Policy responses

9.9.5 Surface water-groundwater conjunctive management

Groundwater depletion can lead to streamflow depletion (Hunt 1999; Kendy and Bredehoeft 2006), while streamflow diversions can limit groundwater recharge. Managing these two sources as separate entities arises from limited knowledge of groundwater systems and their spatial and temporal relationships with surface waters, a situation that is no longer justifiable (Famiglietti 2014; McNutt 2014). Current experiences highlight the value of conjunctively managing and using surface and groundwater as ‘one water’ (Sticklor 2014), thereby buffering against both droughts and floods. Sound management would consider the potential long-term impact of sustained groundwater abstraction on groundwater-dependent ecosystems in arid or semi-arid areas.

Box 9.5: Hermanus, near Cape Town, Western Cape Province, South Africa: A case study for conjunctive surface- and groundwater development and management

Groundwater was used for private housing developments and garden irrigation between 1971 and 2001. The greater Hermanus area water demand was met by the DeBos Dam (blue line, running concurrently with the purple total supply line in Figure 9.22). During 2002, 7,750 kilolitres/year of groundwater (green line) came online, with 24,191 kl/year added in 2009, as illustrated by the total supply (purple line) separating from the DeBos Dam inflow (blue line), with the groundwater addition (green line) keeping the supply line above the red demand line.

Groundwater augmentation was particularly effective in keeping supply above demand in 2010, when the DeBos Dam supply (blue line) could not meet it (red line). The water demand was met by surface-water supply from the dam, augmented by three well fields. Water restrictions were introduced in 2009 in anticipation of reduced surface-water supply and later lifted.

In contrast to other towns throughout the Western Cape Province suffering from severe drought, residents in the Greater Hermanus area were only advised on 27 February 2018 that it would be necessary to introduce Level 1B water restrictions from 1 March 2018; although water tariffs would only be increased once the dam had dropped to 40 per cent full level. The DeBos Dam was 46.5 per cent full on this date. (Overstrand Municipality 2018).

Aquifer storage and recovery recharge (Pyne 1995) or managed aquifer recharge (Dillon et al. 2009) are becoming important tools to battle chronic water scarcity (e.g. in the state of Arizona, United States of America) (Lacher et al. 2014; Scanlon et al. 2016; Stefan and Ansems 2017). Underground water storage could play a significant role in semi-arid and arid parts of Africa (e.g. Botswana, South Africa) during episodic heavy rain events, and/or where surface-water storage and transfer options are exhausted (Tredoux, van der Merwe and Peters 2009; Bugan et al. 2016). Capture and storage of monsoon rains in depleted aquifers is being piloted in India (International Water Management Institute 2016). Water sensitive urban design principles are critical to wateruse efficiency, reuse (Wong 2011; Fisher-Jeffes, Carden and Armitage 2017) and flood management (Dai et al. 2018); for example, storing reclaimed storm and wastewater from the urban environment in aquifer(s). This approach is especially effective in mitigating subsidence of, and saline intrusion into, coastal city aquifers (Ortuño et al. 2010; Bugan et al. 2016).

Figure 9.22: Hermanus Conjunctive Use
Source: Overstrand Municipality 2018.

Box 9.5 illustrates conjunctive development of surface and groundwater for Hermanus, a coastal town in South Africa, without inducing saline intrusion – a case aimed at mitigation of drought risks by balancing surface- and groundwater storage.

Underlying successful conjunctive use is comprehensive monitoring, modelling and risk assessment of the aquifer and surface-water source(s), associated catchment areas and social systems in a learn-by-doing approach (Bidwell 2003). Managing aquifer resources requires a land-use zoning system based on aquifer vulnerability and constraints, to enable adequate abstraction rates and natural recharge (Cross et al. 2016).

Figure 9.23: Supply of and demand for water, Greater Hermanus, 1971-2001 (a) and 2002-2017 (b)
Source: Overstrand Municipality (2018).

Monitoring and management of the full water-use cycle by the private sector (e.g. agriculture and mining) is gaining recognition. Examples of stewardship programmes include Woolworths in South Africa (in partnership with WWF-South Africa, WWF-UK, the Alliance for Water Stewardship and Marks and Spencer); Coca-Cola and the United States Agency for International Development (USAID) Water and Development Alliance, H&M and WaterAid (Workers’ Need Project in India), Unilever and Nestlé in Europe. The CEO Water Mandate (https://ceowatermandate.org) was instrumental in promoting the business benefits of water stewardship. This intersection between water governance, use, users, real-time monitoring, and modelling to inform evidence-based resource development and management is gaining momentum. In the fast-growing city of Bangalore, where 40 per cent of the water entering the system is lost to leakages, Water Supply and Sewerage Works formed an alliance with IBM and installed flow meters at several critical points in the water reticulation system. Data is being transmitted via GSM (Global System for Mobile communications) technology to a central Supervisory Control and Data Acquisition (SCADA) server to be transformed, aggregated and presented on a web interface and mobile application for end users.