Surface and groundwater flow modeling for ...

Surface and groundwater flow modeling for calibrating steady state using MODFLOW in Colorado River Delta, Baja California, Mexico Kedir Mohammed Bushira, Jorge Ramirez Hernandez & Zhuping Sheng

Modeling Earth Systems and Environment ISSN 2363-6203 Model. Earth Syst. Environ. DOI 10.1007/s40808-017-0337-5

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Author's personal copy Model. Earth Syst. Environ. DOI 10.1007/s40808-017-0337-5

ORIGINAL ARTICLE

Surface and groundwater flow modeling for calibrating steady state using MODFLOW in Colorado River Delta, Baja California, Mexico Kedir Mohammed Bushira1 · Jorge Ramirez Hernandez1 · Zhuping Sheng2

Received: 2 May 2017 / Accepted: 6 May 2017 © Springer International Publishing Switzerland 2017

Abstract This study presents the data-scarce and hydrogeologically important surface and groundwater system of Colorado river delta, Mexico, with the aim of understanding dynamics of surface–groundwater interactions in the Delta aquifers applying hydrological conceptual model into integrated hydrological numerical model for Colorado river delta (MCRD) aquifer, calibrated based on averages of daily basis data throughout 8-year period. The model was developed using MODFLOW-OWHM code under the ModelMuse Graphical User Interface, where surface– groundwater interactions through unsaturated zone were simulated using River package (RIV) and UnsaturatedZone Flow (UZF1) MODFLOW packages under data scare conditions. In the steady-state calibration: gross recharge, contributed 93.3%, lateral inflow 3.2% and stream leakage 3.4% of the total groundwater inflow. The groundwater outflow consisted of groundwater evapotranspiration 87.5%, stream leakage 3.1%, groundwater pumping 3.09% and lateral outflow 6.31%. Processes encountered in the calibrated parameterizations show groundwater flows axially from almost all directions of the model towards the golf of California at the south border of the model, match the course of the Colorado River and laterally towards new river (Rio * Kedir Mohammed Bushira [email protected] Jorge Ramirez Hernandez [email protected] Zhuping Sheng [email protected] 1

Instituto de Ingeniería, Universidad Autonoma de Baja California, Mexicali 21280, Baja California, Mexico

2

Texas A&M AgriLife Research Center, 1380 A&M Circle, El Paso, TX 79927, USA

Nuevo) in the North-west, with a larger portion flowing out southward than north-west ward. Though this study shows Groundwater and surface water interactions in MCRD, cannot be embedded in operational water management yet, it provides a means to assess focal areas for future data collection and model improvements. Keywords Colorado River Delta · Numerical modeling · MODFLOW · Groundwater-Surface water interactions

Introduction The study of surface–groundwater interactions has gained special attention in the field of water resources management in recent decades. This is due to the fact that surface and groundwater flow systems, in many cases, interact with each other. For instance, groundwater abstraction can reduce base flow and adversely affect river hydrology. Conversely, surface water abstraction can reduce groundwater recharge and reduce groundwater potentials of the aquifer system. Moreover, surface water can gain solute from groundwater while the quality of groundwater can be impaired by surface waters. From these facts, the management of surface and groundwater are hardly separable. Krause et al. (2007) pointed out that interactions between surface and groundwater and the exchange of fluxes between them have high spatial and temporal variability. In that regard, the type of interaction is determined by the direction of flux exchange. For example, a surface water source experiences influent condition when it loses water into an aquifer and experiences effluent condition when it gains water from the aquifer system. Formerly, the surface and groundwater flow systems were analyzed separately because the flows take place

