**5. Methods**

The methods for the investigation of aquifer systems such as remote sensing (RS) and geographic information system (GIS), resistivity test, and pumping tests will be discussed. Several related approaches also will be discussed such as seepage meter, Darcy's law, heat tracer method, and environmental tracer method for the investigation of SW-GW interactions.

#### **5.1 Resistivity survey**

In groundwater system, evaluation geophysical methods (geothermal gravity, electrical resistivity, etc.) have been well recognized. The electrical resistivity survey is one of the tools that is very effective to identify subsurface profiles without interfering with the structure of the soil [22]. The usage of this method enables the measurement of groundwater quantities and quality. This includes detailed knowledge concerning the geological and hydrological information of the GW system such as subsurface mapping to identify aquifer-protective structures, the analysis of infiltration of the vadose zone, measuring the extent of volume and internal aquifer structure, and groundwater contamination [23]. It is effectively used to estimate soil porosity and soil permeability as a non-destructive process. In addition, it is commonly utilized for the interaction of changes in the resistivity of the subsurface with the soil characteristics. The negligible porosity and permeability of the hard rock, as well as igneous and metamorphic rocks, in terms of soil exploitability, but the alteration processes taking place in the first 10–100 m of depth can significantly increase their fracture permeability. In the zone influenced by modification, this may create moderate secondary porosity aquifers.

These aquifers are very critical for irrigation and the availability of potable water in many parts of the world. Altered methods often influence the overall porosity of the rock such as water content which results in a varying spectrum of electric resistivity within the transition region [24]. Consequently, it is a good potential technique for the study of alteration zones in hard rocks, electrical resistivity in rocks influenced by differing weathering degrees. Schlumberger array system [25] was used to perform the resistivity survey. "ABEM SAS 1000 Terrameter" was the device used for performing Vertical Electrical Sounding (VES). For resistance measurement, four electrodes were selected at a certain time. Two existing electrodes situated on the outside of the potential electrodes were inserting currents into the field. The potentially different electrodes were quantified and the ground resistance was measured by Eq. (2).

$$
\rho = K\_{\,\,\,\,\,\,\,} \* \,\,\, resistance \,\text{of} \,\,\, \text{earth} = K\_{\,\,\,\,\,\,} \* \left(\frac{V}{I}\right) \tag{7}
$$

$$K\_{\mathcal{A}} = \left\{ \pi \left( \frac{AB}{2} \right)^2 \* \left( \frac{MN}{2} \right)^2 \right\} / MN \tag{8}$$

where ρ denotes the apparent resistivity (ohm-meter), *Kg* is the geometric constant, *I* indicate current (ampere),*V* is the voltage (volt), *AB* is spacing between the current electrode (m) and *MN* is spacing between the potential electrode (m). The geometric factor ( *Kg* ) is based on field observation calculation and by multiplying the geometric factor with data of resistivity the apparent resistivity values can be calculated. For instance, the transmissivity estimates were 0.588, 0.578, and 0.756 m2 /min, respectively, by the analysis of grain size distribution, the resistivity survey, and the pumping test [25]. The finding on the results indicated that the values of aquifer transmissivity have been found much similar to each other by measurement of grain size distribution, pumping test, and resistivity survey.

#### **5.2 Pumping test**

Pumping test is a field technique and it is used for the assessment of the aquifer characteristics such as hydraulic conductivity (*K*), storage coefficient (*S*), and transmissivity (*T*). Aquifer hydraulic parameters are spatially and temporarily influenced by their heterogeneity, complicated geologic conditions, as well as multipart boundaries but these characteristics in various aquifer areas, are challenging to describe efficiently [26]. The geological formation of the aquifer (confined, leaky, unconfined, and fractured aquifer) influences the hydraulic parameters to estimate; thus, various interpretive techniques are applied. Implementation of geophysical studies and pumping test techniques may be used to maximize the comprehension of hydrogeology models by accurately detecting such essential aquifer characteristics: permeability, thickness, porosity, transmissivity, hydraulic conductivity, etc. Various pumping test methods are used to determine aquifer hydraulic characteristics; but, long term, step pumping, and recovery tests are mostly utilized. Aquifer characteristics can be found by using easy methods such as the first analytical solutions proposed by [27] Thiem (1906) for a steady-state condition that gives an equation for the groundwater flow in aquifers subject to pumping. After this, [28] Theis (1935) and Cooper and Jacob (1946) [29] find extremely restrictive conditions in terms of a transient state that limit their implementation to aquifers that are uniform, homogeneous and isotropic, constant thickness, porous and permeable which produce pumping with a constant discharge in a completely penetrating well. The following formulas calculate the aquifer properties by Theis-Jacob method:

