Suchergebnisse

The food may cause serious loss of life and property. The evaluation of food events is necessary for the planning and design of engineering projects. In a dam, food problems should be considered for both upstream and downstream conditions. The characteristics of food problems can be derived from observation of dam sites. Tis paper aims to evaluate the impact of food hazards from spillway based on downstream conditions after dam construction. Also, the paper discusses downstream food problems depending on stream characteristics in an example dam site. In results, three reasons are determined for downstream foods problems: control problems of spillway gates, the naturally developing vegetation through channel flow line and incompetence of stream cross-section for carrying of food flows. Therefore, downstream conditions should be investigated before dam construction. Tis investigation can be considered in the planning phase. In addition, the cross-section and longitudinal profile of stream should be controlled via maintenance of stream after dam construction. In stream cross-section problems (such as vegetation, incompetence and irregularities), some modifications (e.g. straighten, deepen, and widen) can be applied with engineering works. First published online: 18 Mar 2014

The food may cause serious loss of life and property. The evaluation of food events is necessary for the planning and design of engineering projects. In a dam, food problems should be considered for both upstream and downstream conditions. The characteristics of food problems can be derived from observation of dam sites. Tis paper aims to evaluate the impact of food hazards from spillway based on downstream conditions after dam construction. Also, the paper discusses downstream food problems depending on stream characteristics in an example dam site. In results, three reasons are determined for downstream foods problems: control problems of spillway gates, the naturally developing vegetation through channel flow line and incompetence of stream cross-section for carrying of food flows. Therefore, downstream conditions should be investigated before dam construction. Tis investigation can be considered in the planning phase. In addition, the cross-section and longitudinal profile of stream should be controlled via maintenance of stream after dam construction. In stream cross-section problems (such as vegetation, incompetence and irregularities), some modifications (e.g. straighten, deepen, and widen) can be applied with engineering works. First published online: 18 Mar 2014

AbstractThe concentration of dissolved oxygen (DO) is an important indicator of water quality because aquatic life survives on the DO in water. A free overfall jet from a weir plunging into downstream water causes entrainment of air bubbles if the free overfall jet velocity exceeds a certain critical value and hence aeration occurs. This paper investigates the free overfall jets from sharp‐crested weirs and their effect on air entrainment and aeration efficiency. The results indicate that the air entrainment and aeration efficiency of triangular sharp‐crested weirs are significantly better than those for the other sharp‐crested weir types. Therefore, the triangular sharp‐crested weirs can be used as highly effective aerators in streams, rivers, constructed channels, fish hatcheries, water treatment plants, etc. Regression equations were obtained for the triangular sharp‐crested weirs relating air entrainment rate and aeration efficiency to drop height, discharge and angle in the triangular sharp‐crested weir. There was good agreement between the measured values and the values computed from the predictive equations.

AbstractDissolved oxygen content is a prime indicator of water quality. The oxygen transfer across the air–water interface at a hydraulic structure, such as a weir or spillway, occurs by self‐aeration along the chute and by flow aeration in the hydraulic jump at the downstream end of the structure. Despite increased research activities in the field of stepped spillways, the aeration efficiency of stepped spillways is not yet known. This paper investigates the aeration efficiency of stepped spillways, in particular the effects of varying chute angle and step height. Empirical correlations predicting length of the nonaerated flow region and aeration efficiency were developed. The results indicate that stepped spillways are effective for oxygen transfer.