Overland Water Flow Research Articles

Overland water flow contributes little to survival, growth, reproduction, and ecophysiology ofOlneya tesota(Desert Ironwood) trees

Abstract We studied the responses of Desert Ironwood trees (Olneya tesota), located in desert washes of the Sonoran Desert in California, to a reduction in overland water flow. We hypothesized that trees with access to overland water runoff would have different morphological and ecophysiological responses than trees that did not. We studied responses including branch growth, water potentials, leaf carbon isotope ratios, leaf mass per area, flower production, seed production, and tree population densities. Only branch growth and predawn water potentials were found to be significantly different between treatments. Predawn water potentials indicated seasonally increased water stress in trees without access to overland water runoff. Trees with access to overland water runoff also responded with increased branch growth. The lack of differences between treatments observed for all other morphological and ecophysiological responses may indicate that environmental conditions, especially water availability, were si...

Calibration of infiltration, roughness and longitudinal dispersivity coefficients in furrow fertigation using inverse modelling with a genetic algorithm

Determining soil hydraulic properties in surface irrigation which the soil surface is used both to convey and infiltrate water is very important. It becomes an issue of great concern when fertilisers were also added to irrigation water during fertigation. The purpose of this study was to estimate infiltration, roughness and longitudinal dispersivity coefficients in conventional and alternate furrow fertigation using inverse modelling with a genetic algorithm. A surface fertigation model was used to simulate overland water flow and solute transport. To discover optimum values of the coefficients, a genetic algorithm with fifteen objective functions were used to minimise the differences between observed and simulated values of advance time, recession time, runoff hydrograph and runoff nitrate concentration. The results indicated that the infiltration, roughness and fertiliser dispersivity parameters were more sensitive to runoff, recession time and runoff nitrate concentration, respectively. The best simulations of advance and recession phases were obtained by the coefficients which were estimated from objective function that minimised the differences between observed and simulated values of advance and recession time, respectively. For improving simulation of runoff discharge, minimising the differences between observed and simulated values of runoff hydrograph as well as advance time was necessary. Similarly, the improved simulation of runoff nitrate concentration needed minimising differences between simulated and measured values of both advance and runoff nitrate concentration. The proposed inverse modelling approach with GA resulted in better performance as compared to the two-point method, particularly in fixed and variable alternate furrow fertigation.

A physical model considered the effect of overland water flow on rainfall-induced shallow landslides

Abstract Background It is well know that many shallow landslides are triggered by rainfalls. In previous studies of shallow landslide models, the effect of overland water flow on slope stability was ignored. Results In this paper, a physical model considered the effect of overland water flow on rainfall-induced shallow landslides is derived and applied to predict the landslides. The slope stability model is developed by considering the depth of overland water flow in infinite slope stability theory. Hillslope hydrology is modelled by coupling the overland uniform water flow equation with Rosso’s seepage flow equation. And then, the model is used to assess the slope stability in Dujiangyan of China, and the results is compare with Rosso’s model. Conclusions This model is simple, but has the capability of taking into account the effect of overland water flow in the triggering mechanism of shallow landslide. The results of case study show that the overland water flow can make an obvious effect on shallow landslides, so it is quite important to consider the overland water flow in shallow landslide hazard assessment.

Reversing desertification as a spatial resonance problem

An important environmental application of pattern control by periodic spatial forcing is the restoration of vegetation patterns in water-limited ecosystems that went through desertification. Vegetation restoration is often based on periodic landscape modulations that intercept overland water flow and form favorable conditions for vegetation growth. Viewing this method as a spatial resonance problem, we show that plain realizations of this method, assuming a complete vegetation response to the imposed modulation pattern, suffer from poor resilience to rainfall variability. By contrast, less intuitive realizations, based on the inherent spatial modes of vegetation growth and involving partial vegetation implantation, can be highly resilient and equally productive. We derive these results using two complementary models, a realistic vegetation model, and a simple pattern formation model that lends itself to mathematical analysis and highlights the universal aspects of the behaviors found with the vegetation model. We focus on reversing desertification as an outstanding environmental problem, but the main conclusions hold for any spatially forced system near the onset of a finite-wave-number instability that is subjected to noisy conditions.

