Surface Depression Storage Research Articles

Effect of microrelief features of tillage methods under different rainfall intensities on runoff and soil erosion in slopes

Tillage methods play a crucial role in controlling rainwater partitioning and soil erosion. This study utilized rainfall simulation experiments to investigate the impact of four tillage methods (manual digging (MD), manual hoeing (MH), traditional ploughing (TP), and ridged ploughing (RP)) on runoff and soil erosion at the plot scale. The smooth slope (SS) was used as a benchmark. Rainfall intensities of 30, 60, 90, and 120 mm h−1 were considered. The study revealed that tillage altered rainwater distribution into depression storage, infiltration, and runoff. Tillage reduces runoff and increases infiltration. The four tillage methods (30–73%) increased the proportion of rainwater converted to infiltration to varying degrees compared to the SS (22–53%). Microrelief features influenced the role of tillage methods in soil erosion. Surface roughness and depression storage accounted for 79% of the variation in sediment yield. The four tillage methods reduced runoff by 2.1–64.7% and sediment yield by 2.5–77.2%. Moreover, increased rainfall intensity weakens the ability of tillage to control soil erosion. When rainfall intensity increased to 120 mm h−1, there was no significant difference in runoff yield among RP, TP, MH, and SS. Therefore, assessing the effectiveness of tillage in reducing soil erosion should consider changes in rainfall intensity. Additionally, the cover management (C) factor of the RUSLE was used to assess the effects of different tillage methods on soil loss. Overall, the C factor values for tilled slopes are in the order MH > TP > RP > MD with a range of 0.23–0.97. As the surface roughness increases, the C factor tends to decrease, and the two are exponential functions (R2 = 0.86). These studies contribute to our understanding of how different tillage methods impact runoff and soil erosion in sloped farmland and provide guidance for selecting appropriate local manual tillage methods.

Topographic hydro-conditioning to resolve surface depression storage and ponding in a fully distributed hydrologic model

Land surface depressions play a central role in the transformation of rainfall to ponding, infiltration and runoff, yet digital elevation models (DEMs) used by spatially distributed hydrologic models that resolve land surface processes rarely capture land surface depressions at spatial scales relevant to this transformation. Methods to generate DEMs through processing of remote sensing data, such as optical and light detection and ranging (LiDAR) have favored surfaces without depressions to avoid adverse slopes that are problematic for many hydrologic routing methods. Here we present a new topographic conditioning workflow, Depression-Preserved DEM Processing (D2P) algorithm, which is designed to preserve physically meaningful surface depressions for depression-integrated and efficient hydrologic modeling. D2P includes several features: (1) an adaptive screening interval for delineation of depressions, (2) the ability to filter out anthropogenic land surface features (e.g., bridges), (3) the ability to blend river smoothing (e.g., a general downslope profile) and depression resolving functionality. From a case study in the Goodwin Creek Experimental Watershed, D2P successfully resolved 86% of the ponds at a DEM resolution of 10 m. Topographic conditioning was achieved with minimum impact as D2P reduced the number of modified cells from the original DEM by 51% compared to a conventional algorithm. Furthermore, hydrologic simulation using a D2P processed DEM resulted in a more robust characterization on surface water dynamics based on higher surface water storage as well as an attenuated and delayed peak streamflow.

Identification and Quantification of Surface Depressions on Grassy Land Surfaces of Different Topographic Attributes Using High-Resolution Terrestrial Laser Scanning Point Cloud and Triangulated Irregular Network

The objective of this study was to identify and quantify surface depressions on grass-covered land surfaces using a high-resolution terrestrial laser scanning (TLS) point cloud, and a triangulated irregular network (TIN). The entire grassy land surface in the study area was divided into five subwatersheds of different topographic attributes (i.e., depression depth and surface slope). Surface depressions were identified and quantified using a TIN generated from a high-resolution TLS point cloud. The results indicated that microtopography of the grassy land surface was well-characterized within each subwatershed in comparison with field observations. With the terrestrial light detection and ranging (LIDAR) point cloud of 15-mm point spacing and the TIN method, surface depression storage depths of the five subwatersheds ranged from 1.73 to 14.28 mm in the study area. The surface depression storage depth, as expected, increased with the maximum depth of surface depression. It was also found to increase when the land surface slope became milder. A sensitivity analysis indicated that a point cloud with a point spacing of 30 mm was sufficient to obtain an accurate representation of the terrain surface in the study area. This study also indicated the TIN method can represent the ground surface and the surface depression more realistically than the commonly used digital elevation model (DEM) method due to the TIN method’s higher capability of identifying and filtering out surface obstructions such as blades of grass. Moreover, by using the high-resolution TLS technology and the TIN method, our study provides an important and broad range of reference data on the surface depression storage depth commonly needed in application of the Storm Water Management Model (SWMM) and other watershed models.

