world bank global water partnership associate program Sustainable Groundwater Management: Concepts and Tools GW • MATE Briefing Note Series Sustainable Groundwater Management Concepts & Tools global water partnership associate program Briefing Note Series Note 16 2009 Groundwater Resource Accounting critical for effective management in a ‘changing world’ Authors: Stephen Foster, Chris Perry 1 , Ricardo Hirata & Héctor Garduño ( 1 representing International Commission on Irrigation & Drainage ICID) Why are groundwater balances often found inadequate for resource management ? ● Groundwater resource accounting provides the essential technical foundation for making sound management decisions. While normally expressed in terms of the ‘groundwater balance’ of a specified ‘groundwater body’ – between recharge (replenishment) and discharge (including use) – it is most important to realise that it is the detailed understanding and breakdown of the components of this balance which provide vital information for management. ● It is precisely because this breakdown is often insufficient or incorrect that groundwater balances are frequently found inadequate for resource management purposes – and this is commonly associated with the following considerations : • on the ‘recharge side’ of the equation – failure to recognise the level of dependence upon land- use practices or upon streambed infiltration in a river system, both of which may be subject to temporal change • on the ‘discharge side’ of the equation – failure to recognise the level of non-consumptive use and ‘return flow’ implicit in a given type of major groundwater abstraction or the level of dependence of a given aquatic or terrestrial ecosystem on direct transpiration from the groundwater body. ● In this context ‘questions of scale’ – the spatial and temporal definition of the ‘groundwater balance calculation’ – are equally important. It is thus recommended : • to elect carefully the ‘time basis’ for calculation in climates where the incidence of major rainfall (and therefore of natural recharge) episodes has a long period of return, taking into consideration the potential effect on the groundwater body of temporal imbalances • to define the ‘groundwater body’ carefully in relation to the resource management issues that need to be addressed – a ‘groundwater body’ being a flow-boundary delimited part of a large aquifer system or a grouping of small interdependent aquifer units • to relate the ‘groundwater body’ to the corresponding larger hydrological unit (usually river basin), recognising its potential role of providing ‘baseflow’ (especially dry-weather flow) in that river. 1 Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized Public Disclosure Authorized