Rainfall Simulation Plots Research Articles

The Impact of Soil Water Repellency and Slope upon Runoff and Erosion

Soil water repellency (SWR) increases the amount of runoff and erosion from soils. Previous experiments on water-repellent soils had shown intricate runoff movement and high rates of water and soil losses; our aim was to observe these processes, noting their influences and quantifying impacts. The experiment used a 60 × 60 cm rainfall simulation plot setup to represent an agricultural plot with packed water repellent soil and no interference of plants. We measured inputs, and monitored surface flows and erosion on 3°, 6° and 9° slopes. A surfactant treated plot was used as a control. Eroded sediment samples were collected and measured for particle size, and together with runoff analysed for organic carbon, nitrogen and macronutrients. Runoff coefficients were high (0.53 to 0.78) for untreated soil with erosion decreasing over the course of the experiment (1.41 t ha-1 to 0.74 t ha-1 over five 2 mm rainfall events, of 2 min duration, on the 9° slope). This resulted in cumulative erosion of up to 5.35 t ha-1 after a total of 10 mm of rainfall (5 × 2 mm). Importantly, silt and clay were preferentially eroded (up to 12 × higher in eroded soil than the baseline composition) and this correlated with the loss of organic carbon, nitrogen, and macronutrients. As expected, the steepest slope (9°) caused greater runoff and erosion than the lowest (3°), however, there was no significant difference in runoff and erosion between the 6° and 9° slope. Surfactant significantly decreased runoff coefficients by two orders of magnitude compared to the untreated soil. Surface flow was initially characterised by beading and rivulet formation, minimising soil contact. Over time, however, a perched, protective water layer formed over the surface, allowing subsequent water flow with reduced soil interaction. The runoff mechanisms for these small rain events were only observed on the water-repellent soils and likely reduced the degree of erosion given the high runoff coefficients. Initial water flow also promoted armouring of the soil by the attraction of smaller particles, leading to increased loss of organic carbon and nitrogen as well as macronutrients.

Estimation of potential erosion under two sugarcane cutting systems using the universal soil loss equation

In order to compare soil losses in two cutting systems traditio-nally used in the cultivation of sugar cane for the production of panela, a study was carried out in which measurements were made in the field using a rainfall simulator and runoff plots in a vertisol of the municipality of Quebradanegra, Cun-dinamarca, where both types of cut are presented simulta-neously: the cut-off system, in which everything is harvested at once having a homogeneous maturity in the crop and the thinning cut system, in which have an inhomogeneous ma-turity so that only a percentage of the plants is cut at the same time. To estimate the potential soil losses associated with both cutting systems, the Universal Soil Loss Equation (USLE) was used to obtain a mean C factor associated with the type of cut, using the data determined in the field and the erosivity of simulated rainfall intensities. Finally, the anual potential losses of soil was determined under the two cutting systems, where it was observed that the cut-off system has an annual potential erosion 2.2 times greater than the thin-ning cuy system. On the other hand, when comparing the potential losses of soil with a newly prepared and planted lot, without plant cover, the capacity of the sugarcane cane crop is demonstrated to offer a protection to the soil, presenting a potential erosion 9 times smaller, in the case of the cut-off system, with respect to a soil condition without plant cover.

Metals in Soil and Runoff from a Piedmont Hay Field Amended with Broiler Litter and Flue Gas Desulfurization Gypsum

