The removal of channel bank vegetation on Cottonwood Ranch is intended to effect bank erosion and channel widening. Bank-stored sediment is, thus, expected to be reintroduced into the channel. Deposition of this material may occur downstream. The mechanics of river sediment transport processes need to be examined to determine the effects of channel management actions on bank erosion and sediment transport, and to detect and evaluate possible impacts of deposition.

The overall goal of this monitoring and research is to provide data necessary to evaluate channel rehabilitation practices. Specific questions focus on whether management actions cause the channel to widen, whether measurable changes in the channel structure occur downstream, whether these changes can be linked to the management action, and whether widened channels can be sustained by river processes.

The monitoring and research program is designed to link the detection of geomorphologic response with a mechanism to investigate its cause. Two components of data collection allow the necessary temporal and spatial resolution: 1) A general monitoring component that focuses on the integrated effects of management within the Cottonwood Ranch property and associated impacts downstream and provides initial information to the long term monitoring program devised for adaptive management, and 2) an intensive research component that examines the combined management activity in order to understand direct affects on the local channel system.

The general monitoring component focuses on collecting information from cross sections of the river and examining serial aerial photography. Measurements at these cross sections include channel topography, vegetation, bed and bank material grain size, and ground photography. These measurements will provide a baseline of information regarding the natural variability present in this reach of the river, the need for additional parameters, and specifically in the management reach, the potential for trend detection throughout the first increment of the Program.

The intensive research component will focus on collecting data sets with fine spatial resolution on three reaches of the middle channel undergoing riparian vegetation modification of the Platte River within the Cottonwood Ranch. Data collection will consist of detailed topographic surveying, bed and bank sediment sampling, observations of in-channel and bank vegetation, and ground photography. The three reaches were selected to represent the conditions of the river above the management area, in the management area, and below the management area. Results of the intensive research component will be used to separate normal variability in the channel from changes that are specifically produced by the management activities.

Specific objectives are as follows:

Objective 1) General river monitoring within Cottonwood Ranch that will become part of the overall adaptive management program along the central Platte River

A) To document physical characteristics of the Platte River channels both within the Cottonwood Ranch and immediately downstream.

B) To integrate the general monitoring program within Cottonwood Ranch Property into the monitoring scheme devised for adaptive management within the Platte River Endangered Species Partnership (PRESP's) area of interest.

Objective 2) Intensive research aimed at estimating channel changes and sediment movement resulting from integrated management practices

A) To evaluate channel changes (e.g. changes in channel width, distribution of depths within cross sections, and bank stability) resulting from specific vegetation clearing activities along islands and river banks

B) To determine the sediment budget and sediment movement of mobilized bed and bank material to downstream areas from the managed channel before and after vegetation removal in the management channel.

C) To evaluate the effects of natural river processes (eg. seasonal distribution of flow depths and erosion potential on banks) to maintain or augment the management activities.

General Monitoring transects to be surveyed include eight research cross sections spaced one mile apart. Three of these transects are on the Cottonwood Ranch property and five are located downstream of Cottonwood Ranch and upstream of the Kearney Canal Diversion.  At present, data for these eight General Monitoring cross sections are collected through the research project. The Platte River General Monitoring Program will maintain data collection at some or all of these cross sections after the completion of this research project.

The data collection in year 2000 will serve as the pilot year for purposes of refining the Platte River General Monitoring Protocol. Data collected at these initial General Monitoring cross sections will: 1) Provide first year data for long term monitoring, 2) refine estimates of costs for collecting data at these widely spaced monitoring cross sections, and 3) identify statistical characteristics of variables including variance and dependence estimates and the sensitivity of trend detection. Data collected at each transect will include topographic survey, bed sediment sampling, and ground photography.

1) Streamflow

Streamflow is collected at a stream gage placed on the middle channel of the Cottonwood Ranch property below the management activities. This gage is 06768035-- Platte River Middle Channel, Cottonwood Ranch, Near Elm Creek, NE. The gage provides streamflow discharge for that specific channel and total river flow comparisons with the gage, Platte River at Overton, NE. Suspended-sediment concentration is collected at the streamflow gage on the middle channel. Suspended-sediment concentration and the size distribution of the suspended material provide information on changes in fine-grained sediment movement and changes from the managed section upstream. To provide a continuous record of fine-grained sediment transport, an Optical Backscatter sensor is used.

