The overall construction and individual functions of a reservoir will vary depending on the goals of the builder and the environment it's born in. The flow rate of the river or water source where the reservoir will be located, as well as the overall amount of water that it’s expected to hold, and for how long, will define its shape and materials. When it comes to dams, which are often used in the case of larger reservoirs, considerations will need to be made for excess run-off coming from an uncontrolled water-source in the design of the dam and reservoir itself.
Excavated vs Impounded
- Excavated reservoir - This is a man-made storage basin dug within a closed watershed. This is usually a pre-existing lake or pond made even larger and deeper by enlarging the already present depression via excavation.
- Impounded Reservoir - This is an embankment pond formed by blocking the end of a narrow valley. Building artificial embankments allows for a completely new body of water, like in the case of a bankside reservoir. These are generally able to hold significantly more water. On-stream impounded reservoirs, like in the case of dams, will need to include spillways and outlets to allow excess runoff to flow downstream, as well as flood controls.
Location Scouting
The geography of the local environment will help determine which location is the most ecologically appropriate and practical. Additionally, the goals of the reservoir and the purposes it serves will specify the depths and dimensions of the basin.
- When affordability is a priority, the reservoir will ideally be located where the maximum amount of water storage can be achieved with the least embankments/impoundments, or other containing methods required. In most cases, this appears in the form of a dam built across the narrow part of a valley (a Dammed Valley Reservoir). The natural steep slope of the surrounding earth typically allows a much larger amount of water to be stored with less new embankments needing to be constructed.
- When intending to construct a container for water supply, shallow water should largely be avoided. Large areas of shallow depths will encourage evaporation and make plant-growth more difficult to regulate and control.
- A basin or reservoir that’s intended to encourage wildlife is best served with a wide array of depths and aquatic flora. Fish will stay in shallower areas around 2 or 6 feet deep in order to feed and lay their eggs but spend most of their time 10 feet or deeper in the water. Waterfowl also prefer a variety of depths for nesting and feeding, while amphibians and young fish are most comfortable in shallow, plant-rich waters.
- Pollution from upstream drainage and run-off should also be considered. When choosing a location for a pond, it should ideally be placed where drainage containing toxins or chemicals from irrigation, pastureland, sewage lines, or industrial waste can’t reach the pond. When complete avoidance isn’t an option, the offending run-off should be redirected from flowing into the reservoir via channels or pipes.
- Especially in the case of extremely large reservoirs, the body of water should be placed as far away as possible from where it’s failure would cause loss of life, or damage to buildings, highways, utilities, or residences. When this is impossible to avoid, intensive investigations and emergency plans should be considered in the case of reservoir/dam failure or in the face of damage from a natural disaster or other emergency.
- It’s important to avoid excavating the pond in an area that will cross over buried pipes or cables. The excavating equipment can cause extensive and costly damage to utilities and can be very dangerous for the operator or anyone nearby. Consultation with the local utility supplier will provide insight into where buried services may be located, and how to proceed if construction cannot avoid conflict.
