NOMOGRAPHS FOR MANAGING RIPARIAN WATER SUPPLY WELLS

T. W. Soong, Yanqing Lian, Chittaranjan Ray, George Roadcap, and Miguel Restrepo

Illinois State Water Survey and University of Hawaii at Manoa
 

Abstract

Driven by the nation's economic and population growth, demands for fresh water have increased and resource managers are compelled to seek alternative resources. Many communities, including some 13 to 15 towns along the Illinois River, have used or plan to use alluvial aquifers for public water supplies. In addition to the sites being more readily available, the quality of pumped water from alluvial aquifers is generally better than the quality of river water. With proper management practices, alluvial aquifers can be plausible alternative water resources for small or large communities where deep-rock aquifers or reservoir sites are not available. 

One major concern in using riparian wells is the impact on water quality of induced infiltration. Currently many researchers are focusing on the fate and transport of selected contaminants in the bank filtration zone. Before that knowledge is established and applications fully developed, however, it will be beneficial to provide some operational measures that riparian well users can follow to assess the water protection needed. Information on the percentage of mixture of river water in the pumped water has been selected as the criterion for nomograph development. Such a criterion can also be the basis for incorporating water quality issues in the management of riparian water supply wells.

We have generated several types of nomographs relating river recharge to a decision factor (pumping rates) and to external stress (river stages) for an experimental site. Nomographs on river recharge have been developed for the following: water table level at the well versus pumpage rates, water table level at the well versus river stages, and river stages versus pumpage rates. These nomographs summarize extensive information in a systematic and easy-to-understand manner. They can clearly show the advantages and disadvantages of different practices and therefore are suitable for making management decisions. The procedures can be applied to other sites. On the other hand, many input parameters used in the system model contain uncertainties. Their values cannot be specified with absolute accuracy due to imperfect knowledge. An attempt at uncertainty analysis on river recharge is included. Although this analysis was conducted on a preliminary level, it successfully identified the most sensitive parameter that governs the river recharge at different operational scenarios. One can then define measures to reduce the uncertainty of the model system, or to design preventive measures to protect the riparian wells.