The Impact of Soil Acidity in Soil and Water Conservation and the Current Practices of Soil and Water Conservation Response to Acid Affected Soils in Ethiopia: A Review

Land degradation is a global negative environmental process that causes the decline in the productivity of land resources’ capacity to perform their functions. Ethiopia has an experience long term in soil and water conservation efforts since1970s and it has established six national Ethiopian Soil Conservation Research Programs were initiated in 1981 and their focus over agro-ecology, land physiographic, climate and farming system but not considerable soil mechanics, hydraulic and geotechnical processes. Agronomic or biological measures are in helping to minimize the soil erosion by increasing soil surface cover, surface roughness, and surface depression storage, soil infiltration and decapitating potential and kinetic energy. In acid affected soil, before installed biological or agronomic soil and water conservation measures should be identified suitable technologies or recommendation either acid soil tolerant or reclaim the soils. Biological soil and water conservation and soil management measure more rehabilitee acid affected soils than physical soil and water conservation due to addition of bio mass, resulting decomposition improve soil structure, aeration, apparition infiltration ultimate reduction of soil erosion functions . Keywords: soil acidity, soil and water conservation DOI: 10.7176/JRDM/86-02 Publication date: June 30 th 2022

Estimation of surface depression storage capacity from random roughness and slope

Depression storage capacity (DSC) models found in the literature were developed using statistical regression for relatively large soil surface roughness and slope values resulting in several fitting parameters. In this research, we developed and tested a conceptual model to estimate surface depression storage having small roughness values usually encountered in rainwater harvesting micro-catchments and bare soil in arid regions with only one fitting parameter. Laboratory impermeable surfaces of 30 x 30 cm2 were constructed with 4 sizes of gravel and mortar resulting in random roughness values ranging from 0.9 to 6.3 mm. A series of laboratory experiments were conducted under 9 slope values using simulated rain. Depression storage for each combination of relative roughness and slope was estimated by the mass balance approach. Analysis of experimental results indicated that the developed linear model between DSC and the square root of the ratio of random roughness (RR) to slope was significant at p < 0.001 and coefficient of determination R2 = 0.90. The developed model predicted depression storage of small relief at higher accuracy compared to other models found in the literature. However, the model is based on small-scale laboratory plots and further testing in the field will provide more insight for practical applications.

Surface Depression and Wetland Water Storage Improves Major River Basin Hydrologic Predictions.

Surface water storage in small yet abundant landscape depressions—including wetlands and other small waterbodies—is largely disregarded in conventional hydrologic modeling practices. No quantitative evidence exists of how their exclusion may lead to potentially inaccurate model projections and understanding of hydrologic dynamics across the world’s major river basins. To fill this knowledge gap, we developed the first-ever major river basin-scale modeling approach integrating surface depressions and focusing on the 450,000-km2 Upper Mississippi River Basin (UMRB) in the United States. We applied a novel topography-based algorithm to estimate areas and volumes of ~455,000 surface depressions (>1 ha) across the UMRB (in addition to lakes and reservoirs) and subsequently aggregated their effects per subbasin. Compared to a “no depression” conventional model, our depression-integrated model (a) improved streamflow simulation accuracy with increasing upstream abundance of depression storage, (b) significantly altered the spatial patterns and magnitudes of water yields across 315,000 km2 (70%) of the basin area, and (c) provided realistic spatial distributions of rootzone wetness conditions corresponding to satellite-based data. Results further suggest that storage capacity (i.e., volume) alone does not fully explain depressions’ cumulative effects on landscape hydrologic responses. Local (i.e., subbasin level) climatic and geophysical drivers and downstream flowpath-regulating structures (e.g., reservoirs and dams) influence the extent to which depression storage volume in a subbasin causes hydrologic effects. With these new insights, our study supports the integration of surface depression storage and thereby catalyzes a reassessment of current hydrological modeling and management practices for basin-scale studies.