Modeling runoff and microbial overland transport with KINEROS2/STWIR model: Accuracy and uncertainty as affected by source of infiltration parameters

Summary Infiltration is important to modeling the overland transport of microorganisms in environmental waters. In watershed- and hillslope scale-models, infiltration is commonly described by simple equations relating infiltration rate to soil saturated conductivity and by empirical parameters defining changes in infiltration rate with soil water content. For the microbial transport model KINEROS2/STWIR used in this study, infiltration in unsaturated soil is accounted for by a net capillary drive parameter, G , in the Parlange equation. Scarce experimental data and multiple approaches for estimating parameter G introduce uncertainty, reducing reliability of overland water flow and microbial transport models. Our objectives were to evaluate reliability and robustness of three methods to estimate parameter G and associated accuracy and uncertainty in predicting runoff and fecal coliform (FC) transport. These methods include (i) KINEROS2 fitting to the experimental cumulative runoff data; (ii) estimating solely on soil texture; and (iii) estimating by individual pedotransfer functions (PTFs) and an ensemble of PTFs from basic soil properties. Results show that the most accurate prediction was obtained when the G parameter was fitted to the cumulative runoff. The KINEROS2-recommended parameter slightly overestimated the calibrated value of parameter G and yielded less accurate predictions of runoff, FC concentrations and total FC. The PTFs-estimated parameters systematically deviated from calibrated G values that caused high uncertainty in the KINEROS2/STWIR predictions. Averaging PTF estimates considerably improved model accuracy, reducing the uncertainty of runoff and FC concentration predictions. Overall, ensemble-based PTF estimation of the capillary drive can be efficient for simulations of runoff and bacteria overland transport when a single effective value is used across the study area.

Effect of terrace forms on water and tillage erosion on a hilly landscape in the Yangtze River Basin, China

In long-term agricultural practices, cultivated land on long slopes in hilly areas is sometimes terraced to diminish soil loss caused by water and facilitate farming operations. In the Upper Yangtze River Basin, the forms of the terraces vary with the landform, soil resources and traditional techniques used in different areas. This study assessed the pattern of soil redistribution and soil particle size redistribution for two major types of terraces: with and without embankments. Samples of 137Cs and soil texture were collected at the upper and lower parts of terraces, and at an interval of 5m along the transect of the toposequence of individual terraces. The non-embankment terrace (NET) landscape showed increasing 137Cs downslope, whereas the embankment terrace (ET) landscape exhibited an abrupt change in 137Cs at the embankment. Tillage erosion dominated the soil redistribution, with smaller contributions made by water erosion in the ET landscape. In addition to tillage erosion, water erosion played an important role in the soil redistribution in the NET landscape, resulting in a net soil loss at both the upper and lower parts of the terrace. Soil fine particle fractions exhibited a trend of gradual increase along the transect of the toposequence in the NET landscape, and a similar fraction of fine particles was found at the upper and lower parts of the terrace. The establishment of embankments at the lower end of the terrace obstructed the formation and development of overland water flow, thereby creating a line of null downslope soil transport leading to tillage-induced soil accumulation on the upslope side of the embankment with little granulometric sorting. In the NET landscape, soil loss seemed to increase as a result of tillage erosion (an important delivery mechanism for water erosion), accelerating the on-site soil loss. The embankments at the lower end of the sloping terrace played a crucial role in the soil redistribution patterns of the toposequence, resulting in a shift from a water-dominated erosion process to a tillage-dominated process and a distinct pattern of soil particle size distribution.