Flue gas desulfurization gypsum (FGDG) from coal-fired power plants is readily available for agricultural use in many US regions. Broiler litter (BL) provides plant available N, P, and K but can be a source of unwanted As, Cu, and Zn. As a source of Ca and S, FGDG can reduce losses of P and other elements in runoff from BL-amended areas. Rainfall simulation plots (2.0 m) were established on a Piedmont Cecil soil growing 'Coastal' bermudagrass ( L.) for hay. Accumulation and transport of As, Cu, Cd, Cr, Hg, Pb, and Zn were evaluated after annual BL applications (13.5 Mg ha) with four FGDG rates (0, 2.2, 4.5, 9.0 Mg ha) and two FGDG treatments (0 and 9 Mg ha) without BL. Runoff As concentrations were sixfold greater with BL than without ( ≤ 0.01) and were similar to BL with FGDG at 2.2, 4.5 or 9.0 Mg ha ( ≤ 0.10). Runoff concentrations of target elements did not increase where FGDG was applied alone. After three annual applications of FGDG and BL, soil concentrations of As, Cr, Pb, Hg, and Cu were well below levels of environmental concern. Our findings indicate that runoff losses of As from BL application are not reduced with FGDG but support other research indicating no identifiable environmental risks from FGDG beneficial use in agricultural systems.

The effects of thinning trees and scattering slash on runoff and sediment yield within dense piñon-juniper woodlands in New Mexico, United States

This study evaluated the hydrologic effects of thinning piñon-juniper (P-J) (<i>Pinus edulis</i> var. <i>Engl.</i> and <i>Juniperus</i> spp.) woodlands in conjunction with oil and gas (O&amp;G) development in dense woodlands. Utilizing rainfall simulation we compared the effects on the thinned areas to pipelines, undisturbed sites, and existing nearby roads with specific interest in (1) runoff and runoff per unit of precipitation (runoff/ppt), (2) infiltration, and (3) suspended sediment and sediment yield. Trees were removed with a combination of chainsaw cutting and mastication in 2004. Randomly selected within each of the eight research blocks and five treatments, rainfall simulation plots were randomly placed within intercanopy and canopy areas. Thinned intercanopy plots with basal areas of 1.2 m² ha⁻¹ (5 ft² ac⁻¹) had significantly less runoff and lower runoff/ppt levels when compared to the basal area 2.3 m² ha⁻¹ (10 ft² ac⁻¹) and control intercanopy plots. Roads exhibited significantly greater runoff than every other treatment in the analysis. Suspended sediment was hypothesized to trend similar to runoff; however, the results of this analysis revealed that only roads differed statistically from other treatments. Sediment yield was similar to the results for suspended sediment with the exception of the intercanopy plots. Both thinning treatments (363.1 and 234. 7 kg ha⁻¹ [324.2 and 209.6 lb ac⁻¹]) were significantly less than the control mean (719.7 kg ha⁻¹ [642.7 lb ac⁻¹]). When comparing whole treatments (combining basal area 5 [BA5] and basal area 10 [BA10] plots), there is convincing evidence that mean runoff/ppt was different among all treatments, except between the control and pipeline. Analysis of suspended sediment indicated that all treatments were significantly different from the roads, but not between all other treatments. There was, however, convincing evidence (<i>p</i> = 0.0033) that sediment yield of the treatment was less than the control. These whole treatment comparisons demonstrate the success of the treatments in reducing runoff/ppt and sediment yield within P-J woodlands and the potential for management to improve the hydrological function along O&amp;G disturbances within the San Juan Basin.

