Why does the reservoir increase the flood discharge after the rainstorm when the storage capacity is full?

The reservoir is most willing to see rain. After all, if it doesn't rain all the time, there will be no water in the reservoir and there will be no benefit. If there is a rainstorm, the inflow of the reservoir will increase sharply, and the storage capacity of the smaller reservoir will be filled up quickly. Only when the reservoir is full will the reservoir increase flood discharge. The main reason is economic benefit, and the secondary reason is the technical limitation of reservoir operation at this stage.

The function orientation of the reservoir The main function of the reservoir is to "promote benefits and eliminate pests". Generally speaking, promoting profit means using the stored water for water supply, irrigation, power generation, etc. , and the elimination of pests is mainly to stop the flood when it comes and reduce the damage of the flood to the downstream. The primary function of most reservoirs in China is flood control. After all, natural rivers may have a large peak flow, which will cause great damage to the downstream.

Reservoir flood discharge

If the peak flow on the river is 10000 m? /s, if there is no reservoir flood control, this 10000 m? /s will rush directly to the downstream, and generally the downstream flow will increase due to confluence, that is, at this time, the downstream may bear more than 1 10,000 m? /s traffic injuries. And if there is a reservoir, this 1 ten thousand m? The flood peak of /s reaches the reservoir first, and the reservoir will lift this water and discharge it according to the set flow, such as 2000m? /s, at this time, the reservoir is put into storage 10000, out of storage is 2000, and the surplus is 8000m? /s exists in the reservoir, the water level of the reservoir will rise, but the downstream peak flow will drop to 2000m? /s, far less than the loss caused by natural floods.

Although reservoir flood control is the most important function, it generally does not produce direct economic benefits. Power generation, water supply and irrigation can directly generate economic benefits. Can charge or earn fees, so reservoir managers are more inclined to make use of the reservoir's money-making function.

Why should the reservoir wait until its capacity is full before increasing the flood discharge? Since reservoir managers are pursuing the economic benefits of promoting profits, they will try their best to store more water in the reservoir. For example, when a rainstorm comes, it takes time for rainfall to reach the runoff yield and confluence. Therefore, reservoir managers usually wait for the water level of the reservoir to rise to the highest level before increasing flood discharge. Only in this way can we maximize the benefits of the reservoir.

On the other hand, increasing the flood discharge when the reservoir capacity is not full may cause the upstream inflow to stop after flood discharge, and the reservoir will operate at a low water level and low storage capacity, thus wasting a lot of overflow water. This is the last thing managers want to see, and it can also be understood that reservoir managers will not let go of redundant and useless water until the reservoir is really full. If the reservoir overflows in advance, there will be certain risks, the reservoir will not be full and the interests will be damaged.

This is only from the perspective of managers. Once the reservoir is full, it will not be able to stop the flood, which will greatly reduce the flood control capacity of the reservoir, which is actually very unfavorable to flood control, especially the continuous rainstorm, which is likely to cause serious floods in the downstream.

The technical level of the reservoir is also one of the reasons for increasing flood discharge when the reservoir is full. In addition to profit, there are technical reasons, that is, the inaccurate forecast of rainfall and runoff at present, especially in summer rainy season, which increases the difficulty of reservoir management.

For example, if it is predicted that there will be a rainstorm, or even the reservoir area is suffering from a rainstorm, the reservoir manager will not easily increase the flow, because the rainstorm is short-term and partial. If the discharge is increased in advance, there may be too little incoming water in the later period, resulting in insufficient water storage in the reservoir and affecting the function of the reservoir.

If the large inflow can be completely predicted technically and the reservoir is not full, it is possible to increase the flood discharge. For example, some reservoirs in southern China are equipped with a large number of rain gauges, which have high forecasting accuracy and can achieve high precision and accurate dispatching. For most small reservoirs, it is still in the backward management mode, and there is no need to upgrade intelligent management, so it is also a situation of increasing flood discharge after the storage capacity is full.