Author(s): Hyoseop Woo; Chanju Lee; Chang-Rae Jang; Hyung-Jin Cho
Linked Author(s): Chang-Lae Jang
Keywords: Vegetation recruitment; Unregulated stream; Flow and sediment regime; Hydrochory; Shields number
Abstract: We investigated the effect of flow regime on the riparian vegetation recruitment and establishment in an unregulated sandy stream, focusing on the limiting condition of pioneer plants that are recruited on the stream shore mainly by hydrochory. For this study, we used the factor of the critical bed shear stress, the dominant physical factor affecting the stability of sediment bars with pioneer vegetation. This study focuses on a sharply curved, almost 180-degree curved reach in a sandy stream, which had maintained white sand bars along the curved channel in the reach, since probably before 1965, when the oldest aerial photo is available, without virtually allowing any recruitment of vegetation. We used a verified numerical model to evaluate the two - dimensional distribution of bed shear stresses at the study reach at some critical periods of recorded years. Soil moisture, another critical constraint on the germination and survival of pioneer plants, was not considered, for saturated shorelines and hydrochory are primary concerns in this study. By this study, we have found that the Shields number, or the dimensionless critical shear stress, to bury and wash away pioneer vegetation of node smartweed (Persicaria nodosa) varies with the age of the vegetation; smaller than 0.4 for a two-month-old plant and larger than 1.2 for a four-month-old one. This result substantiates the hypothesis that, in the monsoon climate zone, floods in late spring and early summer are critical to the change from “white river” to “green river."
Year: 2020