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at different temporal scales (Gupta 2010) and, thus, its representation was a very difficult undertaking. This approach allowed surface and groundwater flow regimes to be analyzed in separation using the uncoupled or stand-alone models. For instance, the HBV, PRMS and SWAT codes focus more on modeling surface water and simplify groundwater flow processes. Likewise, the codes like standard MODFLOW and AQUIFEM-1 emphasize more on groundwater flow processes and simplify surface water flow processes. However, the ever-increasing developments in computing facilities have enabled the flow systems to be analyzed together in both spatial and temporal domains. The conjunctive analysis of surface and groundwater flows is performed through the integrated or coupled models. The typical examples of such models include, among others, MODFLOW-2005, MODFLOWNWT, GSFLOW and MODFLOW-OWHM. It should be pointed out that selection of an appropriate code to deal with a particular problem at hand is of paramount importance. For example, an uncoupled groundwater model can perform better in a particular environment where a coupled model cannot do the same. The ever-increasing demands of water are largely fulfilled by surface water and/or groundwater resources to satisfy cultural, social and economic uses. In this case, the delta of Colorado River is no exceptional that the over increasing of the groundwater wells in the area highly exploited the groundwater source to satisfy their consumptive needs. The transformation of the Colorado River delta from wilderness to the highly productive agriculture region raises many questions and become an interesting research area for ground water-surface water study. The ultimate aim of this research is to improve understanding of the conjunctive relationships between surface and ground water and to analyze the effects of one over the other in the delta for sustainable use and to influence future effective decision making in water resource management in the delta and specifically in the Colorado River irrigation district 014 (MCRD). Moreover, it aims to improve more societal benefits by ensuring availability of water for agricultural activities, recreational and sustenance of ecological systems in the study area. In order to be able to model the interactions in the Delta, this research uses the MODFLOW-OWHM codes running under Model Muse as the graphic user interphase. The model codes, among others, employed the Unsaturated Zone Flow (UZF1), River package (RIV), Well package (WEL), Drain package (DRN), General Head boundary package (GHB) and Head Observation (HOB) to facilitate the study of surface–groundwater interactions and to calculate the final water balance in the study area.

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Area of study and hydrogeological behavior The State of Baja California is located to the Northwest of Mexico, bounded on the north by the State of California, USA, to the east by the State of Sonora, Mexico, to the west by the Pacific Ocean and south by the State of Baja California Sur. The Colorado River Delta (CRD) is one of the world’s largest deltas covering over 8600 km2 of terrain and extending across the international border between the United States (US) and the Republic of Mexico (Mexico). The areal extent of the model domain (referred to hereafter as the modeled Colorado River delta or MCRD) proposed to Include most of the agricultural areas in the Mexicali and San Luis Valley’s (also known as Colorado River Irrigation District 014) (Fig. 1). The MCRD is made up of low-lying terrain and is flanked on the west by two narrow and abutting NNW–SSE trending mountain ranges: The Sierra Cucapá toward the north and Sierra El Mayor toward the south. East of the MCRD is the Altar basin, an expansive desert within the Salton Trough that occupies a now inactive portion of the CRD (Pacheco et al. 2006). To the south of the MCRD, is a series of marshes and tidal flats that extend into the Gulf of California and it’s nearshore estuaries and coastal marine environments. The MCRD has an even topography that gently loses elevation in the southward direction toward the Gulf of California. Digital Elevation Model (DEM) below in Fig. 2 illustrates the elevation decrease in the MCRD from the high of 254 m in the NE to the low of 0 m in the south. Geologic mapping and an aquifer testing campaign in the MCRD would greatly increase the applicability of the Yuma data to the portion of the CRD within Mexico (Feirstein et al. 2008). The aquifer system is presented in more detail in Hill (1993) and Olmsted et al. (1973). According to Olmsted et al. (1973); the aquifer system is divided into two parts: upper fine-grained zone and wedge zone and coarse gravel zone. In the MCRD, the uppermost sediment vary spatially and include coarse alluvial piedmont sand and gravel sediments derived from the Sierra Cucapah, which dominate in the SW (Puente and De La Pena 1979), and fluvially transported fine, medium, and coarse-grained sediments of clay, sand, and gravel which dominate in the east (Pacheco et al. 2006; Sykes 1935). The fine-grained sediments of clay, silt, and sand in the north central MCRD are reported as being lagoonal or estuarine material and may be associated with prehistoric Lake Cahuilla (Portugal et al. 2005), a freshwater lake that formed intermittently when Colorado River water naturally flowed west instead of south at least four times between A.D. 700 and 1580 (Feirstein et al. 2008).

