Volume Of Overland Flow Research Articles

Simulation-based modeling of urban waterlogging in Khulna City

Abstract Khulna City is extremely vulnerable to the effects of climate change. The city experiences frequent waterlogging during extreme rainfall events. This research prepared a drainage simulation model considering climate change issues for investigating the extent of waterlogging in the city. Watershed and precipitation were analyzed to examine the existing scenario of the study area. Finally, a Mike Urban-based hydrological simulation model was formulated to investigate the severity of waterlogging. As found by precipitation analysis, 180 mm, 346 mm, and 396 mm rainfall might occur for the 5-year, 50-year, and 100-year return period, respectively. This research identified that volume of overland flow might be affected by climate change-induced rainfall. According to the simulation, 62.52% of the study area was waterlogged with different inundation depths. It was found that traffic movements were severely disrupted and structures were hampered due to waterlogging. 45% paved, 77% brick soling, and 65% unpaved roads were inundated by different inundation levels. On the other hand, 61.1% of structures of the study area were affected by waterlogging. The findings of the research might help the concerned authority in decision-making, especially for the drainage and water-related issues, to solve the waterlogging.

Runoff processes and lateral transport of soil total carbon induced by water erosion in the hilly region of southern China under rainstorm conditions

Soil erosion by water destroys the physical protection of carbon in soil aggregates and accelerates decomposition, thus impacting soil organic carbon stocks and making the soil barren. Runoff process and lateral transport of soil total carbon were studied using sloping flumes in an artificial rainfall simulator. The flumes were filled with soil collected from the surface horizon, the underlying laterite horizon, and the deeper sand horizon, three portions of a weathered granite soil profile. The results showed that the initial runoff-yielding time was faster under large rainfall intensities and steep slope gradients. The runoff process on sand soil slopes showed a trend of increasing with the increase of rainfall duration, while the trend on surface soil slopes and laterite soil slopes were mainly increasing rapidly and then stable. The volume of overland flow on surface soil slopes was the largest under the same conditions, with an average value of 14,259 mL, while it was the smallest on sand soil slopes. There was no interflow on surface soil slopes, and the interflow curves of the sandy soil slopes and the laterite soil slopes were all single-peak curves. The TC concentration curves of overland flow on sand soil slopes presented a high initial concentration and were then decreasing to a stable state, but the trends on laterite soil slopes and surface soil slopes was not obvious. The TC concentration curves of interflow on sand soil slopes and laterite soil slopes were similar to those of the runoff process curves, and the TC concentration on laterite soil slopes peaked faster. The TC loss gross amount on sand soil slopes and laterite soil slopes was much larger than that on surface soil slopes. Sediment was the main carrier of TC on sandy soil slopes, which TC loss with sediment was more than 50% in each rainfall test. Runoff was the main carrier of TC on laterite soil slopes and surface soil slopes; TC loss with runoff was above 60% on surface soil slopes. At the same time, partial correlation coefficients showed that rainfall intensity was the most important factor affecting TC loss. The results can provide a calculation method and scientific basis for the estimation of the TC loss on weathered granite soil slopes in the south of China.

Water quality changes in a short-rotation woody crop riparian buffer

Converting riparian buffers in agricultural areas from annual row crops to short rotation woody crops (SRWCs) grown for biofuel can provide both water quality benefits and a financial incentive for buffer adoption among agricultural producers. A randomized complete block design was used to determine water quality changes resulting from converting plots previously cultivated in corn to SRWC willow (Salix. spp) adjacent to a stream in Storrs, CT. Both overland flow and ground water samples were analyzed for total nitrogen (TN) and total phosphorus (TP). Additionally, overland flow was analyzed for suspended solids concentration (SSC) and ground water samples were analyzed for nitrate + nitrite (NO2+NO3-N). Lower (p = 0.05) concentrations of TN (41%) and TP (53%) were observed in overland flow from willow plots than from corn plots. Shallow ground water concentrations at the edge of willow plots were lower in TN (56%) and NO3+NO2-N (64%), but 35% higher in TP, than at the edge of corn plots. SSC was also lower (71%) in overland flow associated with willow compared to corn. The treatment had no effect on the depth or volume of overland flow or mass export. The changes in concentrations resulting from conversion of corn to SRWC in a riparian buffer are similar to those observed in restored and established buffers.

