Grassed drainage channels—hydraullic resistance characteristic

Current methods of estimating the hydraulic resistance of grass were developed for the relatively high water depths found in rivers and large channels, and for cultivars not common in the UK. This paper describes work carried out to determine the hydraulic resistance of grass-lined drainage channels, with particular emphasis on shallow channels used for road drainage. Grass types that are common in the UK, which have slow growth rates and are tolerant to salt and wet conditions, were identified as suitable for drainage channels. Experimental work with natural grass led to the development of resistance formulae where the Manning's n coefficient is dependent on the grass height and on the product of the velocity and hydraulic radius. Issues related to the construction and maintenance of grassed channels are also discussed in the paper.