Characterizing infiltration and internal drainage of South African dryland soils

AbstractSurface infiltration and internal drainage properties of five soil types from arid drylands of South Africa were studied under double ring infiltrometer, rainfall simulation plots (1 m2) and instantaneous drainage plots (9 m2). Changes in soil water content during 40 minute rainfall simulation for a rainstorm with average intensity of 1.61 mm min−1 and 30 day drainage period were measured at various depths by 1.5 m long capacitance soil water measuring (DFM) probe. Different (P &lt; 0.05) mean surface steady infiltration rate ranged from 0.05 to 4.47 mm min−1 and had a negative power relationship (R2 = 0.65) with horizon clay plus fine silt content. Power regression (R2 ≥ 86%) described rainstorm infiltration and obtained steady rates within an average time of 15 minutes. Mean total infiltrated soil water content was lowest (P &lt; 0.05) from surface horizons with either 47.7% clay plus fine silt content or bulk density of 1.91 g cm−3 and exchangeable sodium of not less than 44 mg kg−1. Surface horizons with lower surface bulk density and total sand fraction of more than 72% had infiltrated depth and mean total infiltrated soil water content up to 40 cm deeper and 0.55 mm mm−1 greater, respectively. Drainage rate at drained upper limit calculated from the Wilcox drainage model (R2 ≤ 0.97%) was 0.2 mm day−1 or less were from underlying horizons with either clay plus fine silt of 45% or soft calcium carbonate. Higher drainage rate with accumulative drainage amount greater than 60 mm were from soil profile horizons with clay plus fine silt content of less than 20% and above unity steady infiltration rates. Rainstorm infiltration and drainage rates was shown to depend on permeability and coarseness of the respective soil surface and subsurface horizons; a phenomenon critical for harnessing rain and flood water to recharge groundwater. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Determination of Watershed Infiltration and Erosion Parameters from Field Rainfall Simulation Analyses

Realistic modeling of infiltration, runoff and erosion processes from watersheds requires estimation of the effective hydraulic conductivity (Km) of the hillslope soils and how it varies with soil tilth, depth and cover conditions. Field rainfall simulation (RS) plot studies provide an opportunity to assess the surface soil hydraulic and erodibility conditions, but a standardized interpretation and comparison of results of this kind from a wide variety of test conditions has been difficult. Here, we develop solutions to the combined set of time-to-ponding/runoff and Green– Ampt infiltration equations to determine Km values from RS test plot results and compare them to the simpler calculation of steady rain minus runoff rates. Relating soil detachment rates to stream power, we also examine the determination of “erodibility” as the ratio thereof. Using data from over 400 RS plot studies across the Lake Tahoe Basin area that employ a wide range of rain rates across a range of soil slopes and conditions, we find that the Km values can be determined from the combined infiltration equation for ~80% of the plot data and that the laminar flow form of stream power best described a constant “erodibility” across a range of volcanic skirun soil conditions. Moreover, definition of stream power based on laminar flows obviates the need for assumption of an arbitrary Mannings “n” value and the restriction to mild slopes (&lt;10%). The infiltration equation based Km values, though more variable, were on average equivalent to that determined from the simpler calculation of steady rain minus steady runoff rates from the RS plots. However, these Km values were much smaller than those determined from other field test methods. Finally, we compare RS plot results from use of different rainfall simulators in the basin and demonstrate that despite the varying configurations and rain intensities, similar erodibilities were determined across a range of infiltration and runoff rates using the laminar form of the stream power equation.

Ecohydrologic response and recovery of a semi-arid shrubland over a five year period following burning

Increasing trends in wildfire activity on semi-arid rangelands necessitate advancement in understanding of fire impacts on vegetation, soils, and runoff and erosion processes. This study used artificially applied rainfall and concentrated overland flow experiments to evaluate the ecohydrologic response and recovery of a semi-arid shrubland in the Great Basin Region, USA, following fire. Rainfall experiments were conducted at the 0.5m2 plot scale to assess fire impacts on rainsplash and sheetflow processes. Concentrated flow experiments were applied on 9m2 plots to evaluate fire impacts on concentrated overland flow processes. Vegetation, soil, hydrologic, and erosion variables were assessed at each scale pre-fire and 1, 2, and 5yr post-fire. Infiltration and runoff on rainfall simulation plots were affected more by measured background soil water repellency than fire effects on vegetation and soils. Runoff from rainfall on shrub-dominated plots was unchanged 1yr post-fire, but runoff from interspace plots between shrubs declined 1yr post-fire. Runoff increased on shrub and interspace rainfall plots 2yr post-fire and then declined in the 5yr post-fire. Bare ground generally declined across study years, implicating the temporal variability in soil water repellency as the causal factor for infiltration and runoff trends. Erosion on rainfall plots increased by factors of 8 to more than 10 following fire removal of vegetation and ground cover and declined with vegetation recovery through five growing seasons. Concentrated overland flow plots generated slightly more total runoff and 26-fold more total sediment 1yr following burning relative to pre-fire measures. Erosion from concentrated overland flow remained greater on burned than unburned plots after five growing seasons even though ground cover returned to approximately 85%. The relative recovery of vegetation and total ground cover were typical for the shrubland community assessed, but elevated erosion with 85% ground cover 5yr post-fire was unexpected. The persistent high sediment delivery from concentrated plots is attributed to the fine textured soils and thin litter accumulation. The importance of considering erodibility in context with sediment supply and vegetative recovery is discussed. The results demonstrate the complexity of post-fire ecohydrologic interactions, advance process understanding of post-fire ecohydrologic responses for semi-arid rangelands, and underscore the need for additional studies on post-fire recovery over time.