Terrestrial laser scanning data combined with 3D hydrological modeling decipher the role of tillage in field water balance and runoff generation

Soil tillage is an anthropogenic factor affecting hydrological processes in agricultural fields. To demonstrate a novel method for increasing mechanistic understanding of the tillage impacts, we combined a process-based three-dimensional (3D) hydrological model with terrestrial laser scanning (TLS) data. This study aimed to (1) exploit high-resolution TLS data to estimate soil surface depression storage (SSDS) and roughness after different soil tillage operations (ploughing, harrowing vs direct drilling) on a heavy clay soil, (2) combine the estimates of SSDS and roughness with a 3D hydrological model to demonstrate the potential of the method in analyzing hydrological impacts of tillage, and (3) evaluate the value and uncertainties in coupling spatial microtopographical data and process-based modeling. The SSDS values showed low mean (0.3–2.9 mm) and rare high values (>5 mm) with clearly the highest variation of SSDS and roughness values in the ploughed conditions. These tillage impacts were reflected in the amounts of surface layer runoff (max. increase 23% due to the SSDS and roughness changes) and drain discharge (max. decrease 8%). The impact on other water balance components was negligible, and factors such as drainage methods and terrain slope were shown to have more control on the water balance. The tillage impacts had also a clear effect on peak surface runoff values. Most (99%) of the hydrological changes were caused by the SSDS variation whereas the roughness had a minor role. The simulations showed that tillage-induced long-term changes on soil hydraulic properties (such as conductivity and macroporosity), which were not detected by the TLS data, can have a high impact on surface layer runoff generation, as these tillage-impacts increased runoff by 25%. While the simulations showed how the various hydrological impacts of tillage can be discerned, a more comprehensive assessment would require more data derived from several sites and tillage conditions.

Depression threshold control proxy to improve HEC-HMS modeling of depression-dominated watersheds

ABSTRACTMany hydrologic models utilize delineation results from traditional methods which create a hydrologically connected drainage system. In depression-dominated areas, topographic characteristics of depressions are vital to modeling unique hydrologic processes associated with puddle-to-puddle (P2P) filling-spilling dynamics. The objective of this study is to evaluate the impacts of the P2P processes and dynamic changes in contributing area on outlet discharge. To do so, an improved HEC-HMS model is developed by incorporating a depression threshold control proxy (DTCP) and an improved conceptual framework. The DTCP uses a storage–discharge function to simulate the P2P dynamics. The improved conceptual framework counteracts the effect of full hydrologic connectivity created by traditional delineation methods by introducing depressional and non-depressional areas to each sub-basin. Application of the improved HEC-HMS model demonstrated that it was capable of accurately simulating outlet discharge and providing the details on surface connectivity and depression storage.

Fall Tillage Reduced Nutrient Loads from Liquid Manure Application during the Freezing Season.

Reducing agricultural runoff is important year round, particularly on landscapes that receive wintertime applications of manure. No-tillage systems are typically associated with reduced runoff loads during the growing season, but surface roughness from fall tillage may aid infiltration on frozen soils by providing surface depressional storage. The timing of winter manure applications may also affect runoff, depending on snow and soil frost conditions. Therefore, the objective of this study was to evaluate runoff and nutrient loads during the freezing season from combinations of tillage and manure application timings. Six management treatments were tested in south-central Wisconsin during the winters of 2015-2016 and 2016-2017 with a complete factorial design: two tillage treatments (fall chisel plow vs. no-tillage) and three manure application timings (early December, late January, and unmanured). Nutrient loads from winter manure application were lower on chisel-plowed versus untilled soils during both monitoring years. Loads were also lower from manure applied to soils with less frost development. Wintertime manure applications pose a risk of surface nutrient losses, but fall tillage and timing applications to thawed soils can help reduce loads.

