ETL 1110-2-536
31 Dec 94
APPENDIX C: ZINTEL CANYON PROJECT
C-1. Project Description
b. Geology and foundation. Zintel Canyon is
located on the southwest flank of the Pasco Basin, a
a. General. The Zintel Canyon Project
structural feature formed by downward folding and
(Figures C-1 through C-4) was authorized for con-
faulting of the Columbia River Basalt formation.
struction by resolution of the House and Senate Com-
Erosion and deposition has modified the structural
mittees on Public Works, December 1970, under
features by partially filling the basin with sediments
authority of section 201, Flood Control Act of 1965
and covering the rock slope with a mantel of fine-
(Public Law 298, 89 Congress). The project was
grained materials. Bedrock is close to the surface
constructed substantially as authorized. Detention
within the drainage area of Zintel Canyon and where
storage was reduced from 2,560 to 1,260 acre-ft since
the dam was located. The foundation rock was com-
this was considered the optimum economic size of the
posed of hard, dense basalt with closely spaced frac-
dam. This alternative will not prevent damages in
tures. The moderately unweathered pieces were
some areas of Kennewick or avoid the use of streets
bounded by weathered fracture surfaces. Fracture
as a channel during flooding in excess of 50 years
fillings, particularly near the surface, were filled with
(100-year thunderstorm). Zintel Canyon Project
silt and clay. Because the rock would easily dislodge
includes a dam and a floodway channel with required
when the joint filling dried, as well as from subse-
structures that carry the combined flows from the
quent construction activities, the exposed foundation
dam and areas below the dam through a developed
rock was covered with a minimum 8-in. layer of
section of Kennewick to a discharge point at the
pumped concrete prior to RCC placement.
Columbia River. Zintel Canyon Dam is a 90-ft reten-
c. Dam, spillway and outlet. The dam is a
tion straight axis concrete gravity structure totaling
straight axis concrete gravity structure with a crest
approximately 70,000 cu yd of roller compacted
length of 520 ft and a 160-ft, centrally located,
concrete (RCC). The purpose of the dam is to pro-
ungated overflow spillway. The height of above
vide flood protection to the city of Kennewick, Wash-
foundation is 126 ft and 86 ft above the existing
ington, by impounding flood flows behind the dam up
channel with a 20-ft crest width in the nonoverflow
section. The slope of the downstream face was
volume over a 20-day period. The Floodway Chan-
.85 horizontal to 1 vertical to facilitate free forming
nel improvements consists of a buried conduit
of the downstream face. The upper 24 ft of the
designed to pass up to a 50-year composite flood
downstream face of the dam (adjacent to the spill-
level. The 78-in. buried conduit is designed to carry
way) was constructed using vertical concrete facing
400 cfs from its intake at West 7th Avenue and Van-
panels as was the upstream face. An 80-ft long
couver to the outlet in the Tri-City Country Club Golf
hydraulic jump-type stilling basin was located at the
Course. From there the natural channel is designed
toe of the structure. This stilling basin consists of a
to pass 620 cfs through the Burlington Northern
12-ft-thick RCC base slab integrally constructed with
railroad fill (Figure A-1). Downstream of the railroad
an RCC endsill and RCC gravity training walls. The
fill the channel is designed to provide standard proj-
spillway was designed to discharge a flow of
ect protection. The project is co-funded by the
38,950 cfs. The full width of the spillway crest was
U.S. Army Corps of Engineers (75 percent) and the
surfaced with a two-foot thickness of wet-mix shot-
city of Kennewick (25 percent). The project is
crete for a distance of 30 ft, until it transitions to the
located in a semi-arid region of eastern Washington
natural RCC surface. A fixed orifice in the intake
and borders on the south end of Kennewick, Wash-
tower regulates discharge to a maximum of 60 cfs.
ington. The basin, a well defined water course called
This discharge rate was sized to drain the reservoir in
Zintel Canyon, is normally dry and drains approxi-
20 days and produce minimal flows in the down-
mately 28 square miles of the north side of the Horse
stream channel. An intake tower, attached to the
Heaven Hills of which approximately 19 square miles
upstream face of the dam, provides inlet control for
in area is upstream of the dam. The drainage
increasing heights of sediment deposition. The tower,
upstream of the dam collects winterstorm and thun-
a typical U.S. Soil Conservation Service design, con-
derstorm runoff, thereby providing a 100-year flood
sists of a double weir overflow at the top and portal
storage volume of 1,260 acre-ft.
C-1