Wilk’s Method Based Model for Regulations Related to Radiological Impact of Opencast Uranium Mining on Water Reservoirs

Opencast mining of uranium may lead to natural erosion of ore material due to overland flow of water accumulated from rainfall. The overland flow may ultimately reach the nearby surface water body. This process may lead to the release of 238U and its daughter products into the surface water body. A model is developed to assess the radiological impact of the erosion in terms of dose through drinking water pathway due to 238U and its progeny in the surface water body. The in-growth of progeny is taken into account using Bateman equations. The study brings out the importance of incorporating decay chain transport in the radiological impact assessment studies. It is also observed that 210Po, 210Pb, 226Ra, and 230Th together contribute to about 95.5 % of the total dose. The model is then extended to incorporate the uncertainty associated with the dose due to consumption of the reservoir water by employing Wilk’s Method. Such a model can be very useful in establishing regulations related to dose through drinking water pathway around an opencast mine. Wilk’s method is computationally less expensive as compared to the exact methods like Monte Carlo method. Wilk’s method is used to calculate a value greater than α percentile value for the dose to the public due to 238U and its progeny in the reservoir through drinking water pathway with confidence level β (α/β value). When applied to a hypothetical case using some literature data on surface water bodies, it is found that with increase in the value of α or β, the α/β value in general, shows an increasing trend as expected. Depending upon the nature of the problem under study, one can calculate an α/β value i.e. 95/95 value, 99/95 value etc., and that value can be helpful in establishing the regulatory limiting value. Also, the α/β value can be used to check whether dose due to a particular radioactive release is within the specified limits.

Comparison of floodplain surface roughness parameters derived from land cover data and field measurements

Summary Parameterizing surface roughness is a key element in the application of tidal and storm surge inundation models. In this context, surface roughness refers to the ability of the terrain to act as a momentum sink to the overland water flow and also the prevailing winds that help drive this flow. These effects are typically parameterized using estimates of Manning’s n , surface canopy coverage and effective aerodynamic roughness length which vary spatially across the modeling domain as a function of the physical landscape. The current methodology for coastal inundation in the United States assigns these parameters based on published land use/land cover data such as the National Land Cover Dataset. This paper compares those assigned values to values computed based on field measurements at 24 sites in Florida that are representative of land use/land cover classes affected by storm surge. It is shown that while the land use/land cover method is capable of automatically parameterizing surface roughness over a large model domain, parameter prediction errors due to variability within land cover types, misclassification, and parameter value selection for specific land cover classes at the local level are significant which could result in inaccurate estimates of inundation extent and duration.

Periglacial debris-flow initiation and susceptibility and glacier recession from imagery, airborne LiDAR, and ground-based mapping

Climate changes in the Pacific Northwest, USA, may cause both retreat of alpine glaciers and increases in the frequency and magnitude of storms delivering rainfall at high elevations absent significant snowpack, and both of these changes may affect the frequency and severity of destructive debris flows initiating on the region9s composite volcanoes. A better understanding of debris-flow susceptibility on these volcanoes’ slopes is therefore warranted. Field mapping and remote sensing data, including airborne light detection and ranging (LiDAR), were used to locate and characterize initiation sites of six debris flows that occurred during an “atmospheric river” event (warm wet storm) on Mount Rainier, Washington, in November 2006, and data from prior studies identified six more debris flows that occurred in 2001–2005. These 12 debris flows had initiation sources at the heads of 17 gullies distributed over seven distinct initiation zones near the termini of glaciers, and all debris-flow initiation sites were located within areas exposed by glacier retreat in the past century. Gully locations were identified by their steep walls and heads on a 1-m digital elevation model (DEM) from LiDAR data collected in 2007–2008. Gullies in which debris flows initiated were differentiated from numerous non-initiating gullies primarily by the greater upslope contributing areas of the former. Initiation mechanisms were inferred from pre- and post-2006 gully width measurements from aerial photos and the LiDAR DEM, respectively, field observations of gully banks, and elevation changes calculated from repeated LiDAR, and these data indicate that debris flows were initiated by distributed sources, including bank mass failures, related to erosion by overland flow of water. Using gully-head initiation sites for debris flows that occurred during 2001–2006, a data model was developed to explore the viability of the method for characterization of debris-flow initiation susceptibilities on Mount Rainier. The initiation sites were found to occupy a restricted part of the four-dimensional space defined by mean and standard deviation of simulated glacial meltwater flow, slope angle, and minimum distance to an area of recent (1994–2008) glacier retreat. The model identifies the heads of most gullies, including all sites of known debris-flow initiation, as high-susceptibility areas, but does not appear to differentiate between areas of varying gully-head density or between debris-flow and no-debris-flow gullies. The model and field data, despite limitations, do provide insight into debris-flow processes, as well as feasible methods for mapping and assessment of debris-flow susceptibilities on periglacial areas of the Cascade Range.

The ecology of pulse events: insights from an extreme climatic event in a polar desert ecosystem

Climate change is occurring globally, with wide ranging impacts on organisms and ecosystems alike. While most studies focus on increases in mean temperatures and changes in precipitation, there is growing evidence that an increase in extreme events may be particularly important to altering ecosystem structure and function. During extreme events organisms encounter environmental conditions well beyond the range normally experienced. Such conditions may cause rapid changes in community composition and ecosystem states. We present the impact of an extreme pulse event (a flood) on soil communities in an Antarctic polar desert. Taylor Valley, McMurdo Dry Valleys, is dominated by large expanses of dry, saline soils. During the austral summer, melting of glaciers, snow patches and subsurface ice supplies water to ephemeral streams and wetlands. We show how the activation of a non‐annual ephemeral stream, Wormherder Creek, and the associated wetland during an exceptional high‐flow event alters soil properties and communities. The flow of water increased soil water availability and decreased salinity within the wetted zone compared with the surrounding dry soils. We propose that periodic leaching of salts from flooding reduces soil osmotic stress to levels that are more favorable for soil organisms, improving the habitat suitability, which has a strong positive effect on soil animal abundance and diversity. Moreover, we found that communities differentiated along a soil moisture gradient and that overland water flow created greater connectivity within the landscape, and is expected to promote soil faunal dispersal. Thus, floods can ‘precondition' soils to support belowground communities by creating conditions below or above key environmental thresholds. We conclude that pulse events can have significant long‐term impacts on soil habitat suitability, and knowledge of pulse events is essential for understanding the present distribution and functioning of communities in soil ecosystems.

Environmental Influences of Flooding on Urban Growth and Development of Ado-Ekiti, Nigeria

This study examined the environmental consequences of urban flood on the growth and development of Ado-Ekiti, Nigeria. Urban flood is any overland flow of water, over urban street, sufficient to cause significant damage to lives and property, traffic obstructions, nuisance and health hazards. Data for this study were collected from primary sources, through the administration of three hundred (300) questionnaires on respondents in the study area. Results from this study revealed that high intensity of rainfall, unturned road, dumping of refuse on drainage channels, poor construction of drainage channels and poor town planning practices are the main causes of urban flood problems in the study area. This study therefore recommends adequate drainage system, proper land use planning, construction of embankments, proper refuse disposal and environmental enlightenment programmes as a panacea to urban flood problems. Key words: Environment; Consequences; Urban-flood; Developments

The effects of different inflow hydrograph shapes on furrow irrigation fertigation

