Lake Whatcom - Hydrology

Hydrology

Lake Whatcom is a monomictic lake. The water body is stratified for part of the year (late spring through mid-fall) and mixed during the rest. This phenomenon is important to the hydrology of the lake. The top layer of water (epilimnion) is warmed by the sun and sits atop the metalimnion (also a thermocline). In this middle layer water temperatures take a pronounced decline and eventually a distinct third layer forms (hypolimnion), much colder and isolated from the rest of the water body. Minimal oxygen from the air diffuses down to the hypolimnion, causing very low dissolved oxygen (DO) levels. This combined with sediment oxidation, cause for near or complete anoxic conditions in the deeper levels of the lake. This stratification is more pronounced in Basin 3 where water is deepest. This layering of the lake, as well as the distinct physical barriers (sills) between basins cause for slow movement of water through the lake. (Ecology TMDL, 2008)

Another important hydrological phenomenon on Lake Whatcom is the occurrence of seiches. A seiche is the slow sloshing of water from one side of the lake to the other, due to winds in Lake Whatcom’s case. Winds will push water to one side of the lake, causing water levels to rise on one end and lower on the other. When the wind stops, the water rebounds back and forth until it is settled again. This up and down movement of the water causes the thermocline to rise and fall as well, which can result in the cold, anoxic water from Basin 3, to spill over the Strawberry Sill into Basin 2.

Major outputs of lake water are Whatcom Creek (77.5% of outflow), City of Bellingham intake (11.3%), evaporation (7.9%) and hatchery (2.5%). The estimated residence time of water entering the lake until it leaves is 7.4 years. (Lake Whatcom Annual Report, 2008/09 http://ceratium.ietc.wwu.edu/IWS2)