UPPER KLAMATH BASIN GROUND-WATER STUDY

Phase II: Intensive Data Collection and Development of Conceptual Model

Objectives

Collect the data required to define the geohydrologic system.
Develop an improved conceptual model of the Upper Klamath Basin geohydrologic system to serve as the basis for a numerical ground-water flow model.
Develop a preliminary steady-state model of the basin for concept testing.
Refine the modeling approach for phase III.

Approach

Data gathered during the first year of Phase II is to be analyzed to improve concepts of how the hydrologic system works. A preliminary, steady-state ground-water model will be developed in the second year of phase II and will be used to answer model design questions such as grid spacing, number of layers, and boundary conditions. The modeling approach for phase III can be modified if necessary.

Watershed (rainfall-runoff) models will be constructed in phase II for each subbasin of the Upper Klamath Basin to quantify the relations between precipitation, runoff, evapotranspiration, and recharge to the ground-water system. These models will provide estimates of the distribution of recharge in the basin and the variability of recharge with climate and land-use. These estimates will be as direct input to the numerical ground-water flow model.

The watershed models will be coupled to the ground-water flow model either directly or indirectly. There are current research efforts within the USGS to link existing watershed models with MODFLOW. Linked models will provide advantages over methods that we now use wherein the simulated water budget information from the watershed model is manually formatted and input to the ground-water model. Linked models would make it possible to simulate more complex management scenarios.
 

Conceptual Model

Geologic Framework

A key element of developing a conceptual model of the basin is defining the geologic framework and how it affects the distribution and movement of ground water and the interactions between ground water and surface water within the basin. Many sources of new and existing data will be used to interpret the regional geologic framework, including: existing literature, interviews with previous investigators, lithologic descriptions on water well reports, aerial photographs, drill cuttings submitted by well drillers, geophysical logging, and some field reconnaissance. The interpretations will be presented on a composite geologic map, geologic cross-sections, and possibly contour maps of hydrogeologic units. Some of the work elements of this task are listed below:

Delineate stratigraphy of graben-fill deposits o Construct regional litho-facies maps o Determine location and offset of major structures
Assess effects of faults and other structures on ground-water movement
Assess change in permeability with depth due to secondary mineralization
Assess the relation between the thermal and non-thermal ground-water systems
Analyze drill-cuttings from water wells and BOR test holes
Run borehole geophysical logs on selected wells
Construct regional cross-sections
Define and map any regionally significant hydrogeologic units
Compile regional geologic map and develop consistent stratigraphic nomenclature

Hydrogeologic units are regions within the subsurface which have relatively uniform hydraulic characteristics and which can be differentiated from adjacent units. Any regionally significant units will be delineated using geologic maps and subsurface information. Subsurface information can come from water well reports, other well reports, available geologic logs, and available or possibly project-derived geophysical logs. Borehole geophysical logging can include natural-gamma, resistivity, temperature, flow-meter, down hole camera, and caliper logs. Using surficial geophysical logging to obtain subsurface information is an option that will be evaluated in phase I.

Project personnel will contact local drillers in phase I to request borehole drill cuttings for selected new wells in the basin. The cuttings help improve interpretations of lithologic descriptions found on water well reports and geophysical logs and can be analyzed for mineralogy and chemistry.

 Hydraulic Properties

This project will analyze aquifer test data representing different hydrogeologic units. Data may come from existing reports, the USGS, pump tests submitted to OWRD, well logs, BOR/OWRD aquifer tests, and possibly project aquifer tests. Project aquifer tests will occur where data representing a geographic area and/or hydrogeologic unit is inadequate or missing.

Data analyses will include aquifer hydraulic properties (transmissivity or hydraulic conductivity, and storage coefficients), delayed yield, and boundary conditions. The analyses are needed to assess:

• The ability of different hydrogeologic units to transmit water;
• The existence of confined versus unconfined conditions;
• The presence of interconnections between different hydrogeologic units;
• The presence of recharge boundaries indicating ground-water/surface-water interaction; and
• The presence of no-flow boundaries which may relate to geologic structures or changing lithology.

Aquifer tests may be conducted to obtain representative values of vertical and horizontal hydraulic conductivity within the Upper Klamath Basin; this effort could be coordinated with the BOR test well project.

Flow System

The task of field-inventorying wells will be completed in the early part of phase II. Approximately 500 wells will be inventoried during phase I and up to an additional 500 wells may be inventoried in phase II. Observation wells used by previous studies within the Upper Klamath Basin will be revisited and, if possible, measured to determine historical changes in ground-water level.

Two synoptic mass water-level measurements will be made in approximately 500 wells during one year: one in August-September 1999, and a second in March-April 2000. The expanded quarterly observation well network of approximately 100 wells initiated in phase I will be continued throughout phase II. Approximately fifteen additional recorders will be placed in wells; this will bring the total recorder network to approximately 30 wells (including those installed in phase I) to monitor short term response of the ground-water system to stresses such as climatic variation, surface-water stage variation, and seasonal ground-water pumping.