Rainwater harvesting capacity of soils subjected to reservoir tillage during rainfall on the Loess Plateau of China

Soil rainwater harvesting (SRWH) is an important process in rainfed farming areas. Improving the capacity for SRWH via tillage is essential in many parts of the world. In recent years, reservoir tillage (RT) has attracted attention because it was said that RT contributes to SRWH. The objectives of this study were to measure the cumulative soil-harvested rainwater (SHR) of slopes subjected to RT and to evaluate the contribution of RT to SRWH under different rainfall conditions. A smooth surface (SS) served as a control surface. Three slope degrees (5°, 15° and 25°) were subjected to low and heavy (60 and 120 mm/h) and long-term rainfall (90 min). The results showed that the cumulative SHR decreased to different extents under different rainfall intensities as the slope degree increased. On the gentle slope (5°) and under low rainfall intensity (60 mm/h), no significant differences in cumulative SHR were detected between the RT and SS treatments, whereas significant differences in cumulative SHR were detected between them on the steep slopes (15° and 25°) and under high rainfall intensity (120 mm/h). The differences in cumulative SHR among the different conditions occurred because the contribution of RT to SRWH varied as the soil surface properties changed (especially as surface depression storage decreased due to sediment deposition) under the conditions of long-term rainfall. For example, on the 5° slope at a rainfall intensity of 120 mm/h, the contribution of RT to SRWH was 18.58% during the 0-30-min rainfall stage but -14.84% during the 60–90-min stage, resulting in nearly equal cumulative SHR values between the RT slope and the SS slope. Our results suggest that RT is not necessary contribute to SRWH in all cases.

An Improved Method to Estimate Soil Hydrodynamic and Hydraulic Roughness Parameters by Using Easily Measurable Data During Flood Irrigation Experiments and Inverse Modelling

Surface irrigation is known as a highly water-consuming system and needs to be optimized to save water. Models can be used for this purpose but require soil parameters at the field scale. This paper aims to estimate effective soil parameters by combining: (i) a surface flow-infiltration model, namely CALHY; (ii) an automatic fitting algorithm based on the SIMPLEX method; and (iii) easily accessible and measurable data, some of which had never been used in such a process, thus minimizing parameter estimation errors. The validation of the proposed approach was performed through three successive steps: (1) examine the physical meaning of the fitted parameters; (2) verify the accuracy of the proposed approach using data that had not been served in the fitting process; and (3) validate using data obtained from independent irrigation events. Three parameters were estimated with a low uncertainty: the saturated hydraulic conductivity Ks, the hydraulic roughness k, and the soil water depletion ∆θ. The estimation uncertainty of the soil surface depressional storage parameter H0 was of the same order of magnitude of its value. All experimental datasets were simulated very well. Performance criteria were similar during both the fitting and validation stages.

The effects of initial soil moisture conditions on swale flow hydrographs

AbstractThe effects of soil water content (SWC) on the formation of run‐off in grass swales draining into a storm sewer system were studied in two 30‐m test swales with trapezoidal cross sections. Swale 1 was built in a loamy fine‐sand soil, on a slope of 1.5%, and Swale 2 was built in a sandy loam soil, on a slope of 0.7%. In experimental runs, the swales were irrigated with 2 flow rates reproducing run‐off from block rainfalls with intensities approximately corresponding to 2‐month and 3‐year events. Run‐off experiments were conducted for initial SWC (SWCini) ranging from 0.18 to 0.43 m3/m3. For low SWCini, the run‐off volume was greatly reduced by up to 82%, but at high SWCini, the volume reduction was as low as 15%. The relative swale flow volume reductions decreased with increasing SWCini and, for the conditions studied, indicated a transition of the dominating swale functions from run‐off dissipation to conveyance. Run‐off flow peaks were reduced proportionally to the flow volume reductions, in the range from 4% to 55%. The swale outflow hydrograph lag times varied from 5 to 15 min, with the high values corresponding to low SWCini. Analysis of swale inflow/outflow hydrographs for high SWCini allowed estimations of the saturated hydraulic conductivities as 3.27 and 4.84 cm/hr in Swales 1 and 2, respectively. Such estimates differed from averages (N = 9) of double‐ring infiltrometer measurements (9.41 and 1.78 cm/hr). Irregularities in swale bottom slopes created bottom surface depression storage of 0.35 and 0.61 m3 for Swales 1 and 2, respectively, and functioned similarly as check berms contributing to run‐off attenuation. The experimental findings offer implications for drainage swale planning and design: (a) SWCini strongly affect swale functioning in run‐off dissipation and conveyance during the early phase of run‐off, which is particularly important for design storms and their antecedent moisture conditions, and (b) concerning the longevity of swale operation, Swale 1 remains fully functional even after almost 60 years of operation, as judged from its attractive appearance, good infiltration rates (3.27 cm/hr), and high flow capacity.