A Method for Subsurface-Banding Poultry Litter in Plots Not Accessible with Conventional Field Equipment

<abstract> <b><sc>Abstract. </sc></b>Subsurface band application of poultry litter has been shown to be effective in reducing nutrients in runoff and leachate, relative to surface broadcast application of litter. Some field plot arrangements, such as plots having adjacent pits in the soil, prevent the use of conventional field equipment because the equipment cannot traverse the pits. A small trencher and a method using a forklift were developed for making trenches in soil for subsurface band application of poultry litter in plots where conventional field equipment such as a tractor and trailing implement cannot be used. A cantilever beam was mounted to the forklift and the trencher was attached to the end of the beam. The forklift was upslope or downslope from the plots and the forklift traveled parallel to the lengths of the trenches that were formed, so it was not necessary for a vehicle to traverse the pits. The method was used for subsurface band application of broiler litter in rainfall simulation plots which had a pit on each side of each plot. The pits enabled installation of wick and zero-tension pan lysimeters beneath the plots. The method worked well for making trenches in plots in this field experiment. Broiler litter was applied in the trenches and the experiment investigated phosphorus and nitrogen in runoff and leachate during rainfall simulation.

The Characteristics of Runoff and Sediment Yield in Different Land Use Types in Southwest Mountains of Henan Province

By indoor artificial rainfall simulator and slope plot test, the regularity of runoff and sediment yield of five types top soil— timber forest, shrubby grassland, terrace, slope cropland and waste-grassland under six kinds of rainfall intensity were studied in Danjiangkou Reservoir on southwest mountains of Henan Province to provide a scientific basis for comprehensive control of regional soil and water loss, to ensure the safety of water quality in the reservoir. The conclusions were that: (1) Land use types had less influence on the runoff comparing to sediment yield. (2) Sediment yield had obvious power function relationship with the runoff amount. (3) Bed load took up majority in the sediment yield of farmland soil while the bed load almost equaled to the value of silt load in woodland soil.

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

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

Comparative measurements with seven rainfall simulators on uniform bare fallow land

To assess the inflfl uence of rainfall simulator type and plot dimensions on runoff and erosion, seven small portable rainfall simulators from Freiberg, Tubingen, Trier (all Germany), Valencia, Zaragoza (both Spain), Basel (Switzerland) and Wageningen (the Netherlands) were compared on a prepared bare fallow fifi eld. The experiments were carried out during an international rainfall simulator workshop, organized at Trier University (Germany) from 30th of June to 1st of July 2011.The tested rainfall simulators differ in design, rainfall intensities, rain spectra, etc. and represent most of the devices which have been used over the last decade in Europe. The plots for the different rainfall simulators were selected as similar as possible concerning soil physical and chemical properties, aspect and inclination and were chosen to be placed side by side in horizontal direction. Test procedure was standardized in order to examine the inflfl uence of the rainfall simulator andplot dimension only. The results show a clear and consistent relationship in runoff, erosion and infifi ltration behaviour of the different used rainfall simulators. With all the devices total soil loss is measurable, but different plot sizes, intensities and kinetic energies of the simulated rainfall caused differences in soil loss and runoff quantities per unit of area. Regarding course characteristics over runs, similarities could be observed especially in runoff behaviour. The rainfall simulators (> 1 m² plot size) are able to reproduce infifi ltration and interrillerosion processes. With an increase of plot size (≥ 1 m²), rill-erosion will be also reflfl ected. Therefore it can be concluded that up to a certain plot size, the results of the different simulators are comparable and depend in their magnitude on the properties of the applied rainfall. The increase in process complexity with increasing plot size shows, that the scale of the simulation is one of the most important parameters to be taken intoaccount when comparing values of erosion and runoff.

