Combining of MASW and GPR Imaging and Hydrogeological Surveys for the Groundwater Resource Evaluation in a Coastal Urban Area in Southern Spain

Abstract

This paper conceptualizes and evaluates the groundwater resource in a coastal urban area hydrologically influenced by peri-urban irrigation agriculture. Adra town in southern Spain was the case study chosen to evaluate the groundwater resource contributed from the northern steep urban sector (NSUS) to the southern flat urban sector (SFUS), which belongs to the Adra River Delta Groundwater Body (ARDGB). The methodology included (1) geological and hydrogeological data compilation; (2) thirteen Multichannel Analysis of Surface Waves (MASW), and eight Ground Penetrating Radar (GPR) profiles to define shallow geological structures and some hydrogeological features; (3) hydrogeological surveys for aquifer hydraulic definition; (4) conceptualization of the hydrogeological functioning; and (5) the NSUS groundwater resource evaluation. All findings were integrated to prepare a 1:5000 scale hydrogeological map and cross-sections. Ten hydrogeological formations were defined, four of them (Paleozoic weathered bedrock, Pleistocene littoral facies, Holocene colluvial, and anthropogenic filling) in the NSUS contributing to the SFUS. The NSUS groundwater discharge and recharge are, respectively, around 0.28 Mm3 year–1 and 0.31 Mm3 year–1, and the actual groundwater storage is around 0.47 Mm3. The groundwater renewability is high enough to guarantee a durable small exploitation for specific current and future urban water uses which can alleviate the pressure on the ARDGB.

Usefulness of Compiled Geophysical Prospecting Surveys in Groundwater Research in the Metropolitan District of Quito in Northern Ecuador

“…This paper reinterpreted the 2D VS models for the shallow geological definition following the interpretative criteria reported by Paz et al [63] and Alcalá et al [64]. These authors propose that subsurface VS propagation is a site-specific steady property determined by effective compaction and therefore is dependent on the age and depth of each geological material piled vertically [65][66][67][68].…”

“…The section features comprised an imposed prospecting length of 2.5 km, a prospecting depth of 40 m, VS in the range of 120-580 (REMI1) and 190-610 m s -1 (REMI2), and average RMSEs of 10.83 (REMI1) and 9.42 (REMI2) (Figure 3c). The VS values were typical of sedimentary [63,64] and volcano-sedimentary [72] rocks.…”

“…These authors propose that subsurface VS propagation is a site-specific steady property determined by effective compaction and therefore is dependent on the age and depth of each geological material piled vertically [65][66][67][68]. The different relationships between VS and age and depth in different lithologies described in the scientific literature [63][64][65][66][67][68][69][70][71] were used to reinterpret the VS models.…”

“…The VS increased in depth according to the increasing age and compaction of geological materials, from less than 200 m s -1 in recent anthropogenic fillings and lacustrine formations, 200-550 m s -1 in Holocene sedimentary and volcano-sedimentary formations, and more than 550 m s -1 in Pleistocene volcano-sedimentary formations. As in other nearsurface seismic techniques, REMI cannot disambiguate boundaries of different geological formations with similar VS [63,64,70,71]. This limitation to make inner divisions was solved by using external validation data, such as regional [24,25] and local [26,33,34] geological information, geotechnical soundings logs, and other prospecting techniques [63,64].…”

“…As in other nearsurface seismic techniques, REMI cannot disambiguate boundaries of different geological formations with similar VS [63,64,70,71]. This limitation to make inner divisions was solved by using external validation data, such as regional [24,25] and local [26,33,34] geological information, geotechnical soundings logs, and other prospecting techniques [63,64].…”