Lake+History



LAKE VAIHIRIA DRAINAGE BASIN, T AN ELEVATION OF 470-1600m, LIES IN THE WET TROPICAL ZONE, AND IS CHARACTERIZED BY EXTREMELY STEEP SLOPES, HIGH CLOUD COVER, AND HIGH PRECIPIATATION. THE SLOPES OF THE LAKE VAIHIRIA CATCHMENT NATURALLY SUPPORT A MID AND HIGH ALTITUDE HYGROPHILE FOREST VEGETATION, WHICH IS TODAY DOMINATED BY PANDANUS TECTORIUS; BOTANICAL NOMENCLATURE FOLLOWS FLORENCE TROUGHOUT.

LAKE VAIHIRIA IS THE ONLY NATURAL LAKE ON TAHITI TODAY AND IS ONE OF THE FEW BODIES OF FRESHWATER ON ANY ISLAND IN THE SOUTH PACIFIC. LAKE VAIHIRIA IS LOCATED IN THE HEADWATERS OF VAIHIRIA VALLEY, WHICH HAS BEEN DEEPLY ERODED IN VOLCANIC ROCKS; SLOPES ALONG THIS OTHER VALLEYS NORMALLY EXCEED 45°. THE LAKE HAS A SURFACE AREA OF 1.7KM SQUARED AND LIES AT AN ELEVATION OF ABOUT 470 M. THE MAXIMUM WATER DEPTH HAS BEEN SOUNDED AT 28 M. IN JULY 1983 THE TEMPERATURE OF THE LAKE RANGED FROM 20.6° CELSIUS AT A DEPTH OF 0.1 M TO 20.0° CELSIUS AT 4M AND 19.8° CELSIUS BELOW THAT; THE LAKE PH WAS 7.0 AT A DEPTH OF 4 M. AT THE UPSTREAM END OF THE LAKE IS A FLAT ALLUVIAL PLAIN THAT HAS BEEN INCISED BY A NUMBER OF MODERN STREAM CHANNELS, EXPOSING SEVERAL METRES OF INTERBEDDED CLAYEY SILT, SANDY GRAVEL. WATERS ENTER LAKE VAIHIRIA THROUGH THE CHANNELS ON THE ALLUVIAL PLAIN, WHICH IN TURN RECEIVED THEIR WATERS FROM THE ROCK-WALLED TRIBUTARIES FEEDING THAT SYSTEM. IN MANY PLACES, WATER EMANATING AS SPRINGS FROM BETWEEN BASALT FLOWS PLUNGES TO THE VALLEY FLOOR AS WATERFALLS. OUTFLOW FROM LAKE VAIHIRIA IS MAINLY THROUGH THE PERMEABLE DEBRIS DAM. SEEPAGE AT THE TOE OF THE DAM OCCURS IN SEVERAL PLACES AND IS CONCENTRATED DOWN-VALLEY IN A SINGLE CHANNEL. BECKER NOTED THAT SEEPAGE IS FROM AT LEAST FOUR SPRINGS AT AN ELEVATION ABOUT 170 M BELOW THE LEVEL OF THE LAKE, MAINLY ALONG THE CONTACT OF THE BEDROCK WITH THE OVERLYING DEBRIS AND ALLUVIUM.