Relative to the other subwatersheds, the Miller Creek system has not substantially changed from historic conditions.
The Willamette River floodplain bottomland was relatively narrow (less than 1000 feet) but likely contained some wetlands and side channels with high connectivity to the river.
Above the bottomland, Miller Creek was free-flowing in a steep, confined channel. Historic wetlands in the upper subwatershed were likely confined to saturated soils adjacent to seasonal or intermittent streams because of the steep terrain and lack of plateaus for wetland development (City of Portland Bureau of Planning, 1995).
Except for modifications to the lower reach, Miller Creek is a free-flowing stream that supports a greater diversity of aquatic organisms than other Forest Park streams (City of Portland Bureau of Planning, 1995).
In the Willamette River floodplain, the creek has been piped and rerouted for short distances.
The culvert running under HWY 30 was removed in summer 2003. However, just downstream from this daylighted reach, the creek flows through a doubled box culvert about 100 feet long under the railroad and Marina Way that remains a fish passage impediment. Baffles were placed into the box culverts in summer 2003. The intent is that these baffles will create a serious of step pools so that the culverts to aid in passage during winter (adult) migrations. The baffles will likely continue to impede juvenile fish movement during low, summer flows. If these two box culverts were navigable year-round, and additional 1.48 miles of Miller Creek would become more readily available to anadromous fish.
Below the railroad/Marina Way, culvert, the channel flows in a grassy channel for about 900 feet to the river and is crossed by a private access road with a corrugated metal culvert. The channel below the culvert was moved during the 1990’s and it appears the floodplain was extensively modified. The lower creek mouth is still subject to Willamette River flooding.
Remaining wetland habitat in the bottomland also includes an area referred to as the Harborton Wetlands Site adjacent to the Willamette just south of the mouth of Miller Creek (City of Portland BES, 2000). This resource site contains a forested wetland still connected to the floodplain and, with the exception of one riprapped section, the Willamette River shoreline is natural with beaches throughout the length of the resource site.
Above Highway 30, the creek is perennial and spring-fed, and no natural barriers to fish migrations have been documented above this point. Perennial and intermittent tributaries enter mainstem reaches. Miller Creek remains a moderately steep gradient stream constrained by steep, narrow valley walls and hillslopes within relatively narrow valley walls that remain narrow up to the headwaters. Steps formed predominately by cobbles and boulders are present throughout. Aquatic habitat above the culverts is relatively good and has great potential to support thriving salmonid populations; large wood is present (for cover), spawning and rearing habitat is present (riffles and pools), off-channel refugia can be found in tributaries, and in-channel refugia can be found near undercut banks and beavers ponds.
Wetland habitats are most common near the confluence reaches of Miller Creek, although this area has likely been filled to a moderate extent. Wetlands in Forest Park are confined to saturated soils adjacent to seasonal or intermittent streams because of the steep terrain and lack of plateaus for wetland development (City of Portland Bureau of Planning, 1995).
This subwatershed has the most intact aquatic habitat in the Willamette Watershed Area. Because there is no development along this creek system above Highway 30, the aquatic habitat conditions of Miller Creek are likely at or near historic conditions. Below the rail line and NW Marina Way, the channel has been impacted by extensive development and reconfiguration.
A more detailed description of the current conditions as they relate to specific fish habitat parameters is provided below under the ODFW 2001 Stream Channel and Riparian Surveys heading.
ODFW 2001 Stream Channel and Riparian Surveys
The Oregon Department of Fish and Wildlife (ODFW) inventoried the aquatic habitat of Miller Creek in the fall of 2000. The creek is characterized by “reaches” or sections that differ according to channel morphology, land use, hydrology, and riparian vegetation.
Reach 1 flows from Highway 30 to the mouth and is about 330 meters long. The majority of Miller Creek flows through Forest Park. From Highway 30 to an unmarked tributary (1,870 meters or Reach 2), the channel is steep and contains a relatively high amount of silt and organics as well as cobble and gravel (ODFW, 2001). Many landslides have occurred in or near the creek. Riparian habitat, rated “excellent,” is extensive and provides high wood recruitment to the stream. Reach 3 extends 216 meters from an unmarked tributary to near the Wildwood path footbridge. The channel and riparian habitat in this reach are similar to Reach 2 (ODFW 2001). Based on 1990 surveys conducted by the City of Portland, the substrate composition of the creek is described as 35% gravel, 60% cobble, and 5% boulders (City of Portland Bureau of Planning, 1991b). Riffles and pools were observed throughout the creek (City of Portland Bureau of Planning, 1991b).
