EP 1130-2-520
29 Nov 96
APPENDIX AA
DETERMINATION OF THE HYDRAULIC LINE
AA-1. Flow Criteria. The flows which are named below will be used in the determination of the
hydraulic line for the identification and marking of hazardous waters adjacent to Civil Works
structures.
a. Navigation Locks and Dams. The discharge corresponding to ordinary highwater, a
recognized flow throughout the Corps of Engineers to define limits of Federal jurisdiction, will be
used. Should the ordinary highwater discharge exceed the maximum navigation discharge at a
project, the latter will be used. (In any case, the worst case scenario must be used.)
b. Flood Control and Storage Dams. The annually-released bankfull flow, (alternately
known as the non-damaging discharge), will be used. However, the customary flow of the project
will be used, if less than bankfull.
c. Local Flood Reduction Projects, Hydroelectric Plants, Training Structures, Intakes and
Pumping Stations. The one-year discharge (i.e., the maximum flow which has a 100% chance of
occurring each year), will be used.
AA-2. Upstream of Structures.
a. Navigation, Flood Control/Storage, and Local Flood Reduction Projects. The hydraulic
line will be determined where the drawdown commences upstream of the dam, chute, drop
structure, or diversion - for prescribe flow in paragraph 1 above. Said location will delineate the
beginning of the accelerating velocity of approach and the change in water-surface slope due to the
presence of the dam or structure.
(1) Frequently, this location has been seen to occur at a distance upstream equal to about
three times the head on the crest of the dam for fixed crests dams with straight approaches, and a
variable amount for gated dams that can be computed or observed depending on the schedule of
gate openings. However, each project must be analyzed on its own merits to locate the hydraulic
line.
(2) Where channel curvature or constrictions exist, the hydraulic line will be located to
include these effects, where pertinent.
(3) For lock intake areas, the hydraulic line will be set upstream at a distance at least equal
to twice the water passage opening.
b. Hydroelectric Plants, Intakes, Training Structures, and Pumping Stations.
(1) For pump stations, submerged inlets, and hydroelectric plants, the hydraulic line will be
set at a distance equal to twice the width of the structure intake.
(2) For training structures such as dikes and spurs, the hydraulic line will be set at least an
amount upstream equal to two times the greatest dimension of the structure.
AA-1
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