Before water resources can be developed and managed, they need to be evaluated. 'Evaluation' is used here in the sense of determining what water resources are available in a catchment (groundwater or surface water), and what proportion of those resources can safely (that is, sustainably) be exploited for various uses, having set aside a proportion for environmental or ecological needs. Resource evaluation requires a multi-disciplinary approach, taking into account many different aspects, such as:

• The catchment boundaries and topography of the groundwater and surface water systems.
• The geology, hydrogeology, and hydrogeochemistry of the groundwater system.
• The hydrology and water quality of the surface water system.
• The nature and magnitude of any interaction between groundwater and surface water.
• The influence of meteorology and climate, especially on rainfall and evapotranspiration.
• Land use, including potential sources of pollution and historical changes in these factors.
• The environmental or ecological status of the catchment and its habitats.
• Current abstraction of water, water demand, and water or effluent discharges.

Schlumberger Water Services has extensive experience of all these aspects, and some examples of projects are given below. Techniques such as numerical modelling of groundwater and surface water systems are very useful for the evaluation of water resources. Services/Modelling.

Project Examples:

Title:	Measham resource evaluation
Location:	UK
Client:	Environment Agency
Description:	Schlumberger Water Services was commissioned to undertake an assessment of the groundwater resources of Measham Groundwater Unit, a Triassic sandstone aquifer. The surface and groundwater resources of this aquifer management unit were thoroughly reassessed to obtain a better estimate of the maximum licensable resources. The geology, hydrogeology, soils, land use, meteorology, hydrology etc, were described. The effects of groundwater abstraction on rivers and streams was examined, recharge estimated, a water balance conducted, and recommendations made for improved monitoring.

Title:	Saline water resources study
Location:	India
Client:	Confidential (international oil company)
Description:	Schlumberger Water Services was asked to carry out, at short notice, a detailed and comprehensive study of the groundwater resources of a semi-arid area in India, to meet a requirement for large quantities of saline water to inject into a deep oil reservoir to aid oil recovery. The project includes data collection, hydrogeological conceptual modelling, numerical groundwater modelling, exploratory drilling and test pumping, resource evaluation, and assessment of the impact on shallow fresh groundwater of abstracting deep saline groundwater from various aquifer units.