Riparian Grazing Impacts on Streambank Erosion and Phosphorus Loss Via Surface Runoff1

Tufekcioglu, Mustafa, Richard C. Schultz, George N. Zaimes, Thomas M. Isenhart, and Aydin Tufekcioglu, 2012. Riparian Grazing Impacts on Streambank Erosion and Phosphorus Loss via Surface Runoff. Journal of the American Water Resources Association (JAWRA) 1‐11. DOI: 10.1111/j.1752‐1688.2012.12004.xAbstract: Surface runoff is one of the major pathways of sediment and phosphorus (P) transport to surface waters. Rainfall simulations were conducted on nine grazed pasture sites with different stocking rates in three different Iowa (United States) regions. The purpose of the simulations was to determine the impacts of cattle grazing on the amounts of sediment and P in surface runoff within a 15‐m wide strip on both sides of the stream from different source areas (SAs). These riparian SAs included stream‐side loafing areas, cattle streambank access paths to the stream, and the other vegetated areas adjacent to the streambanks. The runoff samples collected during the simulations were analyzed for suspended sediment (SS) and total phosphorus (TP). Soil bulk density and antecedent soil moisture samples were collected around the rainfall simulation plots to identify differences in compaction, infiltration, and surface runoff among the SAs. SS and TP losses from access paths and loafing areas within the 15‐m wide strips accounted for up to 72 and 55% of the total losses, respectively, even though they accounted for only 2.7% of the total area within the 15‐m wide strips. This suggests that access paths and loafing areas require special attention to mitigate the impacts of cattle on stream water pollution. Significant correlations were found between stocking rates and both SS and TP losses suggesting that low stocking rates can reduce sediment and P export to streams from the SAs.

The effects of fuel reduction treatments on runoff, infiltration and erosion in two shrubland areas in the north of Spain

The immediate effects of prescribed burning, shrub clearing and shrub mastication on runoff, infiltration and erosion were evaluated in two contrasting shrubland areas in northern Spain. Rainfall simulations (67mmh(-1) for 30min) were conducted immediately after fuel reduction treatments in each runoff plot. Compared to shrub mastication and shrub clearing, prescribed burning generated the lowest infiltration rate and highest runoff and erosion rates at both study sites. However, sediment yields measured immediately after treatments were low in all cases, from 0.31 to 2.22gm(-2) after shrub clearing, 0.40-1.63gm(-2) after shrub mastication and 2.30-8.11gm(-2) after prescribed burning. Slope, type of fuel reduction treatment and the depth and cover of the soil organic layer remaining after treatment were the most important variables determining runoff and erosion during the first rainfall event following treatment. In the rainfall simulation plots subjected to prescribed burning, the maximum temperatures reached at the organic layer/mineral soil interface during burning also had a significant effect on soil loss. The findings show that good fuel management prescriptions make fire hazard reduction and soil conservation compatible in cases where the remaining soil cover is about 70%.

