Mathematical Models For Sandbag Checkdam.

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ABSTRACT

The study was aimed at developing mathematical models on the hydraulic performance of Sandbags as Checkdam for erosion control. Pilot studies were carried out at two sites. Site ‘A’ was a natural gully at a location in Ezinihitte-Mbaise, Imo State while site ‘B’ was an artificial channel excavated on the slope of Otamiri River at Federal University of Technology, Owerri. Artificial runoff was simulated into site ‘B’ by pumping water from Otamiri River. Sandbags of various patterns and heights were placed across the gullies and hydraulic effects upstream recorded. Two mathematical models were developed based on material balance and regression analysis respectively. Model 1 relates sediment concentration (C) with flow rate (Q) and rate of storage (S) while Model 2 relates height of sandbag (hs) with a dimensionless parameter Sf (storage factor). Model verification indicated a high level of correlation between measured and predicted values of the variables. The coefficients of correlation (R2) were computed as 0.964 and 0.966 for models 1 and 2 respectively. Similarly standard errors of estimates (Se) were 0.00384 and 0.00196 respectively. Comparative studies on patterns of placement of sandbags showed that transverse arrangement yielded better results compared to longitudinal pattern. Based on capital costs, sandbags are comparatively cheaper than conventional concrete check dams (average cost ratio =1:12). However, a major limitation lies in its poor durability leading to increased maintenance costs for long term application. The mathematical and graphical relationships obtained in this study will be useful in the design and sustainable use of sandbags for erosion control.

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Mathematical Models For Sandbag Checkdam.

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