Annual agricultural diversions from the Dungeness River have reduced over the last two decades from about 115 cfs in 1979 to about 55 cfs in 2000 (Figure 12). According to Mike Jeldness of the Sequim-Dungeness Valley Agricultural Water Users Association (pers. comm., 2002), this reduction is largely due to:

• Lining of ditches and laterals;
• Improvement of on-farm irrigation efficiencies; and,
• Replacement of pasture crops to crops with lower water demands (e.g. lavender and seed crops).

In addition, both within and outside the irrigation season, diversion for stockwater has diminished from an estimated 25-30 cfs to approximately 15-20 cfs due to a general reduction in livestock raised and a recent regulation limiting diversion for stockwater for only those situations where no other nearby source (such as wells) are available (ibid). Finally, below-average snowpack has caused minor reductions in irrigation diversions from the Dungeness River between 1998 and 2000, and substantial reductions in 2001 (ibid).

The overall reduction in irrigation diversions is associated with specific changes in irrigation practices in the vicinity of the City's wellfields. The following subsections present a general overview of these changes, based on discussions with Mike Jeldness, Greg Stone of the Sequim-Prairie Tri Irrigation Association (pers. comm., 2002), and Steve Gather of the Highland Irrigation District (pers. comm., 2002).

7.1 Irrigation Trends in the Port Williams Wellfield Vicinity

• The old Sequim-Prairie Company ditch along Old Olympic Highway was tightlined in 1996 between Evans Road and Sequim-Dungeness Way; however, a 700-foot stretch remains unlined immediately east of Sequim-Dungeness Way. An unlined tailwater conveyance, approximately 1500 feet long, delivers about 0.1 to 0.5 cfs inflow to Gierin Creek during the irrigation season. A lateral off this ditch, running through the Stone property (due west of the Port Williams Wellfield) was also tightlined in 2001.
• The Sequim-Prairie Tri Irrigation Company ditch along Evans Road had notably high seepage losses until it was tightlined. The portion of the ditch south of Old Olympic Highway, previously managed by the Eureka Company, was tightlined in the mid 1980's. The portion of the ditch north of Old Olympic Highway has been lined incrementally from the mid 1980's to present as residential development has expanded along Evans Road.
• In 2001, the City of Sequim lined much of the Sequim-Prairie Tri Irrigation Company ditch that runs east-west, about one mile south of the Port Williams Wellfield. The ditch was lined between 5th Avenue and the siphon at Sequim-Dungeness Way, which conveys the water to about 500 feet west of Brown Road. The ditch is still open between Brown Road and the woods to the east, but was partially lined in the woods during the 1990's.
• Changes in stormwater control practices since 1998, and the concurrent construction of the SR101 bypass, have resulted in less water conveyed by ditches that pass through residential areas. In the past, stormwater ran off into ditches and conveyances (e.g. Bell Creek) and was allowed to flow down laterals, ultimately flooding fields and seeping into surface soils. Spillways have now been constructed that conduct storm runoff into streams and wetlands.

7.2 Irrigation Trends in the Silberhorn Wellfield Vicinity

• Laterals of the Sequim-Prairie Tri Irrigation Company and Highland Irrigation District occur in the vicinity of the Silberhorn Wellfield. The ditches run over very rocky substrate and exhibit high leakage losses, especially when the ditch bottom is disturbed. The ditches are predominantly unlined, except for a short lateral near Riverside Road (approximately ½ mile west of River Road in Section 25 of T30N, R4W).
• The ditches run at high flow during the summer irrigation season, between April 15 and September 15. Overall, little changes in ditch lining or operation are noted during the summer months. During the winter months the ditches convey water for stock use, and associated diversions are turned down to lower flow rates. The lower winter flow rates cause some laterals to go dry in more distant reaches. Due to reductions in stock raising and new stock watering rules (discussed above), winter stock diversions are smaller than historic rates.

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