Effect of soil surface roughness on infiltration water, ponding and runoff on tilled soils under rainfall simulation experiments

Agriculture has a large effect on the properties of the soil and with that on soil hydrology. The partitioning of rainfall into infiltration and runoff is relevant to understand runoff generation, infiltration and soil erosion. Tillage manages soil surface properties and generates soil surface roughness (SSR) that affects the partitioning of the rainfall. The objective of this study was to quantify the amount of rainwater that infiltrates, is temporarily stored in surface depressions and flows out of the surfaces during rainfall events. A set of tillage-induced rough surfaces with slope steepness of 10° and 15° was used under simulated rainfall, and a smooth surface served as a control. Rainfall intensities were 60 and 120 mm h−1, and two soil erosion periods, overland flow erosion period (OFEP) and rill flow erosion period (RFEP), were monitored for each rainfall intensity. The results showed that for OFEP, infiltration water was 58% and 76% of the total rainwater on the rough surfaces and was approximately 1.5 and 2 times greater than that on the smooth surfaces for the different rainfall intensities. The surface runoff was consistently small for the OFEP but significantly increased for the RFEP. For example, for the RFEP, the amount of surface runoff was up to 78.66% of the total rainwater on the rough surfaces under rainfall of 120 mm h−1 in intensity. The amount of rainwater stored in surface depressions was significantly less than infiltration water and surface runoff for all conditions. The mean transformation ratio of rainwater into surface depression storage, infiltration water and surface runoff in the OFEP and RFEP was 0.07:0.49:0.44 for the rough surfaces and 0.01:0.29:0.70 for the smooth surfaces. For the tilled surfaces, more than 50% of rainwater was be harvested through tillage technique during a rainfall event, whereas for the smooth surfaces, only 29% of rainwater. Our result will be useful when evaluating the impact of tillage on soil moisture content and even studying soil erosion in agriculture land.

How does DEM resolution affect microtopographic characteristics, hydrologic connectivity, and modelling of hydrologic processes?

AbstractThe resolution of a digital elevation model (DEM) is a crucial factor in watershed hydrologic and environmental modelling. DEM resolution can cause significant variability in the representation of surface topography, which further affects quantification of hydrologic connectivity and simulation of hydrologic processes. The objective of this study is to examine the effects of DEM resolution on (1) surface microtopographic characteristics, (2) hydrologic connectivity, and (3) the spatial and temporal variations of hydrologic processes. A puddle‐to‐puddle modelling system was utilized for surface delineation and modelling of the puddle‐to‐puddle overland flow dynamics, surface runoff, infiltration, and unsaturated flow for nine DEM resolution scenarios of a field plot surface. Comparisons of the nine modelling scenarios demonstrated that coarser DEM resolutions tended to eliminate topographic features, reduce surface depression storage, and strengthen hydrologic connectivity and surface runoff. We found that reduction in maximum depression storage and maximum ponding area was as high as 97.56% and 76.36%, respectively, as the DEM grid size increased from 2 to 80 cm. The paired t‐test and fractal analysis demonstrated the existence of a threshold DEM resolution (10 cm for the field plot), within which the DEM‐based hydrologic modelling was effective and acceptable. The effects of DEM resolution were further evaluated for a larger surface in the Prairie Pothole Region subjected to observed rainfall events. It was found that simulations based on coarser resolution DEMs (>10 m) tended to overestimate ponded areas and underestimate runoff discharge peaks. The simulated peak discharge from the Prairie Pothole Region surface reduced by approximately 50% as the DEM resolution changed from 2 to 90 m. Fractal analysis results elucidated scale dependency of hydrologic and topographic processes. In particular, scale analysis highlighted a unique constant–threshold–power relationship between DEM scale and topographic and hydrologic parameters/variables. Not only does this finding allow one to identify threshold DEM but also further develop functional relationships for scaling to achieve valid topographic characterization as well as effective and efficient hydrologic modelling. Copyright © 2016 John Wiley & Sons, Ltd.

