m. yasi

Mountain streams are characterized by coarse-bed materials, steep slopes, and low flow depth. In these type of streams, direct measurement of discharges and/or flow velocities is often difficult, particulaly in high flows. Therefore, the use of flow resistance relationships will be inevitable. The present research aims to develop dimensionless relationships of hydraulic geometry in estimating the discharge without measuring the water depth. In this study, flow resistance in three mountain streams, including Ansarood, SaeedAbad and Lighvan with various bed-forms was investigated based on measured data, and a new equation was proposed. The present study results revealed that in the case of mountain rivers, the inclusion of the geometric standard deviation of bed materials in the non-dimensional hydraulic geometry relationships increases the correlation coefficient and the accuracy of the predictive equations.

The main aim of the present study was to use different Hydro-Ecological methods to determine the environmental flow requirements in a typical perennial river, the Gadar River, in the Urmia Lake Basin, Iran. The ecological needs of the Gadar River were investigated in two different reaches along the river. Eight Eco-Hydrological methods (1- Tennant, 2- Tessman, 3- Flow Duration Curve Analysis (FDCA), 4- Smakhtin, 5-FDC shifting, 6- DRM, 7- RVA, 8- Q Equation) were used for the assessment of the minimum river environmental flow requirements. In order to maintain the Gadar River at minimum acceptable environmental status (i.e. Class C of the environmental management of rivers), average annual flows of 3.28 and 3.25 m3/s are to be allocated along the river in Naqadeh Bridge and Bahramlu Bridge Stations (located 40 and 18 km upstream from the Urmia Lake), respectively. Also, the prescribed monthly distribution of environmental flow requirements has been considered and proposed for the Gadar riverine life. Restoration of Urmia Lake needs the evaluation of the potential flows from the in-basin rivers and the revision of agricultural water rights. Monitoring the minimum environmental flow regime is necessary along the rivers to make sure the delivery of the water into the Urmia Lake.

Application of numerical models in river engineering projects is unavoidable. However, the reliability of model, minimum requirement for field data, and fewer computational processes are of major concern. The main purpose of the present study was to test the reliability of some well-known numerical models in the simulation of flow characteristics in different river planforms. Comparison were made between the flow characteristics in a river physical model and the simulation results from three numerical models, under two different river training schemes, with identical initial and boundary conditions. In this study, a reach of the Nazloo River in Urmia, Iran, was selected. A fixed-bed physical model of the River Reach (1200 m long, with horizontal scale of 1:100 and vertical scale of 1:20, and with the Nazloo cross bridge included within the reach) was constructed, calibrated and verified. Two training schemes were planned, using longitudinal and transversal structures, i.e, levees and groynes. Flow parameters (such as,: depth and point velocity) were measured for four different flows. Three river models: 1D model HEC-RAS, Quasi-2D model BRI-STARS, and 2D model FAST-2D were selected. Six flow parameters (i.e. river flow capacity, water surface elevation, mean flow depth, mean velocity, mean bed shear stress and Froude number) were compared between the physical model and the three numerical models. Four different flow conditions were examined, and the results were compared in three sub-reaches along the river reach (from downstream to upstream of the bridge).The averaged predictive errors from these three models were determined for corresponding flow parameters. The HEC-RAS, FAST-2D, and BRI-STARS models are considered to be the best fitted models with the true physical model, respectively. Simulation results from the HEC-RAS model are well adapted to the river flows confined between the two-sided levees, where the geometry of the river reach is more uniformly defined, and in minor flood flows. The prediction from the FAST-2D model is superior along the river reach with groynes involved, particularly in higher flow levels. The application of each of the three models is recommended in river projects subject to the inclusion of the order of certainties provided by the present study.

A labyrinth spillway is an overflow spillway to regulate and control flow in canals, rivers and reservoirs. The main hypothesis for the development of such a spillway is to increase the discharge per unit width of structure for a given headwater. This type of structure is often an efficient alternative to a gated-spillway type where either the increase of the flood-passage capacity or the control of the water surface upstream is concerned. This study was aimed to investigate the hydraulic performance of labyrinth spillways of general trapezoidal planform with simple curved apexes. In the experimental work, twelve spillway models with double cycles were considered using three different curved apexes (R/w= 0.15, 0.2, 0.25), each with four different crest heights (w/P= 1.5, 2, 3, 4). Based on the cited recommendations, the length magnification was set to a constant ratio of (l/w= 3) the crest shape was to be of a semi-circular form with simple radius (r= 15 mm) and the spillway walls were vertical with the thickness of T= 2r. An intensive experiment was carried out over a wide range of flows, providing 720 flow data ranging from free flow to submerged flow conditions. 1D flow equation was presented using combined mathematical and dimensional analysis. A coefficient of discharge, Cd, was introduced to represent the influence of the effective geometric and hydraulic parameters on the flow capacity over the spillway. Modular limit was also controlled to see whether the flow over the spillway would be submerged. The results of the study indicate that the modified curved planform of the spillway apexes with consistent divergence in the downstream channel introduces a significant improvement in the flow efficiency over the labyrinth spillways. Spillways with narrower curved apexes (i.e. R/w≤ 0.2), and with the vertical-aspect ratio of (2≤w/P<3) provide more stable and higher hydraulic performance than any other labyrinth planforms over a wide range of flows (i.e. 0.1<h0</h/P<0.6). In terms of the flow capacity, the proposed spillway model is shown to be more efficient than other zig-zag planforms (i.e. triangular and trapezoidal shapes) with an identical crest length.