Estimating discharge at the outflow structure of a lake

In summary, a fisheries biologist is interested in manipulating a lake level by six inches through a new outlet structure. They are trying to determine the pressure and velocity of the water behind the lake, as well as the discharge for different square openings in the structure. They are using Bernoulli's equation to calculate the velocity, which is proportional to the square-root of the depth, and the total flow is proportional to the vertical area of the hole.
  • #1
salconflu
1
0
I am a fisheries biologist interested in manipulating a lake level by about six inches via a box cement outlet structure on a small lake. The outlet structure is currently governed by two adjacent 5ft by 0.5ft dam boards,which have historically been removed one at a time in the spring and replaced in the fall. However pulling whole boards releases too much water at once so I am trying to figure out whether incrementally lower boards would make a meaningful difference in Q.

As a starting point I am trying to figure out how much pressure is behind the 70 acre lake and what the average velocity (ft/sec) would be across the 2.5 square ft opening without the benefit of a flow meter. Is there a mathematical relationship between the impounded water and the velocity at the outlet? If there is then I could figure out the discharge for different square openings in the outlet structure, ie: cfs = ft/sec* length*width of the opening...
 
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  • #2
Welcome to PF!

Hi salconflu! Welcome to PF! :smile:

Pressure depends only on depth, and not on horizontal area …

the pressure from the whole lake is exactly the same as the pressure at the same height in your bath. :wink:

From Bernoulli's equation the velocity is proportional to the square-root of the depth: v2 = 2ρgh.

And obviously the total flow is also proportional to the vertical area of the hole.
 

Related to Estimating discharge at the outflow structure of a lake

1. How is discharge measured at the outflow structure of a lake?

The most common method for measuring discharge at the outflow structure of a lake is through the use of a flow meter, such as a current meter or acoustic Doppler current profiler. These instruments measure the velocity of the water at the outflow and combine it with the cross-sectional area to calculate the discharge.

2. What factors affect the accuracy of discharge measurements at the outflow structure of a lake?

There are several factors that can affect the accuracy of discharge measurements at the outflow structure of a lake. These include the type of flow meter used, the location of the measurement, the water level and flow conditions, and any obstructions or changes in the channel geometry.

3. How often should discharge be measured at the outflow structure of a lake?

The frequency of discharge measurements at the outflow structure of a lake depends on the purpose of the measurement. For routine monitoring, measurements should be taken at least once a month. For more accurate and detailed assessments, measurements should be taken more frequently, such as daily or weekly.

4. What are the main applications of estimating discharge at the outflow structure of a lake?

Estimating discharge at the outflow structure of a lake is important for a variety of applications. These include water resource management, flood control, environmental impact assessments, and hydrological modeling. It is also essential for understanding the overall health and functioning of a lake ecosystem.

5. How do seasonal variations affect discharge at the outflow structure of a lake?

Seasonal variations, such as changes in precipitation and temperature, can have a significant impact on the discharge at the outflow structure of a lake. During the wet season, discharge is typically higher due to increased water inputs, while during the dry season, discharge may be lower. These variations must be taken into account when estimating and monitoring discharge at the outflow structure of a lake.

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