Grazing strategies for reducing contaminant losses to water from forage crop fields grazed by cattle during winter

ABSTRACTA paired catchment study quantified fluxes of Nitrogen (N), Phosphorus (P), sediment and Escherichia coli (E. coli) in flow from fields where cattle were wintered on swede (Brassica napus) and kale (Brassica oleracea) crops. The effectiveness of a strategic grazing approach that protected critical source areas was evaluated to determine if these fluxes could be reduced. Reduced soil infiltration caused by cattle treading was a contributing factor to overland flow events that mostly occurred in the six to eight weeks following crop grazing. Estimated annual fluxes of contaminants in overland flow ranged up to 27, 3.8 and 3740 kg ha−1 for N, P and sediment, respectively, and up to 4.3 × 1010 MPN ha−1 for E. coli. Strategic grazing significantly reduced overland flow volumes compared to standard grazing practice, reducing contaminant fluxes to levels similar to those observed when the catchments were returned to pasture and lightly grazed by sheep.

Overland flow directs soil moisture and ecosystem processes at patch scale in Mediterranean restored hillslopes

Semiarid and arid environments are frequently structured in vegetation patches that heterogeneously distribute water resources (water runoff and soil moisture). This redistribution is interrelated with episodes of rainfall triggering pulses of plant growth according to the Trigger–Transfer–Reserve–Pulse (TTRP) model. Spatial heterogeneity in the hydrological behaviour of surface patches has been described in Mediterranean mining restored hillslopes. Nevertheless studies describing the interactions of this hydrological heterogeneity with ecological processes on restored environments are lacking. This study investigates the relationships between overland flow running at hillslope scale and ecosystem processes at patch scale in restored hillslopes. We selected three approximately 20year old restored hillslopes along a gradient of overland flow (hillslope runoff coefficients are 15.9%, 2.2% and 0.3% for the three experimental hillslopes). We studied environmental conditions describing the ecohydrological interactions under the TTRP approach for arid and semiarid environments. Our results indicate that in restored hillslopes: 1) soil moisture content was associated to the type of vegetation patches; 2) higher soil water content enhanced vegetation diversity and soil properties, improving vegetation performance and colonization opportunities; and 3) there was an inverse relationship between the volume of overland flow and soil moisture at the hillslope scale, influencing, in turn, ecohydrological processes at the patch scale. Overall our results highlight the importance of overland flow modifying soil moisture distribution at patch scale and hence, influencing vegetation dynamics and ecological succession in these novel ecosystems.

Effect of soil erosion on dissolved organic carbon redistribution in subtropical red soil under rainfall simulation

Water erosion governs soil carbon reserves and distribution across the watershed or ecosystem. The dynamics of dissolved organic carbon (DOC) under water erosion in red agricultural soil is not clear. To determine the effect of tillage management and water erosion on vertical and lateral transportation of soil organic carbon (SOC) and DOC production under distinct rainfall intensities in the hilly red soil region of southern China, a chisel tillage plot with low rainfall intensity (CT-L) and two no-tillage plots with high (NT-H) and low rainfall intensity (NT-L) studies were conducted. Soil samples were collected from 0–5, 5–10, 10–20, and 20–40cm soil layers from triplicate soil blocks pre- and post-rainfall for determining concentration of SOC and DOC. Runoff samples were collected at every 6min for determining concentration of DOC and sediments during rainfall simulations on runoff plots (2m×5m) with various intensities. No fertilizer was applied in any plots. Results clearly show that runoff volumes, sediments and SOC entrained with sediment, and laterally mobilized DOC were significantly larger on NT-H compared to other plots, coinciding with changes in rainfall intensity; and the extent of roughness of the plot surface (CT vs. NT) was the variation in runoff DOC concentration. During the simulated rainfall events, DOC exports average 0.76, 0.64, and 0.27gCm−2h−1; SOC exports average 3.52, 1.08, and 0.07gm−2h−1 in the NT-H, NT-L, and CT-L soils, respectively. The maximum export of DOC was obtained under a high intensity rainfall plot, which lagged behind maximum runoff volumes, sediments, and SOC losses with sediment. Export of DOC was proportional to SOC content of soil loss. The least DOC losses in surface runoff and SOC losses with sediment were observed in CT-L plots. Vertical DOC mobilization achieved its maximum with low intensity rainfall under CT treatment. The DOC did not accumulate at the soil surface and was distributed mainly in the second and third soil horizons. The distribution of DOC content down the soil profile increased compared to pre-rainfall, except for subplots E at NT-H and NT-L. Results indicate that rainfall significantly increased DOC content in experimental plots. The SOC content of sediment leaving the erosion zone was significantly correlated with overland flow volume and soil loss. These observations lead to the conclusion that soil erosion is an important factor controlling the export of dissolved organic carbon.

