Discussion of “Comparison of Four Numerical Methods for Flood Routing”

The negative sign in Eq. 11 should precede 1 / CP as well as precede the first term in Eq. 18.Normally Q I will be known as a function of time arising from advance knowledge of the release schedules from an upstream reservoir or flow past a telemetered upstream gage-both far enough upstream to be unaffected by backwater.The computation of the steady and unsteady flow profile in the tributary from the dam or gage to the confluence was then assumed to be included along with the unsteady computation for the main stem or Sacramento River, as would be normally done in a branching pressure conduit system.The selection of Colusa was arbitrary and certainly most any other gaged location would be acceptable.Colusa is an important river forecast point and is located about 80 miles upstream from Sacramento and the fall in the river is about 40 ft over the distance.Again, as with tributary inflow, it is recognized that upstream flows and stages can be influenced by downstream conditions but that the unsteady-state conditions of discharge and stage are known at or calculated by similar methods for the section above Colusa.Eq. 29 should of course be expressed in terms of absolute velocity.Also, Eqs .30 and 31 present an acceptable solution to account for the stage-discharge loop affect at the downstream boundary.There are several terms which, after a conversation with Fread, were clarified as follows: (I) Adjusted invert slope is the same as average invert slope; (2) Y~ and V~ are located Ax upstream; and (3) A parenthesis should be set to the left of Y~ in Eq. 3 I.The second paragraph of Yen and Sevuk's discussion pointed out several practical inconsistencies which would confuse the uninformed reader.Also the use of dx and dt in place of Ax and At in the text and the inclusion of Eq .11 (p .409, line 5 from the bottom) in the system of equations is not correct.Their suggestions regarding backwater influence in the tributary, similar to Fread 's is answered previously.The writer's statement regarding increasing 11 with increasing stage is an observation related to local flood bank friction patterns .