Area Capacity Curve | Reservoir Capacity Curve | Download Excel file for area capacity curve

 Introduction

An area capacity curve, also known as a reservoir capacity curve or a capacity-elevation curve, is a graphical representation of the relationship between the water surface elevation of a dam or reservoir, and the corresponding area of the reservoir that is flooded.

The curve is typically plotted with the water surface elevation on the y-axis and the corresponding area of the reservoir on the x-axis.

In dam projects, the area capacity curve is used to determine the storage capacity of a reservoir at various water surface elevations. This information is important for the design and operation of the dam, as it determines the amount of water that can be stored in the reservoir at different times of the year, and how much water can be released to meet downstream demands. The curve is also useful for determining the flood control capacity of the reservoir.

The area capacity curve is determined through a combination of field surveys, topographic maps, and hydrologic and hydraulic modeling. It is typically developed during the design phase of a dam project, and is updated as necessary during the construction and operation of the dam.

There are a few different methods that can be used to calculate the area capacity curve for a dam or reservoir project, which include:

• Surveying:

This method involves physically measuring the water surface elevation at various points around the reservoir, and then using these measurements to calculate the corresponding area of the reservoir that is flooded. This method is typically used for small reservoirs or dams, where the topography is relatively simple.

The storage capacity of the reservoir may be determined by taking contour areas at equal interval and summing up by trapezoidal formula, cone formula or prismoid formula. If V is the storage volume and A1, A2, A3,……An are the areas enclosed by the successive contours at an interval h, then the various formulae are as follow:

1. Trapezoidal formula:

2. Cone formula:

3. Prismoid formula:

• Topographic Maps:

This method involves using topographic maps to determine the contours of the reservoir, and then using these contours to calculate the area of the reservoir that is flooded at various water surface elevations. This method is typically used for larger reservoirs or dams, where the topography is more complex.

• Hydrologic and hydraulic modeling:

This method involves using a computer model to simulate the behavior of the reservoir and its watershed, taking into account factors such as precipitation, evaporation, and inflow and outflow. The model is then used to calculate the area of the reservoir that is flooded at various water surface elevations. This method is typically used for large and complex reservoirs or dams, and is considered to be the most accurate of the three methods.

It's worth mentioning that the choice of method depends on the size, complexity, and location of the dam or reservoir, as well as the accuracy and level of detail needed for the project.

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