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Fig. 1 Location map of model Colorado River Delta (MCRD)

Fig. 2 Digital elevation model (DEM) of the MCRD model domain

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Transmissivity values for the upper fine grained zone were determined to be 150–930 m2/day Hill (1993). A storage coefficient of 1 0−3 and specific yield of between 0.18 and 0.35 were estimated by Harshbarger (1971) and reported in Hill (1993). According to Olmsted et al. (1973), the Wedge zone is considered single heterogeneous water bearing hydraulic unit composed of irregularly layered sands, gravels, silts, and clays. The coarse gravel zone overlies the Wedge zone and is a highly permeable water-bearing unit composed primarily of irregularly layered coarse gravel and sand. This unit constitutes the main pathway for horizontal groundwater flow in the system (Mock et al. 1988). Together the wedge zone and coarse gravel zone may represent what is described in research of the MCRD area (i.e. Pacheco et al. 2006; Portugal et al. 2005; Chavez et al. 1999; Barragan et al. 2001) as the upper sediments of the Mexican CRD basin with a composition of fluvial and alluvial not- consolidated sediments of Pleistocene to Recent ages. Transmissivity values for the Wedge zone and Coarse Gravel zone combined were determined to range from between 835 to 22,300 m2/day Olmsted et al. (1973). Horizontal hydraulic conductivity was calculated to range up to 400 m/day. Vertical hydraulic conductivity, storage coefficient, and specific yield were determined equal values to the upper fine-grained zone. Harshbarger (1971) and reported in Hill (1993). The primary sources of groundwater in the MCRD are infiltrated Colorado River water and agricultural irrigation (Hill 1993; Harshbarger 1971; Olmsted et al. 1973). Surface water is also transmitted in the MCRD via canals, drains, and the main tributary of the Colorado River, the Rio Hardy (Fig. 1). Modern day Colorado River flows crossing the international boundary are regulated in accordance with the 1944 US. Mexico treaty which states that no less than 1,850,234,000 m3/year of Colorado River water is to be released into Mexico each year (US–Mexico Joint Projects 1944 treaty). As specified in the treaty, surface water is diverted into Mexico at Morelos Diversion Dam 1.8 km downstream of the Northern International Border (NIB) and approximately 25 km upstream of the Southern International Border (SIB) (Fig. 1).

Model development The groundwater flow was simulated with the threedimensional finite difference block centered groundwater model code MODFLOW-OWHM. The model was applied under the ModelMuse Graphical User Interface (GUI) (Winston 2009) to pre-process input data and

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post-process outputs. MODFLOW-OWHM with river package (RIV), well package (WELL), drainage package (DRN) and unsaturated flow package (UZF1) and for calibration, Head observation package (HOB) were used. Conceptual model and spatial and temporal discretization The regional stratigraphy was conceptualized in two layers. The first layer has a thickness of 120 m from the ground surface (upper fine-grained zone) and the second layer (combination of wedge zone and course gravel zone) has a thickness of 800 m from the ground surface (Fig. 3d). The mesh starts at the coordinates of 624,420E and 3,626,461.998 N (UTM WGS84 zone 11) and discretized in 113 columns and 73 rows following the recommendations of USGS MODFLOW (Harbaugh 2005). The grid cells are ranging from 2000 m × 2000 m to the refining area 375 × 375 m. The criterion to achieve the refinement followed the recommendations of MODFLOW (Harbaugh 2005) preventing size difference between adjacent cells should not be more than 1.5. Model domain, initial and boundary conditions The areal extent of the MCRD domain (Active cell) was designed to include most of the agricultural areas within the Mexicali and San Luis Valley’s (also known as Colorado River Irrigation District 014). Irrigation District 014 is divided into irrigation units, for which pumping and irrigation data are aggregated and maintained by the National Water Commission of Mexico (CONAGUA). The MCRD domain (Active cells) includes part or all of 18 out of 22 existing irrigation units and has an overall area of 247,118 hectares (Fig. 3a). The geohydrological boarders considered in this model were in W and SW, Cucapá mountain range and El Mayor which were impermeable, In the NW the Rio Nuevo and Mexicali were considered as outflow zones. In the north, the Drain Mesa and In the East, the Sonora/Arizona, were considered as points of inflow to the aquifer system. In the south, the Golf of California was considered as a border of constant potential that is a zone where outflow from the aquifer considered to occur. In this model, all the boundaries were simulated by using general head boundary (GHB) except in W and SW which was simulated using No flow boundary in MODFLOW (Fig. 3c). The distribution of the initial value for horizontal hydraulic conductivity for the first layer was obtained and presented in Fig. 3b.


