Water resources of the Tulalip Indian Reservation, Washington

Abstract

Water will play a significant role in the future development of the Tulalip Indian Reservation. Ground-water resources are sufficient to supply several times the 1978 population. Potential problems associated with increased ground-water development are saltwater encroachment in the coastal areas and septic-tank contamination of shallow aquifers. There are sufficient good-quality surface-water resources to allow for significant expansion of the tribe)s fisheries activities. The tribal well field is the only place where the ground-water system has been stressed) resulting in declining water levels (1,5 feet per year), The well field has a useful life of at least 1.5-20 years, This can be increased by drilling additional wells to expand the present well field, Inflow of water to the reservation is in the form of precipitation (103 cubic feet per second) ft3/s)) surface-water inflow (13 ft3/s)) and ground-water inflow (4 ft3/s), Outflow is as evapotranspiration (62 ft3/s)) surface-water outflow (40 ft3/s)) and ground-water outflow (18 ft3/s), Total inflow and outflow are equal (120 ft3/s). Ground water is generally suitable for domestic use without treatment) but a serious quality problem is the presence of coliform bacteria in some shallow wells, High values of turbidity and color and large concentrations of iron and manganese are common problems regarding the esthetic quality of the water, In a few places, large concentrations of chloride and dissolved solids indicate the possibility of saltwater encroachment, but no ongoing trend has been identified, Surface waters have been observed to contain undesirably high concentrations of total phosphorus and total and fecal-coliform bacteria) and to have temperatures too high for fish-rearing. The concentration of nutrients appears to be related to flow conditions. Nitrate and total nitrogen are greater in wet-season runoff than during low-flow periods) and total phosphorus shows an inverse relationship. Total phosphorus and ammonia concentrations are greatest in dry-season storm runoff. Generally) surface-water quality is adequate for fish-rearing and (with treatment) for public supply,