grass coverage rates and distribution patterns have significant effects on hydrological characteristics of overland flow.

Design and Engineering of Open Weave Jute Soil Saver for Potential Application in the Field of Soil Erosion Control and Hill Slope Management

Out of several natural agents causing extensive damages to roads, landslides can claim to be a major destroyer. There are several causes for landslides such as hazardous ground conditions, landform configuration adversities, occasionally occurring natural physical forces and anthropogenic impact on the environment. In such vulnerable situations the top soil on hill slopes get disintegrated due to intensive precipitation or shaking due to tremors and eventually flows down rapidly down the slope. The situation deserves the search for a biocover which can reduce the velocity of overland flow and entrap detached soil particles thereby controlling top soil loss. Jute Geotextile (JGT) if properly designed can fulfill the said criteria besides facilitating growth of vegetation. This paper discusses optimization of property parameters of open weave Jute Geotextile in tune with different parameters of design concerning protection of hill slope along with comparative analysis of the results of different tests on one hand and determination of tolerance limit of the prime property parameters of the developed JGT samples, on the other, which have been employed in different case studies to prove their potentiality and technoeconomic viability.

Using thermal tracers to estimate flow velocities of shallow flows: laboratory and field experiments

Abstract Accurate measurement of shallow flows is important for hydraulics, hydrology and water resources management. The objective of this paper is to discuss a technique for shallow flow and overland flow velocity estimation that uses infrared thermography. Laboratory flumes and different bare, vegetated and paved field surfaces were used to test the technique. Results show that shallow flow surface velocities estimated using thermal tracers and infrared technology are similar to estimates obtained using the Acoustic Doppler Velocimeter; similar results were also obtained for overland flow velocity estimates using thermography, here comparing with the dye tracer technique. The thermographic approach revealed some potential as a flow visualization technique, and leaves space for future studies and research.

模拟降雨下植被盖度对坡面流水动力学特性的影响

Soil and water loss has caused severe land resources depletion and eco-environment degradation in many areas of China,which leads to reduction of local agricultural and industrial productivity. Furthermore,as a severe environmental problem,soil and water loss will affect many respects,such as nature,economy,society and science. Many factors are influencing the degree of soil erosion,Plant vegetation coverage,rainfall intensity and duration,soil type and texture,etc.In this study we chose slope,rainfall intensity and vegetation coverage as impact factors to the degree of soil erosion. Plant ryegrass is one of the feasible measures to avoid soil and water loss. In order to understand the process of runoff movement under the complex surface conditions and the effect of flow and different surface conditions on hydraulics parameters,we utilized the artificial rainfall approach to study the process of runoff and sediment yield and its hydraulic characteristics to explore how ryegrass play a role in the work of soil and water conservation. The experiment was designed with 30 mm / h and60 mm / h rainfall intensity and slopes of 10° and 20° with different coverage of ryegrass(0,20%,40%,60%,80% and100%) in Jiufeng experimental forest farm of Beijing Forestry University. During the simulated rainfall process,the runoff samples were collected at fixed time: in the first ten minutes,the runoff was sampled every two minutes due to the fast increase of runoff amount,and then the runoff was sampled every five minutes in the last fifty minutes as the change of runoff amount went slow. At the end of the experiment,the volume of runoff was measured,and then standing the runoff samples were placed and dried for 24 hours,respectively,to obtain the amount of sediment. During the simulated rainfallprocess,the velocity of overland flow was measured every ten minutes. Then the surface runoff and hydraulic parameters were calculated with runoff,sediment and surface runoff velocity. By choosing Reynolds number,Froude number and drag coefficient as factors to characterize the water advance and water recession process,the results showed that: the Reynolds number increases with the slope degree and rainfall intensity. The increase of ryegrass could play important roles in both the decrease of the Reynolds number and the Froude number,and the Reynolds number and the Froude number under different coverage are: bare land 20% 40% 60% 80% and bare land 20% 40% 60% 80%,respectively. The drag coefficient and sediment yield rate were well-fitting,and the sediment yield rate decreased as the drag coefficient increased.When the drag coefficient was between zero and one,the growth rate of sediment yield was larger than the drag coefficient.By this study,we know that ryegrass has a great significance to soil and water conservation. Moreover,the increase of ryegrass coverage leads to the enhancement of the soil and water conservation function. The results of the ryegrass regulating runoff and preventing soil erosion in this study have theoretical significance to understanding the process of soil erosion.

