The New Year's Eve Flood on Oahu, Hawaii December 31, 1987 - January 1, 1988 (1991) / Chapter Skim
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4 HYDROLOGY AND HYDRAULICS
4 HYDROLOGY AND HYDRAULICS
Pages 33-50
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From page 33... ...
Nakahara, personal communication, 19883. The historical records of the Inoaole, Kuliouou, Makawao, and the Maunawili streams allow for the calculation of a recurrence interval (flood frequency)
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34 Cal Ct ._ 3 Ct Cal o en 3 Cal o o 3 o Cal o A_ o ._ Cal i_ ._ z 4 Cal Cal Cal ._ Pa U
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KAWAINUI MARSH FLOODING To understand the cause of flooding in the Kailua area, it is important to understand the dynamic processes of the events that took place during the storm in the Kawainui Marsh area. Adjacent to the Coconut Grove area in Kailua, the Kawainui Marsh drains 11.2 square miles on the windward side of the Koolau Mountains (U.S.
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From page 36... ...
Geological Survey, Honolulu district office.
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2488 Data Period: 1958- 1986 2 3 5 10 20 30 50 100 200 RECURRENCE INTERVAL (Years) Figure 13 Gumbel Type I frequency distribution of an annual maximum instantaneous streamflow for Inoaole Stream (station no.
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From page 38... ...
The flooding of the Kawainui Marsh and the Coconut Grove area to the east of the Kawainui Marsh on New Year's Eve resulted from a complicated overland flow event in the upstream watershed, the hydraulic routing process of the 740-acre marsh, and an overtopping of the levee. A detailed engineering analysis of the dynamic processes of the marsh under flooding conditions is required to determine the modifications needed to prevent a recurrence of the floods.
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From page 39... ...
Research and detailed engineering analysis are not the primary objective of this postdisaster study team's mission. Therefore, certain important parameters such as the time history of sedimentation and debris flow deposition in the Kawainui Marsh since its original construction in 1966, inflow retardation due to floating vegetal mat in the marsh, and backwater and tidal effects on the Oneawa drainage channel-were not investigated.
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From page 40... ...
Kekuna, Oabu Civil Defense Agency, personal communication, 1988~. Floodways in the upper valleys had an accumulation of dead trees or debris from prior floods, as seen in Figures 17a-e.
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r ~ .; . Figure 17b Figures 17a-e Floodways in upper Niu Valley.
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42 THE NEW YEAR'S EVE FLOOD ON OAHU, HAWAII Figure 17d Figure 17c Figure 17e
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From page 43... ...
Geological Survey, Menlo Park/Vancouver, personal communication, 1988) observed that none of these landslides reached a channel in the valley floor except one in the upper Niu Valley that directly contributed to the debris flow (Figures 22a-c)
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From page 45... ...
. Figure 19a L ::' I' Figure l9b 45 Figures 19a and b This debris basin on Kuliouou Stream (photo taken 1/8/88)
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46 Figure 20a THE NEW YEAR'S ME FLOOD ON MU, HAW~I Figures 20c Figures 20a-c Kahena Street, Hahaione Valley on January 2, 1988. Flood waters gouged a 10-20 ft channel in the roadway.
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From page 47... ...
HYDROLOGY AlID HYDRAULICS 47 Figure 21a Hahaione Valley Figure 21b Kuliouou Valley .~.... Figure 21c Kuliouou Valley Figures 21a-c Landslides in Hahaione Valley and the Kuliouou Valley.
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From page 48... ...
48 THE NEW YEAR'S EVE FLOOD ON OAHU, HAWAII Figure 22a Figure 22b Figure 22c Figures 22a-c Landslides in the Niu Valley.
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From page 49... ...
100 or less 100 or less with sump, tailwater effect, and for the design of roadway culverts and bridges 100 or greater and all steams 10 50 Based on maximum recorded Bow ~ SOURCE: City and County of Honolulu (1969~. TABLE 11 Recommended Recurrence Interval, 1986 Drainage Area (acres)
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From page 50... ...
Thiede, Department of Public Works, Honolulu, personal communication, 1988~. That is, no consideration is given to the possibility that the flows in the storm drainage channels may carry sediment and debris that add bulk to the flow, increase its volume, and can potentially block artificial and natural stream channels.
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