Greetings!
When land becomes urbanized, impervious surface and storm water drain lines are added. The loss of groundwater recharge results in less dry season flow in urban streams. An increase in the frequency and volume of runoff, can damage the physical structure of stream channels and alter wetlands. Storm events that were once absorbed by the landscape become "flashy" flows, rapidly rising and falling surface waters that correlate with passing storms.
During a storm, the flow in an urban stream can   increase over
one hundred-fold in a matter of hours. (Click to see hydrograph).
A storm can quickly change urban streams from a trickle to a gushing
torrent. Runoff from storm events carry the pollutants of urban life:
oil from cars, metals from brake linings, pesticides from lawns, moss
killers from roofs, pet feces, garbage and a host of other pollutants.
With
so little stormwater infiltrating into the ground, our streams suffer
in the dry season. Historically, the groundwater system would feed
streams with cooling flows in the summer. With groundwater in short supply,
urban streams are reduced to a trickle and heat up. Low flows and high
temperatures are compounded by low oxygen levels. The streams that once supported young steelhead and cutthroat trout in the summer can no
longer support these fish.
 Research by the University of Washington and others documents the negative impacts on streams and aquatic life when impervious cover reaches 4% - 15%. Clean Water Services estimated back in 2001 that 28% of the Tualatin River Watershed within the urban growth boundary was covered by impervious surfaces such as roads, parking lots and roof tops.
Low Impact Development can reduce the amount of impervious surface in an urban area, but Low Impact Development techniques are not currently required in the Tualatin basin. Thus, new development means more impervious area, more runoff, and more negative impacts to our neighborhood streams.
Currently Washington County is considering designating 35,000 more acres as "Urban Reserves", available for urban development over the next 40-50 years. The negative impact of such a large amount of urbanized landscape and the impervious area that goes with it on our streams is undeniable.
DEQ is also renegotiating the Municipal Separate Storm Sewer (MS4) permits that regulate how stormwater is managed in our cities. These permits currently allow unlimited growth in impervious area.
A Call To Action
There are a number of actions that you can take to protect the future of the Tualatin River.
Learn more about what areas are being proposed as Urban Reserves.
Contact the "Core 4" Reserves Steering Committee and urge them to hold the line on urban expansion in the Tualatin Basin. Tell them how urbanization damages our streams and the Tualatin River.
Contact the Washington County Commissioners and ask them to reduce the amount of Urban Reserves, particularly on sloped areas like Cooper Mountain, where stormwater runoff is especially problematic. Tell them in your own words areas that are particularly important for protection from urban development, like Dairy Creek and the Tualatin River National Wildlife Refuge.
Write to DEQ and tell them to require the reduction impervious area in the next Municipal Separate Storm Sewer permit. Urge them to hold the line of the further degadation of the Tualatin River and its tributaries.
Send a copy of your communications to brian@tualatinriverkeepers.org.
Sign up for our Citizen Action Alerts to learn of more opportunities to help protect the Tualatin River and our neighborhood streams.
Brian Wegener
Watershed Watch Coordinator
Tualatin Riverkeepers
ps - Your financial support helps us protect the Tualatin River and our neighborhood streams. Donate now.
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