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

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

Soil erosion characteristics of ditch banks during reclamation of a saline/sodic soil in a coastal region of China: Field investigation and rainfall simulation

Understanding soil erosion processes is essential for assessing the extent and causes of soil erosion and for planning soil conservation including those on the banks of excavated ditches. Based on a field investigation and laboratory rainfall simulation experiments, the soil erosion characteristics of a saline/sodic soil undergoing reclamation that was exposed on irrigation/drainage ditch banks in a coastal region of China were investigated. Preliminary analyses of the data indicated that the soil erosion was more severe from the ditch banks in the coastal region than from those in other areas of China. The annual erosion loss from ditch banks in the most recently reclaimed farmland (2007) was 140kg/m2, but the erosion modulus decreased significantly (p<0.05) with increasing reclamation time. Increasing rainfall intensity and/or slope gradient increased runoff and sediment yield rates. However, there was a critical slope gradient of about 25°, above which no further increases occurred. As rainfall intensity and/or slope gradient increased, the overland flow velocity and the Froude number (Fr) increased notably. The Reynolds number (Re) increased with increasing rainfall intensity, but decreased and was more affected by increases in slope gradient. Positive parabolic relationships were found between sediment yield rates and Re. The resistance to flow decreased with increasing rainfall intensity and slope gradient. Negative correlations were found between the sediment yield rate and the resistance force (f and n). Covering the soil surface greatly decreased runoff and soil erosion by increasing the surface roughness and decreasing the runoff velocity. Compared with covers of stones or netting, and with no cover, the slope runoff coefficient and sediment yield rate of soil under straw mulch were the lowest with values of 0.043 and 0.14kg/m2min, respectively. Therefore, using straw mulch would be a way to control erosion until salt-tolerant plants colonized and protected the ditches.

Connecting the power-law scaling structure of peak-discharges to spatially variable rainfall and catchment physical properties

We have conducted extensive hydrologic simulation experiments in order to investigate how the flood scaling parameters in the power-law relationship Q(A)=αAθ, between peak-discharges resulting from a single rainfall–runoff event Q(A) and upstream area A, change as a function of rainfall, runoff coefficient (Cr) that we use as a proxy for catchment antecedent moisture state, hillslope overland flow velocity (vh), and channel flow velocity (vc), all of which are variable in space. We use a physically-based distributed numerical framework that is based on an accurate representation of the drainage network and apply it to the Cedar River basin (A=16,861km2), which is located in Eastern Iowa, USA. Our work is motivated by seminal empirical studies that show that the flood scaling parameters α and θ change from event to event. Uncovering the underlying physical mechanism behind the event-to-event variability of α and θ in terms of catchment physical processes and rainfall properties would significantly improve our ability to predict peak-discharge in ungauged basins (PUB). The simulation results demonstrate how both α and θ are systematically controlled by the interplay among rainfall duration T, spatially averaged rainfall intensity E[I], as well as E[Cr], E[vh], and vc. Specifically, we found that the value of θ generally decreases with increasing values of E[I], E[Cr], and E[vh], whereas its value generally increases with increasing T. Moreover, while α is primarily controlled by E[I], it increases with increasing E[Cr] and E[vh]. These results highlight the fact that the flood scaling parameters are able to be estimated from the aforementioned catchment rainfall and physical variables, which can be measured either directly or indirectly.