Fertilisers are widely applied to agricultural fields using surface fertigation. However, there are still no adequate guidelines for the proper design and management of surface fertigation. The proper management of surface irrigation fertigation is important because of low uniformity of distribution of water in surface irrigation. The efficient application and distribution of water by furrow irrigation is highly dependent on parameters such as inflow rate and inflow hydrograph shape. Some modified furrow inflow hydrograph shapes were introduced, evaluated for field conditions and simulated using modified zero-inertia model for surface irrigation fertigation. An automatic device was designed to apply different furrow inflow hydrograph shapes to the furrows. The one dimensional advection-dispersion model of the overland water and solute flow was used to simulate furrow irrigation fertigation. The results show that the modified inflow hydrograph shapes reduced tailwater runoff significantly. The use of modified increased discharge inflow hydrograph shape resulted in higher solute uniformity. The fertigation model was able to simulate the experimental field data with good accuracy. The fertigation application was highly affected by the shape of furrow inflow hydrograph. Fertiliser losses due to runoff were between 20 and 67% for different inflow hydrograph shapes. The fertiliser losses due to runoff were highest for the constant inflow hydrograph shape and lowest for the modified increased discharge inflow hydrograph shape. The use of correct inflow hydrograph shape can reduce fertiliser losses due to tailwater runoff significantly.

The Effect of Trails on Soil in the Oak Openings of Northwest Ohio

Trails are a form of recreational disturbance affecting natural areas. Trail disturbances can cause soil degradation such as compaction, which facilitates soil erosion and overland water flow. This study analyzed the effects of four different types of trails—paved, gravel, equestrian, and hiking—on soils in the Oak Openings of Northwest Ohio, a globally rare ecosystem that harbors more than a third of Ohio's rare plant species. Bulk density and soil moisture content were measured in order to determine physical impacts of trails. Soil pH, ammonium, nitrate, phosphate, and dissolved organic C and N concentrations were measured to determine effects on soil chemistry. Finally, soil microbial biomass and exoenzyme activities were measured to determine biological responses to trail disturbances. Soils from the gravel trail were the most affected by the trail, with significant effects on chemical (PO43-concentration) and biological (phosphatase and NAG activity, and MB-N) properties. The soils near the paved trail were the second most affected after the gravel trail, with a trend toward a pH change and a significant biological (microbial peptidase activity) effect of this trail. The soils of the horse and natural trails were generally not significantly different from the soils in the surrounding ecosystem. The only significant disturbance in the horse trail was increased bulk density in the trail, while the natural hiking trail had no statistically significant differences, but trends lean toward increased bulk density and reduced microbial phosphatase activity. These results suggest that the natural and horse trails have the least impact on the Oak Openings ecosystem.

Evidence for paleolakes in Erythraea Fossa, Mars: Implications for an ancient hydrological cycle

There is now widespread agreement that the surface of Mars underwent some degree of fluvial modification, but there is not yet full understanding of its surface hydrological cycle and the nature of standing bodies of water, rivers, and precipitation that affected its surface. In this paper we explore Erythraea Fossa (31.5 W, 27.3 S), a graben adjacent to Holden crater, which exhibits strong evidence that it once housed a chain of three lakes, had overland water flow, and was subject to precipitation. The inlet valley, outlet valley, and fan morphologies in the paleolakes are used to qualitatively discern the hydrologic history of the paleolakes; based on topography constraints, the three basins combined once held 56 km 3 of water. Depositional features within the basins that change with drainage area and nearby valleys that start near drainage divides indicate that the paleolakes may have been fed by precipitation driven runoff. This suggests the presence of an atmosphere, at least locally, that was capable of supporting a hydrological cycle.

Performance and reproduction of an exotic invader across temperate forest gradients

Widespread colonization by invasive species often obscures their underlying niche requirements. A robust inference into habitat requirements demands direct measures of invasive species performance linked with associated environmental conditions. In the context of general ecological theory, we investigated the niche requirements of Microstegium vimineum, an invasive grass in the U.S. that overruns native vegetation in forest understories. We examined M. vimineum's performance and reproduction as a function of environmental drivers across forested and unforested habitats along a 100-km regional and climatic gradient in the southeastern U.S. from the southern Appalachian Mountains to the Georgia piedmont. We then measured M. vimineum performance and reproduction in response to direct environmental drivers (diffuse light, litter cover, soil moisture, herbaceous cover, soil pH, clay content and temperature) in paired invaded and uninvaded plots. Lastly, we experimentally investigated recruitment in the context of experimental and natural disturbances. We find that all habitats are not equally suitable for M. vimineum—even those within which it occurs—and that the environmental conditions associated with roadsides and waterways are most suitable for M. vimineum persistence and spread. Microstegium vimineum's soil moisture, light and leaf litter requirements may delineate the boundaries of suitable habitat for the exotic invader. Significant decreases in M. vimineum recruitment, performance and reproduction along these environmental gradients suggest its potential niche limitations. Nevertheless, we also find significant dispersal limits on M. vimineum populations not subject to conspicuous overland water flow. We discuss our findings in the context of spread, impact and management of invasive species.