Connectivity of overland flow by drainage network expansion in a rain forest catchment

Soils in various places of the Panama Canal Watershed feature a low saturated hydraulic conductivity (Ks) at shallow depth, which promotes overland-flow generation and associated flashy catchment responses. In undisturbed forests of these areas, overland flow is concentrated in flow lines that extend the channel network and provide hydrological connectivity between hillslopes and streams. To understand the dynamics of overland-flow connectivity, as well as the impact of connectivity on catchment response, we studied an undisturbed headwater catchment by monitoring overland-flow occurrence in all flow lines and discharge, suspended sediment, and total phosphorus at the catchment outlet. We find that connectivity is strongly influenced by seasonal variation in antecedent wetness and can develop even under light rainfall conditions. Connectivity increased rapidly as rainfall frequency increased, eventually leading to full connectivity and surficial drainage of entire hillslopes. Connectivity was nonlinearly related to catchment response. However, additional information on factors such as overland-flow volume would be required to constrain relationships between connectivity, stormflow, and the export of suspended sediment and phosphorus. The effort to monitor those factors would be substantial, so we advocate applying the established links between rain event characteristics, drainage network expansion by flow lines, and catchment response for predictive modeling and catchment classification in forests of the Panama Canal Watershed and in similar regions elsewhere.

Nutrient losses from two contrasting dairy cow grazing systems

A key concern in farming systems that seek to maximise the grass content of livestock diets is the management of grazing so as to avoid damage to soil structure during periods with high antecedent soil moisture conditions. The aim of this study was to investigate, under the current codes of good agricultural practice, the impact of two contrasting grazing systems on soil structure and nutrient export from grazed grasslands. The two grazing treatments were (1) WinterCalf treatment, involving winter-calving Holstein-Friesian dairy cows, which had a mean ‘start of turnout’ date of 28 March, and were offered 5.0kg concentrate/cow/day throughout a 214-day grazing season; and (2) SpringCalf treatment, involving spring-calving Jersey Holstein-Friesian dairy cows, which had a ‘start of turnout’ date of 17 February, and were offered between 1.0 and 2.0kg concentrate/cow/day throughout a 260-day grazing season. Maximum reliance on grazed grass was a key objective of the latter system. Mean stocking rates during the grazing season were 5.1 and 4.3 cows per hectare with WinterCalf and SpringCalf systems, respectively. The experimental site was divided into four replicated blocks (A, B, C and D), with each block containing two grazing plots (425m and 500m, for the WinterCalf and SpringCalf systems, respectively). In addition to the two grazed treatments, an ungrazed treatment (UG) was established within each of the WinterCalf and SpringCalf treatment plots by fencing off a 12m exclusion sub-plots, which livestock could graze but not tread on. Changes in soil structure were recorded before and after grazing on all plots and with rainfall simulation to investigate the impact of soil structural changes on nutrient export to water. The results of the study demonstrated that over a complete grazing season, under the current code of good grazing practice, nutrient export from the SpringCalf treatment was not significantly greater than that from the WinterCalf treatment. However, results highlighted an increase in nutrient export from the SpringCalf treatment compared to the ungrazed treatment. These increases were as a result of a significant increase in overland flow volume from the SpringCalf treatment compared to the UG treatment. The time taken to initiate overland flow was a key factor in this relationship, with an increase from an average value of 536 seconds for the SpringCalf treatment to 1709 seconds for the Ungrazed treatment. Allowing time for soil to recover from compaction could be an effective mitigation strategy for reducing nutrient export from soil, particularly in areas where soil P is significantly above the agronomic optimum for grass production.

