Project Summary

Mountain watersheds are primary water resources in the western United States, but society lacks the detailed scientific knowledge to make credible decisions regarding use of this resource. Presently, we are unable to accurately predict the influence of fractures on watershed-scale ground-water systems. Most research related to fracture flow has focused on detailed definition of individual fractures. Such methods hold little practical value for assessing fractured ground-water systems for the purpose of water resource management because the data are too expensive to obtain. The hypothesis of this project is that commonly available, inexpensive data can provide sufficient information to characterize the flow system in fractured rock and estimate the scale at which and equivalent porous media model can represent its behavior. The project identifies the value of commonly available data in achieving these assessments.

The Turkey Creek watershed, approximately 20 miles west of Denver Colorado and typical of the Rocky Mountain region, serves as the study area. It is comprised of a fractured-crystalline rock aquifer with individual domestic wells and sewage disposal systems. The rapid growth of population and development in the watershed has caused a number of agencies to collect water resource data. The data are in different forms at many locations, have not been integrated, and there no plans to utilize the data to understand fracture flow systems or to assess which data are most useful in characterizing the ground-water system. The unusual wealth of common and exotic data in the watershed allows evaluation of the value of low-cost, commonly available data to characterize fracture flow systems and estimation of the scale at which equivalent porous media models can predict behavior of flow in fractured crystalline rock. Existing data are being compiled along with data collected specifically for the project.

The following tasks are underway:

1) compile and organize available data, supplemented with additional field measurements;

2) evaluate the data by viewing their distribution from a variety of perspectives;

3) utilize the data to develop synthetic equivalent-porous-media and fracture flow models, with characteristics similar to the watershed, to

a) evaluate attributes generally believed to differentiate porous media and fracture flow systems,

b) compare the character of hydraulic head and water quality observed in the watershed to synthetic model behavior, so as to

c) create guidelines delineating the use of commonly available data (inexpensive, holistic measures of system character) to estimate the scale at which the watershed can be represented as an equivalent porous media;

4) use results of task 3 to generate regional models of the watershed, calibrate the models using nonlinear regression techniques, identify the commonly available data that are instrumental in describing the flow system, use the unusual, expensive data to assess the value of the commonly available data, and identify the type and location of new data that will improve the calibration or confirm the value of the commonly available data;

5) collect data identified in task 4, covering two base-flow recession periods, and incorporate the data into the model calibration to modify and improve the representative models;

6) using both the fracture and porous media models, compare the character of the three-dimensional flow system, estimate the scale at which equivalent porous media models can be used to predict system response, and predict the impact, and associated uncertainty, for one scenario of increased development on the quantity and quality of water resources;

7) identify the data that are instrumental to accurate prediction and evaluate the type of data that would reduce prediction uncertainty or confirm the value of the low cost data;

8) disseminate the results via journal articles and web postings including the database; and

9) train Geological Engineers and enhance the scientific knowledge and skill of K12 teachers.