Page 158 - Hydrogeology Principles and Practice

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5

Groundwater investigation techniques

5.1 Introduction surface, and in completing a flow net (see Box 2.3).
Values of hydraulic head are also essential in the pro-
The purpose of this chapter is to introduce basic cess of designing and testing a numerical groundwa-
field methods and techniques used in hydrogeolo- ter flow model for the purpose of making predictions
gical investigations. The assessment and management of aquifer behaviour under future conditions
of groundwater resources requires measurement of
water flows into and out of an aquifer. In that ground-
water is intimately linked to surface water within a 5.2.1 Water level measurement
river basin, it is useful to adopt the concept of a catch-
ment water balance, in which all known inflows and Measurement of groundwater level in the field is
outflows are accounted for, when discussing meas- undertaken using either a water level dipper or by
urement requirements. Discussion of groundwater use of a submersible pressure transducer positioned
development schemes, including a catchment water just below the lowest expected groundwater level.
balance equation, is provided in Section 8.2, but the The required field measurement is the depth from a
measurements needed to complete a water balance, convenient measurement datum, for example the
such as precipitation, evaporation, streamflow and well top or borehole flange, to the position of the
groundwater recharge, are presented in this chapter. groundwater level. If the elevation of the measure-
Pumping test methods for the assessment of the ment datum is known from levelling techniques
aquifer properties of transmissivity and storativity (Pugh 1975) then the elevation of the groundwater
and the application of tracer techniques in ground- level (or groundwater head, h) can be recorded as the
water investigations are also discussed, together with height above or below a local base level, typically
an introduction to the application of geophysical tech- mean sea level.
niques and numerical groundwater flow and solute A water level dipper for use in the field comprises a
transport modelling in hydrogeology. length of twin-core cable, graduated in centimetres
and metres, wound on to a drum and with a pair
of electrodes attached to the end (Fig. 5.1). When
5.2 Measurement and interpretation of the electrodes touch the water surface, a circuit is
groundwater level data completed which activates either a light or a buzzer
or both. Water levels can be measured to a precision
The measurement and collection of groundwater level of ±0.005 m (Brassington 1998).
data are of fundamental importance in hydrogeology. A pressure transducer consists of a solid-state
Groundwater level data for an aquifer unit can be pressure sensor encapsulated in a stainless steel, sub-
used for several purposes including plotting a hydro- mersible housing. A waterproof cable, moulded to
graph, determining the direction of groundwater the transducer, connects the water pressure sensor to
flow by constructing a map of the potentiometric a monitoring device such as a data logger from which