PhDENV (Hydrology) / Department of Hydrology and Water Resources / This study developed operating rules for groundwater supply from a probabilistic (risk-based)
approach. Groundwater supply systems are often operated without relating groundwater
yield/availability to demand which makes groundwater resource planning and management
challenging and unpredictable. Risk-based approaches for developing groundwater operating rules
comprehensively incorporate assurance of supply and also account for uncertainty due to model
inputs, model structure and climate variability. A groundwater resource unit (GRU) was delineated
and its hydrogeological conceptual model developed. Automatic curve matching was used to identify
appropriate aquifer models and test solutions for estimating hydraulic characteristics (storativity,
transmissivity and hydraulic conductivity) based on Aquifer Test Solver (AQTESOLV) Pro version 4.5.
Limited groundwater levels and rainfall data were infilled and/or extended using Output Error-Nonlinear
Hammerstein Weiner (OE-NLHW) and non-parametric regression (NPR), respectively.
Performances of these models were based on relative error (RE), correlation coefficient (COR), root
mean square error (RMSE), coefficient of determination (R2) and Nash Sutcliffe coefficient of efficiency
(NSE). A program for generation of monthly groundwater levels for the GRU was coded in FORTRAN
based on the revised version of the Pitman model (referred to as GW-PITMAN model). The model was
calibrated using groundwater levels from a neighbouring borehole due to lack of observed
representative data for the GRU. Validation was done by establishing the realistic nature of simulated
runoff, recharge and groundwater levels. A Variable Length Block (VLB) bootstrapping model was used
for simultaneous generation of stochastic inputs (rainfall, evaporation and groundwater levels) of the
groundwater operating rules model. Operating rules were developed from statistical analysis of 100
base yields for the GRU simulated from 5-year long stochastically generated sequences (with length
of 34 years) of rainfall, evaporation and groundwater levels. The hydrogeological conceptual model
indicated presence of faults and diabase dykes which influence preferential flow paths and storage of
water in the aquifer. Identified aquifer test solutions were found to be suitable for estimation of
hydraulic characteristics, since they had generally good model fits and low mean residual errors.
Heterogeneous aquifer types were identified though leaky aquifer dominated. Storativity,
transmissivity and hydraulic conductivity values ranged from 0.0003-0.060, 0.78-12.3 m2/day and
0.074-0.460 m/day, respectively, indicating limited storage with potential for local groundwater
supply for private consumption. Graphical fits for observed and estimated rainfall and groundwater
levels were mostly comparable, though scatter plots indicated cases of underestimation and
overestimation of observed values. R2, COR, NSE, RMSE and RE values were 0.76 and 0.7, 0.87 and
0.84, 0.75 and 0.68, 3.67 and 3.03 mm and 30 and 29% for both calibration and validation runs,
respectively, for NPR model. R2, COR, NSE, RMSE and RE were 0.99 and 0.86, 0.97 and 0.93, 0.99 and
0.84, 0.03 and 0.01 m and 0.08 and 0.11% for both calibration and validation runs, respectively, for
OE-NLHW model. The models were therefore found to have efficient calibration and validation, and
were thus, suitable for data extension. Estimated groundwater levels, streamflow and groundwater
recharge for both calibration and validation runs of the GW-PITMAN model, generally fluctuated with
changes in rainfall, indicating that they are realistic. Majority (9 out of 10) of the historical statistics
were mostly well preserved by VLB, except for skewness. Historic highest groundwater levels were
also not well preserved. Superimposing the cumulative demands on the base yield curves and analysis
of percentages of water demands that can be supplied indicated that the groundwater system could
not meet the water demands at all times. To promote sustainable multipurpose use of water that can
enhance rural livelihoods, allocating water using priority classification was found to be essential.
Operating rule curves for groundwater supply were derived using a risk-based approach. The
operating rule curves indicated that if priority classification is used all water demands are met up to
maximum groundwater level of 25 m. The developed operating rule curves are therefore expected to
improve water supply to both domestic and productive water uses, if they are adequately
implemented and hence improve livelihoods. The procedures followed in developing risk-based
groundwater operating rules for Siloam Village were summarised to assist in their application in any
delineated groundwater resource unit. Though minimal infrastructure is available to support
implementation of the operating rules, additional monitoring boreholes are required to aid in
estimation of average groundwater levels for further calibration and validation of the GW-PITMAN
model. Detailed geological and geophysical investigation are required to improve on characterisation
of the GRU and its hydrogeological conceptual model. Undertaking a study of this nature in other areas
including those which are data-scarce could promote wide implementation of risk-based groundwater
operating rules. / NRF
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:univen/oai:univendspace.univen.ac.za:11602/1417 |
| Date | 20 September 2019 |
| Creators | Makungo, Rachel |
| Contributors | Odiyo, J. O., Ndiritu, J. G., Mwaka, B. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1 online resource (xx, 217 leaves: color illustrations, color maps) |
| Rights | University of Venda |
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