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Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.A.,La Trobe University
Environmental Earth Sciences

Lake Burrumbeet, which is located in the basalt plains of western Victoria, Australia, has a much lower salinity than other lakes in the region. To determine the factors causing the freshness of this water body, an assessment was carried out using existing geological information to reconstruct the palaeotopography beneath basalt flows, and using hydrogeological data, bore hydrographs and hydrological data together with a time variant lake water balance analysis calibrated from 1998 to 2008. The calibrated water balance of Lake Burrumbeet shows that groundwater outflow has a major influence on lake levels (31 % of water losses). The lake water budget analysis confirms that the interaction of Lake Burrumbeet with the surrounding groundwater system is volumetrically significant. Geological re-construction of the course of the buried river valley sediments (Deep Lead underlying the basalt) shows that they run directly beneath Lake Burrumbeet. Groundwater leakage into these sediments is sufficient to transfer enough salt from the lake to maintain a low to moderate lake salinity. The conceptual hydrogeological model of Lake Burrumbeet, coupled with the time variant water budget analysis, show that the difference in salinity among the lakes in the region can be explained by variations in the configuration and hydrogeological setting of the lakes, and this hypothesis provides new understanding of the relative freshness of the lake. © 2014, Springer-Verlag Berlin Heidelberg. Source

Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Yihdego Y.,University of Twente | Becht R.,University of Twente
Journal of Hydrology

Aquifers near Lake Naivasha, Kenya are important water resources and are used extensively for irrigation and for municipal and domestic water supplies. Head data for a 79-year period (1932-2010) were analyzed to develop a conceptual model of aquifer-lake interaction and used to develop a three-dimensional numerical model. A three-dimensional groundwater flow model with four layers was used to simulate ground-water flow in the aquifers and lake-aquifer interaction. The lake is simulated by specifying a high hydraulic conductivity for lake-volume grid cells. The 90. m Digital Elevation Model (DEM) that includes the bathymetry improved the 3-D representation of the lake in the groundwater system and helped to define the deformed layer that honors the stratigraphy. The calibration process was carried out using PEST in conjunction with pilot points and regularization. The finite difference groundwater model results were comparable with measured head data and isotopic and hydro-chemical data. The sensitivity of the computed lake level was tested using the "high-K" method to the choice of K2/K1, where K2 and K1 are the hydraulic conductivity of the lake node and the aquifer (respectively). Higher values of K2/K1 should be used with higher regional gradients on the order of 0.002 to ensure mainly accurate calculations of seepage rates to and from the lake. © 2013 Elsevier B.V. Source

Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University
Water Resources Management

In western Victoria, Australia the water table and lake level in the Glenelg-Hopkins catchment have been declining for the last 15 years, and this is attributed to either the low rainfall over this time and/or a substantial change in land use. Stream flow modelling was carried out using monthly empirical water balance model (modified tanh function together with double mass curve analysis), on 37 stream gauges to assess whether the impact of land use change could be detected by a change in the magnitude of the resulting runoff. The empirical hydrological model was able to distinguish impact of land use change on stream flow from the climatic variables. There were substantial decreases in stream flow in the 1970s-1980s, probably related to increasing livestock densities in the region. Furthermore, the methodology can be a powerful tool to monitor and evaluate the possible impacts of future land use changes. It can be concluded that the use of such empirical hydrological modelling greatly improves the ability to analyse the impact of land use on catchment runoff. The model is a practical tool that can be readily used for identifying and quantifying the effect of landuse changes on catchment for water resource decision-making, which could be hardly possible using the time consuming, data hungry and expensive physical process models available. © 2013 Springer Science+Business Media Dordrecht. Source

Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University
Journal of Environmental Management

In southwestern Victoria a large number of lakes are scattered across the volcanic plains; many have problems with increasing salinity. To identify the hydrologic components behind this problem, three lakes, Burrumbeet, Linlithgow and Buninjon, were selected for detailed water and salt budget modelling using monthly values of rainfall, evaporation, surface inflow and outflow, and groundwater inflow and outflow (using the new modified difference method developed in this study). On average, rainfall begins to exceed evaporation with the onset of winter rainfall in May, so lake levels rise and lake salinities decline. The modelled lakes have become more saline over the last decade, a time of drought with below average rainfall, and all eventually dried out, their salinities rising to very high levels as they shallowed. Lake Burrumbeet is generally much less saline than Lakes Linlithgow and Buninjon, because it has substantial groundwater outflow, probably due to leakage through one or more volcanic necks. This limits the amount of time the lake water is subject to evaporation, and also allows significant salt export. The other lakes do not leak. The modelling indicates that when the lakes dry out, salt is lost from the lake-beds, probably due to wind deflation of salt crusts and leakage into the underlying groundwater. The removal of salt during drying-out phases resets the salinity of the lakes, limiting their ability to become more saline with time. Drying-out phases may therefore be essential in preventing the increased salinisation of lakes and wetland environments across the volcanic plains. © 2012 Elsevier Ltd. Source

Yihdego Y.,La Trobe University | Yihdego Y.,Snowy Mountains Engineering Corporation SMEC | Webb J.,La Trobe University | Leahy P.,Applied science Group
Hydrological Sciences Journal

Lake Purrumbete is a deep volcanic freshwater lake, cylindrical in shape, located within an extensive basalt plain in southeastern Australia. A modified difference water budget method for lakes, that estimates net groundwater flux through the difference between the level of the lake and the water table, along with the specific yield and area of the aquifer, successfully modelled the lake level fluctuations. The major influences are evaporation and direct precipitation; however groundwater fluxes are significant (~17%). The salt balance modelling shows that the salinity in Lake Purrumbete is largely controlled by groundwater and surface water fluxes. Lake Purrumbete has a greater interaction with the surrounding groundwater system than other nearby volcanic lakes due to its significant depth and the presence of highly permeable basalts along the upgradient shoreline. Its low salinity reflects the substantial salt export in the groundwater and surface outflow, as well as the lake’s relatively small evaporation due to the low surface area/volume ratio. The fluctuations in lake level and salinity for Lake Purrumbete are much less than for other lakes in the region, even during the 1997–2010 drought, due partly to the large, relatively constant groundwater flux. Low salinity, deep water and estimated depth of stratification from this study, which leads to a distinct limnology, implies that the creatures need to adapt to a different habitat to survive in the vicinity of Lake Purrumbete. Thus, Lake Purrumbete will be an important aquatic ecosystem refugium if climate change causes frequent seasonal drying of other lakes in the plain, and it is important to develop management strategies to maintain its water resources and quality. Editor D. Koutsoyiannis Associate editor Not assigned © 2015 IAHS. Source

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