Modeling and analysis of landscape evolution using airborne, terrestrial, and laboratory laser scanning

Current laser scanning (Lidar, light detection and ranging) technologies span a wide range of survey extent and resolutions, from regional airborne Lidar mapping and terrestrial Lidar field surveys to laboratory systems utilizing indoor three-dimensional (3D) laser scanners. Proliferation in Lidar technology and data collection enables new approaches for monitoring and analysis of landscape evolution. For example, repeat Lidar surveys that generate a time series of point cloud data provide an opportunity to transition from traditional, static representations of topography to terrain abstraction as a 3D dynamic layer. Three case studies are presented to illustrate novel techniques for landscape evolution analysis based on time series of Lidar data: (1) application of multiyear airborne Lidar surveys to a study of a dynamic coastal region, where the change is driven by eolian sediment transport, wave-induced beach erosion, and human intervention; (2) monitoring of vegetation growth and the impact of landscape structure on overland flow in an agricultural field using terrestrial laser scanning; and (3) investigation of landscape design impacts on overland water flow and other physical processes using a tangible geospatial modeling system. The presented studies demonstrate new insights into landscape evolution in different environments that can be gained from Lidar scanning spanning 1.0–0.001 m resolutions with geographic information system analysis capabilities.

Mechanisms of vegetation-ring formation in water-limited systems

A common patch form in dryland landscapes is the vegetation ring. Vegetation patch formation has recently been attributed to self-organization processes that act to increase the availability of water to vegetation patches under conditions of water scarcity. The view of ring formation as a water-limited process, however, has remained largely unexplored. Using laboratory experiments and model studies we identify two distinct mechanisms of ring formation. The first mechanism pertains to conditions of high infiltration contrast between vegetated and bare soil, under which overland water flow is intercepted at the patch periphery. The decreasing amount of water that the patch core receives as the patch expands, leads to central dieback and ring formation. The second mechanism pertains to plants with large lateral root zones, and involves central dieback and ring formation due to increasing water uptake by the newly recruited individuals at the patch periphery. In general the two mechanisms act in concert, but the relative importance of each mechanism depends on environmental conditions. We found that strong seasonal rainfall variability favors ring formation by the overland-flow mechanism, while a uniform rainfall regime favors ring formation by the water-uptake mechanism. Our results explain the formation of rings by fast-growing species with confined root zones in a dry-Mediterranean climate, such as Poa bulbosa. They also explain the formation of rings by slowly growing species with highly extended root zones, such as Larrea tridentata (Creosotebush).

Infiltration in Arid Environments: Spatial Patterns between Subsurface Heterogeneity and Water‐Energy Balances

Transient simulations of an arid mountain system were conducted using a fully integrated model of subsurface and overland water flow and the land surface energy balance (ParFlow). An hourly atmospheric time series was constructed and used to force a two‐dimensional model containing detailed, stochastic descriptions of subsurface heterogeneity for alluvial and fractured units. Two cases were simulated for multiple years of simulation: a dry case based on a year with below‐average precipitation, and a wet case with above‐average precipitation. For each case, four realizations of hydraulic conductivity were simulated, along with a homogeneous domain and a domain with lower fracture density. Detailed analysis of water balances from each simulation indicated that recharge (change in subsurface water storage) over multiple years was significant even for the dry case. The fractured model of subsurface heterogeneity, along with episodic infiltration, combined to create localized regions of fully saturated (perched) water. This was shown to be even more substantial in the wet case. By contrast, homogeneous simulations did not exhibit this behavior and estimated lower recharge than the heterogeneous simulations. Geospatial statistics were subsequently used to evaluate correlations in land‐energy fluxes. The land‐energy fluxes exhibited clear spatial correlation and were influenced by both the shallow and deeper soil structures. This indicates that land–atmosphere fluxes may provide an integrated measure of subsurface heterogeneity. Finally, the vertical spatial structure of soil saturation in the fractured system was shown to exhibit multiscale behavior.