(Miller Creek Length and Habitat Summary Table)
The creek is bound by terraces and hillslopes, within relatively narrow valley walls. Valley walls remain narrow upto the headwaters; the confluence region broadens as it enters the Willamette River floodplain.
Intact floodplain interactions play a critical role in maintaining watershed functions in this system. It has likely allowed the creek to adjust to higher storm flows, and helped to maintain summer base flows via springs, seeps and hyporheic flows. Notably, floodprone width is greater than the active channel width indicating that flood flows top the creek banks and interact with the floodway. However, albeit present, floodplain interactions are nominal; the floodprone width generally does not extend beyond 1.5 times the active channel width in all three basins, hence, floodflows do not extend far into each respective floodplain.
Miller Creek has low stream gradient in the confluence, low-land area, then steadily increases moving upstream into the headwaters. Industrial development limits potential floodplain interactions in lower reaches, and notably impacts confluence regions with Multnomah Channel.
Areas with greatest potential to realize floodplain interactions:
· Road crossings impact stream connectivity. These impediments in connectivity and impacts from fragmenting the riparian corridor significantly impair potential floodplain interactions that could be realized in the future.
· Beaver ponds provide opportunities for flood storage where present.
· Areas where stream gradient is low provide additional opportunities for floodplain interactions; as do tributary junctions.
(Miller Creek Floodplain Connectivity Summary Table)
Riparian condition is relatively good in forested. Riparian width generally equals, or extends beyond 30-m, tree canopy cover is high, and well-established, large (30-50 centimeters (cm) diameter at breast height (dbh)) trees predominate. Notably, the Park area resembles historic conditions of mixed conifer deciduous forest, while confluence regions are deciduous dominated. The confluence region of Miller Creek is characterized as “narrow”, “thin” and “unstable” (ODFW, 2000). Although large trees persist throughout the riparian corridor, grasses and shrubs, rather than intermediate sized trees (and species composition), comprise the understorey of these forested areas.
As residential and urban land-use is more common (particluarly in lower Miller Creek), riparian integrity declines; corridors are more fragmented due to presence of roadways, residential dwellings encroach onto the stream bank, vegetative cover diminishes (or is more characteristic of landscaping species) and the proportion of impervious area increases.
Common tree species include big leaf maple, vine maple, willow, western hemlock, red alder, western red cedar, and douglas-fir. Hazelnut and cherry (orchard trees) were intermittently encountered in lower Miller Creek. The creek meanders through narrow valley walls, bound by terraces and hillslopes. See also the Riparian Habitat section for this subwatershed.
(Miller Creek Riparian Conditions Summary Table)
A railroad and street crossing impairs stream connectivity in the lower reach. Refer to Table # regarding key culverts impacting fish passage No natural barriers to fish migrations have been documented, however the upstream extent of fish distribution can be evaluated based on channel and habitat characteristics
Dry channel beds in middle (11% wetted area) and upper (34% wetted area) Miller Creek intermittently impair fish passage. The hydrologic conditions at which these dry channel areas are inundated, or the severity and duration of dry channel is has not been characterized.
Steps formed predominately by cobbles and boulders are present to a lesser degree throughout, ranging from two to six reach-wide. However, a proportionally higher number of steps were documented in the middle reach. These natural forms are discrete breaks in the channel bottom, and vary in height (from 0.25-m to 1.4-m). They may temporarily impede juvenile fish migrations during low, summer flows. Although the severity and duration of impairment is not presently known, steps are common habitat forms in most stream-type systems; hence aquatic biota have evolved knowing when to opportunistically navigate these structures.
(Miller Creek Connectivity Summary Table)
The confluence of Miller Creek and Multnomah channel has the potential to provide important off-channel habitat to Willamette Basin salmonids, year-round. This area was historically utilized by chinook, coho, steelhead and cutthroat trout, and presently is used by chinook, coho and steelhead, during different parts of the year.
Off-channel refugia is primarily associated with perennial and intermittent tributaries. One perennial tributary and one intermittent tributary enters Miller Creek. These tributaries likely provide important off-channel habitat to instream species during high storm flows, and may provide important cool water habitat in the summer. In addition, secondary channels, such as those found in reach 2 likely provide important off-channel refugia to fish during high storm flows.
