Prediction of water temperature in stratified reservoir and effects on downstream irrigation area: A case study of Xiahushan reservoir
Highlights
► Simulated the water temperature of a stratified reservoir and river channel. ► Illustrated the rice growth will be affected by cool water during April and June. ► Predicted the influence range on the irrigation area.
Introduction
Water temperature plays a critical role in aquatic environment. The deep water of a stratified reservoir is usually low-temperature and anoxic, it will cause the sediments decomposing to release heavy metals, phosphate and toxic substance, etc. The aquatic ecosystem, water quality and crops will be influenced by the cool water releasing from the reservoir.
Given the importance of water temperature’s role in ecosystem, there has been growing interest in simulating water temperature and analyzing the impact. Yearsley (2009) developed a one-dimensional stream temperature model and analyzed the impact of climate changes on stream temperature in the Columbia River system. Improvements to existing forecast models and semi-weekly 10-day water temperature forecasts have been made during the salmon migration season (Morrison and Foreman, 2005). Bonnet et al. (2000) designed a numerical model of the hydrodynamic and thermal structure of an artificial lake, which was developed as a basis for an ecological water-quality model and it is applied to discuss the impact of withdraw level of a reservoir. Gu et al. (1999) studied the weather-dependent flow requirements for summer river temperature control by quantitative temperature–flow relationships. The study result of Gu et al. (1993) showed that the cold water from reservoir affect the early rice most, late rice followed.
We usually use one-dimensional water temperature model to calculate river temperature, two or three- dimensional model to simulate lake and reservoir temperature. However, for large water, three-dimensional model is time consuming and uneconomic. So in general case, two-dimensional water temperature model can well simulate the flow field and temperature field of a reservoir.
This study simulates the vertical distribution of water temperature in Xiahushan reservoir which is planning to be built, and predicts the re-warming process along the downstream river and irrigation canal. And then analysis of the effects on downstream irrigation areas has been made.
Section snippets
Model description
The water temperature simulating calculation has two steps: reservoir simulation and channel simulation. Environmental Fluid Dynamic Code (EFDC) is adopted to calculate the water temperature in reservoir, and then 1-D longitudinal stream temperature model is used for calculating water temperature in channel.
The study area
This study was carried out in the Xiahushan reservoir which is planning to be built on the upstream section in Dashahe River in eastern China (116°40′E, 30°52′N). The Xiahushan reservoir is designed to serve flood control, irrigation and hydropower generation, and irrigation releases are given priority over power generation releases. In order to protect the river ecosystem, the dam is including a stratified intake facility. The irrigation area of Xiahushan reservoir is 274.3 km2, where rice, rape
Release water temperature prediction
In the hydrological and meteorological condition of the typical normal year (1984), the prediction of reservoir water temperature is showed in the following figures.
Fig. 2 shows the water temperature of Xiahushan reservoir in April–August. Fig. 3 presents the monthly air temperature, nature river temperature, release water temperature, surface and bottom water temperature in the reservoir. Between March and July, the release water temperature is 2.3 °C lower than the nature river temperature
Conclusions
The EFDC model and the 1-D stream temperature model were used to simulate the reservoir water temperature structure and determine the influence range of low-temperature water. Xiahushan reservoir was taken as a case study. The results of the calculation indicated that, in the period between April and June, the maximum influence range is 55 km. The water temperature can reach the lowest growth temperature of rice out of this distance.
In order to reduce the influence range, some management and
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