Untitled DocumentGroundwater sources, flowpaths, and residence times in the Middle Verde River Watershed
Macro Theme Area:
Basin Scale Water Balance [Project ID: B23]
PI:
James Hogan
CO-PI(s):
Tom Meixner
Basin focus:
Colorado
Specific area in
basin /
field sites:
Middle Verde River Basin
Summary/Goals: N/A
Activities and outcomes during past year:
As of this time this project is just getting started with preliminary sample collection and analysis occuring in November 2006. When competed this project will provide the following: (1) new understanding of the source of groundwaters and the associated recharge rates; (2) constraints on of the hydrogeology of the Middle Verde River Watershed with a focus on the hydrologic connection of aquifer units in the recharge zone of the Coconino Plateau and the valley floor; and (3) quantification of groundwater-surface water exchanges that maintain baseflow within the Verde River. Our results will improve calibration of a USGS regional groundwater flow model that will be used to evaluate the current groundwater conceptual model and provide a basic quantitative understanding to support water resources planning. In addition, we believe our isotopic data will provide a useful method to evaluate the hydrologic impacts of drought and water management in the basin. Through our relationships with SAHRA and the AWI we will work to communicate our results to water resources managers and the general public.
Plans for the upcoming year:
In order to address our two research questions we will focus our sampling along two transects. The first will be an elevational transect from the Verde River to the Coconino Plateau to determine the flowpaths and the hydraulic connectivity of aquifer units. Our USGS partners will collect precipitation samples along this elevational gradient in order to determine how oxygen and hydrogen isotopic composition varies with elevation . With this information we will be able to assess the season/elevation of groundwater sources and hence constrain recharge location. Our partners from NAU will undertake spring sampling, that, when analyzed, will identify water sources and residence times; with this knowledge we will be able to estimate recharge rates along the Coconino Plateau. Finally we will sample regional groundwater from wells and baseflow from the major canyons draining the Co-conino Plateau. Critical to these samples will be solute isotopes and geochemistry that will allow for the interpretation of flowpaths between the plateau and the river. As needed speciation and chemical mass balance modeling (PHREEQC) will be employed to understand origin of waters in relationship geologic units in the watershed and their final geochemical composition. In addition the chemical mass balance NETPATH model will be used to correct 14C age dates to correct for the dissolution of limestone can make samples appear significantly older
The second transect will parallel the Verde River in order to assess riparian water sources and improve our understanding of groundwater/surface water exchange, specifically through baseflow discharge and storm-driven riparian recharge. We will approach this problem by using isotopic techniques to quantitatively classify riparian water sources into two categories: basin aquifer groundwater and flood event recharge. For the Verde River floods occur primarily during spring snowmelt. We will establish study sites spanning a perennial-to-intermittent gradient along the Verde River, and at each study site we will analyze the isotopic composition of groundwater from all available riparian wells as well as baseflow sam-pled seasonally. In addition we will collect representative samples of basin groundwater and seasonal run-off to provide characterization of the various water sources as well as agricultural diversions and returns to account for the effects of irrigation. Water source information for both riparian groundwater and base-flow will then be quantified, using a two-end member mixing analysis (e.g., Baillie, 2005; Figure 3) and will be related to the flow regimes of the reaches being studied. Irrigation impacts will be assessed using a combination of O and H isotopes (distinct changes due to evaporation) and changes in solute concentra-tion and ratios (e.g. with evapotranspiration Cl concentration will increase but the Cl/Br ratio will not change).
Organization Involvement:
The USGS has a project focused on developing a regional-scale groundwater flow model that accu-rately represents groundwater flowpaths, aquifer connectivity, and recharge rates for the Verde River watershed. See the attached letter from the project manager, Kyle Blasch, as to the nature and scope of collaboration. Most significantly, our results will be useful for improving the conceptual model and calibrating the numerical groundwater flow model. Integrating our isotopic data into this modeling ef-fort should result in recharge estimates that are superior to either method alone. Because of the strong matching support and complementary research goals, USGS researchers are considered to be full re-search partners with joint publications and presentations anticipated.
Shared Resources / Joint Activities:
Our USGS partners will collect precipitation samples along this elevational gradient in order to determine how oxygen and hydrogen isotopic composition varies with elevation.
Location: Tucson, AZ, USA
URL: N/A
Yavapai County Water Advisory Committee
Organization Involvement:
The YC-WAC is a coalition of communities and selected stakeholders that are dedicated to developing a management plan for the sustainable use of their water supply. We are working with YCWAC to further develop our research objectives so as to best meet their current needs for improved hydrologic data and understanding. Specifically, we are working with YCWAC to refine our sampling strategy. Furthermore we will communicate the results of our findings to ensure their application to the critical water sustainability issues in the Verde River watershed.
Organization Involvement:
We have engage the Arizona State Parks within the Middle Verde in this project. Specifically we are:
1. Undertaking surface water and groundwater sampling (from existing wells) at Slide Rock, Dead Horse Ranch, Oak Creek, and Tonto Natural Bridge.
2. Using facilities at Deadhorse State Park as a base of operations for sampling. We would plan to use camping facilities and space for filtering and storing (refrigerated if possible) samples while sampling.
3. Install a series of 1-10 meter deep piezometers (1.5" diameter PVC) along the Verde River floodplain to evaluate groundwater -surface water exchange. This will be done in conjunction with the University of Arizona Hydrology Field Camp and all equipment will be removed at the end of the project.