Effectiveness of Hydromulching to Reduce Runoff and Erosion in a Recently Burnt Pine Plantation in Central Portugal

AbstractForest fires can greatly increase runoff and surface erosion rates. Post‐fire soil erosion control measures are intended to minimize this response and facilitate ecosystem recovery. In a few recent cases, hydromulch has been applied, and this consists of a mixture of organic fibers, water and seeds. The objectives of this research were to (i) analyze the effectiveness of hydromulch in reducing post‐fire runoff and sediment production and (ii) determine the underlying processes and mechanisms that control post‐fire runoff and erosion. After a wildfire occurred in August 2008, 14 plots ranging in size from 0·25 to 10 m2 were installed on a 25 degree slope in a burnt pine plantation that had also been subjected to salvage logging. Half of the plots were randomly selected and treated with hydromulch. One of two slope strips adjacent to the plots was also hydromulched and used for monitoring some soil properties. Measurements made in each of the first 3 years following the wildfire included (i) the plot‐scale runoff volumes and sediment yields; (ii) soil shear strength, soil moisture, and soil water repellency; and (iii) surface cover. The hydromulch reduced overland flow volume by 70% and soil erosion by 83%. The decrease in runoff was attributed to the increase in soil water retention capacity and the decrease in soil water repellency, whereas the reduction in soil erosion was initially attributed to the protective cover provided by the hydromulch and lately to an enhanced vegetative regrowth in the third year after burning. Copyright © 2013 John Wiley & Sons, Ltd.

Influencia de la exposición sobre la producción de sedimentos y escorrentía en ambientes semiáridos

By means of experiments with simulated rainfall the influence of aspect on runoff and erosion dynamics is analysed in a basin where the vegetation is distributed within a mosaic of Stipa tenacissima L. shrubs and inter-shrubs. In the inter-shrubs areas three different types of areas exist: Stone pavement (with rack fragments), Crusted surfaces (with surface crust) and vegetation covered areas (Brachypodium retusum). 
 The erosion and runoff rates are very low beneath the vegetation (Esparto tussocks and Brachypodium retusum grass), while in the intershrubs areas (Crusted and Stone pavement) rates are higher. The vegetation controls runoff generation through its effect on the infiltration rates.
 Both runoff and erosion processes are influenced by aspect. The northjacing slopes have higher infiltration rates, and runojf is attenuated and reduced. The soil losses are neglegible in compararison to the southjacing slope. Vegetation cover is inversely and non-linearly related to the volume of overland flow, and the relationship exhibit a threshold due to the patch distribution of the vegetation. Modelling and predictioning the geomorphological processes under semiarid conditions is very complicated due to the high spatial variability of bis factors, specially the vegetation.

Intensity of ecohydrological interactions in reclaimed Mediterranean slopes: effects of run‐off redistribution on plant performance

ABSTRACTWe have conducted a field experiment to ascertain the role of ecohydrological interactions between run‐off source areas and sink patches in the dynamics of artificial slopes derived from open cast coal mining in central‐eastern Spain. We analysed the effects of run‐off interruption on soil moisture, on the leaf water potential of woody species and on the herbaceous biomass in vegetation patches of three reclaimed slopes subjected to a different disturbance degree resulting from different overland flow volumes running down the slopes. Soil moisture and plant performance were seriously affected by run‐off exclusion, and this effect was more intense as level of disturbance increased. In fact, run‐off redistribution appeared to be determinant for plant performance in the more disturbed slope, whereas the presence of the shrub Genista scorpius appeared to be more determinant for plants in the less disturbed slope. Our results confirm the validity of the Trigger–Transfer–Reserve–Pulse model in artificial slopes during the aggradation process. These results point out the importance of run‐off redistribution between vegetation patches in the evolution of artificial slopes by creating fertility islands that improve the performance of vegetation. Restoration practices in drylands may thus significantly improve if a ‘run‐off expert management’ strategy is adopted. Copyright © 2012 John Wiley & Sons, Ltd.

