Impact of the roughness coefficient for the hydraulic conductivity of regulated rives

Abstract

The article presents hydraulic conductivity modelling results of the some regulated Southeast Lithuanian streams overgrown with woody vegetation. Possibilities to plan naturalization of the regulated streams are also presented in the article. The research of woody vegetation was carried out in the Neris river basin within the period of 2006 to 2007. Having evaluated the influence of hydraulic roughness (Manning coefficient of roughness) on hydraulic conductivity of the rivers Nemėža and 2-2 streams it was established that the density of woody vegetation in the investigated section varied from 0.01 to 0.68 units m-2 in Nemėža stream and from 0.17 to 3.12 units m-2 in 2-2 stream. At the existing density of woody vegetation the hydraulic roughness coefficient n established by hydraulic calculations reached in 0.025-0.045 In Nemėža stream and 0.033-0.053 in 2-2 stream. Under present hydraulic roughness coefficient assessed by natural Investigations in all investigated streams sections, when spring flood discharge probability is 10%, water overflow indicator is positive; the water depth in the bed (zV) of the natural reaches was lower than the depth of a regulated stream (hG).The reserve of hydraulic conductivity in the investigated Nemėža stream section is lost when roughness coefficient reaches the limit of 0.080, in 2-2 stream 0.060. When roughness coefficient reaches 0.170, water overflowing indicator is negative in all investigated sections of the streams.