Fast-moving or highly turbid water can carve deep ravines throughout a waterway or reservoir. Time and the natural erosion of moving water will also eventually eat away around the riverbed. Gully and bank stabilization can be achieved by installing earth fill or rockfill, and by allowing vegetation to grow and brace the soil. This may involve needing to soften the gradient around the edges of the channels in order to reduce erosion and encourage plant growth.
The gentler the slope, the more growth will be encouraged for both underwater greenery and the creatures that like to live and reproduce in these plant-rich shallows. Shallow water and gentle banks can also encourage mosquito reproduction, which can range from a nuisance to a serious health-concern. Recommendations for reducing mosquito spawning will vary from region to region. Most counties or states will have a local mosquito abatement authority that is available for consultation.
Trapping Sediment
Sediment, picked up by high-velocity runoff, can be caught in a basin that serves as a kind of sediment trap. This should allow run-off the appropriate time for floating sediment and particles to settle. The total capacity should allow for the average amount and frequency of sediment deposits, detention or dry storage, as well as emergency and overflow capacities in the case of a flood.
Flood Management
Flood control or flood-mitigation reservoirs are used to protect areas downstream from a large and sudden increase in waterflow, like a flood.
- Flood control reservoirs collect water entering the reservoir in order to slow-down the discharge rate into safe levels further down the channel. After the water is collected and dispersed, the flood control reservoir is emptied further to allow storage capacity for the next flood.
- These reservoirs are differentiated from typical storage reservoirs by a large sluiceway capacity in order to permit rapid drawdown directly before or after a flood.
- Flood Control Detention Basin - These are fitted with gates and valves in order to fine-tune the releasing of water through spillways and outlets. These are also known as flood control storage reservoirs.
- Flood Control Retarding Basin - These reservoir’s spillways have no gates, and instead release water through a series of descending outlets, reducing the amount and/or speed of the water as it heads downstream. This helps reduce the flow rate during peak flooding.
Let’s Just Dam It!
Dams are usually the most practical method for creating a large reservoir, not least because you don’t have to concern yourself with filling it! However, this convenience is balanced by significant responsibility. First and foremost, most states have strict requirements and standards when it comes to constructing a dam. Interrupting a major part of the watershed will have serious impacts downstream, and any intended use or distribution of the captured water will likely require a permit. A water resources engineer, or dam technician will know how to communicate with the local or State authority in order to ensure designs are compliant with these standards.
The most basic parts of a dam include the embankment, typically earth fill or rockfill, a spillway, and overflow outlets. The freeboard is the distance from the crest of the embankment to the maximum allowed water level. In a properly constructed dam, water that reaches maximum level will automatically enter the primary spillway, before it encroaches on the freeboard.
