IGCP 565 Project Workshops

IGCP 565 Workshop 4: Integration of geodetic observations and products in models of the hydrological cycle Support for water management through hydrological models and data assimilation November 21-22, 2011 Johannesburg, South Africa

Gateway Wellfield Project, Hermanus, South Africa: Implementation, system testing, aquifer monitoring and hydrogeodetic observation

Chris Hartnady (1), Andiswa Mlisa (1), Eric Calais (2), Richard Wonnacott (3), Helen Seyler (1)
(1) Umvoto Africa (Pty) Ltd
(2) Purdue University
(3) Chief Directorate: National Geospatial Information

The Overstrand municipality of the Greater Hermanus Area (Western Cape, South Africa) has implemented a groundwater scheme to augment the existing, surface water-dominated municipal supply. Fundamental to sustainable development of the groundwater resource, a comprehensive monitoring programme is crucial for generating an appropriate hydraulic understanding of the interconnections between surface-water drainage basins, the shallow porous sedimentary aquifer and the deeper, confined fractured-rock aquifers, and for long-term, effective, beneficial management of resource abstraction. On the basis of about 10 years of monitoring records, informing the development of a conceptual model for groundwater behaviour in this area, the further development and calibration of a numerical model for groundwater flow highlights computer-based modelling as a conceptual text-bed and a practical aquifer-management tool.

The Gateway Wellfield, targetting the confined Peninsula Formation, Table Mountain Group (TMG) beneath the coastal platform, consists of 3 production wells fitted with continuous water-level measurements, individual electrical conductivity (EC) meters and flow meters in the borehole pipes, and a combined flow meter and pH/redox meter for water-quality monitoring; all being connected to a telemetry system which transmits readings to the internet hourly and is fitted with SMS alarms that allow 24-hour emergency response for low water levels or high EC’s. The monitoring network comprises 17 monitoring points in total throughout the area in the confined Peninsula fractured-rock aquifer around the wellfield, in the unconfined Peninsula separated from the wellfield, in the unconfined Skurweberg Formation (TMG) and in the shallow, discontinuous Bredasdorp sedimentary aquifer. Twelve of these monitoring points are connected to the telemetry and transmit to the internet 12-hourly.

The Gateway operational infrastructure currently also hosts a three-year (2008-2011) project on “Development and Application of Global Navigational Satellite Systems (GNSS) Methodology for Groundwater Resource Assessment”, with the following three aims:

1. To demonstrate the use of high-precision GNSS technology as a tool for groundwater resource monitoring and assessment;
2. To develop the methodology for relating GNSS measurements of natural or abstraction-induced surface deformation and conjunctive hydrogeological data in order to derive the in-situ, bulk elastic properties (e.g., skeletal compressibility) of an underlying confined fractured-rock aquifer;
3. To build South African capacity to establish the technical infrastructure (e.g., data telemetry) and implement the data-processing methods required for a pilot GNSS-for-Groundwater scheme at the Gateway Wellfield, Hermanus
   We will provide a summary of recent monitoring observations and developments that made the Gateway Wellfield critical to Hermanus water supply during the 2009-2011 drought period, and give an update of the hydrogeodetic observations.