Chimacum Drainage Analysis
A Summary of Chimacum Drainage District Environmental Challenges and Opportunities
The Chimacum Creek valleys with their rich peat soils have been the agricultural life blood of Jefferson County. The agricultural development of these valleys was made possible by major alterations in the natural drainage system, including channelization of Chimacum Creek, excavation of many miles of drainage ditches, and installation of miles of subsurface drainage.
These dramatic alterations to the landscape enabled agriculture to thrive, albeit for only a couple generations in much of the watershed. The vast majority of the drainage improvements were undertaken in the 1920s by Jefferson County Drainage District #1, also known as the Chimacum Drainage District (DD#1). DD#1 was formed in 1919 but has been inactive since 1974, leaving drainage maintenance and management work up to individual landowners.
This map shows the boundaries of DD#1. The map below shows the drainage district divided into multiple reaches for analysis purposes. You can expand the map and zoom in and out. Click on individual reaches to view various data about each.
The drainage accomplishments and the resulting agricultural achievements have come with significant environmental impacts, including water quality impairments and habitat degradation.
Once-thriving runs of coho and chum salmon were extirpated from Chimacum Creek in the 1980s but were reintroduced with stock from neighboring streams.
Today, much of the once-thriving agriculture land in the Chimacum Creek valleys is highly impaired by long periods of saturated soils and inundation.
You can view photos of the stream and landscape by clicking on the purple diamond icons.
The creek, its tributaries and drainage ditches are clogged with introduced and highly invasive reed canarygrass (RCG). RCG inhibits stream flow and sediment transport, which exacerbates flooding and hinders fish passage. It also contributes to low dissolved oxygen as it decomposes.
Trees and shrubs have been planted to shade out RCG and improve habitat. However, in many areas this has attracted beaver, which have chewed down trees and built dams, worsening flooding problems.
Beaver dam on east Chimacum Creek impounding about 3' of water.
Portions of Chimacum Creek are listed as impaired by the Washington Department of Ecology because of high bacterial contamination, high water temperatures, and low dissolved oxygen. Click on the stream reaches to see the water quality information in the data tables.
1955 Soil Conservation Service map showing watershed drainage and flooding problem areas (shaded)
Most of the valley bottom soils are organic (peats and mucks). Organic soils are notoriously challenging to manage under cultivation. In fact, farming organic soils is unsustainable without complex water management. Too much water, and the land cannot be farmed. Too much drainage, and the soil literally disappears by oxidation (aerobic decomposition), converting the carbon tied up in the organic matter to atmospheric carbon.
Time lapse aerial imagery from 1990-2023 of the area around Chimacum.
Among the various things to note on the map is how the Organic Soils and Productive Farmland map layers do not overlap very much, due largely to the chronic inundation and saturation of the organic soils.
Other interesting features are the number and length of ditches in the two valleys.
Please visit the Jefferson County Conservation District webpage https://www.jeffersoncd.org/chimacum-creek for more information and resources, including the full drainage district analysis report.
