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Institute for Urban Environmental
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EVALUATION OF UNCERTAINTY IN STREAM NATURALIZATION PROCEDURES

Primary Investigator: Charles S. Melching

Sponsor: Wisconsin Foundation of Independent Colleges, Environmental Sciences Initiative

Duration: May 2004 – June 2005

Funding Level: $8,500

Background

To meet the needs for flood and stormwater management and wastewater conveyance in urban areas streams have been substantially changed from their natural state both physically and biologically. Meandering streams have been straightened and pool and riffle sequences have been smoothed to uniform depths throughout the river. During dry weather periods groundwater flows have been reduced because of reductions in infiltration resulting from impervious land cover, and treated wastewater flows often replace the natural groundwater flow as the primary source of baseflow. Natural riparian vegetation often is cut to improve the hydraulic efficiency of the drainage, and the natural channel bed may be replaced with concrete. These and many other effects of urbanization have resulted in streams changing from attractive, biologically diverse ecosystems to unattractive, biologically limited drainage ditches.

In recent years, many communities have tried to restore urban streams to a more natural condition. Naturalization is not restoring a stream to its natural state, but rather restoring the stream so that it may provide more natural habitat while still meeting its flood and stormwater management and wastewater conveyance functions. The introduction of a pool and riffle sequence to the North Branch of the Chicago River in downtown Northbrook, Ill., is an example of such stream naturalization. A number of procedures have been developed for stream naturalization/restoration. However, considerable uncertainty exists in the application of these procedures particularly with respect to stream stability. For example, many stream restorations do not survive their first large storm and many others are made so strong that concrete is replaced with “green” concrete (rip-rap, concrete blocks, etc.) that looks better than concrete, but does not restore biological functions. Because of the large uncertainty in the evaluation of stream stability large safety factors often are applied in design. These safety factors would be best determined through uncertainty analysis rather than the current use of “rules of thumb.”

Objective

The objective of this project is to develop an approach to relate the safety factors used in the design of stream stabilization measures applied in stream naturalization/ restoration to the probability of failure. This analysis will be the first step toward developing more reliable stream stabilization design procedures, and more cost effective stream stabilization. One test case in Maryland - Piney Run Creek - was used to develop and illustrate the uncertainty analysis procedures. The design procedures and data for this test case was supplied to Marquette University by Ms. Hala Flores of the Prince George’s County, Maryland, Department of Environmental Resources.

Publications:

Paper from XXXI IAHR Congress, Seoul, Korea, September 11-16, 2005:
Uncertainty evaluation in the design of instream structures for stream restoration

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