Bulk Flow Resistance in Vegetated Channels: Analysis of Momentum Balance Approaches Based on Data Obtained in Aging Live Vegetation

Abstract

Previous work has sought to investigate flow resistance caused by vegetation in open channels. However, many existing flow resistance models are based on data from artificial plant mimics in laboratory channels and are untested with live, aging vegetation and may neglect some of the key effects. This paper presents results from a study using two types of live vegetation grown within a laboratory channel. A series of flow resistance tests were conducted over a time period sufficient to observe changes caused by growth. The effects of the vegetation on bulk flow resistance are presented and discussed. The results are compared with predictions made by existing practical momentum balance based models for flow through emergent vegetation, and new empirical relationships are presented. The work shows that momentum balance methods can provide an accurate prediction of flow depth in live vegetation provided that the relationship between bulk drag coefficient and flow is known. This relationship has been shown to vary with changes in plant properties during growth.