Longitudinal variations of hydraulic characteristics of overland flow with different roughness

The evolution of the overland flow velocity along the distance downslope on smooth and granular beds in different cases is investigated by means of the electrolyte tracer via flume experiments. The results demonstrate that a non-uniform flow regime and a uniform flow regime exist in the development process of the overland flow. Owing to the different attributes of beds' roughness, the position of those zones with different flow regimes varies correspondingly: (1) the overland flow on granular beds enters into the uniform regime much sooner, additionally, the roll waves tend to appear because of the presence of the proper flow resistance imparted by the roughness (coarse sands), and large slopes (20° and 25°) which makes the flow velocities and depths to undulate spatially. Furthermore, the flow resistance of the overland flows with different roughness elements, that is the non-sands, the fine sands and the coarse sands, is calculated. A quadratic interpolation method of the third order accuracy is employed in the calculation of the longitudinal flow resistance. The results show that it is rational to use the bed slope to approximate the hydraulic energy slope over a relative small roughness (the present roughness), however on the other hand, if the mean flow velocities and depths rather than the local parameters are used to calculate the flow resistance, a considerable error will be induced within the non-uniform regime of the overland flows, including the acceleration zone and the roll-wave zone.

Using a thermal tracer to estimate overland and rill flow velocities

ABSTRACTFlow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models, such as soil erosion and rill development models, as well as for modelling sediment and solute transport by runoff. This study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities. Laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer (heated dye) into shallow flowing surface water. The leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared. The results show that thermal tracers can be used to estimate both overland and rill flow velocities, since measurements are similar to those resulting from using dye tracers. The main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Exploring the effects of hillslope-channel link dynamics and excess rainfall properties on the scaling structure of peak-discharge

Several studies revealed that peak discharges (Q) observed in a nested drainage network following a runoff-generating rainfall event exhibit power law scaling with respect to drainage area (A) as Q(A)=αAθ. However, multiple aspects of how rainfall-runoff process controls the value of the intercept (α) and the scaling exponent (θ) are not fully understood. We use the rainfall-runoff model CUENCAS and apply it to three different river basins in Iowa to investigate how the interplay among rainfall intensity, duration, hillslope overland flow velocity, channel flow velocity, and the drainage network structure affects these parameters. We show that, for a given catchment: (1) rainfall duration and hillslope overland flow velocity play a dominant role in controlling θ, followed by channel flow velocity and rainfall intensity; (2) α is systematically controlled by the interplay among rainfall intensity, duration, hillslope overland flow velocity, and channel flow velocity, which highlights that it is the combined effect of these factors that controls the exact values of α and θ; and (3) a scale break occurs when runoff generated on hillslopes runs off into the drainage network very rapidly and the scale at which the break happens is determined by the interplay among rainfall duration, hillslope overland flow velocity, and channel flow velocity.

Implementing contour bank farming practices into the J2000 model to improve hydrological and erosion modelling in semi-arid Western Cape Province of South Africa

Contour bank farming is a well-known agricultural management technique in areas which are characterised by intensive and erosive rainfalls. Contour banks are designed to reduce the flow velocity of overland flow and to intercept water before it concentrates in rills, thereby reducing the risk of soil erosion and land degradation. By their structure, contour banks noticeably impact surface runoff pattern both temporally and spatially. Also subsurface flow may be affected by contour banks. For example, if contour banks intersect the A- and B-horizon of the soil, it can cause significant infiltration of water into the C-horizon, which if saline, can generate saline interflow to downslope areas. Although these aspects have been highlighted in previous research efforts, the quantitative and qualitative impacts of contours on runoff generation and associated erosion dynamics or salinisation are rarely considered in process-based hydrological modelling approaches. In this study an approach was developed to improve distributed hydrological and erosion modelling by integrating contour banks in the delineation and routing of Hydrological Response Units. Applying the distributed and process-based hydrological model J2000 which was modified with a contour bank and erosion module it could be shown that the implementation of contour banks improved the model performance significantly.

