Seepage behaviour through earth dams with zones of different filling materials

Since more than one-third of dam failures have been attributed to uncontrolled seepage, it is of great importance to investigate the behaviour of this phenomenon in order to achieve the maximum degree of safety for such dams. The present work investigated the influence of the permeability coefficient of the different materials used in zoned earth dams on different seepage parameters. For the modelling and analysis processes, the Seep/w and Seep2D software were employed. The numerical results prove that the optimum relative hydraulic conductivity between the inner and transition shells is about 0.001, and it is better to use filling materials with less hydraulic conductivity in the upstream transition and outer shells than in the downstream ones. A good agreement was noted between the obtained results from Seep/w and those from Seep2D. Reducing the hydraulic conductivity of both the upstream and the downstream shells, or of the downstream shells only, causes the pore water pressure in the dam body to increase significantly, and causes a remarkable reduction in the seeped water quantity and velocity. A moderate reduction in the different seepage parameters is achieved by reducing the hydraulic conductivity of the upstream transition shell, and a small reduction is noticed by reducing the hydraulic conductivity of the upstream outer shell

Reflecting on Evictions and Unlawful Occupation of Land in South Africa: Where Do Some Gaps Still Remain?

The issue of unlawful occupation and homelessness has been a very prominent topic for many decades. While our approach to evictions and unlawful occupation has clearly shifted from a draconian approach under the Prevention of Illegal Squatting Act 51 of 1951 (hereafter PISA) to an approach that focusses on human rights under the Prevention of Illegal Eviction from and Unlawful Occupation of Land Act 19 of 1998 (hereafter PIE), there are still various aspects that potentially fall short in protecting the rights of the various stakeholders involved in these disputes. In particular, this paper focusses on three areas where PIE potentially falls short. In this regard we examine cases of the impossibility of eviction orders, our current understanding of the notion of "home", and whether or not PIE applies to both occupied and unoccupied structures. We also briefly explore issues relating to the non-implementation of PIE, especially in relation to the government's goal of preventing unlawful occupation. Central to these discussions is whether our current approach is sufficient and in line with constitutional obligations or whether we need to rethink our approaches to ensure that we do not undo the progress made since apartheid

Utilization of hydrodynamic modelling to quantify water losses from the Sundays River between Darlington Dam and Korhaans Drift Weir

This study quantified transfer losses over the 2021/2022 water year for irrigation releases from Darlington Dam into the Sundays River, which are diverted at the Korhaans Drift Weir.  A one-dimensional (1D) hydrodynamic model was set up and calibrated to simulate the transfer losses which were assumed to consist primarily of evaporation and evapotranspiration (ET). Flow measurements were undertaken with an acoustic doppler current profiler (ADCP) to verify the calibrations of the Parshall flumes at Darlington Dam and at Korhaans Drift Weir.  The ADCP results showed that the Department of Water and Sanitation’s (DWS’s) existing discharge tables underestimated lower flows by 13% and higher flows by 16%.  The hydrodynamic model results also estimated transfer losses between Darlington Dam and Korhaans Drift to range between 2.0% and 5.3%.  It was determined that the transfer losses were seasonal and were lower than those determined by similar studies for other South African rivers

Alternative streamflow-based approach to estimate catchment response time in medium to large catchments: case study in Primary Drainage Region X, South Africa

Event-based estimates of the design flood in ungauged catchments are normally based on a single catchment response time parameter expressed as either the time of concentration (TC), lag time (TL) and/or time to peak (TP). In small, gauged catchments, a simplified convolution process between a single observed hyetograph and hydrograph is generally used to estimate these time parameters. In medium to large heterogeneous, gauged catchments, such a simplification is neither practical nor applicable, given that the variable antecedent soil moisture status resulting from previous rainfall events and spatially non-uniform rainfall hyetographs can result in multi-peaked hydrographs. In ungauged catchments, time parameters are estimated using either empirical or hydraulic methods. In South Africa (SA), unfortunately, the majority of the empirical methods recommended for general use were developed and verified in catchments ≤ 0.45 km² without using any local data. This paper presents the further development and verification of the streamflow-based approach developed by Gericke (2016) to estimate observed TP values and to derive a regional empirical TP equation in Primary Drainage Region X, SA. A semi-automated hydrograph analysis tool was developed to extract and analyse complete hydrographs for time parameter estimation using primary streamflow data from 51 flow-gauging sites. The observed TP values were estimated using three methods: (i) duration of total net rise of a multi-peaked hydrograph, (ii) triangular-shaped direct runoff hydrograph approximations, and (iii) linear catchment response functions. The combined use of these methods incorporated the high variability of event-based time parameters, and Method (iii), in conjunction with an ensemble-event approach sampled from the time parameter distributions, should replace the event-based approaches to enable the improved calibration of empirical time parameter equations. The conceptual approach used to derive the regional empirical TP equation should also be adopted when regional equations need to be derived at a national scale in SA

Investigation of the effect of variable-sized energy dissipating blocks on sluice gate performance

The present research used a combination of experimental and numerical methods to investigate energy dissipation blocks of different heights placed downstream of a sluice gate in an open channel flow. Numerical model simulations were performed using a 3D computational fluid dynamics (CFD) technique, using the Reynolds-averaged Navier-Stokes (RANS) equations with the volume of fluid (VOF) and k-ε turbulence models. The accuracy of the numerical model and the grid sensitivity was assessed according to a recommended procedure in the literature. Different hydraulic and geometry conditions were investigated to understand the energy dissipation behaviour of the blocks. The hydrodynamic effects of different block spacings, heights and configurations were analysed by means of CFD simulations. The results show that the variable size blocks have a high energy dissipation efficiency in sluice gate flows, particularly at high Froude numbers. The energy dissipation efficiency of the blocks downstream of a sluice gate can reach up to 55% for high discharges (Q = 35 L/s). Interestingly, the energy dissipation performance of small gate openings exceeds that of large gate openings, reaching a peak efficiency of 40% for the same discharge. In addition, the block spacing has a minimal effect on the energy dissipation, while smaller block spacing results in a smoother water surface profile

Water SA reviewers 2023

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