Did You Know… Creating Watershed Ponds
Continuing from my previous article, we’re focusing on considerations when developing our own “watershed” type sport-fishing ponds. This article is the 2nd of four parts and reviews the importance of location, determining adequate watershed area, pond size, design and layout.
Do not locate large dams where their failure could cause loss of life, injury to people or livestock, damage to buildings, or the interruption of the use of railways, highways or public utilities. Recreational ponds are not as deep as public reservoirs and dam failures are rare. However, if the site involves some degree of risk to the public, a professional engineer with experience in dam construction should be consulted. Almost every state has a dam safety law. Contact an Extension fisheries specialist or aquaculturist for more information.
The location of buried pipelines, electrical lines or telephone wires should be researched before any construction begins. Breaking a fiber optic communication cable will put most pond construction budgets into the red!
The amount and quality of water entering the pond from the surrounding watershed is dependent on several factors—slope, soil type, vegetative cover and the amount of precipitation. There are no set criteria for determining whether a watershed is sufficient for a given size pond, but there are some general rules. Watersheds containing mostly pasture with heavy clay soils may supply 1 acre of water for every 5 acres of land. At the other extreme, timberland on sandy soil may require a ratio of 30 acres of land to 1 acre of water.
Excessively large watersheds can be just as problematic as limited watersheds. Too much water may dilute water amendments such as lime and salt, allow valuable fish to escape during floods, and make it necessary to install expensive flood or diversion devices. Ponds with excessive watersheds also may fill in faster with sediments, requiring frequent and costly renovations. An undersized watershed may cause pond water to remain shallow, allowing weeds to get a foothold and preventing the use of emergency aeration devices when fish become stressed.
Because of the liability involved with dams, most pond owners should confer with a person experienced in the design of sport-fishing ponds. The Natural Resources and Conservation Service, a federal agency, offers technical assistance in pond design in most states. This agency designs ponds that incorporate exact safety standards, well-established design criteria, and the latest conservation practices. They are almost always approved by a professional engineer or the NRCS approval authorities. However, the NRCS can’t always respond to requests quickly because of its small staff. Private engineers or consultants may be available for a fee. Be sure to get referrals and check any state codes for pond construction before paying for the services of a consultant.
A good site survey and layout design will contain the following information: 1. Location, top width, slopes, earth fill requirements, and elevation of the dam 2. Emergency spillway location and size, 3. Shoreline dimensions, 4. Soils investigation report, 5. Dimensions of the cutoff trench and core, 6. Location, dimensions and elevations of the riser and barrel pipes, 7. Estimate of the total cut and fill in cubic yards (This figure will account for most of the expense in pond construction.) 8. Watershed area and characteristics and 9. A bill of materials needed, including valves, concrete and lumber for the pipe ballast, pipes, vegetative materials (seed, fertilizer, lime), and any diversion pipes or valves.
The size of a watershed pond should be based on the availability of water from the watershed. The water should be deep enough to compensate for evaporation and seepage. Even during summer drought the water should be at least 3 to 4 feet deep. Ideally, the average water depth in a commercial watershed pond should be 4 to 5 feet. The maximum depth should be 8 to 10 feet because of the limited size of commercial seines.
The dam should have a minimum inside slope of 3:1, 4:l if economically feasible. A 4:1 slope makes it easier and safer to position emergency aerators and load and unload boats. However, 4:1 slopes are more expensive because there must be more earth fill. The outside slope can be 3:1. This slope will allow for maintenance duties such as bush hogging and driving around emergency aeration equipment with pickup trucks. Occasionally it is necessary to drain a pond to repair drains or renovate banks. Pond bottoms should be graded toward the drain at a 0.1 to 0.3 percent fall to ensure complete drainage.
Information for today’s article was adapted from “Fact Sheet No. 102, Watershed Fish Production Ponds: Guide to Site Selection and Construction”, by the Southern Regional Aquaculture Center. The entire article can be located online at: http://srac.tamu.edu. For additional information, please contact Mike Frinsko, Area Aquaculture Agent, Jones County Center at: 252.448.9621 or firstname.lastname@example.org
Also, for those interested in learning more about general pond management, we will be having a workshop May 22 at the Craven County Extension Center. For more information and to register, please contact Dr. Diana Rashash at the Onslow County Center at: 910.455.5873 or check out the agenda online at: onslow.ces.ncsu.edu/2013/03/pond-management-workshop/
North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
This article is scheduled to be published in the Jones Post newspaper on April 11, 2013 and was compiled by Mike Frinsko, Area Commerical Aquaculture Agent.