Comparison of roughness models to simulate overland flow and tracer transport experiments under simulated rainfall at plot scale

The Saint-Venant equations have consistently proved capable of accurately simulating hydrographs at plot scale. However, recent works showed that even though the hydrograph is satisfyingly reproduced, the flow velocity field within the plot might be wrong, with the highest velocity largely underestimated. Moreover, the choice of roughness models to be used in the Saint-Venant equations is most often done in the purpose of increasing the hydrograph quality, while the actual travel time of water is ignored. This paper presents a tracer experiment made on a 10-m by 4-m rainfall simulation plot, where travel time and tracer mass recovery as well as local flow velocity have been measured. Four roughness models are tested: (i) Darcy-Weisbach's model, (ii) Lawrence's model, (iii) Manning's model with a constant roughness coefficient, and (iv) Manning's model with a variable roughness coefficient which decreases as a power law of the runoff water depth. Models with a constant friction factor largely underestimate high velocities. Moreover, they are not able to simulate tracer travel-times. Lawrence's model correctly simulates low and high velocities as well as tracer breakthrough curves. However, a specific set of parameters are required for each breakthrough curve from the same experiment. The best results are obtained with the Manning's model with a water-depth dependent roughness coefficient: simulated velocities are consistent with measurements, and a single set of parameters captures the entire set of breakthrough curves, as well as tracer mass recovery. The study reported here brings the following findings: (i) roughness coefficient is flow-dependent, (ii) faithful simulation of the velocity fields does not imply a good prediction of travel time and mass recovery, (iii) the best model is a Manning type model with a roughness coefficient which decreases as a power law of water depth. The full dataset used in this work is available on request. It can be used as benchmark for overland flow and transport models.

Fine gravel controls hydrologic and erodibility responses to trampling disturbance for coarse-textured soils with weak cyanobacterial crusts

We compared short-term effects of lug-soled boot trampling disturbance on water infiltration and soil erodibility on coarse-textured soils covered by a mixture of fine gravel and coarse sand over weak cyanobacterially-dominated biological soil crusts. Trampling significantly reduced final infiltration rate and total infiltration and increased sediment generation from small (0.5 m2) rainfall simulation plots (p < 0.01). Trampling had no effect on time to runoff or time to peak runoff. Trampling had similar effects at sites with both low and very low levels of cyanobacterial biomass, as indicated by chlorophyll a concentrations. We concluded that trampling effects are relatively independent of differences in the relatively low levels of cyanobacterial biomass in this environment. Instead, trampling appears to reduce infiltration by significantly reducing the cover of gravel and coarse sand on the soil surface, facilitating the development of a physical crust during rainfall events. The results of this study underscore the importance of carefully characterizing both soil physical and biological properties to understand how disturbance affects ecosystem processes.

The role of soil surface conditions in regulating runoff and erosion processes on a metamorphic hillslope (Southern Spain)

Abstract This study presents the results of an analysis into the role of soil surface conditions in the regulation of soil hydrology and erosive processes at one hillslope under dry Mediterranean climatic conditions. The methodology was based on the analysis of hillslope surface components and their hydrological and erosive function on a patch to scale by means of rainfall simulation and experimental plots. The results showed the existence of a complex eco-geomorphological system composed of a multitude of vegetation patches distributed at random on the hillslope, and where the presence of different surface conditions on the soil can have a sizeable influence on hydrological and erosive behavior. From the hydrological point of view, the runoff generation mechanisms follow a seasonal pattern depending on the moisture of the soil with a different spatial condition, with frequent hydrological disconnections between parts of the hillslope, as in other Mediterranean mountainous regions. Soil surface rock fragments, the layout of tussocks intra-hillslope and previous soil moisture as dynamic control factors in the hydrological and erosive processes are all important.

Assessing dominant factors affecting soil erosion using a portable rainfall simulator

