Side weirs are diverting structures and usually used for diverting and controlling the water flow into the side open channel. The present study deals with an experimental study regarding the hydraulic performance of side weirs with semi-circular vertical sections along the main channel. As flow depth of the main channel increases the top flow width of the semi-circular side weir (SCSW) increases which is an advantage when high discharge enters the main channel and should be immediately diverted for safety reasons. In this study, the flow discharge of semi-circular sharp-crested side weirs and their affecting parameters are investigated. To investigate the hydraulic behavior and geometric characteristics of the SCSWs, a comprehensive laboratory study including 155 tests (for three weir diameters 0.25, 0.30 and 0.40 m) was conducted in a physical model under subcritical flow conditions. Flow discharge of the SCSW was investigated in relation to height, diameter and flow head of side weir, also approach Froude number (Froude number at upstream end of the side weir) and main channel width. Three different discharge models were developed based on; purely dimensional analysis technique, classical weir equation with linear water surface and classical weir equation with horizontal water surface profile (conventional weir theory along with dimensional analysis technique). The presented mathematical discharge models enable estimation of discharge along the SCSW with acceptable accuracy (best model has an average error of 1.87% with a maximum error of 6.31%) compared with the measured data under subcritical flow conditions. Additionally, a relationship was proposed for computing the limiting flow depth at the downstream end of the SCSW. Experimental results confirm that the proposed relationship well explains the behavior of flow over the SCSW regarding the downstream flow conditions.

侧堰是一种导流结构，通常用于分流和控制流入侧明渠的水流。本研究涉及有关沿主河道具有半圆形垂直截面的侧堰的水力性能的试验研究。随着主通道流深的增加，半圆形侧堰（SCSW）的顶部流宽度增加，这在高流量进入主通道时是有利的，出于安全原因应立即分流。本研究对半圆形尖顶侧堰的流量及其影响参数进行了研究。为了研究 SCSW 的水力行为和几何特性，一项综合实验室研究包括 155 次测试（三个堰直径 0.25、0.30 和 0. 40 m) 是在亚临界流动条件下的物理模型中进行的。研究了SCSW的流量与侧堰的高度、直径和水头，以及接近弗劳德数（侧堰上游端的弗劳德数）和主通道宽度的关系。开发了三种不同的放电模型；纯量纲分析技术，线性水面的经典堰方程和水平水面剖面的经典堰方程（常规堰理论和量纲分析技术）。与亚临界流动条件下的测量数据相比，所提出的数学流量模型能够以可接受的精度估计沿 SCSW 的流量（最佳模型的平均误差为 1.87%，最大误差为 6.31%）。此外，提出了一种关系来计算 SCSW 下游端的限制水流深度。实验结果证实，所提出的关系很好地解释了关于下游流动条件的 SCSW 上的流动行为。