Enhancements and Modifications to the Full Equations (FEQ) Model, March 1995 to August 1999
Note: This document is separate from the U.S. Geological Survey report by Franz and Melching (1997). This description of enhancements and modifications to the Full Equations Utilities Model has not been approved by the Director of the U.S. Geological Survey.

Input description update for section 13.6 Network-Matrix Control Block-- Network-Matrix Table, Franz and Melching, 1997a, p. 179

Section 13.6 Network-Matrix Control Block--Network-Matrix Table, Code 13

To RELEASE.TXT

If CODE13 (Conservation of momentum or energy):

N(1) is the upstream node on the source channel

N(2) is the downstream node on the source channel

N(3) is the number of side-inflow nodes. These must be on branches so that the momentum flux of the entering water can be estimated. Old forms of Code 13 take this value to be 0 so that no momentum flux is computed.

N(4:5) are the side nodes giving the flow and the flow area in the side channels as they enter the main channel.

F(1) is the loss coefficient to apply to energy equation. The coefficient is a factor on the change in velocity head that occurs when water is taken from the channel. The loss coefficient must be non-negative and less than 1. The losses when water is discharged from a channel are generally small. Care must be used in setting this value because if too large it can cause computational failure.

F(2) is the angle of water entry for the side node at N(4). This is not the angle of entry of the side channel but of the water as it leaves the side channel. This angle of entry of the water is always less than the angle of entry of the side channel. Rough estimates based on extrapolation from limited laboratory studies in idealized equal-width rectangular junctions with non-rounded corners indications that the angle of water entry is 0.7 or less of the angle of channel entry for sub-critical flows with small Froude numbers. A small Froude number is taken to be less than 0.5 in the main channel downstream of the junction.

F(3) is the angle of entry for the side node at N(5).

Discussion: This option is the preferred option for representing an inflow or outflow that takes place to another stream. If there is inflow then conservation of momentum is used and if there is outflow conservation of specific energy is used. Note that the water-entry angles in F(2) and F(3) are only used in the conservation of momentum approximation. There are several restrictions on this option. The nodes must be on branches in the normal manner. That is, the upstream node for this option must be the downstream node on the branch upstream of the junction and the downstream node for this option must be the upstream node for the branch downstream of the junction. Also the bottom elevations must match and the cross section table numbers must be identical.

The effect of the separation zone at a junction has not been included because the separation zone is probably small in most natural cases. It was small even in the idealized sharp cornered junctions when the angle of the channels was 15 degrees or less. The separation zone's effect is exerted via changes in some of the pressure forces on the control volume and are thought to be of secondary importance.

Some thought has been given to creating another junction option for which the cross sections on the main channel above and below the side channel entry point no longer have to be the same size. However, no studies of that situation have been discovered.

Back to Franz and Melching (1997a), p. 179, for Code 14