Dynamics of critical source areas: Does connectivity explain chemistry?

Critical source area approaches to catchment management are increasingly being recognised as effective tools to mitigate sediment and nutrient transfers. These approaches often assume hydrological connectivity as a driver for environmental risk, however this assumption has rarely been tested. Using high resolution monitoring, 14 rainfall events of contrasting intensity were examined in detail for spatial and temporal dynamics of overland flow generation at a hydrologically isolated grassland hillslope in Co. Down, Northern Ireland. Interactions between overland flow connectivity and nutrient transfers were studied to test the critical source area hypothesis. While total and soluble phosphorus loads were found to be representative of the size of the overland flow contributing area (P=<0.05), the dynamics of concentrations throughout storm hydrographs were found to be complex and storm dependant. Near linear relationships were observed between the contributing area and total overland flow volumes (R2=0.86). Export coefficients (kgha−1) calculated using plot size were found to under estimate annual losses of total phosphorus by a factor of 17, when compared to those calculated using the contributing area. This study shows that current critical source area definitions for implementing mitigation measures may be overlooking the importance of storm characteristics in determining nutrient transfers and hence may be insufficient in determining catchment scale risk.

Predicting runoff and sediment connectivity and soil erosion by water for different land use scenarios in the Spanish Pre-Pyrenees

Abstract Overland flow connectivity and runoff and sediment trap effectiveness are currently the cutting edge topics in soil erosion research. The effect of agricultural terraces, irrigation channels and trails on runoff and soil erosion modelling at catchment scale is still a remaining research question. In this study we run the index of connectivity of Borselli et al. (2008) and a modified version of the revised Morgan, Morgan and Finney (RMMF) model to predict the hydrological connectivity and the rates of soil erosion under four different scenarios of land uses and land abandonment. This goal is achieved by using geographic information systems (GIS) in the Estanque de Arriba catchment (74 ha; Spanish Pre-Pyrenees) where 83 soil samples were collected. The different maps of hydrological connectivity were used to create runoff and sediment trap effectiveness masks that were included in the assessment of the effective cumulative runoff. The results showed that the index of connectivity was very high in the irrigation channels and walls of the agricultural terraces for the past and current scenarios. The runoff and sediment connectivity of the catchment from the hillsides to the lake decreased with an increasing vegetation cover and a decreasing number of linear landscape elements. The connectivity decreased from the past to the current scenario and from the current to the future scenario with vegetation recovery in the abandoned fields. The vegetation factor appeared to be more important than the disappearance of the agricultural terraces and channels to explain the changes in the connectivity at catchment scale. Random changes in the IC values appeared between the current and the future scenario without vegetation recovery in some parts of the catchment and were related to the mathematical procedure of the model that combines the upslope and downslope components at each pixel. This information is of special relevance in areas disturbed by humans and those with complex topography. The average erosion rates ranged between 1.5 and 3.7 Mg ha− 1 year− 1 for the different land use scenarios decreasing with the increase of the vegetation recovery in the abandoned fields. A significant percentage of the study area will suffer more erosion in the early stage of future land abandonment with an increasing volume of overland flow in the fields at the bottom of the catchment whereas soil erosion will decrease significantly after long-term land abandonment with vegetation recovery. Further research is proposed to better account the changes that happen in the soil and vegetation parameters at the early stages of land abandonment. The results of this study suggest that current active systems could be stabilized by trapping and retaining eroded sediment by increasing the vegetation cover and preserving the agricultural terraces.

