An Urban Watershed - Fanno Creek
In an urban setting we don’t always see and can’t really imagine the way things looked to the early settlers. Forests change or disappear. Creeks like Tanner Creek of Portland almost totally disappear. Fanno Creek was named after an early settler and has also changed. Just not as much as Tanner Creek which now runs from 7 feet to 50 feet underground until it enters the Willamette River.
Where Tanner Creek runs mainly north Fanno Creek is a 15.1 mile south running tributary of the Tualatin River, which is a tributary of the Columbia River. The Fanno Creek watershed covers about 34 square miles and includes several smaller streams and creeks as its tributaries.
The main stem of Fanno Creek begins in the Hillsdale neighborhood of south west Portland (at 478 feet above sea level) and flows west along the north side of Oregon Route 10 in Multnomah County. Shortly after reaching the stream gauge at S.W. 56th (11.9 miles from its mouth) it enters Washington County at the Raleigh Hills neighborhood. From there it crosses Highway 10 and passes through Bauman Park, the Portland Golf Course, vista Brook Park and Fanno Creek Trail Park as it begins to turn south. Then it turns sharply south to go under Hwy 217 - a high traffic connector between Hwy 26 and I 5. At that point Fanno Creek parallels Hwy 217 for about 2 miles through Fanno Creek Park and Greenway Park before passing under Scholls Ferry Road and entering Tigard where it passes under Hwy 99W. On it rolls through Fanno Park and Bonita Park as well as even more residential neighborhoods before finally entering Durham and flowing through Durham City Park to complete the 15.1 mile run from Portland’s West Hills to the Tualatin River ( at 108 feet above sea level).
While it passes through 14 parks, nearly all the watershed is urban. The stream at the headwaters emerges mainly from Columbia River basalt and flows over up to 25 feet of wind deposited silt. Significant erosion along the course is common. Because of the high percentage of surrounding impervious surfaces (streets, parking lots, roofs, and sidewalks) it is difficult to improve water quality which is currently rated as ‘poor’. That is an improvement from its earlier rating as ‘very poor’. Despite the difficulties presented by all the hard surfaces both governmental and private local groups are continuing to work to slow run off from the hard surfaces, reduce erosion and to keep pollutants out of the water.
In 2010, the U.S. Geological Survey (USGS) began investigating the sources and sinks of organic matter in Fanno Creek. Organic matter, more specifically organic carbon, is abundant in Fanno Creek and has been tied to a variety of water-quality concerns. Since organic carbon is commonly found in the fine-grained, organic-rich sediment covering much of the watershed, developing a better understanding of sediment transport dynamics should greatly improve the quality of restoration efforts underway. To address this, a geomorphic approach was adopted, including mapping fine sediment erosion and deposition and measuring changes in sediment. Erosion and deposition mapping within the geomorphic floodplain in the summer of 2012 was used to identify specific sources and sinks of fine sediment and other features that might potentially contribute to the sediment cycle. The distribution of mapped features along Fanno Creek varies by reach. Areas having a high potential for erosion were greatest in the uppermost basin although other middle and lower basin reaches had relatively large areas subject to erosion. Areal deposition is largest in wide, low gradient wetland reaches such as in the middle basin. . In-stream habitat suffers from lack of structure (e.g., wood, boulders) and high proportions of sand and silt substrate, contributed by eroding stream banks due partly to increased stormwater runoff from upland development.
The average stream flow as measured at the Durham Station is 43.9 feet per second (fps). The maximum flow was measured at 1,670 fps on Dec. 3, 2007. The minimum flow was measured at 1 fps on Sept. 13, 2001 and Sept. 15, 2009.
Fanno Creek is an important part of the urban environment with all the parks and trails. There are chances for everyone to get out to enjoy a walk, run or ride in a stream environment while still in the middle of all the development going on around it.
Questions: 1.What is the elevation at the coordinates?
2.What is the elevation drop from the headwaters to the coordinates and what is the elevation drop from the coordinates to the mouth of Fanno Creek at the Tualatin River?
3.What does this tell you about the possibilities of flooding along this part of its course and why would it be a problem or not?
4.What two signs of erosion can be seen along the creek and name something that can be done to prevent further erosion?