Investigating the causes of soil erosion is difficult in natural conditions owing to the presence of other factors. Without simplifying the experimental conditions, studying soil behavior with its numerous parameters while considering factors such as vegetation cover, topography, and rainfall is difficult and in most conditions impossible. The application of simulation approaches is therefore necessary to simplify the prototype. In this research, the effects of physical soil factors such as texture and antecedent soil moisture, along with land slope and vegetation cover were evaluated in the Taleghan watershed, Iran, using a rainfall simulator and soil erosion plots. For this purpose, a 89 u 120 cm rainfall simulator producing 24.5 and 32 mm/h rainfall intensities of 30 min duration, as a common condition of the study area, was used at 144 locations over soil erosion plots with dimensions of 95 u 125 cm. Plots had slope classes of 12–20 and 20–30 %, different soil textures, different antecedent soil moistures, and medium to poor vegetation cover conditions. It was found that for 24.5 and 32 mm/h rainfall intensities, the sediment yield had high correlations of −0.771 and −0.796 with vegetation cover and slight correlations of 0.045 and 0.029 with land slope respectively. Regression equations for predicting the sediment yield were also developed for different conditions.

Evaluation of pollutant build-up and wash-off from selected land uses at the Port of Brisbane, Australia

The quality of stormwater runoff from seaports can be an important source of pollution to the marine environment. Currently, little knowledge exists with regards to the pollutant generation capacity specific to seaports as they do not necessarily compare well with conventional urban land use. The research project focussed on the assessment of pollutant build-up and wash-off. The study was undertaken using rainfall simulation and small impervious plots for different port land uses with the results obtained compared to typical urban land uses. The study outcomes confirmed that the Port land uses exhibit comparatively lower pollutant concentrations. However, the pollutant characteristics varied across different land uses. Hence, the provision of stereotypical water quality improvement measures could be of limited value. Particle size <150 μm was predominant in suspended solids. Therefore, if suspended solids are targeted as the surrogate parameter for water quality improvement, this particle size range needs to be removed.

Immediate effects of prescribed burning, chopping and clearing on runoff, infiltration and erosion in a shrubland area in Galicia (NW Spain)

AbstractThe immediate effects of three different fuel management treatments on runoff, infiltration and erosion were evaluated in a mixed heathland in Galicia (NW Spain). The treatments compared were: prescribed burning, shrub chopping and shrub clearing.Rainfall simulations were conducted immediately before and after fuel reduction treatments. A rainfall rate of 67 mm h−1 was applied for 30 min to each runoff plot.Application of treatments significantly affected runoff and infiltration, but the parameter most affected by treatment was soil erosion, especially after prescribed burning. However, sediment yields measured immediately after treatments were low in all the cases, varying from 32 kg ha−1 after shrub clearing to 248 kg ha−1 after prescribed burning. In the rainfall simulation plots subjected to prescribed burning, the maximum temperatures reached at mineral soil surface during burns significantly affected soil losses. The organic layer remaining after treatments and soil moisture contents appeared to be critical variables in controlling runoff and erosion during the first rainfall event following fuel reduction treatments. When the remaining organic layer was removed just after treatments and a new rainfall simulation was carried out, mean infiltration rate trended to decrease and cumulative runoff and sediment yield tended to increase.The above information could be useful for determining whether fuel management prescriptions are compatible with fire hazard reduction and soil conservation. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Large-Scale Rainfall Simulation Experiments on Juniper Rangelands

The effects of shrub clearing on surface and subsurface water movement in the Edwards Aquifer region were investigated using two large-scale rainfall simulation plots. Multiple replications of a large (168 mm) rainfall event were applied at an ashe juniper covered plot before and after shrub removal and at a plot with longstanding herbaceous cover. The study sites were equipped for monitoring of throughfall, stemflow, surface runoff, and soil water. Lateral subsurface flow was measured in a trench at the downhill end of each plot. The canopy plot produced high lateral subsurface flow during rainfall but no surface runoff, even for high rainfall intensities. In contrast, hydrologic response at the inter-canopy plot was dominated by rapid surface runoff. Following shrub removal at the canopy plot, water movement beyond the soil layer increased due to reduced canopy interception. Soil water storage capacity at the shrub plot remained small for both conditions, with much water apparently bypassing the litter and soil layers via macropore pathways. This additional water could move off site as macropore flow or remain on site as matrix and conduit storage. Differences in surface runoff and subsurfaceflow are attributable to vegetation and geologic differences.