Scientific Investigations Report 2006-5153
The surface– and ground–water resources of the Punaluu area of northeast Oahu, Hawaii, have been and continue to be important for cultural, domestic, agricultural, recreational, and aesthetic purposes. Punaluu Stream flows perennially because rain falls frequently in the area and ground water discharges to the stream. Flow in Punaluu Stream is reduced by the direct diversion of water for off-stream uses and possibly from the withdrawal of ground water near the stream. Punaluu Ditch diverts water from Punaluu Stream near an altitude of 210 feet.
During the recent period 1995—2004, discharge in Punaluu Stream that was equaled or exceeded 50 percent of the time (median or Q50 discharge) and discharge that was equaled or exceeded 95 percent of the time (Q95 discharge) measured immediately upstream from the Punaluu Ditch diversion intake, respectively, were 18 and 13 cubic feet per second, whereas the Q50 and Q95 discharges measured immediately downstream from the diversion intake, respectively, were 7.0 and 1.3 cubic feet per second. Thus, near an altitude of 210 feet, diversion of surface water by the Punaluu Ditch caused the Q50 discharge in Punaluu Stream to be reduced to 39 percent of the natural Q50 discharge, and the Q95 discharge was reduced to 10 percent of the natural value. The relative effects of the Punaluu Ditch diversion on flow in Punaluu Stream decreased in a downstream direction, mainly because of the compensating effects of tributary inflows and ditch return flows. At an altitude of 10 feet, the Q50 discharge in Punaluu Stream was 82 percent of the natural Q50 discharge, and the Q95 discharge was 69 percent of the natural value.
Changes in streamflow affect the quantity and quality of physical habitat used by native stream fauna. The Physical Habitat Simulation System (PHABSIM) approach was used to evaluate the effects of different diversion scenarios on physical habitat for selected native species in Punaluu Stream. Habitat-suitability criteria developed for streams in northeast Maui, Hawaii, were used to determine the effects of incremental changes in streamflow on physical habitat, in terms of weighted usable area (WUA) in Punaluu Stream.
The effects of different diversion conditions on WUA for Neritina granosa and Awaous guamensis were evaluated by determining the average number of days per year for which WUA values are less than a specified reference value (during periods when discharge is less than or equal to the median natural discharge). For recent diverted conditions (1995—2004), the average number of days per year that WUA values are less than 50 or 75 percent of the WUA value at median natural discharge generally (1) decreases in a downstream direction, reflecting the effects of tributary inflows and ditch return flows, (2) is less than the corresponding number of days for constant diversion rates greater than about 4–5 cubic feet per second at a stream altitude of 10 feet, and (3) is greater than the corresponding number of days for a constant diversion rate of 10 cubic feet per second at stream altitudes of 40, 100, and 140 feet. The number of days that WUA values are less than 75 percent of the WUA value at median natural discharge generally increases substantially for constant diversion rates exceeding about 4–5 cubic feet per second. At stream altitudes of 10, 40, 100, and 200 feet and for constant diversion rates of up to 4 cubic feet per second, WUA values are less than 75 percent of the WUA value at median natural discharge for fewer than 13 days per year. At stream altitudes above 40 feet and for a constant diversion rate of 10 cubic feet per second, WUA values are less than 75 percent of the WUA value at median natural discharge for 131 to 183 days per year.
Stream temperature is a factor that potentially could affect the abundance and distribution of native aquatic species. Measured stream temperatures immediately upstream and downstream from the diversion intake did not indicate a significant change in temperature caused by a reduction in flow. Measured daily maximum temperatures did not exceed 25°C and daily minimum temperatures did not drop below 17.5°C at any of the six sites between altitudes of 10 and 210 feet where temperatures were measured. At all six sites, daily maximum temperatures remained below the upper–lethal–temperature limits for native aquatic species.
On the basis of (1) measured water levels in wells, relative to stream-channel altitudes and (2) discharge measurements indicating where the stream commonly gains water, Punaluu Stream is likely connected to the main ground-water body below an altitude of about 25 feet. Measured water levels in monitoring wells in the volcanic rocks indicate that ground-water withdrawals west of Punaluu Stream cause ground–water–level declines east of the stream. Thus, water levels in the volcanic–rock aquifer beneath and adjacent to Punaluu Stream are affected by withdrawals from existing well fields. If a continuous zone of saturation exists between the stream and the underlying volcanic rocks, long–term water–level declines caused by withdrawals from existing wells in the volcanic rocks will ultimately extend to the stream and cause a reduction of ground–water discharge to the stream. The magnitude of streamflow reduction is unknown, but may be immeasurable, depending on the rate of withdrawal, because of the presence of low-permeability sedimentary deposits separating the stream and underlying volcanic rocks. The effects of ground-water withdrawal on streamflow may be best evaluated using a numerical ground–water model that accounts for the hydraulic characteristics of the rocks between sites of ground–water withdrawal and the stream.
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Abstract
Introduction
Objectives
Purpose and Scope
Acknowledgements
Setting
Land Use
Climate
Geologic Setting
Volcanic Rocks
Sedimentary Deposits
Surface–Water Resources
Punaluu Stream
Base-Flow Characteristics
Peak-Flow Characteristics
Interaction Between Ground Water and Surface Water
Gains and Losses Below an Altitude of 210 Feet
Seepage Runs and Additional Discharge Measurements
Punaluu Ditch
Punaluu Ditch Flow Characteristics
Ditch Discharge Measurements
Stream Fauna
Life History Characteristics of Native Species
Native Species in Punaluu Stream
Non–Native Species
Potential Factors Affecting Abundance of Native Species
Non–Native Species
Agricultural Activities
Aquaculture
Effects of Surface–Water Diversion on Streamflow
Immediately Downstream from Punaluu Ditch Diversion (210–Feet Altitude)
Altitudes of 140 to 10 Feet
Methods
Flow Characteristics for Diverted Conditions
Flow Characteristics for Natural Conditions
Altitudes 140, 100, and 40 Feet
Altitude 10 Feet
Effects of Surface–Water Diversion on Habitat
Stream Habitat Data Collection
Study Reaches
Cross Sections
Quantification of Suitable Habitat
Habitat–Duration Characteristics
Neritina granosa (hihiwai)
Awaous guamensis (oopu nakea)
Limitations
Effects of Surface-Water Diversion on Stream Temperatures
Daily Mean Temperatures
Diurnal Temperature Variations
Ground–Water–Flow System
Water in the Sedimentary Deposits
Dike–Impounded Water
Freshwater Lens
Perched Systems
Withdrawals
Water Levels
Salinity
Effects of Ground–Water Withdrawal on Streamflow
Potentially Affected Stream Areas
Water–Level Variations Caused by Withdrawal
Hydrologic Effect of Dikes
Approaches to Quantify Streamflow Reduction
Summary and Conclusions
References Cited
Appendix A.
Table 1. Discharge measurements made during 2004 and 2005 in Punaluu Ditch and Punaluu Stream and tributaries, Oahu, Hawaii, sorted by date.
Table 2. Discharge measurements made during 2004 and 2005 in Punaluu Ditch and Punaluu Stream and tributaries, Oahu, Hawaii, sorted by site.
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