Using photogrammetry to assess rutting caused by a forwarder—A comparison of different tires and bogie tracks

Rutting caused by heavy machinery during logging operations can lead to loss of trafficability which is a considerable problem in designated skid trail systems. Wide base tires and bogie tracks are common accepted technical options to minimize rut formation. In this work the suitability of 940mm super wide base tires on trafficability preservation was tested in comparison to 710mm wide base tires and common used ECO-TRACK™ bogie tracks. An experiment with repeated passes by a heavy forest machine (forwarder) was conducted. Digital elevation models (DEM) of the ruts were created using photogrammetry to assess rut morphology parameters: rut depth, material displacement and erosion relevant depression storage capacity. Photogrammetry was discovered to be a time and cost efficient method to provide highly resolved 3D-data with high precision. Super wide base tires distinctly reduced rut formation compared to 710mm tires and bogie tracks by more than 50% and 40%, respectively. Displacement of soil material led to the formation of prominent bulges that can be prone to erosion. 710mm tires and bogie tracks caused the most voluminous bulges due to their strong rut formation. The investigated tire equipment differently affected the surface depression storage of water in the skid trails due to their different lug morphology. Ruts of bogie tracks could retain significantly more surface water than ruts produced by tires. Nonetheless, the absolute depression storage in all cases is rather low, implying that erosion would occur in case of heavy precipitation.

Evaluation of 2D models for the prediction of surface depression storage using realistic reference values

AbstractDepression storage (DS) is the maximum storage of precipitation and runoff in the soil surface at a given slope. The DS is determined by soil roughness that in agricultural soils is largely affected by tillage. The direct measurement of DS is not straightforward because of the natural permeability of the soil. Therefore, DS has generally been estimated from 2D/3D empirical relationships and numerical algorithms based on roughness indexes and height measurements of the soil surface, respectively. The objective of this work was to evaluate the performance of some 2D models for DS, using direct and reliable measurements of DS in an agricultural soil as reference values. The study was carried out in experimental microplots where DS was measured in six situations resulting from the combination of three types of tillage carried out parallel and perpendicular to the main slope. Those data were used as reference to evaluate four empirical models and a numerical method. Longitudinal altitudinal profiles of the relief were obtained by a laser profilometer. Infiltration measurements were carried out before and after tillage. The DS was largely affected by tillage and its direction. Highest values of DS are found on rougher surfaces mainly when macroforms cut off the dominant slope. The empirical models had a limited performance while the numerical method was the most effective, even so, with an important variability. In addition, a correct hydrological management should take into account that each type of soil tillage affects infiltration rate differently. Copyright © 2016 John Wiley & Sons, Ltd.

Impact of DEM Resolution on Puddle Characterization: Comparison of Different Surfaces and Methods

DEM-based topographic characterization and quantification of surface depression storage are critical to hydrologic and environmental modeling. Mixed conclusions have been obtained from previous studies on the relationship between maximum depression storage (MDS) and DEM grid spacing, which is affected by different factors, such as topographic characteristics, surface delineation methods and DEM interpolation/aggregation methods. The objective of this study was to evaluate the effects of DEM resolution on topographic characterization with the consideration of these three factors. Twenty-three topographic surfaces (including ideal surfaces, laboratory-scale soil surfaces and watershed-scale land surfaces) were selected, and five software packages, ArcHydro, PCRaster, HEC-GeoHMS, TauDEM and PD (puddle delineation), were used for surface delineation. Our results indicated that MDS, maximum ponding area (MPA) and the number of puddles (NP) decreased with increasing grid spacing for most smoother surfaces due to the loss of topographic detail. For most rough surfaces (e.g., mountain-type surfaces with significant variations in surface elevations), however, the changing patterns of MDS and MPA varied with an increase in grid spacing mainly due to the unreal “artificial depressions/puddles” generated during the interpolation/aggregation process. This study emphasizes the importance of topographic characteristics, DEM resolution and surface delineation methods.

