Water Resources of Michigan

Development and Implementation of Random-Walk Particle-Tracking Analyses of Water Supply Intakes on Rivers and Lakes: A Case Study of St. Clair-Detroit River Waterway

PROPOSAL SUMMARY:

BACKGROUND

Water utilities commonly use surface-water bodies for public water supply. In Michigan, 70 surface-water intakes provide drinking water to over 75 percent of the persons served by public water systems or about 50 percent of the state's population. Assessing the vulnerability of these water intakes to contaminants carried by tributaries, CSO discharges, spills, point and nonpoint sources is complex. The dynamic hydraulics of the surface-water bodies, driven by continuously varying stage, streamflow, and wind conditions, and the uncertainty concerning the magnitude, timing, duration, location, and chemical characteristics of potential contaminant sources complicate source water assessment.

PROBLEM

Quantifying the vulnerability of water supply intakes on surface-water bodies to contaminants is problematic because of limitations of existing software, knowledge, and methodology for conducting detailed source water assessments. In particular, existing particle-tracking software needed for effective utilization of the RMA2 two-dimensional hydrodynamic model is not compatible with the current model output format, nor does it include the capability to mimic the stochastic water movements associated with turbulence and flow dispersion. In addition, little information on field data collection or analysis techniques is available to help identify or parameterize the stochastic component of flow dispersion needed for random-walk particle tracking analysis. Finally, statistical methodology needed to integrate results of flow simulations and particle-tracking analysis for probabilistic assessment of source water vulnerabilities have not been generally documented.

OBJECTIVE

This project component will develop methodology and provide software in the public domain to help identify areas that likely contribute water to public intakes on rivers and lakes. Knowledge of these areas will help assess the vulnerability of public water supplies to discharges from tributaries, combined sewer overflows, and spills. The work also will provide a basis for identifying how potentially sensitive areas may be impacted by discharges from point sources. The results will be illustrated by application to the St. Clair-Detroit River Waterway.

APPROACH

As part of the program support provided by the American Water Works Association Research Foundation (AwwaRF) and Detroit Water and Sewerage Department (DWSD), the U.S. Army Corps of Engineers (USACE) Waterway Experiment Station (WES) will develop a computer program to track the movement of hypothetical massless, non-reactive particles through a two-dimensional flow field defined by RMA2 simulations. In addition to the simulated advective component, particle movements will be influenced by random perturbations of specified magnitudes to simulate the effect of turbulent mixing and molecular diffusion on the dispersion characteristics of constituents in the water.

Figure 1. Particle tracking simulation of dispersion characteristics in a river from a point source.

Field investigations will be conducted to identify and parameterize a random-walk model describing the longitudinal and traverse components of flow dispersion characteristics. The field investigations will include drifting buoy deployments and detailed flow velocity measurements obtained by use of acoustic Doppler current profilers (ADCP). Flow simulation results will be combined with probabilistic information from random-walk particle tracking analysis to quantitatively assess the vulnerability of water supply intakes on rivers and lakes. The methodology will be demonstrated by application of an existing two-dimensional flow model of the St. Clair-Detroit River and illustrated by use scientific visualization techniques incorporated into the SMSŪ pre- and post-processor software for RMA2.

ANTICIPATED RESULTS

The results of this research will provide enhanced software tools and statistical techniques to quantitatively assess the vulnerability of water supply intakes on rivers and lakes to contaminants and to identify areas likely to be impacted by point and nonpoint discharges. The particle-tracking software will be maintained in the public domain to provide access and continued maintenance and support by U.S. Army Corps of Engineers. A U.S. Geological Survey Water-Resources Investigations Report will be prepared documenting the methodology for quantifying vulnerability based on hydrodynamic flow simulations with particle tracking analysis. Results for St. Clair-Detroit River will provide a case study for applications in other areas

Please contact David J. Holtschlag for additional information.