Canal Geometry, Flow Velocity, Dallisgrass (Paspalum dilatatum Poir.) Density and Soil Phosphorous Effects on Hydraulic Resistance of Vegetated Canals

Abstract

Normal 0 false false false MicrosoftInternetExplorer4 Dallisgrass (Paspalum dilatatum Poir.) reduces discharges in irrigation canals and causes problems in operation and maintenance of canals. This study has been conducted to determine roughness coefficient in vegetated canals caused by dallisgrass and to investigate the relationship between available soil phosphorous and dry mass of dallisgrass. The study also aims to find out the relationships among roughness coefficient, dallisgrass density and soil phosphorous in vegetated canals in Moghan plain, Iran. The results showed that the roughness coefficient varied from 0.01 to 0.32 and averaged at 0.09. The variation in roughness coefficient in vegetated canals by dallisgrass may be explained solely by the flow velocity and canal slope, assuming that there are no spatial variability’s of the other affecting variables. Therefore, a regression model comprises both the roughness coefficient as a dependent variable and the flow velocity and canal slope as an independent variable is developed. The available soil phosphorus both on the sides and at the bottom of vegetated canals were from 4.2 to 37 mg kg-1. The highest dry mass of 16 kg per 100 m2 was acquired from the canal with soil phosphorus of 16.7 mg kg-1. Also, another model was developed to describe the roughness coefficient as a function of the flow velocity, canal slope, dallisgrass density and soil phosphorous. It is recommended that identifying phosphorus sources and limiting its distribution in irrigation canals is necessary to reduce the dallisgrass density in canals.