eWater has developed and adopted a three pronged quality assurance approach for developing and applying water management models. The key elements of this approach are: (a) a structured process for model development, including user requirements, software testing, trial applications and supporting documentation; (b) provision of a peer reviewed family of guidelines outlining a best practice approach to model application, including generic guidelines representing the highest level in the hierarchy that provide the framework for a consistent set of more detailed, plus supporting guidelines for certain domains relevant to eWater Source; and (c) training and support, including online modules and a community of practice. This paper provides an overview of the main features, development and implementation of eWater's quality assurance approach.
Increased sediment and nutrient fluxes arising after wildfires may affect downstteam water quality. We use mineral magnetic tracers to elucidate linkage between different slope units, river channel and a reservoir sediment column in the gorge-dissected landscape of a burnt water supply basin. Comparison of magnetic properties of source areas with downstream (sub-aerially stored) channel deposits suggests predominantly ridge-top origin with significant storage of sediment within footslopes. Magnetic properties of the sediment column provide insight into the nature of sediment accumulation on the reservoir floor and the role of immediate post-fire rainfall events. Comparison of source signaUires with sub-aqueously stored sediment is complicated by the apparent fragility of some fine pyrogenic mineral grains; these may have to be accounted for in sediment column interpretation. Tracing tools provide river basin managers with important process-based evidence of post-fire sediment redistribution, useful for more effective mitigation of these infrequent, but significant, sediment redistribution events.
Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality.
Abstract Macroscopic analytical methods, based upon the capillary rise formula and the Hagen‐Poiseuille equation, were used to quantify the combined effects of soil‐pore size and preferential flow on the hydraulic conductivity of forest soils. A density function was derived that relates effective pore diameters of heterogeneous soil‐pore systems to measured hydraulic conductivity. Density functions derived for soils from sites with different topographic influences and disturbance effects characterized the effect of preferential flow on their hydraulic conductivity. It was shown that macroscopic methods can describe preferential flow without having to resort to microscopic examination of individual pores. If the required properties of the undisturbed parent soil (hydraulic conductivity and equivalent pore size) have been characterized, then these methods can predict the effect of disturbance on the hydraulic behavior of the soils.
The rainfall‐runoff events following five fires that occurred within a 40‐year period in eucalypt forests of the Nattai catchment, southeastern Australia, were investigated to quantify the postwildfire hydrological response and to provide context for lower than expected erosion and sediment transport rates measured after wildfires in 2001. Daily rainfall and hourly instantaneous discharge records were used to examine rainfall‐runoff events in two gauged subcatchments (>100 km 2 ) for up to 3 years after fire and compared with nonfire periods. Radar imagery, available from 2001, was used to determine the intensity and duration of rainfall events. Wildfires in the study catchment appear to have no detectable impact on surface runoff at the large catchment scale, regardless of fire severity, extent or time after fire. Instead, the magnitude of postfire runoff is related to the characteristics of rainfall after fire. Rainfall is highly variable in terms of annual totals and the number, size, and type of events. Rainfall events that cause substantial surface runoff are characterized by moderate‐high intensity falls lasting one or more days (≥1 year average recurrence interval). These are triggered by synoptic‐scale weather patterns, which do not reliably occur in the postfire window and are independent of broad‐scale climate dominated by the El Niño–Southern Oscillation (ENSO). This study highlights the importance of considering the characteristics of rainfall, as well as local factors, in interpreting the postfire hydrological response.
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