Influence of georeference for saturated excess overland flow modelling using 3D volumetric soft geo-objects

Existing 2D data structures are often insufficient for analysing the dynamism of saturation excess overland flow (SEOF) within a basin. Moreover, all stream networks and soil surface structures in GIS must be preserved within appropriate projection plane fitting techniques known as georeferencing. Inclusion of 3D volumetric structure of the current soft geo-objects simulation model would offer a substantial effort towards representing 3D soft geo-objects of SEOF dynamically within a basin by visualising saturated flow and overland flow volume. This research attempts to visualise the influence of a georeference system towards the dynamism of overland flow coverage and total overland flow volume generated from the SEOF process using VSG data structure. The data structure is driven by Green–Ampt methods and the Topographic Wetness Index (TWI). VSGs are analysed by focusing on spatial object preservation techniques of the conformal-based Malaysian Rectified Skew Orthomorphic (MRSO) and the equidistant-based Cassini-Soldner projection plane under the existing geodetic Malaysian Revised Triangulation 1948 (MRT48) and the newly implemented Geocentric Datum for Malaysia (GDM2000) datum. The simulated result visualises deformation of SEOF coverage under different georeference systems via its projection planes, which delineate dissimilar computation of SEOF areas and overland flow volumes. The integration of Georeference, 3D GIS and the saturation excess mechanism provides unifying evidence towards successful landslide and flood disaster management through envisioning the streamflow generating process (mainly SEOF) in a 3D environment.

Influence of land-use change on near-surface hydrological processes: Undisturbed forest to pasture

Soil compaction that follows the clearing of tropical forest for cattle pasture is associated with lower soil hydraulic conductivity and increased frequency and volume of overland flow. We investigated the frequency of perched water tables, overland flow and stormflow in an Amazon forest and in an adjacent 25-year-old pasture cleared from the same forest. We compared the results with the frequencies of these phenomena estimated from comparisons of rainfall intensity and soil hydraulic conductivity. The frequency of perched water tables based on rainfall intensity and soil hydraulic conductivity was expected to double in pasture compared with forest. This corresponded closely with an approximate doubling of the frequency of stormflow and overland flow in pasture. In contrast, the stormflow volume in pasture increased 17-fold. This disproportional increase of stormflow resulted from overland flow generation over large areas of pasture, while overland flow generation in the forest was spatially limited and was observed only very near the stream channel. In both catchments, stormflow was generated by saturation excess because of perched water tables and near-surface groundwater levels. Stormflow was occasionally generated in the forest by rapid return flow from macropores, while slow return flow from a continuous perched water table was more common in the pasture. These results suggest that deforestation for pasture alters fundamental mechanisms of stormflow generation and may increase runoff volumes over wide regions of Amazonia.

Overland flow generation in chaparral ecosystems: temporal and spatial variability

AbstractFire is an important and natural process in the lifecycle of chaparral systems, removing old growth and recycling nutrients. Recent catastrophic wildfires in southern California chaparral have heightened concerns about increased runoff and nutrient export. The goal of this study was to improve understanding of how overland flow is generated in unburned and post‐fire chaparral watersheds. Samples of overland flow were collected from burned and unburned watersheds after rainfall events and multiple regression analysis was used to examine the influence of individual storm characteristics and system moisture on overland flow volume. The results indicate that variation in overland flow generation in the unburned watershed is best explained by storm size, while overland flow in the burned watershed was positively related to storm size and time between storms. These findings suggest that the burned system had decreased infiltration rates and increased soil water repellency. In contrast, there is a statistically significant negative relationship between overland flow 1 year after a fire against different system and precipitation factors revealed a negative correlation with drying period and a positive relationship with rainfall intensity, a combination that suggests reduced repellency. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Soil erosion prediction using MMF model on highly dissected hilly terrain of Ekiti environs in southwestern Nigeria

Assessment of soil erosion risk is important to formulate effective soil conservation plans for sustainable development. Information from remote sensing techniques can help decision makers prepare resource map accurately in less time and cost. GIS assists in linking those maps with other information related to geographic location and helps modeling, analyzing and solving complex problems. The objective of this study was to assess the potential of Morgan, Morgan and Finney (MMF) Model (Morgan et al., 1984) in predicting soil erosion in an agrarian Ekiti environment with highly dissected hilly and rolling terrain in southwestern Nigeria. Soil loss prediction by MMF approach involve factor maps from kinetic energy of rainfall, topsoil rooting depth, percentage rainfall contri-buting to permanent interception and stream flow, crop cover management factor, ratio of actual to potential evapotranspiration, soil moisture storage capacity. These were used to generate output maps like volume of overland flow, rate of soil detachment by raindrop impact and transport capacity of overland flow. Annual soil loss estimation was calculated by comparing two maps of soil detachment rate and transport capacity and taking the minimum value from them. Results showed that MMF model could predict erosion risks effectively in the highly dissected hilly and rolling landscape of Ekiti environ. Erosion was low in the area in spite of the landscape. The highest soil loss was 1.275 kgm-2 yr-1 from rock hill with slope greater than 15%. The lowest was 0.942 kgm-2 yr-1 at low lands covered with riparian forest. The average estimated annual soil loss of the study area was 1.112 kgm-2, which is less than tolerable standard of 1 kg 1233 m-2 yr-1. The MMF model shows that the current land-use/cover in Ekiti environs is sustainable because erosion risk is below the critical level. Key words: Soil erosion, MMF model, land use, hilly landscape, Nigeria.

Prediction of overland flow and seepage zones associated with the interaction of multiple infiltration devices (cascading infiltration devices)

AbstractInfiltration devices are traditionally evaluated as standalone entities that do not interact with each other. A model is outlined that will allow interactions between proposed infiltration devices to be predicted prior to a development commencing. The model allows prediction of seepage into downslope devices and the assessment of the locations where the combined ground‐water mound will reach the surface and result in overland flow. The volume of overland flow discharged by the seepage zone may exceed the overland and piped flow received by the infiltration devices. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Effects of grassland management practices and environmental conditions on nutrient concentrations in overland flow

The loss of nutrients from agricultural land to water bodies is a serious concern in river basin management in many countries. To gain information on the contributions of agricultural grassland to the eutrophication of water bodies, this study set out to assess phosphorus (P) loss from grassland areas on poorly drained soils. A second aim was to look at the impact of grassland management practices on nutrient concentrations in overland flow. Edge-of-field measurements of overland flow quantity and of P and nitrogen (N) concentrations in overland flow were carried out at three study sites with different soil P levels. The amounts of overland flow and the P concentrations in overland flow varied considerably during events, and among sites and events. Despite this variability, there was a clear increase in P loss in overland flow from the low to the medium and high soil P sites. The inter-site variability of the P concentrations in overland flow greatly exceeded the variability of the amounts of overland flow from the different sites. Thus, P concentrations had a larger impact than the volume of overland flow on the differences in P exports from the three sites. Management practices which, at times, influenced the P and N concentrations in overland flow were grazing and N fertilisation.

Vegetation barrier and tillage effects on runoff and sediment in an alley crop system on a Luvisol in Burkina Faso

The effects of vegetation barriers and tillage on runoff and soil loss were evaluated in an alley crop system at a research station in central Burkina Faso. On a 2% slope of a sandy loam various local species (grasses, woody species and a succulent) were planted as conservation barriers in order to examine their influence on sediment transport. After each erosive storm, runoff and sediment yield was determined. The dense effective barriers ( Andropogon gayanus and dense natural vegetation) slow down flow velocity, build up backwater and promote sedimentation uphill. The through flow in the less effective barriers with woody species and succulents ( Ziziphus mauritania and Agave sisalana) was slightly hampered and flow velocity was not reduced enough, resulting in a higher soil transport. Under degraded conditions soil loss diminished 50% with less effective and 70–90% with effective barriers. During the initial cropping phase (light tillage; sowing) erosion was reduced 40–60% with effective barriers and showed an increase of 45% with less effective barriers. In the full tillage (weeding) period erosion decreased by 80–90% for effective and 70% for less effective barriers, aided by the development of the barrier and the crop on the alley. Barriers of natural vegetation and A. gayanus are preferred for diminishing soil loss. Sediment yield could best be predicted by the erosivity index ( AI m), second best by runoff amount (mm), closely followed by maximum peak intensity. All these parameters are related to the volume of overland flow needed to transport soil particles. Correlation of soil loss with small rain showers was poor and correlation with big showers was good. Sediment transport with no barrier had the highest correlation, closely followed by less effective barriers. Due to the heterogeneity in development of the effective barrier, correlations were much lower. The bulk of soil loss was only dependent on a few extreme events during the observation period.