Evaluating the effectiveness of wood shred and agricultural straw mulches as a treatment to reduce post-wildfire hillslope erosion in southern British Columbia, Canada

After the 2009 Terrace Mountain fire near Kelowna, BC, Canada, wood shred and agricultural straw mulch effects on post-fire runoff and sediment yields were compared using three experimental techniques: rainfall simulations on 1-m2 plots, concentrated flow (rill) simulations on 9-m long plots, and sediment yields from natural rainfall on 30-m2 plots. All experimental plots were located on and along a planar hillslope burned at high severity. Experiments were conducted once a year for three consecutive years beginning in Sep 2009, except for the rainfall simulations which only were conducted the first two years. Although results varied by experiment and time since fire, both agricultural straw and wood shred mulch treatments performed similarly for reducing runoff and sediment; thus were combined into a single “treated” class for analyses. The mulch treatments were effective in reducing sediment yields as compared to the controls in all three experiments in 2009. In the rill simulation experiment, the mulch treatments significantly reduced overland flow velocity and increased the proportion of overland flow that infiltrated the soil before reaching the plot outlet. The elapsed time since the fire, which was strongly related to the increase in vegetative ground cover, was a significant factor for predicting sediment yields in the statistical models. Favorable spring rainfall in 2010 and 2011 supported rapid regrowth of vegetation, which recovered similarly on all plots regardless of treatment. The runoff and sediment yields on the treated plots were similar to those measured on the control plots a year later; we concluded that the mulch was, in effect, a surrogate for a year of recovery. Given that agricultural straw mulch is an established and effective post-fire hillslope treatment, it was important to find that wood shred mulch was similarly effective in reducing post-fire runoff and sediment yields. Thus, the choice of agricultural straw or wood shreds for a post-fire mulch treatment may be based on the performance characteristics (longevity, potential to carry invasive species seeds, cost, etc.) that best fit the needs of the site.

The performance of grass filter strips in controlling high‐concentration suspended sediment from overland flow under rainfall/non‐rainfall conditions

ABSTRACTThere is little information on the performance of vegetative filter strips (VFS) in filtering high‐concentration sediment from subcritical overland flow. Flume experiments on simulated grass strips were conducted using combinations of three slope gradients (3°, 9° and 15°), five 1‐m‐wide slope positions (from upslope to downslope), two flow rates (60 and 20 L min‐1 m‐1) and sediment concentrations of 100–300 kg m‐3 under simulated rainfall and non‐rainfall conditions. The results showed that sediment deposition efficiency increased with VFS width as a power function. Rainfall significantly reduced sediment deposited within VFS. Higher sediment concentration corresponded to a larger sediment deposition load but reduced deposition efficiency. Flow rate had a negative effect on deposition efficiency but no effect on deposition load. Sediments were more easily deposited at the upper slope position than downslope, and the upper slope position had a higher percentage of coarse sediments. The deposited sediment had significantly greater median diameters (D50) than the inflow sediment. A greater proportion of coarse sediments larger than 25 µm in diameter were deposited, and particles smaller than 1 µm and of 10–25 µm had a better deposition performance than particles of 1–10 µm. Rainfall reduced the deposited sediment D50 at a slope gradient of 3° and had no significant influence on it at 9° or 15°. A higher sediment concentration led to a smaller D50 of the deposited sediment. Rainfall had no significant effect on overland flow velocity. Both the deposited sediment load and D50 decreased with increasing flow velocity, and flow velocity was the most sensitive factor impacting sediment deposition. The results from this study should be useful to control sediment flowing into rivers in areas with serious soil erosion. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Effects of patterned Artemisia capillaris on overland flow velocity under simulated rainfall