Fig. 3 a Model domain showing a grid and active cell boundary, b spatial distribution of the horizontal hydraulic conductivity for the first layer, c distribution of pumping wells and d cross-section showing aquifer of MCRD

Hydrogeological parameters To hydraulically characterize the hydrogeological units in the MCRD, data were reviewed on transmissivity, specific storage and storage coefficient from previous studies (Olmsted et al. 1973; Harshbarger 1971; Hill 1993; Table 1). The degree of permeability in the first layer,

Table 1 Initial values for hydraulic conductivity (K), storage coefficient (Ss) and specific yield (S) for the different layers of the model Layer

Kx(m/day)

1 2

30–600 0.001

Ky(m/day) 0.03 0.03

Ss (1/Metre)

Sy

1E−5 1E−5

0.2 0.2

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Fig. 4 a Precipitation (P), infiltration rate (Inf), and potential evapotranspiration (PET) for 8-year periods (hydrologic years 2002 to 2010). b Piezometric points used for calibration using HOB of MODFLOW

in the horizontal direction, is spatially differentiated (Fig. 3b). Recharge In this model, the only external sources of recharge considered were Agriculture related water that infiltrates into

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the aquifer and stream leakages from Colorado River. Extremely low precipitation rates in the area, on average below 55 mm/year and most of it evaporates before reaching to the aquifer. Agriculture is the main water user within the MCRD and recharge associated with agriculture, mainly irrigation, may be considered a primary source of recharge to the MCRD aquifer (Cohen and Henges-Jeck 2001; Hill 1993; Mock


Fig. 5 Calibrated hydraulic conductivity values (m/day) per zone

Table 2 Error metrics for calibrated sets off in total 27 observations

Error metric

Values of 27 observations

ME (m) MAE (m) RMSE (m)

−0.08 0.50 0.53

et al. 1988; Olmsted et al. 1973). The agriculture-related recharge for each Irrigation units based on the irrigation seasons was obtained from previous studies and the available agriculture-related recharge was converted into infiltration rate and prepared as an input for the UZF1 package. The UZF1 package is a recently developed package that replaces the Recharge and Evapotranspiration Packages of MODFLOW-2005 (Niswonger et al. 2006). It uses a kinematic wave approximation of vertical, 1D variably saturated flow by applying the kinematic wave approximation equation.

𝜕𝜃 𝜕K(𝜃) + + a = 0, 𝜕t 𝜕z

(1)

where, θ is the volumetric water content (L− 3/L 3); t is time (T), Z is the distance in the vertical direction (L); K (θ) is the unsaturated hydraulic conductivity (L/T); a is the evapotranspiration rate per unit length of roots (per T); and L and T denote length and time units. The inputs assigned to the UZF1 package, including extinction water content (EXTWC), extinction depth (EXTDP), potential Evapotranspiration (PET) and infiltration rate.

High infiltration rate was observed during the periods with a high rate of irrigation application, the estimated infiltration was the highest in May 2006 with 4.5 mm/day (Fig. 4a). The estimated infiltration rate ranged from 0 to 4.5 mm/day with an average of 1.687 mm/day. That infiltration rate was applied in the steady-state model calibration. McMahon et al. (2013) defined PET as the rate at which evapotranspiration would occur from a large area completely and uniformly covered with growing vegetation which has access to an unlimited supply of soil water, and without advection or heat storage effects. PET is one of the driving forces in the applied modeling solution involving UZF1 package. In UZF1, the PET is applied at the land surface and decreases linearly with depth down to the assigned extinction depth where evapotranspiration no longer occurs (Allander et al. 2014). There are two methods to convert E T0 to PET. The first is the single crop coefficient, in which the evapotranspiration differences between reference grass and the crop is combined into one single coefficient and depends only on crop characteristics, crop type, and growth stage. The second is the dual crop coefficient which requires detailed data on the crop and soil. In this approach, the crop coefficient is split into two factors describing separately the differences in evaporation and transpiration between the crop and reference surface (Allen et al. 1998). Since detailed data about the crop/vegetation and soil of the area is not available, the single crop coefficient (Kc) method was applied in this study. Following that method, PET is calculated using the following Equation.

PET = ETo ∗ Kc,

(2)

where, ETo is the reference evapotranspiration (mm/day) and Kc is the crop coefficient [−]. Andrade, San Luis, Zacatecas, Nuevo Leon and Mexicali Meteorological stations were used to estimate the meteorological data, such as precipitation, reference evapotranspiration (ETO) and Temperature on daily basis. This data was aggregated to daily time step in order to match the UZF1 package input requirement. The ETo values obtained from the meteorological stations for different years were converted into PET using the Eq. 1 as per the crops cover and the respective crop coefficient in the irrigation District 014. The infiltration rate was assigned as 1.687 mm/day; the evapotranspiration demand (PET) 1.6387 mm/day; extinction water content was fixed to 0.06/m3/m3 as spatially uniform to all cells and the extinction depth, below which no more water will be removed by evapotranspiration, was assigned as a weighted average of 1.2 m. The weight of extinction depth is given according to the main seasonal crops in the area and their coverage of MCRD.

