Numerical simulation of groundwater flow for the Yakima River basin aquifer system, Washington

Abstract

A regional, three-dimensional, transient numerical model of groundwater flow was constructed for the Yakima River basin aquifer system to better understand the groundwaterflow system and its relation to surface-water resources. The model described in this report can be used as a tool by watermanagement agencies and other stakeholders to quantitatively evaluate proposed alternative management strategies that consider the interrelation between groundwater availability and surface-water resources. The model was constructed using the U.S. Geological Survey finite-difference model MODFLOW. The model uses 1,000-foot grid cells that subdivide the model domain by 600 rows and 600 columns. Forty-eight hydrogeologic units in the model are included in 24 model layers. The Yakima River, all major tributaries, and major agricultural drains are included in the model as either drain cells or streamflow-routing cells. Recharge was estimated from previous work using physical process models. Groundwater pumpage specified in the model is derived from monthly pumpage values previously estimated from another component of this study. The pumpage values include estimates for wells with standby/reserve rights that are used in drought years. The model was calibrated to the transient conditions for October 1959 to September 2001. Calibration was completed by using traditional trial-and-error methods and automated parameter-estimation techniques. The model simulates the shape and slope of the water table that generally is consistent with mapped water levels. At well observation points, the average difference between simulated and measured hydraulic heads is-49 feet with a root-mean-square error divided by the total difference in water levels of 4 percent. Simulated river streamflow was compared to measured streamflow at seven sites. Annual differences between measured and simulated streamflow for the sites ranged from 1 to 9 percent. Calibrated model output includes a 42-year estimate of a monthly water budget for the aquifer system. Five applications (scenarios) of the model were completed to obtain a better understanding of the relation between pumpage and surface-water resources and groundwater levels. For the first three scenarios, the calibrated transient model was used to simulate conditions without: (1) pumpage from all hydrogeologic units, (2) pumpage from basalt hydrogeologic units, and (3) exempt-well pumpage. The simulation results indicated potential streamflow capture by the existing pumpage from 1960 through 2001. The quantity of streamflow capture generally was inversely related to the total quantity of pumpage eliminated in the model scenarios. For the fourth scenario, the model simulated 1994 through 2001 under existing conditions with additional pumpage estimated for pending groundwater applications. The differences between the calibrated model streamflow and this scenario indicated additional decreases in streamflow of 91 cubic feet per second in the model domain. Existing conditions representing 1994 through 2001 were p...

Alteration, mass analysis, and magmatic compositions of the Sentinel Bluffs Member, Columbia River flood basalt province: COMMENT

“…The physical properties of the cooling joints within the dense interior portion of the basalt flow produce an essentially impermeable barrier to groundwater movement for all practical purposes (Newcomb, 1969;Oberlander and Miller, 1981;Davies-Smith et al, 1988;Lite and Grondin, 1988;U.S. Department of Energy, 1988;Lindberg, 1989;Wozniak, 1995;Tolan et al, 2009b;Burt et al, 2009;Vaccaro et al, 2009;Ely et al, 2011;Lite, 2013). The fact that CRBG dense flow interiors typically act as aquitards accounts for the confined behavior exhibited by most CRBG aquifers.…”

Riverbed Hydrologic Exchange Dynamics in a Large Regulated River Reach

“…Using the mechanistic simulations from reactive transport or CFD models, reduced order models could be built for to be incorporated to watershed scale models, by combining large fluvial geomorphic features such as valley slope and channel sinuosity with regional hydraulic gradients (Cardenas, ; Gomez‐Velez & Harvey, ), which can be obtained from large‐scale groundwater models such as that from MODFLOW applications (e.g., over the Yakima Basin (Ely et al, )) or an integrated land surface and subsurface model (Bisht et al, ; Maxwell et al, ). We envision such a modeling framework will enhance our understanding on the cumulative effects of river corridor hydrobiogeochemistry and the watershed system responses to environmental changes and human impacts.…”

Pathways and Estimate of Aquifer Recharge in a Flood Basalt Terrain; A Review from the South Fork Palouse River Basin (Columbia River Plateau, USA)

“…This aquifer unit is the larger of the two primary formations (other being the upper Wanapum Formation) and contains transmissive zones associated with the interbedded sediments (layer horizontal flow during aquifer testing) that connect this relatively deep portion of the aquifer to the alluvium of the mountain front. Note that, horizontal hydraulic conductivity (K h ) is defined as the ratio of the transmissivity and screen lengths, i.e., high (K h /K v ~10 2 -10 3 ) flow anisotropy of the fluvio-volcanic deposits of the Columbia Plateau Regional Aquifer System (CPRAS) [55,56]. The Grande Ronde Formation is ~450 m thick, resides about ~200 m below the basin surface, and is divided into lower, intermediate and upper units based on the occurrence of interbedded sedimentary layers and magneto-stratigraphic studies (Figure 2).…”

“…A prior view of primarily vertical recharge in the South Fork Palouse River Basin was sustained into the 2010s because of 14 C isotopes that indicated significant vertical age variation and potential Pleistocene water in the South Fork Palouse River Basin [58,59]. Yet, previous groundwater flow models included vertical flow anisotropies (K h /K v ) ranging from 2000 up to 5500 in the larger CPRAS [55,56]. Previous flow models were realized at the study site using an Equivalent Porous Medium (EPM) approach that confirm a high-flow anisotropy (K h /K v = 90-7000) fitting the lateral continuity of the bedding planes at the Palouse Falls as shown in Figure 4 [60,61].…”