Flow characteristics of streams in Tutuila, American Samoa

The island of Tutuila is the economic and population center of American Samoa. It lies in the tropics and rainfall is abundant. Annual rainfall at upper Faga'alu reservoir averaged 207 inches during the period 1904-75. Available records show that altitude is a significant factor affecting the amount of rainfall. Small, steep basins generally yield perennial flow into streams but the amounts are small and sometimes highly variable. Low-flow frequency and correlation methods were used to determine flow characteristics. The total of the low-flow consecutive 7-day average discharges that can be expected at 10-year recurrence intervals at the 6 continuous-record gaging stations and the 45 partial-record stations analyzed is 5.2 cubic feet per second. About half of this total, 2.4 cubic feet per second, is from streams draining the southwestern part of the island where most of the water collection and distribution systems are being concentrated. High-flow frequency curves show the instantaneous peak discharge of the maximum mean discharge for selected periods of consecutive days and its likelihood of occurrence. (Woodard-USGS)