EFFECT OF SUBMERGED WEEDS ON WATER FLOW IN OPEN CHANNELS

Gamal M. Abdel-aal, Amany A. Habib, Abd- elazeem M. Ali, Marwa F. Shaheen

Abstract


Whenever a cleaning process and removal of weeds from water channels is carried out, the weeds re-appear in a matter of weeks and sometimes days. This costs a lot of effort and money. Hence, there is an urgent need for harmonization between the presence of weeds of acceptable densities and to maintain water levels in the last reaches of the channels which are mainly infested by the weeds. The present paper aims to study experimentally the impact of the existence of submerged weeds on the flow characteristics in case of maintaining the water levels behind the infested areas. The data were collected using a laboratory flume of relatively large dimensions (60cm wide, 65 cm depth, and 20.8 m long) with fixed bed slope (0.0062). Flexible branched roughness elements were used with different intensities (0.0062, 0.0123, and 0.0246). The weeds intensities were tested with different discharges and different tail water depths. Dimensional analysis was used to correlate the flow characteristics to the other relevant parameters of the flow and weeds. Dimensionless general equations in terms of these parameters for computing both heading up, relative energy loss, Manning coefficient and relative shear velocity of the flow through the infested reach were developed and compared with the experimental data. The comparison proved a good reliability and high accuracy. The equation of Manning coefficient was reduced to the case of non-infested canals and verified with different irrigation canals (El-salam main canal and its branches Om El-Reesh , San El-hagar stage 2 and 3 and El-Sheikh Gaber canal).

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