AbstractVegetation cover is an important factor for erosion control. Laboratory‐simulated rainfall experiments were conducted to quantify the effectiveness of patchy distributed Artemisia capillaris in retarding overland flow velocity. Simulated storms (60, 90, 120, and 150 mm h−1) were applied on a bare plot (CK) and four different plant patterns, a banded pattern perpendicular to the slope direction (BP), a single long strip parallel to slope direction (LP), small patches distributed like a checkerboard (SP1), and small patches distributed like a letter “X” (SP2). All treatments had three replicates. Each plot underwent two sets of experiments, intact plant plots and root plots (the above‐ground parts were removed, only roots were reserved), respectively. Results showed that flow velocity increased with rainfall intensity, and the lower slope velocity (Vl) was higher than the upper slope velocity (Vu). The removal of grass shoots increased flow velocity. Compared with bare soil plot, intact plants reduced mean flow velocity by 14%–60%, whereas the reduction declined to &lt;40% for the root plots. BP and both SP treatments performed more effectively than LP in retarding flow velocity, whereas no significant differences were identified between BP and SP. The contributions of A. capillaris shoots and roots to the reductions in flow velocity under different rainfall intensities were different. The shoots made greater contribution of 53%–97% at 60 and 90 mm h–1, and the roots contributed more (51%–81%) at 120 and 150 mm h–1. Runoff and sediment rate had significant (p &lt; 0.05) linear correlations with mean flow velocity. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Tracing of shallow water flows through buoyant fluorescent particles

In this paper, we investigate the feasibility of tracing shallow water flows in illuminated conditions by using buoyant fluorescent particles. We develop an image analysis-based procedure for automatic detection and real-time tracking of particles based on a computationally inexpensive algorithm implemented on recorded videos. The methodology is validated through experiments conducted in a custom-built reclinable miniature channel that is specifically developed for simulating shallow water conditions. The effect of the fluorescent particles’ dimensions on their ability to trace water flows is theoretically assessed through a parametric study in which the particle response to different flow velocities is estimated through the Basset–Boussinesq–Oseen equation. Particle velocities extracted through image analysis are compared to particle image velocimetry measurements for selected combinations of slopes and water depths. Experimental results support the potential integration of this methodology in field measurement systems for hillslope overland flow velocity.

TSUNAMI MODELLING AND RISK MAPPING FOR EAST COAST OF SABAH, MALAYSIA

A tsunami risk mapping study for the east coast of the state of Sabah, Malaysia, has been initiated by the Government of Malaysia. The main objective is to produce tsunami risk maps that can be taken into account in local planning for the coastal zone. The study covers a coastline of more than a thousand kilometers which generally is sparsely populated outside the main population centers. The study is regional in character, but with additional focus on the main population centers. The paper outlines the overall steps of hazard mapping through source identification and modelling followed by tsunami wave propagation and potential modelling of overland flow. Modelling challenges related to sparse bathymetry data, limitations to resolution due to the large coverage required combined with a complex bathymetry with coral reefs, islands and outcrops is discussed. Data and model resolution for overland flow modelling is discussed. For the present study, it was found that the inaccuracies in the topographic data is of similar magnitude to the expected inundation levels, and caution has to be exercised in deriving hazard levels from the overland flow modelling. For a regional scale risk mapping exercise, and in the absence of very detailed topographic data, it may be preferable to use the wave height along the coastline as a hazard indicator rather than potentially inaccurate inundation levels and overland flow velocities.

Impacts of sediment load on Manning coefficient in supercritical shallow flow on steep slopes

AbstractThe Manning equation is one of the most widely used formulae for calculating the velocity of shallow overland flow in hydrological and erosion models. Precise estimation of the Manning's friction coefficient (n) is critical to determining overland flow and soil erosion processes. Few studies have been conducted to quantify the effects of sediment load on Manning's n on steep slopes. This study was conducted to investigate the potential effects of sediment load on Manning's n in a flume with a fixed bed, under wide ranges of hydraulics and sediment loads. Slope gradient varied from 8·7 to 34·2%, unit flow rate from 0·66 to 5·26 × 10−3 m2 s−1, and sediment load from 0 to 6·95 kg m−1 s−1. The Reynolds number ranged from 350 to 5899. Results showed that Manning's n varied in both sediment‐free and sediment‐laden flows ranging from 0·012 to 0·055. The apparent Manning's coefficients of sediment‐laden flow were much greater than those of sediment‐free flow. The mean Manning coefficient of sediment‐laden flow was 51·27% greater than the mean value of sediment‐free flow. For sediment‐laden flow, Manning's n could be estimated with a power function of unit flow discharge and sediment content. Further studies are needed to quantify the potential effects of sediment load on the Manning's n on erodible beds and in fields. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Correction factor to dye-measured flow velocity under varying water and sediment discharges

