In a study conducted at Quicksand, which ran from 1981 to 1984, PMK-24 (PI-421612) eastern gamagrass was included with about 50 other species in a screening test to determine their abilities to withstand various lengths of inundation of flooding by water. Through this project, an attempt was being made to select a plant or plants which would survive long periods of inundation and then resume growth after the water level dropped. Such plants will help solve a problem that is common in constructed channels, on streambanks, and along the shorelines of large water impoundments, particularly, flood control reservoirs.
The study was carried out in an experimental constructed channel in which the water level could be regulated. Plants were subjected to inundation for 0, 3, 10, 22, and 40 days, with either a northern or southern exposure. The plants were established vegetatively in the spring of 1981.
Flooding began on November 1, 1982. The channel was filled to a depth of four feet. It was maintained at this level for three days then dropped one foot. After seven days it was again dropped one foot, to a depth of two feet and maintained. Twelve days later it was dropped another foot. At the end of eighteen days, the channel was entirely drained. Two weeks later the channel was filled back to the four foot level and the cycle repeated. This is the winter flooding cycle. It was repeated three times during the winter of 1982-83. The number of days of continuous inundation for various depth under the winter flooding cycle were 0, 3, 10, 22, and 40 days.
The summer flooding cycle began on April 18, 1983. The channel was filled to the one foot level for six days; two foot level for five days; three foot level for four days; four foot level for three days; dropped back to three foot for four days, two foot for five days, and one foot for six days then drained for two weeks before repeating the cycle. This continued until November 15, 1983, when the winter flooding cycle was resumed. The number of days of continuous inundation for various depth under the summer flooding cycle were 0, 3, 11, 21, and 33 days.
Flooding under the winter cycle was continued through May 15, 1984. The cycle was interrupted in early May 1984, due to flooding at the Center. Generally, the flooding cycles were adhered to very closely, with only an occasional one day deviation due to holidays or weekends.
Evaluations of the plants growing at different levels were made in June 1983, following the winter flooding cycle, September 1983, after three repetitions of the summer flooding cycle, and again in the summer of 1984, following another season of the winter flooding cycle. A surveyor's level was used to set grade stakes throughout the channel to assist in guiding the evaluations on an elevation basis. Separate evaluations were made for the north and south facing sides of the channel, as there were some apparent differences.
After one year of flooding, eastern gamagrass had tolerated 40 days of repeated inundations, separated by two weeks rest. However, the stand was reduced by 50%, and foliage height was 1/3 that of plants grown out of water. Plant height and survival was reduced about 25% when exposed to 22 days inundation. There was only a slight impact on the plants repeatedly subject to 10 days of flooding.
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