Based on imagery of past flooding events depicted in Hulse et al. (2002), the Willamette floodplain was not extensive in the subwatershed and was generally limited to the shoreline at the base of steep bluffs. Limited wetlands may have been found throughout the narrow bottomland next to the Willamette River. Springs and seeps flowing from the base of the bluffs likely fed the bottomland.
The Surveyor General’s Office map from 1852 indicates numerous creeks flowed east to west on the broad sloping terrace above the bluffs. Most of these creeks entered a large wetland complex located in the area currently occupied by the Brooklyn rail yards and adjacent residential areas. This extensive wetland complex (over 290 acres) extended from Powell Boulevard south 2.25 miles to Johnson Creek (Surveyor General's Office, 1852). The remnants of this wetland complex are found at the Crystal Springs Rhododendron Garden in the Johnson Creek watershed and between the rail line and McLoughlin Boulevard. The wetland complex was fed by springs and at least eight tributary streams and drained both to the north and the south. The wetlands extended into the Lents-Insley-Sellwood subwatershed and the Johnson Creek watershed.
Two other historic streams farther to the north are indicated on the Surveyor General’s Office map from 1852. Both streams flowed into the slough draining the wetland complex, one from what is now the Clinton neighborhood and the other fromwhat is now the Colonial Heights neighborhood. The Colonial Heights stream, emptied into a large marsh or wet meadow just to the south of what is now Ladd’s Addition in the Oak-Alder-Division subwatershed (Surveyor General's Office, 1852).
Any wetlands on the historic narrow Willamette riverbank have been filled for railroad development or sand and gravel extraction.
Nearly all of the creeks on the eastside have been diverted into the sewer system, and the large emergent wetland area in the southern part of the subwatershed was filled for industrial and residential development. Only two surface remnants of eastside tributary streams remain in the subwatershed. They are both very small and have been impacted by development. One, less than 50 feet long, is at SE 28th and SE Schiller by the side of the unimproved roadway east of 28th. The other is more than 50 feet long and just to the east at SE Schiller between SE 28th Place and SE 29th Street (Adolfson).
There is an intermittent drainage approximately 1,000 foot long and small 500 square foot wetland on the west slope of Mount Tabor Park, south of the exposed cinder cone (City of Portland Bureau of Planning, 1993).
Processes that have led to alterations aquatic habitat conditions primarily involve the placement of fill for residential and transportation development. Placement of fill alters floodplain function by disturbing native vegetation, modifying absorption rates, and isolating the floodplain from the channel. Placement of fill can also reduce the frequency of inundation from flooding events.