Drawdowns: A Brief Look at Rodman Reservoir
By: Taylor Darnell, agronomy master’s student with UF/IFAS Center for Aquatic and Invasive Plants (CAIP)
Imagine a lakefront house on a pristine lake in Florida. Now, imagine that waterfront view obstructed by tussocks, aquatic plants, and mosquitos. That does not sound enjoyable, does it? This is where aquatic plant management (APM) comes into the spotlight. There are multiple APM tools such as biological, chemical, mechanical, and cultural controls used to remove aquatic unpleasantries.
A cultural method of aquatic plant control, drawdowns, are among the most infrequently used APM tools in Florida. In a drawdown, the water level is lowered within a lake, pond, or another waterbody. Drawdowns provide many benefits to public recreation, homeowners, native species, and can create opportunities for infrastructure repair and improvement.
There are two types of drawdowns: surface and subsurface. Surface drawdowns are the most common form of drawdowns and, since they involve surface water, they are used for aquatic plant management. Surface drawdowns are not a novel concept. This type of drawdown occurs naturally as droughts, but can also be controlled by water resource management techniques like controlled releases of water from behind an impoundment. An impoundment can be anything from a simple earthen dam to a concrete and steel dam and lock system that creates a non-natural water body. Subsurface drawdowns, however, remove water from underground sources.
Drawdowns are not practiced regularly on most waterbodies in Florida, yet this APM tool has been used extensively on Rodman Reservoir located in Putnam County, Florida, for decades.
Every three to four years, the water level in Rodman Reservoir is decreased by approximately 10 feet using drawdowns. This process usually takes seven months. During this time, most of the littoral zones, or shallow water areas, are drained and exposed to direct sunlight and air for six months. Consequently, aquatic plants such as hydrilla (Hydrilla verticillata), coontail (Ceratophyllum demersum), eelgrass (Vallisneria americana), water lettuce (Pistia stratiotes), and water hyacinth (Eichhornia crassipes) dry out and die. Previous drawdown research has shown that, if properly timed, two or more drawdown cycles can significantly reduce the amount of hydrilla biomass in a system.
Drawdowns on Rodman Reservoir are carefully planned between the U.S. Army Corps of Engineers, Florida Department of Environmental Protection (DEP), Florida Fish and Wildlife Conservation Commission (FWC), and water management districts, with careful consideration not to disturb or damage fragile or protected habitats.
In 2019, a drawdown was conducted to control free-floating aquatic plants in order to maintain one of the best largemouth bass (Micropterus salmoides) fisheries in Florida by balancing the bluegill (Lepomis macrochirus) population to the largemouth bass population. These water level fluctuations are necessary to spur native plant growth, such as spatterdock (Nuphar macrophyllum), cattail (Typha spp.), and Illinois Pondweed (Potamogeton illinoensis) as well as decreasing bluegill populations and increasing the largemouth bass populations. For more information on this drawdown, visit this report.
For even better fishing conditions, many anglers frequent Rodman Reservoir during a drawdown because of the way fish tend to cluster or hide while the water is decreased. To help keep the concentrated populations of largemouth bass in the system and to reduce the number of smaller, non-game prey, and nuisance fish, bass fishing on Rodman Reservoir during a drawdown is catch and release only.
For more information, explore the following links for further reading:
This blog post was written by Taylor Darnell, an agronomy master’s student with UF/IFAS CAIP. Questions or comments can be sent to the UF/IFAS CAIP communications manager at email@example.com.
Follow UF/IFAS CAIP on social media at @ufifascaip. Read more blogs like this one on the UF/IFAS CAIP blog.
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