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Annual Flows

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“No man ever steps into the same river twice, for it’s not the same river and he’s not the same man.” –Heraclitus (534-474 B.C.E.)

Watching the Dungeness

People began keeping occasional records of the Dungeness River’s flow in the early 1900s.  Since 1938 continuous records have been kept from a monitoring station (currently at the Schoolhouse Bridge on Anderson Road). The information collected is used to keep track of daily mean flows and to compare changes in the river from year to year.

Since the 1920s the river’s average yearly flow has been about 380 cubic feet per second (cfs), but the flow isn’t consistent. The average Dungeness flow has been less in some years (197 cfs in 1978) and higher in others (697 cfs in 1999). And during one flood in 2002, the flow reached 7,610 cfs. The river’s variations stem from weather patterns, ocean temperature and human use of water from the river.

Weather cycles

Over the course of a Dungeness river water year, measured from October 1 to September 30, the area experiences rainstorms and snow from October to December. The months of January through March usually see additional snow in the mountains but fewer rainstorms. In April the winter’s snowpack in the mountains begins to melt, and the runoff increases during May and June. Runoff eases in July. In most years the river has its lowest flow in late summer and early fall.

Dungeness River High WaterNorthwest weather also cycles through changes on an irregular schedule. Roughly every three to seven years, the El Niño/Southern Oscillation pattern of warmer surface temperatures in the Pacific Ocean brings warmer and dryer periods with less buildup of snowpack in the mountains. In other years La Niña brings cooler, wetter periods. The occasional warm and wet flow of atmospheric moisture called the Pineapple Express yields heavy rains; these can cause higher rates of snowpack melt and flooding downstream.

Oceanographers study an even longer cycle (20-30 years) of surface temperatures in the Pacific Ocean, the Pacific Decadal Oscillation, that seems to accompany shifts between warmer/dryer and cooler/wetter years for the river.  Other scientists, who study long-term climate change, expect more winter rain-on-snow storms to the area, with more winter flooding but less summer runoff from the reduced snowpack.

Irrigation and the river

In 1896 Dungeness Valley farmers began to divert water from the Dungeness River to irrigate farmland. A system of irrigation ditches was part of the process. (The first irrigation ditch, the Sequim Prairie ditch, remains to this day. It crosses under the big bump in Priest Road east of Railroad Bridge Park.)

Sequim Irrigation Ditch monitoring stationAs irrigation increased, downstream river flows lessened, so farmers and conservationists have taken measures to decrease the diversion of water for irrigation. They have replaced open ditches with covered pipe to cut back on evaporation, for example, and they have decreased the amount of cropland to be irrigated.

Studies of the Dungeness River are now more important than ever, not only to farmers in the area but also for preserving wildlife. Native salmon, for example, need enough river flow to be able to swim upriver to spawn.

NOTE: Much of the material in this article is adapted from Chapter 5 of  “Keys to an understanding of the natural history of the Dungeness River System” (1996, Welden & Virginia Clark) and later updates.