Keeping an Eye on Johsnson Creek

By Maggie Skenderian

Johnson Creek at "bankfull" stage last winterBES' Johnson Creek Team spent a lot of time during election week looking at data on the internet. We weren't watching the House and Senate races, but we were watching another close call.

Johnson Creek, known to flood on average every other year, rises quickly during major rain storms - which is why it's characterized as a 'flashy' stream. The creek rose and fell repeatedly during our last storm, and for a day or two, predictions looked like we were in for an event that rivaled November of 2006.

Five of the top twenty floods on record in Johnson Creek happened in November, so this time of year we start keeping an eye on the weather forecast and the creek. We pay particular attention to a stream gage that the United States Geological Survey (USGS) installed in the 1940's to monitor creek flows and water temperature. The Sycamore gage is in Johnson Creek at about SE 150th, just north of Foster Rd.

To view the data from the gage, click here.

We look at the changes in the real-time stream flow data and how it matches up with the prediction of what will happen over the following days. This is a great tool for documenting what's actually happened, but the flood predictions are only as accurate as the weather forecasts so we have to do some interpretation to decide how likely it is that it will flood.

On November 6th, we used Sycamore gage information to watch the creek levels (also called 'river stage') go from about 3.5 feet to about 8.5 feet in less than 12 hours. When the Sycamore gage shows Johnson Creek at 10 feet it is at 'Bankfull Stage'. At 11 feet it is at 'Flood Stage' and has usually gone over its banks in the Bell Station area (SE 72nd and Springwater Trail) and in Lents at about SE 110th and Foster. We also go out and make field visits so we can see what different parts of the creek look like at different high water levels.

Environmental Services is busy doing work to help minimize the negative effects of flooding. Through our Willing Seller Program, we've purchased over 160 acres of frequently flooded property that we will turn into restored floodplain areas. These restored floodplains will accommodate flood waters and provide fish and wildlife habitat, helping to improve the livability for areas of Johnson Creek that been plagued by frequent floods.

Completed projects include the Brookside Wetland and the Kelley Creek Confluence project. Restoration work will be complete in a few weeks in Tideman Johnson Park where floodplain restoration was an important component of addressing an exposed sewer pipe in Johnson Creek. These three projects add about 40 acre feet (an acre at the depth of one foot) of flood storage. Restoration work at the East Powell Butte Floodplain Restoration Project will add about another 70 acre feet when construction is complete in 2007.

Another large project will be complete by 2009 in the area south of Foster Rd., between SE 106th and SE 112th. This $3.6 million dollar project is being done with a $2.7 million dollar grant from FEMA's Pre-disaster Mitigation Program and will add about another 60 acre feet of flood storage.

Over the next 5-15 years, BES will work on acquiring another 140 acres of frequently flooded property and doing more floodplain restoration projects. Once the work is done, Johnson Creek will flood restored floodplains on a regular basis and will hit the roads and private properties only about every 10 years.

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