At the Spartanburg laboratory, comprehensive waterway experiments were made on Cecil sandy clay loam with Bermuda grass, common lespedeza, sericea lespedeza, kudzu, and a mixture of redtop, orchard grass, common lespedeza, and Italian ryegrass. A few tests were run on centipede grass, Sudan grass, and a mixture of Dallis grass and crabgrass. Seeding of Dallis grass in one of the channels resulted in a poor stand, so that crabgrass came in thickly. The experiment was continued because the same thing is likely to occur in field practice.

Bermuda grass, an important pasture plant in the South, proved highly satisfactory as a lining for waterways, particularly because of its vigor and persistence. Velocities of flow that were found to be safe for channels lined with Bermuda grass in various conditions are:

Land slope (percent) Permissible velocity (feet per second)

Table 1  

Bermuda grass offers almost as much resistance to injury by flowing water when dormant as when green. Bermuda grass was injured less easily by the flowing water if it had been cut frequently during the season than if it had recently been cut for the first time.

Common lespedeza, an annual legume that is very widely useful for forage in the South and grows satisfactorily as far north as southern Pennsylvania, was tested in these four conditions: Uncut green vegetation, cut stubble, fall dead stubble, and spring dead stubble. The uncut green lining was found to protect a waterway fairly well, permitting a velocity of about 5 1/2 feet a second. When the green vegetation had been cut, a flow of more than 7 feet a second caused very little damage. In the fall, the dead stubble endured a flow of about 4 1/2 feet a second. By spring, however, the dead plants had rotted at the base and were very easily broken off by flowing water, so that any flow of more than about a foot a second caused damage. The low protective value of the dead stubble in the spring makes common lespedeza unsuitable to be used alone for lining waterways. When seeded together with grasses such as orchard grass, Italian ryegrass, and redtop, this plant does help protect waterways.

Sericea lespedeza, a perennial legume, has been used extensively as a lining for natural waterways in combination with mixed grasses. Sericea lespedeza exposed to flows of moderate velocity tends to permit considerable scour if it is green and woody and somewhat greater scour if it is dormant and uncut. Safe velocities of flow for channels lined with sericea lespedeza in various conditions, according to the results, are:

Table 2  

Mixed grasses are good for linings that are to be grazed, because they provide variety in the forage. The tests made with the mixture of redtop, orchard grass, common lespedeza, and Italian ryegrass showed that this mixture offers excellent protection. For channels lined with this mixture, the permissible velocity is believed to be about 6V2 feet a second in the summer and after cutting in the fall, and 5 feet a second in early spring.

The plants in this mixture give better all-year protection because they have different periods of flush growth and dormancy. In early spring, when the redtop and orchard grass were dormant and the new lespedeza seedlings had not yet appeared, the Italian ryegrass was green and offered good protection.

Moreover, orchard grass and redtop grow in clumps. If either of these grasses were grown alone in a waterway, flows would tend to be rather irregular. The other plants, growing among the clumps, made the lining more uniform, with the result that it had a more satisfactory influence on flow. When flows are deep enough to submerge the plants entirely, the effect of any unevenness of the channel lining largely disappears.

It is believed that under northern conditions equally satisfactory protection would be given to waterways by the Cornell utility mixture, that is, timothy, redtop, Kentucky bluegrass, Canada bluegrass, Mammoth red clover, Alsike clover, and Ladino clover.

Kudzu, a prolific perennial vine that produces dense foliage, was found to have much less protective value than any other kind of vegetation tested.

The test channels were free from sharp changes in grade, alignment, and cross section, and had dense, uniform linings of kudzu. Under less favorable conditions, these velocities would be too high. When kudzu was dormant, the loose mulch of dead leaves, stems, and vines gave very little protection.