Whether you need to create a dry stream bed to carry away storm overflow and improve drainage, or whether you want to create a series of ponds and catch basins for a fish hatchery, you may need to add a stream to an existing backyard pond. Streams require space and can involve a lot of digging, which will require you to rent or borrow a backhoe or trencher. Careful planning will ensure that your stream will add value to your backyard pond without causing water damage to your property or neighboring properties.
Walk around your pond. Check the water level from several angles, on different days, in various weather conditions. Include measurements taken on at least two rainy days. This will help you determine when and where your pond may overflow, if it is not doing so already.
Decide where you want to direct the overflow, if you do not like its current path. Work with the natural contours of your yard to ensure that you direct your stream's flow away from your foundation, any buildings and any neighboring properties.
Lay a rope along both sides of your chosen stream bed, to mark where you want to dig. Adjust the width, depth and degree of all the curves you want to include in your stream bed. Your stream depth and straightness will control the speed of water flow away from your pond. According to Professor Stephen A. Nelson of Tulane University, "Straight stream channels are rare. Velocity is highest in the zone overlying the deepest part of the stream."
Call 811 before you dig, in order to find out where any underground utility lines might be. Wait for the utility companies to mark the depth, direction and position of their lines. Do not dig where underground utilities could be disrupted.
Use a backhoe or trencher to dig your watercourse to the desired depth. Begin 3 feet from your pond. Bank the dirt to decrease the amount of digging you need. Shore your trench as needed, per OSHA rules. Any trench 5 feet or deeper requires a protective system to prevent collapse.
Pour a 3- to 6 -inch layer of sand in your stream bed. Use a reversible plate soil compactor to ensure that loose sand and soil are compacted before you fill your stream bed with water for the first time. Loose sand and soil can be washed into storm drains and enter local waterways, causing eutrophication and leading to water pollution from stormwater runoff.
Cover the base of the entire watercourse with a 6- to 12-inch layer of large, sharp-sided river gravel. Fill the remaining depth of your watercourse with small and medium sharp-sided rocks to within a foot of ground level.
Break through the remaining 3 feet between the end of your watercourse and your pond. Install a fish fence and a working, gated dam at the head of your stream bed if you do not want breeding-age fish to leave your pond. Create a second, third or other subsequent lower ponds or catch basins to hold younger fish and fingerlings. Open your dam when rains are expected to exceed your upper pond's capacity.