$$s(r,t) = \frac{Q}{4\pi T} \left[ \mathcal{W} \left(\frac{4^2 S}{4T t\_p}\right) \right] \tag{9}$$

$$T = KB = \frac{\gamma b\_m^3}{12\,\mu} N\_f \tag{10}$$

where Eq. (5) shows that the *s rt* ( , ) is the drawdown,*Q* is the pumping rate,*T* is the hydraulic transmissivity,*W* is the well function for a confined aquifer, *S* is the aquifer storativity and *<sup>p</sup> t* is the pumping period (*t*) for *t* ≤ *t*p. The Eq. (6) is showing that *K* is the hydraulic conductivity, *N <sup>f</sup>* is defined by imposing *N <sup>f</sup> ×* <sup>3</sup> *bm = n*e *× B*, and *n*e is the effective porosity (≅0.003 ± 0.002) of the studied fractured aquifer given by tracer tests [29]. For example, Alfy et al. [30] were used the pumping test and geophysical logging for the investigation of the hydraulic and petro-physical characteristics of the folded UmmerRadhuma (UeR) Formation, Saudi Arabia. The findings were obtained showing that, concerning efficient porosity, permeability, hydraulic conductivity, and transmissibility, the average values of 220%, >100 mD, 3.30 × 10−5–1.34 × 10−3 m/s, and 1.49 × 10−3–6.04 × 10−2 m2 /s.

#### **5.3 Remote sensing (RS) and geographic information system (GIS)**

Intensive performance applications of RS and GIS are spatial data analysis and monitoring methods for groundwater sources. RS data integration with the GIS environment seems to be very beneficial in considerably identifying the specific groundwater potential areas. In the short time available, RS and GIS cover a vast

and unacceptable region of the earth's surface to assess areas of possible groundwater and to identify natural recharging locations [31]. RS and GIS information are valuable for many geological resources including mineral exploration, hydrogeology conditions, structural, geomorphological, lithological features, depth, and thickness of the aquifer system and other geological areas [32]. Furthermore, in the area of groundwater studies, researchers have used thematic layers such as geomorphology, geology, drainage patterns, lineaments, vegetation, intensities of rainfall, and slopes [33]. A geophysical resistivity survey was performed by [34] and borehole lithology results were compared for aquifer characterization with groundwater potential mapping which was created by RS and GIS. For a hydrogeological study, [35] integrated electrical resistivity survey data with RS outputs in a GIS environment. Moreover, [36] suggested that the geophysical resistivity data integrated with high-resolution satellite data collected from RS and GIS techniques provide more accurate information on geological and hydrological characteristics and also give possible groundwater potential zones in the hard rock formations.

#### **5.4 Seepage meter**

Seepage meter is one of the most common instruments for directly measuring SW-GW seepage flux. Initially, it was developed to measure water loss from a canal in 1940 by [37], and also it is used for other purposes such as measuring seepage flux in small lakes, estuaries, rivers, and several other environments [38]. The basic concept of the seepage meter is the difference between initial (*Vo* ) and final (*Vf* ) volume of water through a surface area (*A*) in time (*t*) and is given as

$$\text{Seepage} \text{flux} \left( \mathbf{Q} \right) = \frac{\left( V\_f - V\_o \right)}{tA} \tag{11}$$

This method was described as a plastic bag type seepage meter, which is based on isolating principle and covers a portion of SW-GW interactions with a bottomless cylinder which important in determining the directions of water exchange at the local scale [38]. The streambed features (riffle-pool sequences) can be recognized by seepage meters at the local scale because this method is useful to investigate the water flux estimates of lower streambed sediments [39]. Seepage meters can also be used to determine the volumetric change in flow, discharge, or recharge zones along with the streambed sediments in the hyporheic zone at a local scale. The seepage meter is favorable for those streams which have low current velocities which represent a local scale stream [17]. For instance, four seepage meters have been used, along with riverbed sediments of Biebrza River, Poland to quantify the hyporheic exchange flux at a local scale [40].

