Using rainfall simulation to guide planning and management of rehabilitated areas: Part II. Computer simulations using parameters from rainfall simulation

This paper reports computer simulations carried out using data from a rainfall simulator study on a steeply sloping revegetated area (a soundbund) at the NorthParkes Mine, near Parkes in New South Wales, Australia. Simulations of slope stability used a combination of daily time‐step models to consider soil water balances and runoff, growth of grass/legume pasture and soil erosion. Simulations indicated that long‐term erosion rates on the soundbund would be low (1·01–1·27 t ha⁻¹ yr⁻¹) due to low runoff rates and good vegetative cover. The simulations highlighted that peak vegetative growth occurred prior to the period of peak erosion hazard, with carry‐over dry matter being crucial for erosion control during the period of peak rainfall erosivity. This, in turn, indicated that grazing during the periods of peak growth and peak erosion hazard should be avoided (to avoid loss of dry matter). It also indicated that there was value in establishing grass species that would give greater growth during summer months, and that may produce dry matter that is more persistent through time. Simulations of stormwater flows in channels draining various lifts on the soundbund compared a range of alternatives with respect to channel length, gradient and roughness. The simulations indicated little effect of channel length on peak flow rates or depths once channel lengths exceeded 250 m and also showed little effect of vegetative roughness on peak flow rates or depths once Manning's n values exceeded 0·05. Implications of these results for design of drainage channels and drop structures on the soundbund are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

The effect of leaching and irrigation on the growth of Atriplex semibaccata

Mining activities along the west coast of South Africa will lead to salinization of the soil if sea-water is used in the mining process. Laboratory studies were conducted to determine the influence of leaching depth and the amount and frequency of irrigation on the growth of Atriplex semibaccata R. Br. Leaching depth as well as the amount and frequency of irrigation had no significant effect on biomass production. However, the interaction between leaching depth and amount of irrigation did influence the biomass production of Atriplex semibaccata. Root:shoot ratio increased as the amount of irrigation decreased.     

Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin—1: method assessment

Revegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion‐control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS‐plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ≈60 mm h⁻¹, approximating the 100‐yr, 15‐min design storm, was applied over replicated 0·64 m² plots in each treatment type and over bare‐soil plots for comparison. Simulated rainfall had a mean drop size of ≈2·1 mm and approximately 70% of ‘natural’ kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45 μm) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2–12 as compared to 0·3–3 g m⁻² mm⁻¹ for granitic soils. Pine‐needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross‐slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd.