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Combining Flows at an Open Channel Junction

Investigators: Larry J. Weber and Eric Shumate

Research Objective

Figure 1. Experimental flume used for data collection.

Figure 1. Experimental flume used for data collection.

The junction of two open channels is a common occurrence in many hydraulic structures ranging from waste water treatment facilities to fish passage conveyance structures. Currently, only limited data exists on the detailed flow conditions occurring at open channel junctions. This study focuses on detailed measurements of velocity, turbulence and water surface mapping in the immediate area of the junction.

Physical Description and Experimental Procedures

The experiments were performed in a 90o combining flow flume located at IIHR’s Oakdale Model Annex. The main channel is 72 ft long and the junction occurs 18 ft downstream of the flume entrance. The branch channel is 12 ft long. The tributary channels and the downstream combined flow channel are all 3.00 ft in width and 1.67 ft in depth. The channel bed is horizontal at all locations.

Figure 2. Plan and elevation view of experimental flume.

Figure 2. Plan and elevation view of experimental flume.

The coordinate system defined for this testing has the positive x-direction oriented in the upstream direction of the main channel. The positive y-direction points to the main channel wall opposite of the channel junction. Thus, the positive z-direction is upward in the vertical direction. The origin from which all points are measured is the bed at the upstream corner of the channel junction. All distances are non-dimensionalized by the channel width, W=3.00 ft. Non-dimensionalization allows the results to be applied in general to any 90o equal width channel junction.

The total combined flow, 6.0 cfs, and downstream depth, 0.97 ft, were held constant. The constant downstream flow rate and depth produced a constant downstream Froude number, Fd = 0.37. The flow rates in the main channel upstream of the junction were varied from 0.5 cfs to 5.5 cfs in increments of 1.0 cfs.

Figure 3. Ninety degree sharp-edged junction (looking downstream).

Figure 3. Ninety degree sharp-edged junction (looking downstream).

A three-component Acoustic Doppler Velocimeter (ADV) was used to measure velocities and turbulence intensities. The velocity measurements were taken at each sampling location for 60 seconds at a sampling rate of 10 Hz. The velocity measurements were taken at channel cross-sections. A channel cross-section consisted of seven evenly spaced vertical profiles. Depth measurements were made using a point gauge with an accuracy of 0.005 in.

Data

All of the data from these experiments are available. The data can be accessed by downloading the file exp_data.zip. The file contains 12 separate data files and a README file. Each of the 12 data files were named according to the branch of the flume and the corresponding flow rate at which the data were collected. For example, the first file is named “05_main” indicating that the data were collected in the main branch of the flume at a flow rate of 0.5 cfs. The corresponding file would be “55_side.” This means the data were taken in the side branch of the flume at a flow rate of 5.5 cfs. There are six files for the main channel of the flume and six files for the side channel of the flume. Each file contains nine columns of data. The following is a description of columns 1-9 of the data files:

  • Column 1: longitudinal distance from base of upstream corner of junction (x-direction)
  • Column 2: lateral distance from base of upstream corner of junction (y-direction)
  • Column 3: vertical distance from floor of flume (z-direction)
  • Column 4: x-component of velocity
  • Column 5: y-component of velocity
  • Column 6: z-component of velocity
  • Column 7: standard deviation of x-component of velocity
  • Column 8: standard deviation of y-component of velocity
  • Column 9: standard deviation of z-component of velocity

Download the data

Publications

Shumate, E.D. and Weber, L. J. (1998). “Experimental Description of Combining Flows at an Open Channel Junction.” Proceedings of the ASCE Water Resources Engineering ’98 Conference, pp. 1679-1684.

Shumate, E.D. (1998). Experimental description of flow at an open-channel junction, M.S. Thesis, University of Iowa

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Last modified on June 25th, 2015
Posted on September 10th, 2012

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