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Fig. 6 Calibrated head distribution a first layer and b second layer of the steady-state model simulation

The infiltration rate and PET values for steady-state simulation were assigned as the average values for the 8 years of simulation period (October 2002 up to September 2010). Pumping The MCRD includes 639 pumping wells all positioned in layer 1. These large-scale production wells are unevenly

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distributed and are primarily located in the eastern portion of the MCRD domain (Fig. 3c). To obtain the monthly extraction rate, in the model, the monthly volumes contributed by federal wells for each crop in each of the modules were considered. For steady state simulation, the average values of the wells located in each module were assigned.


layers showed nearly the same potentiometric surface. The same observation was made by Feirstein et al. (2008). Flow patterns and Water balance under abstraction

Fig. 7 a Groundwater evapotranspiration and b UZF recharge distribution map of MCRD for calibrated steady-state condition

Model result and discussion Calibration The resulting hydraulic conductivity values after steady state calibration are shown in Fig. 5. In general, conductivity is low in the central MCRD and high in the north west and south west due to coarse alluvial piedmont sand and gravel sediments derived from the Sierra Cucapah (Puente and De La Pena 1979). Error assessment of the model calibration was demonstrated by statistical and graphical comparisons of simulated and observed data. The observed groundwater levels in 28 piezometers (Fig. 4b) were used as a reference to compare with simulated heads. Table 2 shows mean error (ME), Root mean squared error (RMS) and mean absolute error (MAE) metrics for the calibrated residuals. Figure 6 shows the distribution of the calibrated heads of the first and second layer after the steady-state model calibration. From the two figures, it can be observed that the water flows from all directions of the model towards the golf of California at the south border of the model, match the course of the Colorado River. The first and second

The simulated GWET loss from groundwater in MCRD in the steady-state condition varied from 0 to −2.1 mm/day (Fig. 7a). The negative sign indicates the water is removed from the groundwater budget. Highest GWET was observed in North West aligned with the stream courses of Rio Nuevo, where the groundwater was the shallowest and similarly near to the Golf of California. UZF recharge for the steady-state model simulation is varied from 0 to 2.16 mm/day, shown in Fig. 7b. The recharge rate was calculated as a partition of the actual infiltration rate in UZF package. Water budgets were constructed to explore the relationship between the sources and sinks to the groundwater system. The main sources to the MCRD groundwater system include losses from stream flow, agricultural recharge, and cross-boundary sub-surface flows from the Drain Mesa and across the eastern domain boundary from Sonora. The main sinks of groundwater include gaining stream conditions, evapotranspiration, groundwater pumping, and cross-boundary sub-surface flows to the Gulf of California, Mexicali and to a lesser extent towards the Salton Sea. Agricultural recharge and stream leakages were the only component for inflow of the water balance of the delta. The outflow components of water balance: Ground Water Evapotranspiration contributed 87.5%, stream discharge at the outlet of the model 3.1%, pumping from groundwater wells 3.09% and lateral groundwater outflow 6.31% of the total outflow from the model area.

Summary and conclusion Groundwater and surface water modeling has become a commonly used tool for hydrogeologists to perform various tasks. The rapid increase of computing power of PCs and availability of user-friendly modeling systems has made it possible to simulate large-scale regional surface and groundwater systems. This study first aimed to understand Surface and groundwater system of MCRD and to explore dynamics of surface–groundwater interactions in the Delta aquifers based on steady state calibration. Results of multiple model parameterizations led to a better understanding when compared to simpler water balance

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models, while at the same time preventing unsubstantiated claims about system behavior as is the case in more complex models. Simulations show that groundwater flows axially from almost all directions of the model towards the golf of California at the south border of the model, match the course of the Colorado River and laterally towards new river (Rio Nuevo) in the North-west, with a larger portion flowing out southward than north-west ward, while inflow takes place in the east and north, showing that the MCRD is not merely draining water to groundwater (longitudinally), but also receives inflow from (lateral) recharge. Though this study shows Groundwater and surface water interactions in MCRD, cannot be embedded in operational water management yet, it provides a means to assess focal areas for future data collection and model improvements.

