Journal of Irrigation and Drainage Engineering

Many of today’s construction sites rely on perimeter control practices to capture and treat sediment-laden stormwater emanating from disturbed lands. Silt fence systems are a common sediment control practice often specified by stormwater designers to be installed as perimeter control applications. Although design considerations are often given to the location and placement of these systems within the boundaries of a site, design characteristics of the silt fence itself (e.g., post size, post spacing, and fence height, among others) are rarely taken into consideration. As a result, silt fence systems often become overloaded and fail due to insufficient support or lack of effluent flow capability. Thus, this research effort sought to identify and evaluate practical methods for managing the discharge of impounded stormwater and improving the structural stability of silt fence systems. Results from full-scale testing suggest the inclusion of a plywood dewatering mechanism resulted in 96% sediment retention and effluent water quality data similar to results associated with standard silt fence installations. Silt fence dewatering time was reduced from over 24 to 4 h with minimal downstream disturbance of soil and vegetation. Finally, structural analysis data from five common silt fence support posts were used to determine post spacing based on structural load limits. Using these data and in-field observations, recommended distances for post spacing were developed for each support post type.

Precise estimation of local head loss ($hl$) remains a challenge for the hydraulic design of drip irrigation. This study develops a robust protocol for estimating the emitter $hl$ based on the Borda-Carnot principle. The method requires cross-sectional flow area measurements with and without emitter obstruction and a contraction coefficient, which is determined by the empirical relationship of the obstruction ratio. For comparison purposes, cross-sectional flow areas were also measured with a profile projector, which resulted in absolute deviations lower than 2.6%. Observed and predicted single-emitter $hl$ deviation values were consistent with previous studies; the three examined emitting pipe types had deviation values of $-6.67\%$, 21.6%, and 1.07%. Thus, the proposed methodology for estimating the cross-sectional area can be applied without compromising $hl$ estimates using a single flat inline emitter operated by the proposed semiempirical model.

Meter gates are widely used in California and all over the world for both flow control and discharge measurement. The calibration data of the popular round Armco meter gates are available in tabular form for gate diameters varying from 0.2 to 1.22 m. The net gate opening area acts as a crescent-shaped submerged orifice that controls the flow discharge through the turnout pipe. The available discharge equations for these gates are not dimensionally homogeneous; however, a general valid equation in physics must be dimensionally homogeneous. In this study, using dimensional analysis and 10,500 data points on the 14 Armco gates, different dimensionally homogeneous equations are proposed to calculate the flow discharge values through the round Armco gates. The dimensional analysis approach was improved using a standard orifice equation and by applying net gate opening area. The results showed that the turnout pipe diameter, $D$, the gate opening, $w$, the gate head loss, $H$, and Reynolds number, R, are key parameters for deducing a generic flow discharge equation. This study resulted in a calibration discharge equation for the submerged round Armco gates for any gate size in the range of the 14 Armco gates ($D=0.2$–1.22 m; and $w=0.051\mathrm{m}$ to fully open, that is, $D$). The proposed generic equation also makes it possible to compute the flow discharge of the gates with custom and intermediate sizes. The average error in the estimated discharge by the proposed continuous discharge equation for all gate sizes is 2.03% compared with original Armco calibration tables.