Achievements

REGIONAL FLOW SYSTEM DELINEATION IN ARID KARSTIC BASINS WITH SPARSE HYDROGEOLOGIC DATA: CUATRO CIENE GAS BASIN, COAHUILA,MEXICO

Updated :09,28,2012

Brad D. Wolaver • John M. Sharp, Jr. Juan Manuel Rodriguez

Abstract: This research develops a procedure for the delineation of regional groundwater flow systems in arid karstic basins with sparse hydrogeologic data using surface topography data, geologic mapping, permeability data, chloride concentration of groundwater and precipitation, and measured spring discharge data. Aquifers are characterized using geographic information systems (GIS) for groundwater catchment delineation, an analytical model for interbasin flow evaluation, a chloride‑balance approach for recharge estimation, and a water budget for mapping contributing catchments over a 45,000km2‑region. The study area includes the Cuatro Cienegas Basin of Coahuila, Mexico, a National Biosphere Reserve containing dozens of springs supporting groundwater dependent ecosystems and irrigated agriculture. Sustainable groundwater development is a key issue on the U.S.‑Mexico border; however, these procedures may be used in arid karstic basins globally.

Keywords: Groundwater recharge/water budget, groundwater flow, water supply, arid regions, karst, carbonate rocks, Cuatro Cienegas, Mexico

 


Introduction

The objective of this study is to map regional groundwater flow systems in the arid Cuatro Cienegas Basin karstic aquifer. Wolaver et al. (2005) calculate recharge volume on a 870km2 intra‑basin recharge area which Lesser y Asociados (2001) suggest produces all spring discharge; recharge calculations generate 0.215Mm3 discharge compared to observed 53Mm3, suggesting interbasin flow. Johannesson et al. (2004) identify high elevation recharge zones from stable isotopes, but not from which catchments. This research tests the hypothesis that most Cuatro Cienegas Basin spring discharge originates as mountain recharge from outside of the basin. Due to the paucity of regional hydrogeologic data, other well-studied carbonate terrains are considered, including the Great Basin Province of the western U.S., the Trans‑Pecos of west Texas, and the Edwards Aquifer of Central Texas.

Methods

A regional flow system is delineated using surface topography, geologic maps, an analytical model for interbasin flow determination, and chloride‑balance recharge estimation using a water budget approach:

R = P Cp / Cr                                                                           (1)

where R=groundwater recharge, P=precipitation, Cp=bulk precipitation chloride concentration, and Cr=groundwater chloride concentration. Groundwater catchments are mapped in GIS using the eight direction pour point model with a 90m2 digital elevation model (DEM). Carbonate rocks forming uplands are delineated from geologic maps. Groundwater flow between basins under topographic divides is evaluated using the analytical model:

 

(2)

 

where h(x)=hydraulic head at any point(x) in an unconfined aquifer with heads(h1andh2) on either side of a topographic divide of hydraulic conductivity(K), length(L), and constant recharge(Ws). A steady‑state water budget is assumed for predevelopment conditions, where inputs are chloride-balance estimated recharge (accounting for evapotranspiration); outputs are spring discharge measured by this project (assuming negligible regional open water evaporation). Regional flow is mapped using a water budget approach; groundwater recharge for successively higher elevation groundwater catchments is summed until observed basin discharge is equal to estimated recharge.

Results and Discussion

Results suggest: 1) groundwater discharges at Cuatro Cienegas Basin because it is the lowest regional elevation; 2) interbasin groundwater flow occurs because topographic divides comprised of highly‑permeable carbonates do not represent groundwater divides (Figure 1) and; 3) up to six hydrogeologically linked groundwater catchments in a 160‑km long flow system discharge in the Cuatro Cienegas Basin. Approaches developed by this research can be used to characterize arid karstic basins with sparse hydrogeologic data globally.


Figure 1. Analytical model results suggest interbasin flow occurs.


References

[1]      Bedinger MS, Langer WH, Reed JE (1986) Synthesis of hydraulic properties of rocks with reference to the Basin and Range Province, southwestern United States. U.S. Geological Survey Water‑Supply Paper 2310:35-44.

[2]      Johannesson KH, Cortés A, Kilroy KC (2004) Reconnaissance isotopic and hydrochemical study of Cuatro Ciénegas groundwater, Coahuila, México. Journal of South American Earth Sciences 17:171‑180.

[3]      Lesser y Asociados (2001) Sinopsis del estudio de evaluación hidrogeologógica e isotópica en el Valle del Hundido, Coahuila. Comisión Nacional del Agua, Subdirección General Técnica, Gerencia de Aguas Subterráneas.

[4]      Mace RE, Angle ES; Mullican WF (2004) Aquifers of the Edwards Plateau. Texas Water Development Board, Report 360.

[5]      Nielson PD, Sharp JM Jr (1985) Tectonic controls on the hydrogeology of the Salt Basin, Trans‑Pecos, Texas. Publication of the West Texas Geological Society 85‑81:231‑234.

[6]      Rodriguez AAA and others (2005) Estudio hidrogeológico de los acuíferos el Hundido y Cuatrociénegas, Coahuila. Secretaria de Medio Ambiente y Recursos Naturales, Instituto Mexicano de Tecnología del Agua, Comisión Nacional del Agua, Instituto Nacional de Ecologia:292.

[7]      Uliana MM (2000) Delineation of regional groundwater flow paths and their relation to structural features in the Salt and Toyah Basins, Trans‑Pecos, Texas. PhD, The University of Texas at Austin.

[8]      Wolaver BD, Banner JL, Sharp JM Jr (2005) Groundwater recharge in the Cuatro Cienegas Basin, Mexico: Insights from strontium isotope and trace element analyses. Poster presented at the Annual Meeting of the Geological Society of America 37:361.