Renewable Energy Technology Assessments - Kauai Island Utility ...

Kaua’i Island Utility Cooperative
Renewable Energy Technology Assessments 8.0 Hydro
Discrete winter storms resulting in high stream flows provide much of the total
precipitation records at these rain gages. Nevertheless light showers are also quite
common throughout Hawaii. 74 Rainfall in Hawaii tends to fall more at night or early
morning. This diurnal variation is more pronounced during the summer than in the
winter. 75 Overall rainfall patterns and geography are favorable to hydropower in Kauai,
but yearly, seasonal, and daily variations will impact the consistency of power
production.
Stream gaging stations is available throughout Kauai. Many of these are
associated with the plantation irrigation systems where hydropower projects are likely to
occur. Because the translation of existing stream flows to site specific flows requires
significant effort, especially in view of the complex irrigation systems in some areas,
individual stream gage data was not reviewed for this report. Flow data was based on
previous studies noted herein.
An example of stream flow is shown below in Figure 8-3. The gaging station is
located between the diversion and powerhouse of the proposed upper Wainiha project.
As this is an uncontrolled stream, the flow curve reflects the precipitation curves for the
existing Wainiha Diversion and Powerhouse in Figure 8-2.
Flow, cubic feet per second
400
350
300
250
200
150
100
50
0
95th Percentile
75th Percentile
Mean
50th Percentile
25th Percentile
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Figure 8-3. Monthly Stream Flows on Wainiha Stream (Source: USGS).
74 National Oceanic and Atmospheric Administration, National Climactic Data Center, “Climate of
Hawaii,” http://www.wrcc.dri.edu/narratives/HAWAII.htm
75 ibid
21 March 2005 8-5 Black & Veatch