Effects of Climate and Land Cover on Hydrology in the Southeastern U.S.: Potential Impacts on Watershed Planning

AbstractThe hydrologic response to statistically downscaled general circulation model simulations of daily surface climate and land cover through 2099 was assessed for the Apalachicola‐Chattahoochee‐Flint River Basin located in the southeastern United States. Projections of climate, urbanization, vegetation, and surface‐depression storage capacity were used as inputs to the Precipitation‐Runoff Modeling System to simulate projected impacts on hydrologic response. Surface runoff substantially increased when land cover change was applied. However, once the surface depression storage was added to mitigate the land cover change and increases of surface runoff (due to urbanization), the groundwater flow component then increased. For hydrologic studies that include projections of land cover change (urbanization in particular), any analysis of runoff beyond the change in total runoff should include effects of stormwater management practices as these features affect flow timing and magnitude and may be useful in mitigating land cover change impacts on streamflow. Potential changes in water availability and how biota may respond to changes in flow regime in response to climate and land cover change may prove challenging for managers attempting to balance the needs of future development and the environment. However, these models are still useful for assessing the relative impacts of climate and land cover change and for evaluating tradeoffs when managing to mitigate different stressors.

Measurements of the initiation of post‐wildfire runoff during rainstorms using in situ overland flow detectors

AbstractOverland flow detectors (OFDs) were deployed in 2012 on a hillslope burned by the 2010 Fourmile Canyon fire near Boulder, Colorado, USA. These detectors were simple, electrical resistor‐type instruments that output a voltage (0–2·5 V) and were designed to measure and record the time of runoff initiation, a signal proportional to water depth, and the runoff hydrograph during natural convective rainstorms.Initiation of runoff was found to be spatially complex and began at different times in different locations on the hillslope. Runoff started first at upstream detectors 56% of the time, at the mid‐stream detectors 6%, and at the downstream detectors 38% of the time. Initiation of post‐wildfire runoff depended on the time‐to‐ponding, travel time between points, and the time to fill surface depression storage. These times ranged from 0·5–54, 0·4–1·1, and 0·2–14 minutes, respectively, indicating the importance of the ponding process in controlling the initiation of runoff at this site. Time‐to‐ponding was modeled as a function of the rainfall acceleration (i.e. the rate of change of rainfall intensity) and either the cumulative rainfall at the start of runoff or the soil–water deficit.Measurements made by the OFDs provided physical insight into the spatial and temporal initiation of post‐wildfire runoff during unsteady flow in response to time varying natural rainfall. They also provided data that can be telemetered and used to determine critical input parameters for hydrologic rainfall–runoff models. Copyright © 2015 John Wiley & Sons, Ltd.

English

Contour ridging is a widely used soil and water conservation practice in Southern Africa. However, in recent years, a number of investigators questioned the effectiveness of contour ridges in controlling surface runoff and soil erosion from smallholder farmers’ fields. To be an effective conservation practice, contour ridges must store infiltration excess surface runoff as surface depression storage in furrows between the ridges. In this study, three experimental runoff plots were established in Chilindamaji and six in Kamundi watershed in Malawi. Of the six plots in Kamundi, three had agroforestry contour hedgerows (AF1, AF2, and AF3) and the other three (K1, K2, and K3) had no contour hedgerows. None of the Chilindamaji plots (C1, C2, and C3) had agroforestry contour hedgerows. Hydrologic response analysis of data obtained from the nine runoff plots revealed that plots that retained more water as infiltration and surface depression storage had less runoff and soil erosion. For both sites, the average soil loss rates for the bare, 50% residue cover, and the contour ridge plots were 115, 66, and 5 ton/ha/year. The average soil loss rates for the three agroforestry plots were 4.2 ton/ha/year. Our results show that 50% residue cover reduced soil loss as compared to a bare soil, but are not as effective as the contour ridge and the agroforestry contour hedgerow treatments in reducing surface runoff and soil loss.   Key words: Contour ridges, infiltration, runoff, soil loss, agroforestry, residue cover.