Summary Dye-tracing technique was a widely used method to determine the velocity of overland flow in soil erosion studies under both laboratory and field conditions. Few studies were performed to quantify the effects of sediment load on correction factor on steep slopes. This study was conducted to investigate the potential effects of sediment load on correction factor of overland flow to determine mean velocity in a glued hydraulic flume under a wide range of hydraulic conditions and sediment load. Slope gradient (S) varied from 8.7% to 34.2%, unit flow rate (q) from 0.66 to 5.26 × 10−3 m2 s−1, and sediment load (Qs) from 0 to 6.95 kg m−1 s−1. The Reynolds number (Re) ranged from 350 to 5899. Mean velocity was calculated from the volumetric relation using measured flow depth by a digital level probe and flow discharge. The results showed that correction factor decreased as S increased and increased as Re increased for sediment-free flow with a mean value of 0.659. Correction factor could be estimated with a logarithmic function of S and Re (R2 = 0.883). For the sediment-laden flow, correction factor varied from 0.233 to 0.682 with a mean value of 0.466. The correction factor decreased as sediment load (Qs) increased and increased as Re increased. It could be estimated with a logarithmic function of Re, and Qs (R2 = 0.796). For the combination of sediment-free and sediment-laden flows, the correction factor varied from 0.233 to 0.783 with a mean of 0.505. The correction factor was inversely related to slope gradient and sediment load, and directly to Reynolds number (R2 = 0.854). The overall results indicated that caution must be exercised and proper correction be made when using the dye tracer method to measure flow velocity in surface hydrology and erosion studies. Further studies with systematic advanced set up for sediment feeding are needed to quantify the potential effects of sediment load on correction factor under varying conditions of roughness element.

Catchment storm runoff modelling using the geomorphologic instantaneous unit hydrograph

A lumped empirical model, the Geomorphologic Instantaneous Unit Hydrograph (GIUH) rainfall-runoff model, is developed for the Can Le catchment in the upstream region of the Sai Gon river Basin (Vietnam). This model can serve to simulate catchment runoff into the Dau Tieng Reservoir and can be used as a flood forecasting tool for the ungauged Can Le catchment. The GIUH couples geomorphology and hydrology quantitatively. The obtained Unit Hydrograph is based on Horton's morphometric parameters; bifurcation, length and area ratios. A new functionality within the ILWIS GIS-RS package, namely ‘DEM-hydro processing’, is applied to effectively process a Digital Elevation Model to extract these ratios from the drainage network. To supplement the limited field data available, various satellites images have been used such as ASTER, SRTM (Shuttle Radar Topography Mission) and METEOSAT 5. A short field campaign to collect missing ground data was executed between September and October 2005. The data collected included discharge (and stage – discharge curve), meteorological data, soil, land use information that are used for paramerisation, calibration and validation of the GIUH. The model was successfully applied for the Can Le catchment. Using the Horton's morphometric parameters derived from the DEM with estimated overland and stream flow velocities, the model is easy-to-use.

Prescribed‐fire effects on rill and interrill runoff and erosion in a mountainous sagebrush landscape

AbstractChanging fire regimes and prescribed‐fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush‐steppe. Small (0·5 m2) and large (32·5 m2) plot rainfall simulations (85 mm h–1, 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post‐fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse‐textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre‐burn levels and sediment yield was greatly reduced with ground cover recovery to 40 per cent 1 year post‐fire. Erosion remained above pre‐burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 per cent two growing seasons post‐fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre‐existing strong soil‐water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 per cent probably protected the site from low‐return‐interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high‐intensity or long duration events until ground cover levels reached 60 per cent. The data demonstrate that the persistence of fire effects on steeply‐sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 per cent and on the strength and persistence of ‘background’ or fire‐induced soil water repellency. Published in 2009 by John Wiley &amp; Sons, Ltd.