FLOOD06499

• County: Statewide
• Basin: Statewide
• Title: Development of Generalized Free Surface Flow Models Using Finite Element Techniques
• Date: 2/1/1979
• Prepared For: US
• Prepared By: COE
• Floodplain - Doc Type: Educational/Technical/Reference Information

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continuity errors on these parameters was also investigated.
Flows on the Rio Grande de Loiza flood plain were
simulated using several networks. This flood plain was
selected because of its complex flow field and a prior study
by the U.S. Army Corps of Engineers (1976) had made the data
readily available. Model performance had previously been
evaluated for simple hypothetical and laboratory flows by
Norton et al (1973) and King et al (1975). The Loiza flood
plain is about 10 by 10 km (6 by 6 miles) in extent and is
characterized by variable bottom topography, one inlet and
two outlets, and several islands. Three of the networks used
in the study are shown in Figs. 1 to 3 illustrating pro-
gressive increase in network detail.
The solution was considered acceptable if flow at all
continuity check lines deviated from inflow by less than t 5%.
Continuity is checked by integrating the normal component of
velocity times depth along lines specified by the modeler.
The continuity check lines used in this study are indicated
by dark lines on Figs. 1 to 3. Note that, because the flow
divides around the islands, in some cases the sum of flows
across two check lines (such as 5 and 6) should be compared
with inflow. Various parameters of the problem are summarized
in Table 1. No attempt was made to calibrate the coefficients
used.
The continuity approximation improved with increasing
network detail, as expected. flow at the worst check line in
the coarsest network (7 + 8) il!lproved from 79.3% to 98.2% of
inflow as network detail was increased. Network character-
istics, computer execution times, and results of the simu-
lations with these three networks are summarized in Table 2.
Average depths and velocities along the continuity check lines
are given in Table 3. The check line numbers in Tables 2 and
3 refer to the lines indicated on Figs. 1-3.

Table 1 Data for Loiza Flood Plain Simulation

1.

Boundary conditions:
a. Inflow (line 1) = 8200 cms (290,000 cfs)
b. Outlets (lines 11 & 12), water surface elevation =
2.5 m (8 ft) MSL
c. All other boundaries; either tangential flow or
stagnation points
Bed roughness: Chezy C spatially varied from 5.5 to 22.
ml/l/sec (10 to 40 ftl/l/sec)
Turbulent exchange coefficients: varied with element size
from 24 to 48 ml/sec (260 to 500 ftl/sec)

c

2.

3.

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