References Allander KK, Niswonger RG, Jeton AE (2014) Simulation of the Lower Walker River Basin Hydrologic System, West-Central Nevada, using PRMS and MODFLOW Models Scientific Investigations Report 2014–5190 Allen R, Pereira LS, Raes D, Smith M (1998) Crop evapotranspiration: Guidelines for computing crop requirements. Irrigation and Drainage Paper No. 56, FAO, no 56, p 300. doi:10.1016/j. eja.2010.12.001 Barragan RM, Birkle P, Portugal ME, Arellano GVM, Alvarez RJ (2001), Geochemical survey of medium temperature geothermal resources from the Baja California peninsula and Sonora, Mexico. J Volcanol Geothermal Res 110:101–119 [pii: S0377-0273(01)00205-0]. Chavez RE, Lazaro-Mancilla O, Campos-Enriquez JO, Flores-Marquez EL (1999) Basement topography of the Mexicali Valley from spectral and ideal body analysis of gravity data. J South Am Earth Sci 12:579–587. [pii: S0895-9811(99)00041-3] Cohen MY, Henges-Jeck C (2001) Missing water. Pacific Institute, Oackland Feirstein E, Zamora-Arroyo F, Vionnet L. Maddock T (2008) Simulation of groundwater conditions in the Colorado River Delta, Mexico. Tesis de Maestría. Tucson, AZ Gupta SK (2010) Modern hydrology and sustainable water development. Wiley, Hoboken Harbaugh A (2005) MODFLOW-2005, The U.S. Geological Survey modular ground-water model—the Ground-Water Flow Process:

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Model. Earth Syst. Environ. U.S. Geological Survey Techniques and Methods 6- A16, p variously Harshbarger JW (1971) Overview report of hydrology and water development, Colorado Delta, United States and Mexico. Preliminary Report PR-235-77-2, Prepared for International Boundary and Water Commission United States Section, Tucson, AZ, USA Hill BM (1993) Hydrogeology, numerical model and scenario simulations of the Yuma area groundwater flow model Arizona, California, and Mexico, modeling Report no. 7, Arizona Department of Water Resources, Phoenix AZ, USA Krause S, Bronstert A, Zehe E (2007) Groundwater-surface water interactions in a North German lowland floodplain—implications for the river discharge dynamics and riparian water balance. J Hydrol 347:404–417. doi:10.1016/j.jhydrol.2007.09.028 McMahon TA, Peel MC, Lowe L, Srikanthan R, McVicar TR (2013) Estimating actual, potential, reference crop and pan evaporation using standard meteorological data: a pragmatic synthesis. Hydrol Earth Syst Sci 17(4):1331–1363. doi:10.5194/ hess-17-1331-2013 Mock PA, Burnett EE, Hammett BA (1988), Digital computer model study of Yuma area groundwater problems associated with increased river flow 115 in the lower Colorado River from January 1983 to June 1984, Arizona Department of Water Resources Open-File Report No. 6, Phoenix AZ, USA Niswonger RG, Prudic DE, Regan SR (2006) Documentation of the Unsaturated-Zone Flow (UZF1) Package for Modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005. Book 6, Modeling Techniques, Section A, Ground Water, p 71 Olmsted F, Loeltz OJ, Irelan B (1973) Geohydrology of the Yuma Area, Arizona, and California, Geological Survey Professional Paper 486-H, United States Government Printing Office Washington, DC Pacheco M, Martin-Barajas A, Elders W, Espinosa-Cardena JM, Helenes J, Segura A (2006) Stratigraphy and structure of the Altar basin of NW Sonora: implications for the history of the Colorado River Delta and the Salton trough. Rev Mex de Cienc Geol 23(1):1–22 Portugal E, Izquierdo G, Truesdell A, Alvarez J (2005) The geochemistry and isotope hydrology of the Southern Mexicali Valley in the area of the Cerro Prieto, Baja California (Mexico) geothermal field. J Hydrol 313:132–148 Puente IC, De La Pena AL (1979) Geology of the Cerro Prieto geothermal field. Geothermics 8:155–175 Sykes GG (1935) The Colorado Delta, Carnegie Institution of Washington. Washington DC Winston RB (2009) Model muse: a graphical user interface for MODFLOW–2005 and PHAST: U.S. Geological Survey Techniques and Methods 6–A29. p 52. Available at http://pubs.hical