The following abstracts summarize studies on the Long Branch Creek Basin (fig. 1) above the Atlanta Conservation Area in Macon County, Missouri that were conducted by the U.S. Geological Survey in cooperation with the Missouri Department of Conservation from 1995-2001. These studies focused on quantifying streamflow, sediment transport, and sediment deposition in the Long Branch Stream system. The first abstract, taken from a published article in the journal Wetlands, summarizes streamflow and sediment deposition data collected from 1995 through 1998. These data were used in a numerical simulation of the system, summarized in the second abstract taken from a 2001 USGS publication, in which streamflow and sediment deposition were simulated for 2-, 5-, 10-, 25-yr floods in a Long Branch study reach.
Sediment transport and deposition along a stream in an agricultural basin (65 km2 ) in northern Missouri, were quantified as part of a long-term study to evaluate effects of silvicultural practices on the hydrology, sediment, vegetation, and wildlife characteristics of remaining forested riparian systems (fig. 2 and fig. 3) Median cumulative sediment deposition measured using feldspar clay pad (fig. 4), increased from August 1995 to August 1998 at a rate of about 1 cm/yr. Median deposition amounts from single floods ranged from 0.03 cm to 0.64 cm. Floodplain and riparian maintenance flows corresponded to monitored floods with calculated recurrence intervals as low as <2 years. Simple linear regression models, using flood event suspended sediment load or streamflow characteristics, explained up to 82 percent of variability in median event sediment deposition on the floodplain clay pads. There was little apparent correlation between cumulative short-term deposition and site elevation, distance from channel, longitudinal distance, or fluvial landform type. This may be because upstream channelization, floodplain complexity, short duration of events, or sediment load characteristics of low-recurrence interval floods (<2 to 5 years) sampled in this study. Dendrogeomorphic measurements (fig. 5 and fig. 6) indicated a substantial increase in the mean rate of deposition on the Long Branch Creek floodplain from about 1950 through 1980. Eighty-nine percent of the clay pad monitoring sites and all dendrogeomorphic monitoring sites experienced net positive deposition emphasizing the role of this riparian area as a net sediment storage site.
From: Heimann, D.C., and Roell, M.J. 2000, Sediment Loads and Accumulation in a Small Riparian Wetland System in Northern Missouri: Wetlands 20:219-231.
This report presents the results of a study conducted by the U.S. Geological Survey in cooperation with the Missouri Department of Conservation to describe the hydrology, sediment transport, and sediment deposition along a selected reach of Long Branch Creek in Macon County, Missouri. The study was designed to investigate spatial and temporal characteristics of sediment deposition in a remnant forested riparian area and compare these factors by magnitude of discharge events both within and outside the measured range of flood magnitudes.
The two-dimensional finite-element numerical models (fig. 7) RMA2-WES and SED2D-WES were used in conjunction with measured data to simulate streamflow (link to fig. 8 and fig. 9) and sediment transport/deposition characteristics (fig. 10) during 2-, 5-, 10-, and 25-year recurrence interval floods. Spatial analysis of simulated sediment deposition results indicated that mean deposition in oxbows and secondary channels exceeded that of the remaining floodplain areas during the 2-, 5-, 10-, and 25-year recurrence interval floods. The simulated mass deposition per area for oxbows and secondary channels was 1.1 to 1.4 centimeters per square meter compared with 0.1 to 0.60 centimeters per square meter for the remaining floodplain.
The temporal variability of total incremental floodplain deposition during a flood was found to be strongly tied to sediment inflow concentrations. Most floodplain deposition, therefore, occurred at the beginning of the streamflow events and corresponded to peaks in sediment discharge. Simulated total sediment deposition in oxbows and secondary channels increased in the 2-year through 10-year floods and decreased in the 25-year flood, while remaining floodplain deposition was highest for the 25-year flood.
Despite increases in sediment inflows from the 2-year through 25-year floods, the retention ratio of sediments (the ratio of floodplain deposition to inflow load) was greatest for the 5-year flood and least for the 25-year flood. The decrease in retention ratio at greater flows is likely the result of higher velocities on the floodplain, resulting in higher bed shear stress, and greater suspension time of deposited material, greater sediment transport through the system.
Simulated sediment deposition was most sensitive to sediment inflow concentrations and modification of floodplain roughness--factors that can be controlled through management practices. The increase in floodplain sediment deposition resulting from a simulated increase in vegetation density (increase in floodplain roughness from a Manning’s n of 0.11 to 0.12) was 142,000 kilograms, or 6.5 percent for a 10-year recurrence interval flood. This increase was comparable to total oxbow and secondary channel deposition mass in the simulations, but would result in a mean increase in floodplain deposition thickness of only 0.025 centimeter.
The hydrodynamic model results show the importance of the secondary channels and meander cutoff channels in this system because these areas quickly bring floodwaters and sediment to areas not close to the main channel. The meander cutoff channels in the simulation also effectively decrease flow and velocities in some main channel sections thereby affecting sediment deposition in the vicinity of these features.
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| 5-yr Flood Velocity | 25-yr Flood Water Depths | 2-yr Flood Sediment Deposition |
From: Heimann, D.C., 2001, Numerical Simulation of Streamflow Distribution, Sediment Transport, and Sediment Deposition along Long Branch Creek in Northeast Missouri:U.S. Geological Survey Water-Resources Investigations Report 01-4269, 61 p.
Missouri Department of Conservation
David C. Heimann
U.S. Geological Survey
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