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Title: Telegraph Canyon Creek Channel Improvement Project, San Diego County, California : hydraulic model investigation
Authors: United States. Army. Corps of Engineers. Los Angeles District
Pickering, Glenn A.
George, John F.
Keywords: Channel improvment
Flood-control channel
Hydraulic models
Hydraulic structures
Telegraph Canyon Creek
Stream channelization
Publisher: Hydraulics Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Series/Report no.: Technical report (U.S. Army Engineer Waterways Experiment Station) ; HL-88-26.
Description: Technical Report
Abstract: Tests were conducted on a 1:20-scale model of Telegraph Canyon to determine the amount of head that would be required to increase the capacity of the culverts from 1,700 cfs to 3,300 cfs, and to develop an energy dissipator design downstream from the existing culverts. Initially, the model reproduced approximately 3,400 ft of the channel and culverts from sta 69+39 to 35+31. Later in the testing program, the model was modified to reproduce upstream channel improvements to sta 78+00 to reflect the change in location of the inlets to the box culverts from sta 59+70 to 67+40. The required wall heights to contain the additional head that was necessary to increase the capacity of the culverts were determined from water-surface measurements Several inlet designs were tested at the headwall to determine the effect of streamlining the entrance on flow conditions and water-surface elevations. Two of the designs tested performed satisfactorily : a 10-ft-radius curve (type 2 design) and an elliptical shape (type 4 design). Relocation of the inlet to sta 67+40 had no significant effect on the capacity of the conduits or on the water-surface elevations a t the entrance to the conduits. The wall heights in the vicinity of the inlet (sta 67+40) were designed to allow flow to overtop the walls just upstream of sta 68+45 to prevent the surface jump from moving upstream as the discharge increased. The headwall at the outlet of the existing culverts was skewed, since each of the 84-in.-diam culverts terminated at a different station. This caused unequal distribution of energy in the stilling basin because more flow was entering the left side of the basin. Test results indicated that extending three of the culverts so that all four culverts terminated at a common headwall at sta 39+67 would produce a uniform distribution of flow entering the stilling basin. The trajectory curve between the outlet and stilling basin as originally designed was 78 ft long. A much shorter (30 ft) and steeper trajectory curve was found to perform just as satisfactorily as the longer and more expensive curve. The original stilling basin was 60 ft wide and 45 ft long with the apron at elevation (el) -0.08 (elevations are in feet referred to the National Geodetic Vertical Datum). Unsatisfactory flow conditions were observed in this basin with the design discharge and minimum tailwater. A satisfactory design was developed with the 60-ft width by lowering the apron elevation 1 ft and rearranging the basin elements. However, a much more economical design was developed by narrowing the basin width to 40 ft and shortening the apron length to 36 ft. The apron of this basin was at el -4.0, which would require more excavation for construction; but the decrease in size of the basin and transition from the outlet would result in a much less costly structure. A 24-in.-thick layer of 12-in. (D50) riprap was stable for all discharge and tailwater combinations tested with the recommended stilling basin. The 12-in. riprap was considered the smallest practical size that should be used in the prototype, and smaller sizes were not tested.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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