Erosion Index Derived from Terrain Attributes using Logistic Regression and Neural Networks

Maps identifying areas prone to channel erosion within agricultural fields could be useful for conservation planners. The objective of this study was to test an approach for creating such maps with logistic regression and neural networks. Survey grade elevation measurements were obtained from on a Central Kentucky farm. The elevation measurements were used to create 4 by 4‐m digital elevation models (DEMs) from which terrain attributes were derived. Areas exhibiting evidence of erosion caused by overland water flow sufficient to justify the placement of grassed waterways were identified. The terrain attributes were used as predictor variables and models were fit using the field assessments of soil erosion. Leave‐one‐field‐out validation analysis was conducted to assess the quality of predictions maps. For the models created with logistic regression, an average of 14% of the 4 by 4‐m grid cells in noneroded areas were incorrectly classified as being eroded and 16% of cells in eroded areas were incorrectly classified as noneroded. For neural network analysis, these error rates were 15 and 19%, respectively. Most of these errors occurred because the analyses did not exactly define the shapes of the eroded features; however, both logistic regression and neural networks identified most waterway features in all fields. The proposed three‐variable logistic regression model for erosion prediction should only be tested with datasets constructed using identical procedures for DEM creation and terrain analysis. This approach could improve the efficiency and accuracy of field site assessments for conservation planning.

Management options to decrease phosphorus and sediment losses from irrigated cropland grazed by cattle and sheep

AbstractIn southern New Zealand, grazing of forage crops is common practice to satisfy feed requirements of animals in winter when pasture growth is limited. This practice has been shown to cause soil physical damage and increased loss of surface water contaminants sediment and phosphorus (P) to water bodies. Strategies to mitigate the loss of sediment and P were trialled on a Pallic soil type (Aeric Fragiaquept) in the North Otago Rolling Downlands of New Zealand. All sites were irrigated and measurements were made of losses in overland and sub‐surface flow from intensive cattle or sheep grazed, winter forage crops, and sheep grazed pasture. Two mitigations (restricted grazing of crop to three hours and the application of aluminium sulphate) were assessed for their potential to decrease contaminant loss from cropland. Volumes of surface runoff and loss of total P, filterable reactive P and sediment showed significant differences (P < 0.05) between the control treatments (i.e. no mitigation) with cattle crop (88 mm surface runoff) > sheep crop (67 mm) > sheep pasture (33 mm). The contribution of irrigation water to overland flow water, as a result of saturation‐excess conditions, varied between treatments with more loss under cattle crop (20% of total) compared with sheep crop (15%) and sheep pasture (11%). These differences are probably an effect of soil physical condition and highlight the importance of accurate irrigation scheduling to keep soil moisture below field capacity. Restricted winter grazing and alum application after grazing significantly (P < 0.05) decreased P losses in surface runoff under cattle (from 1.4 to 0.9 kg P/ha) and sheep (from 1.0 to 0.7 kg/P/ha) grazed crop plots by about 30%. In cattle grazed plots, restricted grazing also decreased suspended sediments (SS) by 60%. The use of restricted grazing is suggested as a means of decreasing P and SS loss from grazed winter forage crops. The use of alum shows some promise for decreasing P losses, but requires further work to determine its long‐term effectiveness and use in other soils and management regimes.