#### **5.5 Heat tracer method**

Subsurface temperature variation is associated with the movement of water. This variation affects the chemistry of water which can be traced by the heat tracer method. According to Anderson [41], the heat tracer method is used to determine hyporheic exchange, GW flow patterns, and rate of discharge and recharge at the local regional scale. SW temperature fluctuates throughout the season and also daily while GW temperature remains constant throughout the year. This method has been used by Schmidt, Raich, and Schirmer [42] for SW-GW interactions at the local scale and suggested that streambed temperatures can be quickly, reliably,

*Characteristics and Assessment of Groundwater DOI: http://dx.doi.org/10.5772/intechopen.93800*

and cheaply assessed the SW-GW interactions at several locations. The successful combination of their conceptual methods described by Constantz [43] with these technical improvements to assess SW-GW interactions, GW discharge or recharge, SW movement through the streambed, and GW flow systems. In the past, heat tracers' methods have been used to evaluate losing and gaining stream. For instance, the temperature was investigated by Cox, Su, and Constantz [44] and also determined the special conductance, and chloride between the aquifers system using the heat tracer method in the Russian River, Mendocino, California. Their results indicated that the special conductance and chloride data were not correlated with RW data. It means GW was not significantly varied by the exchange of SW and GW system and temperature variations in GW were negligible.

#### **5.6 Darcy's law method**

Darcy's law [45] measures the hydraulic gradients, aquifer hydraulic conductivity, cross-sectional area of the aquifer perpendicular to the flow, and to evaluate the rate of GW flow. Darcy's law expressed as,

$$\text{Darccy's law} \left( q \right) = -K \frac{\left( dh \right)}{dl} \tag{12}$$

where *q* is a specific discharge (L/T), *K* is hydraulic conductivity, *l* is the distance (L), and *h* is the hydraulic head. The hydraulic gradient is measured by piezometers and mini-piezometer at both local and regional scales. Piezometer indicates that the hydraulic head difference at great depth or vertical GW flow while mini-piezometer at shallow depths indicate GW downwelling or upwelling processes. The hydraulic conductivity is based on streambed sediments. It can be utilized as the estimation of streambed sediments by the slug test. A slug test is based upon the immediate increase or fall of the water level in the bore and the conformity of the water level to the original position when the water returns. The velocity and direction of GW flow can be determined by the mini-piezometer method. Furthermore, the estimation of flow between the SW-GW aquifer systems through semi-impervious stratum in one dimension which is used based on Darcy's law.

$$\mathbf{D}\mathbf{a}\mathbf{c}\mathbf{c}\mathbf{y}\mathbf{\dot{s}}\mathbf{a}\mathbf{a}w\left(\mathbf{q}\right) = \mathbf{K}\Delta\mathbf{h} \tag{13}$$

where *q* flows between SW-GW, ∆*h* is the river head and aquifer head, and *K* is hydraulic conductivity of the semi-impervious streambed stratum. The investigation of the Platte River by Chen et al. [45] in eight tributaries of eastern and south-central Nebraska, the USA, with the help of this method. The river joins the Missouri River in the eastern part of Nebraska and its interactions with high plains aquifer systems.

#### **5.7 Environmental tracer method**

Environmental tracer method is used to analyze the SW-GW interactions on both local and regional scales which are based on isotope data and geochemical data such as major ions or heavy metals. Stable hydrogen and oxygen isotopes are useful for assessing the flow of precipitation, source of water, age of water, and hydrological processes. In addition, this method has been used to determine the GW influx to a tropical river with major ions to supplement GW flux results [46]. Furthermore, it has been used to determine the gaining, losing disconnected and connected stream reach condition based on the geochemical parameters and stable isotopes [47–53]. Moreover, it is important to understand the recharge or discharge zone along with the GW flow system.
