Civil 3D Earthen Dam Design: Part-2A | Reservoir Volume Calculation

Civil 3D Dam Design: Reservoir Volume Analysis with Contours - The Easy Way

(Surface Comparison & Stage Storage)

Reservoir Volume Calculation in Civil 3D: Two Methods

In Civil 3D, reservoir volume calculation can be performed using two primary methods:

Surface Comparison Method

Stage-Storage Analysis Method

Let’s go through each method in detail:

1. Surface Comparison Method (Cut & Fill Volume Calculation)

This method compares two surfaces—the existing ground surface and the reservoir water surface—to calculate the volume between them.

Steps to Calculate Volume Using Surface Comparison Method:

Create or Import the Existing Ground Surface

This represents the original terrain before water storage.

Create the Water Surface

Define a surface representing the water level (reservoir full level).

You can create this surface by setting an elevation boundary at the desired water level.

Use the ‘Volume Dashboard’ or ‘Surface Properties’ in Civil 3D

Go to Toolspace → Prospector Tab

Right-click on Surfaces → Create a Volume Surface

Select the existing ground surface as the Base Surface

Select the water surface as the Comparison Surface

View the Volume Results

The software calculates the cut (excavation) and fill (water storage) volumes.

The fill volume represents the reservoir storage capacity.

✅ This method is simple and effective for quickly estimating the total water volume at a given water level.

2. Stage-Storage Analysis Method

The Stage-Storage method calculates volume at different elevation levels to create a stage-storage curve (relationship between water level and volume).

Steps to Calculate Volume Using Stage-Storage Method:

Create Contour Intervals for Water Levels

Define elevation intervals (e.g., every 1m or 2m) from the reservoir bottom to full storage level.

Generate contours for each elevation level.

Create Elevation Bands for Each Stage

In Civil 3D, go to Analysis Tab → Surface Properties.

Select Elevation Analysis and divide the water storage area into bands.

3. Calculate Water Surface Area at Each Elevation

For each elevation band, measure the plan area of the corresponding contour.
Civil 3D provides area calculations for each elevation level.

4. Calculate Volume Between Stages (Trapezoidal Formula)

• The volume between two elevation levels can be estimated using: $$V = \frac{(A_1 + A_2)}{2} \times (h_2 - h_1)$$ Where:
  • $A_1$ and $A_2$ are the water surface areas at two consecutive elevation levels.
  • $h_2 - h_1$ is the height difference between those levels.

5. Generate Stage-Storage Curve

Plot a graph of storage volume vs. water level elevation to understand reservoir capacity at various depths.

✅ This method is useful for designing spillways, flood control, and optimizing reservoir storage based on seasonal variations.

Comparison of Both Methods

Method	Use Case	Accuracy	Complexity
Surface Comparison	Quick volume estimation at a fixed water level	High	Simple
Stage-Storage	Detailed volume calculation for multiple elevations	Very High	Moderate

Conclusion

Both methods are essential in earthen dam design. The Surface Comparison Method is great for quick estimates, while the Stage-Storage Method provides a more detailed analysis of how the volume changes with water levels.