Geochemistry will be used in conjunction with head data to help delineate ground-water recharge and discharge areas and determine flow paths and residence times for ground water. This information will be valuable in developing the conceptual model of the system and, ultimately, in calibrating the numerical ground-water model. The types of analyses that will be most useful will be determined in the phase I data evaluation, however, samples from wells and springs would most likely be analyzed for major ions, environmental isotopes, and possibly the environmental tracer, chloroflourocarbon (CFC).

Water Budgets

Ground-water and surface-water budgets must be estimated for subbasins and for the Upper Klamath Basin as a whole. Budgets must be developed for specific time periods in order to quantify how changes in land- and water-use and climate in the basin have affected the hydrologic system. Components of the water budget such as recharge and ground-water pumping, will be inputs to the ground-water flow model; other budget components, such as ground-water discharge to streams, will be simulated by the ground-water flow model. For budget components simulated by the ground-water model, independent estimates or measurements are needed to provide a check on the validity of the model.

Surface-water Budget

The surface-water system includes the Klamath, Sprague, Williamson, Sycan, Wood, and Lost Rivers, their tributaries, smaller tributaries to Upper Klamath Lake, and irrigation canals. Surface-water budgets will be developed for Upper Klamath Lake and selected reaches of streams and rivers in the basin. During phase I, the BOR, irrigation districts and other agencies will be contacted to obtain hydrologic measurements that might help define water budgets for the major rivers, canal systems, and Upper Klamath Lake. The primary purpose of developing water budgets for these surface-water features is to independently estimate the exchange of water between them and the ground-water system. These estimates will be used to calibrate the ground-water model developed in phase III of the study. Gain/loss, or seepage, studies of selected stream reaches will also be conducted as described below under "ground-water discharge".

Ground-water Budget

Recharge: The most likely sources of recharge to the ground-water system are precipitation, irrigation return-flow (on-farm losses), canal leakage, stream leakage, and possibly underflow from adjacent basins. The potential contribution of each of these sources will be assessed in the ground-water budget analysis. 

Watershed modeling will be used to estimate the distribution of recharge from precipitation and irrigation return flow in much the same way it has been in recent regional ground-water assessments of the Willamette and Deschutes Basins (J.R. Risley, D.S. Morgan: USGS, oral communication, April 1998). Many types of spatial and temporal data are required to simulate daily water balances within the subbasin watershed models. Spatial data include land-use and cover, soils, geology, elevation, slope, and aspect. Temporal data consist of daily records of precipitation, and temperature from local weather stations, and weekly or biweekly estimates of irrigation application rates.

Leakage to and from streams in the basin will be evaluated using existing stream gage information and project gaging at additional sites. Project gaging will occur during low-flow periods to better define ground-water/surface-water interaction. Existing shallow wells near perennial streams will be used to determine elevation differences between ground water and the streams, to assess ground-water response to stream elevation.

Leakage from irrigation canals will be assessed using existing canal loss data and project gaging where necessary. Existing shallow wells near canals will be used to assess ground-water response to canal losses.

Water rights information will be used to distinguish areas irrigated from surface-water sources from those irrigated using ground water. In the Oregon part of the basin, OWRD is constructing a database containing the digitized outlines of the place of use (POU) and the points of diversion (POD) for each water right. Links between each POU, its associated POD(s), and the State Water Rights Information System (WRIS) will be established by OWRD. This database will allow us to determine the source of water for each field irrigated in 1999 and identify the location of the well for those field irrigated with ground water. As part of phase I of this project, each ground-water POD (well) will be linked to the driller's report to determine the aquifer unit tapped by the well. It is unlikely that water rights data for the California part of the study area is in digital form similar to that in Oregon; available data for California will be compiled during in phase I and an approach developed for estimating water use with that data.

Well discharge for municipal and industrial uses in the basin will be estimated using data from the OWRD water reporting system, water-rights information files, and similar sources for the California part of the study area.

The Klamath Tribes maintain a large monitoring network of springs in the basin (Craig Benz, Klamath Tribes, personal communication). Over 2,000 springs have been inventoried and about 500 are periodically measured. In phase I, data from this network will be evaluated as to its usefulness in quantifying ground-water discharge to springs within the basin. Some springs may be field-located and measured or sampled by project personnel.

Phreatophytes (plants that draw water directly form the water table) that grow along streams, lakes, and canals can discharge large amounts of ground water to the atmosphere. Phreatophyte area can be mapped from aerial photographs and combined with climatic and physiologic data to estimate amounts of ground-water evapotranspiration (ET) using established techniques. Another approach, which will be evaluated during phase I, is using AVHRR (Advanced Very High Resolution Radiometry) remote-sensing data to estimate ET.

Preliminary Ground-Water Model