Levee Ponds: Engineering Water Storage in Flatlands
Levee ponds are unique man-made structures that stand out for their adaptability and efficient use of landscapes, especially in areas where the topography is flat. Designed to impound water, these ponds play a vital role in many sectors, notably aquaculture. Here’s a deeper look into their construction, advantages, and nuances.
What is a Levee Pond?
A levee pond is constructed by building levees, or embankments, around a specified area to contain water. Given the absence of watersheds in these ponds, the water source typically comes from wells, storage reservoirs, streams, or canals. In areas where groundwater is abundant, levee ponds might be the preferred choice.
Why Choose Levee Ponds?
Aquaculture's Best Friend
Levee ponds have a distinctive advantage when it comes to aquaculture. Their ability to span vast tracts of land makes pond management simpler, paving the way for commercial-scale operations.
Ideal for Flat Terrains
Particularly in regions where the natural runoff from watersheds isn't sufficient to fill traditional ponds, levee ponds emerge as an efficient alternative.
Cost-Effective Construction
On flat land, the construction of levee-type ponds involves moving lesser amounts of dirt as compared to rolling or hilly terrains. This invariably reduces construction expenses.
Construction Considerations
Freeboard Factor
The freeboard, or the levee's height above the normal water level, plays a pivotal role in the stability and utility of the pond. While it shouldn’t exceed 2 feet (as it would inflate construction costs and hinder equipment access), a freeboard of less than 1 foot exposes the levee to erosion risks, especially during intense floods.
The Soil Story
The success of a levee pond significantly depends on the type of soil it's built on. A mixture containing a good percentage of clay is vital to prevent water leakage. Before embarking on construction, get the soil analyzed, possibly through agencies like the USDA-Natural Resources Conservation Service.
Slope Specs
It's generally advised for pond levees to maintain a gentle slope, often at a 2:1 gradient. For larger ponds, even gentler slopes might be necessary. The rationale behind this is multifaceted. Gentle slopes disrupt waves, mitigating the erosive force they exert on the levee. This design choice enhances the pond's lifespan and curtails siltation and maintenance costs.
A Word on Costs and Longevity
While levee ponds offer numerous advantages, it's worth noting that their construction and upkeep tend to be pricier, primarily due to the extensive land they occupy. Furthermore, the longevity and productivity of these ponds are intricately tied to their construction quality and the nature of the soil foundation.
Digging Deeper into Excavated Ponds
As we’ve seen, not all ponds are created from natural valleys or depressions. Some are the result of meticulous design and excavation. One example is the excavated pond.
Construction Process and Considerations:
Building an excavated pond involves digging a pit where water will be stored. Unlike embankment ponds that use existing landscapes, excavated ponds require more intensive work with heavy machinery, especially when constructed from scratch on level terrain.
While they offer flexibility regarding location—being suitable for almost any landscape that can support the weight and supply water—excavated ponds have limitations. For instance, they are less adept at trapping runoff from sloped areas. To ensure fewer complications with permits, it’s often best to opt for a design that neither connects to nor empties into wetlands or streams.
Advantages of Excavated Ponds:
Efficiency in High Evaporation Areas
Excavated ponds can be designed to expose a minimal water surface area relative to their volume. This feature makes them valuable in regions where water is a limited resource and evaporation losses are a concern.
Durability and Maintenance
These ponds are less susceptible to floodflow damage. Their compactness and construction method also means they often require less maintenance, making them a favorite choice in many parts of the country.
Versatility in Location
Although best suited for flat yet well-drained terrains, these ponds can be situated in various topographies. Whether in a natural drainage path or to its side, as long as runoff can be directed into the pond, it’s a potential location.
Increased Capacity on Sloping Terrains
If you decide to place an excavated pond on sloping terrain, the material excavated can be utilized to create a small dam around the pond's lower end and sides, enhancing its water-holding capacity. However, one must ensure the inclusion of an auxiliary spillway to manage excess storm runoff.
Maintaining Water Quality
In places where inflowing water brings a significant amount of silt, including a desilting area or filter strip is essential. Situated in the drainage path right before the pond, this strip should ideally be as wide or wider than the pond and extend over 100 feet or more. Once prepared, this area can be seeded with a mix of grasses and forbs. As water flows through this vegetative barrier, silt gets trapped, ensuring that the water entering the pond remains relatively clean and silt-free.
