To determine the capacity of a reservoir using the contour method in surveying, you need to follow these steps:
1. Survey the area around the reservoir and draw a contour map of the area.
2. Measure the elevation of the reservoir's spillway and the elevation of the bottom of the reservoir.
3. Divide the reservoir into several sections by drawing horizontal lines on the contour map.
4. Calculate the area of each section using the planimeter or by counting the grid squares underneath each section.
5. Multiply the area of each section by the vertical distance between the contour lines to get the volume of each section.
6. Add up the volumes of all the sections to get the total volume of the reservoir.
7. Finally, multiply the total volume by the specific weight of water to get the weight of water in the reservoir, and then divide by the density of water to get the capacity of the reservoir in liters or cubic meters.