3 results for Acharya, G.

  • Modeling Top Soil Erosion and Mass Failures in Steep Agricultural Slopes: Integrating WEPP and a Landslide Model

    Cochrane, T.A.; Acharya, G. (2009)

    Conference Contributions - Published
    University of Canterbury Library

    Steep agricultural hillslopes are not only subjected to soil erosion, but also have a probability of failure. In hilly country were both soil erosion and landslide processes are active, the interaction between these processes is critical. A model called WEPP-SLIP was developed that integrates erosion modeling and landslide prediction to determine sediment delivery pre and post landslide failures. Initially, WEPP is used to estimate pre-failure erosion. The landslide model then predicts where a mass failure may occur along the slope. Changes in topography and soil structure are estimated from the predicted magnitude of the landslide. The WEPP model is then used again with the new topography to predict postfailure erosion. A flume based experiment was used to validate the modeling with loess and sandy type soil representative of hilly sheep pasture land in New Zealand. Results showed a good correlation between predicted and measured erosion and runoff. In fallow conditions, post-failure erosion was shown to be smaller than pre-failure erosion due to changes in slope and soil properties resulting from the failure. The opposite is true for hillslopes covered with grass, as slope failures disturb the cover resulting in greater erosion. Flume based results indicate that sediment yields during failures were high. WEPP-SLIP can be applied for individual hillslope profiles; however, efforts are on the way to create a spatially distributed model. The model will be used to improve management practices and calculate the long term implications of mass movements in hilly slopes.

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  • Development of a forest road erosion calculation GIS tool for forest road planning and design

    Cochrane, T.A.; Egli, M.; Phillips, C.; Acharya, G. (2007)

    Conference Contributions - Published
    University of Canterbury Library

    Forestry plays an important role in New Zealand's economy. The industry is almost entirely based on planted forests covering 1.8 million hectares of New Zealand. Forestry operations, however, need a dense forest road network. On hilly forested terrain, these roads are often the main source of sediment which can cause degradation of streams and waterways. Appropriate road placement and design may help reduce soil erosion and subsequent environmental impacts. To facilitate forest road planning and reduce potential soil erosion, a Forest Road Erosion Calculation Tool (FORECALT) was developed for ArcGIS 9.1 using the Water Erosion Prediction Project (WEPP) model. The FORECALT tool uses a DEM, a GIS vector based road network map, and a series of road definition selection tools to parameterize and run the WEPP model for the combined set of all individual segments of a road network. The model is able to simulate erosion from cut slopes, road surfaces, and road drainage ditches. The model simulates both insloped and outsloped forest roads. Results of erosion and runoff per segment of forest road are displayed via he GIS interface. Outsloped forest road erosion can be displayed graphically as a map layer and total insloped forest road erosion is calculated for selected outlet points. The FORECALT model was applied to a forest road network in the Whangapoua forest in the Coromandel Peninsula of New Zealand. Erosion and runoff predictions were made for a variety of soil and road type configurations. This application illustrates the versatility of the tool and its ability to aid in reducing environmental impacts by improving the design and planning of road networks. Sensitivity analyses of the model showed that the model is sensitive to the definition of the road segment lengths as well as DEM resolution. Segments of up to 80 meters represent the original DEM profile with reasonable accuracy; however, even small variations in calculated slope profiles may impact WEPP model erosion predictions. Runoff predictions are not affected by DEM resolution or segment length selection. Although further research is needed to understand the complex relationship between input DEM resolution and segment length selection, modelling results suggest that the model would be a valuable asset for forest managers.

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  • Rainfall induced shallow landslides on sandy soil and impacts on sediment discharge: A flume based investigation

    Acharya, G.; Cochrane, T.A. (2008)

    Conference Contributions - Published
    University of Canterbury Library

    The impact of rainfall induced shallow landslides on hillslope sediment discharge is not well understood. The aim of the research was to investigate how varying soil profile depth affects the location and occurrence of shallow slope failures as well as how it impacts sediment yields. Four flume based experiments were conducted using a sandy soil and a 30 and 10 degree compound slope configuration under average rainfall intensity of 50 mm/hr for soil profile’s depths set to 20, 30, 40 and 50 cm. Sediment discharge and runoff were collected from the flume outlet at 15 minute intervals. Changes in soil profiles after landslides and changes in soil properties like soil armouring were also recorded. Results showed that sediment yields at the outlet, before landslides occurred, were very low and limited to the finer soil particles as would be expected for a sandy soil. However subsequent variations in sediment discharge were strongly related to failure events and their proximity from the outlet. The sediment yield was also affected by the original soil thickness. The results provide a clear link of landslides and sediment discharge to hydrological processes occurring in the hillslope which are related to the soil thickness.

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