|
<br />....,
<br />
<br />",
<br />
<br />..
<br />
<br />736
<br />
<br />HYDRAUUC ENGINEERING '94
<br />
<br />Information on channel gradient, shape, bed material,
<br />size distribution, sediment and debris transport,
<br />erosion and deposition, etc., need to be documented so
<br />researchers have the data base needed from which to
<br />develop criteria and guidance for the practicing model
<br />user.
<br />Criteria and guidance may simply involve strong
<br />evidence that supercritical flow will not occur, except
<br />in unusual situations, in natural channels.
<br />
<br />ReferencQS
<br />
<br />Arcement, G.J. and V.R. Schneider, Guide for Selecting
<br />Manning's Roughness Coefficients for Natural
<br />Channels and Flood Plains, U.S. Department of
<br />Transportation, Federal Highway Administration,
<br />Report No. FHWA-TS-84-204. April 1984.
<br />Barnes, H.H., Jr., (1967). "Roughness Characteristics
<br />of Natural Channels." U.S. Geological Survey Water
<br />Supply Paper 1849.
<br />Chow, V.TO', (1959). ODen Channel Hvdraulics. McGraw-
<br />Hill, New York, New York, 101-123. Fread, D..L..,
<br />(1988). A NWS DAMBRK Model Theoretical Backaround/
<br />User Documentation. Hydrologic Research Laboratory,
<br />National Weather Service, Silver spring, Maryland.
<br />Jarrett, R.D., (1984). "Hydraulics of High-gradient
<br />Streams." J. Hydr. Engrg., ASCE, 110(11), 1519-
<br />1539.
<br />Jarrett, R.D. and Costa, J.E.., (1986). Hvdroloav.
<br />GeomorDholoav. and Dam-break model lDa of the
<br />Julv 15. 1982. Lawn Lake Dam and Cascade Dam
<br />Failures. Larimer County. colorado. U.S. Geological
<br />Survey Professional Paper 1369.
<br />Trieete, D.T. (1992). "Evaluation of Supercritical/
<br />Subcritical Flowe in a High-Gradient Channel."
<br />J. Hydr. Engrg., ASCE, 118(8), 1107-1118.
<br />Trieste, D.T. and Jarrett, R.D., (1987). "Roughness
<br />Coefficients of Large Floods." Proc., Conf.,
<br />Irrigation Systems for the 21st Century, Portland,
<br />Oregon, 32-40.
<br />U.S. Army Corps of Engineere, (1983). Computer Program
<br />HEC-2, Water Surface Profiles. Hydrologic Engineer-
<br />ing Center, Davis, california.
<br />U.S. Department Of Agriculture, Soil Conservation
<br />Service, Engineering Handbook: Hydraulics, (1955).
<br />Wahl, K.L., (1994). "Evaluation of Supercritical/
<br />Subcritical Flows in High-Gradient Channel,
<br />Discussion of Kenneth L. Wahl." J. Hydr. Engr.,
<br />ASCE, 120(2), 270-272.
<br />
<br />.
<br />
<br />.
<br />
<br />Flow pattern. in a lDouotaia stream..
<br />
<br />Lisa C, Hubbard I and Colin R. Thome2, AmI. member ASCE
<br />
<br />Abstract
<br />This paper deals with the occurrence of suberitical and supercriticalllow, and
<br />Iheir related Ilow patterns, A Ilow pattern theory was presented by Bathurst et aI.,
<br />(1979), that considers the relation between relative submergence, Fronde number BIl;d
<br />Ihe appeatanCe of hydnwlic jumpa, This theory does not seem to represent wbat IS
<br />found in the lield, as the pallerns are not dependant on the Froude number and
<br />velocity. It may be that this relationship is masked by more dominant variables, but the
<br />importance of the relative submergence and depth off1ow is demonstrated.
<br />IntroductloD
<br />All the substantial work on roughness elements to date has been done In the
<br />laboratory.lt is time now, however, far these findings and theories to be tested in the
<br />field. With this purpose, research was carried out on the Roaring River in Colorado, a
<br />steep mountain, cobble and boulder bed river with large scale roughness. Seventeen
<br />boulders were selected, as they were isolated with little interference from other large
<br />roughness elements and represented a variety of sa.cs. In order to obtain velocity
<br />infonnation around a boulder with some degree of precisIon and repeatahlily a grid
<br />was designed to fit over the boulder that showed positions at which the velocity was to
<br />be measured, All velocities were taken at 0.4 of the depth,
<br />Flow paltern anal,sis
<br />Field observation revealed that Ilow patterns depended primarily on stage, with
<br />six flow patterns seen repeatedly and the possibility of a seventh on one occasion.
<br />I.) The lirst was a very low disturbance pattern, on some occasions the boulder's
<br />presence appeared to have no effect on the Ilow, For fractionally higher Slages there
<br />may be a slight build up in the water surface elevation on tbe the front edge of the
<br />boulder, with the speeding up ofllow round the sides causing a slight dip in the water
<br />surface level and small ripples on either side of the boulder; the water in the wake zone
<br />seems undisturbed,(ligure la), These ripples appear to start from Ibe widest point of
<br />the boulder, Thisllow paltern is called the low disturbance Ilow pallem (LD),
<br />2.) The second pattern (Figure Ib) shows the development of Ihe side Ilo~ into
<br />vortices, and hydraulic jump's fonn, one on either side of the boulder. These JUmps
<br />have a coIVing outward trend like a semi-circle that is concave to the boulder. Once
<br />again the location is shape dependent and the build up of water surface elevation in the
<br />
<br />1 Research Contractor, US Army Corpa of Engineers, Waterwaytl Experiment Station,
<br />Hydraulics Laboratory, 3909 Halls Ferry Road, Vicksburg, MS 39180,
<br />2 Head of Geography Department, University ofNoltiogham, University Park,
<br />Nottingham, NG7 2RD England,
<br />
<br />737
<br />
|