2) Topographic survey

There are two types of transects included in the research program: 1) Temporal intensive cross sections that are surveyed four to six times a year (including before and after high flow season and a survey in the Fall) along with ancillary data (i.e. bed and bank material sampling and ground photography), and provide information on intra-annual variability; and 2) spatial intensive cross sections that are surveyed and ancillary data collected once a year on a series of tightly spaced cross section to provide information on changes within specific channel reaches. The spatially intensive cross sections are placed upstream of the managed area, within the managed area, and downstream of the managed area. The temporally intensive cross sections are a subset of the spatially intensive cross sections.

The procedure for surveying river cross-sections employs a survey-grade global positioning system (GPS) to measure the location of bed, bank, and bar locations relative to a fixed horizontal and vertical datum. The cross-section will be oriented orthogonal to the principal flow direction in the reach considered.

The GPS used in the topographic survey computes the position of a rover unit relative to a known horizontal and vertical datum or base station using a satellite network and real time radio communication between the base and rover. Positions will be precise to within 2 centimeters in the vertical direction and 1 centimeter in the horizontal direction. A number of National Geodetic Service (NGS), Bureau of Reclamation (BOR), NPPD, and US Geological Survey (UGSG) elevation benchmarks are located in the vicinity.

3) Bed /Bank Sediment Sampling

The procedures for measuring bed sediment are taken from Edwards and Glysson, 1999. The type of bed material sediment sampler selected for use is a function of the size of the bed sediment measured and the depth and velocity of the river considered. The sampler used consists of a steel cylinder 7 centimeters in diameter and 20 centimeters in length welded to a steel pipe 155 centimeters long.

The general procedure for sampling with this sampler involves dividing the cross section into a series of equally spaced increments or verticals. At each increment the sampler is plunged into the bed of the river until the can portion of the sampler is filled with sediment. Sample depths are 2 inches in order to provide similar data to the BM54 sampler used at bridge sections and to sample bed material that is most readily available for transport.

Bank material is sampled at cut banks along the river’s edge. Bank samples are designated by date and by their location with respect to a surveyed cross section. Samples are taken from near the surface to the bottom of the bank at the water’s edge. Samples are taken within each major stratigraphic zone. A diagram of the bank is produced and depths are recorded from the surface of the bank.

4) Ground photography

Photo stations are located on each bank of cross sections. Photographs are taken upstream, downstream, and cross-stream to document the cross section and the condition of the banks upstream and downstream of the cross section.

Buchanan, T.J., and Somers, W.P., 1969, Discharge measurements at gaging stations: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A8, 65 p.

Buchanan, T.J., and Somers, W.P., 1968, Stage measurement at gaging stations: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A7, 28 p.

Carter, R.W., and Davidian, J., 1968, General Procedure for gaging streams: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A6, 13 p.

Edwards, T.K., and Glysson, G.D., 1999, Field methods for measurement of fluvial sediment: US Geological Survey Techniques Water Resources Investigations, Book 3, Chapter C2, 89 p.

Guy, H.P., 1969, Laboratory theory and methods for sediment analysis: US Geological Survey Techniques Water Resources Investigations, Book 5, Chap C1, 58 p.

Guy, H.P., and Norman, V.W., 1970, Field methods for measurement of fluvial sediment: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap C2, 59 p

Kennedy, E.J., 1984,Levels at streamflow gaging stations: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A19, 31 p.

Kennedy, E.J., 1984, Discharge ratings at gaging stations: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A13, 53 p.

Kennedy, E.J., 1983, Computation of continuous records of streamflow: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A10, 59 p.

Rantz, S.E., and others, 1982, Measurement and computation of streamflow: US Geological Survey Water Supply Paper 2175, volume 1 and 2.

Porterfield, George, 1972, Computation of fluvial-sediment discharge: US Geological Survey Techniques Water Resources Investigations, Book 3, ChapC3, 66 p.

Wagner, C.R., 1995, Stream-gaging cableways: US Geological Survey Techniques Water Resources Investigations, Book 3, Chap A21, 56 p.

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