In-stream structure and cover is generally lacking. Areas that contain some forms or features that presently provide off-channel and/or instream refugia include:
§ Beaver ponds and associated wood clusters provide important inchannel structure and refugia throughout all Miller Creek (Reach 1 – Reach 3).
§ Seeps and springs provide important hyporheic flows. Refer to ODFW 2000 report for noted areas.
§ Undercut banks and wood provide important in-channel cover basin-wide, where present.
Channel Conditions and Habitat Structure
Industrial and residential structures and uses (homes, buildings, roadways, lawns) have resulted in hardened banks in lower Miller creek. Stream banks are actively eroding and unstable, with 72% in the upper watershed (Reach 3), 56% mid-reach (Reach 2) and 47% in the confluence region (Reach 1). Notably, the lower region of Miller creek likely exihibits the least erosion; higher flows coming down from the Forest Park are attenuated and energy dissipates as it enters these low-land area.
Beaver activity is common east of HWY 30 in lower Miller, and in the middle and upper portion of the middle reach.
Riffle (45%) and pools (29%) are predominate habitat forms in lower Miller Creek. Cascades (57%) and riffles (14%) predominate in middle Miller. Notably, cascades comprise 64% of the wetted area in the upper reach, and dry channel comprises the remaining 34%.
Habitat quality suffers from limited stream complexity in all three basins. Large woody debris, pool quantity and quality and riffle quality are discussed in more detail below.
(Miller Creek Length and Habitat Summary Table)
(Miller Creek Pool Area Summary Table)
(Miller Creek Riffle Summary Table)
Pool Area and Quality
Pool area is best in lower and middle reaches of Miller Creek and is low to non-existant in the upper stream reaches of both systems. Plunge pools are the common pool type in upper Miller Creek (Miller 2), indicating instream structures or forms embedded in the stream bottom or lying within the active channel.
The proportion of fine sediment amassed in pools is relatively high (20%-50%), indicating that sediment recruitment, deposition, and transport is out of balance in these basins. Sediments were highest in the confluence reach (59%).
Pools are marginally deep (0.2-1.0 m). Relative to prevailing channel depth, depth refugia is best in the middle reach. If accessible these areas would provide (or presently provide) important protective cover to fish, and areas of slacker water during higher flows (near deep, scoured areas).
Most complex pools (with wood complexity greater than 3.0-km) are found in middle Miller Creek. Like wood complexity, most boulder cover is found in middle reaches of Miller Creek.
(Miller Creek Pool Area Summary Table)
Based on limited pool-type habitat, fish likely do not (or would not) rear year-round, particularly in the summer months, in upper Miller Creek. Lack of substantive pool area limits the upstream extent of fish distribution. However, during higher flows, habitats change, and these areas may indeed provide important pool habitat during fall, winter and spring. Existing pools are notably deeper than prevailing channel depth (75%), and would provide important protective cover, particularly during higher storm flows. Except for upper headwaters reaches, basin would provide good pool habitat (in terms of area and quality) throughout the remainder of the subbasin, if accessible.
Pool quality is best (in terms of deep pools and complex pools with wood and boulder cover) throughout the middle reach, however, pool area is relatively low; hence it is important to retain existing pool environs. Pool area is moderately high (29%) and pools are relatively deep (43% relative pool depth) in lower Miller Creek, however pools contain very little wood or boulder cover, and do not likely provide important channel complexity.
Riffle Area and Quality
Riffle area is high in lower Miller Creek (45%), then decreases dramatically in the middle reach (14%) and does not exist in the upper reach (0%). Riffle gravels are marginally present in lower and middle Miller Creek, comprising 27% and 25% substrate composition. Percent fines is lowest in the middle reach (16%), and likely provides the best quality spawning and rearing ground potential in this system. However, the abundance of riffle area in the lower reach provides great opportunities for habitat enhancement. In the upper reach, primary spawning habitat (if any) is found intermittently in cascades. Gravel composition varies, but generally averages 11%-22% in cascade reaches.
(Miller Creek Riffle Summary Table)
Spawning and Rearing Habitat
This creek provides great spawning and rearing habitat.
Lower Miller Creek exhibited significant proportion of fines with 25%. All other reaches had marginally low to excellent proportions of sediments overlying riffle habitats, yielding relatively good to excellent spawning and rearing habitat where riffle habitat exists.
Sources of sediment loading are not presently understood, since the basin originates, and are relatively enclosed within protected areas Forest Park, except for their respective confluence areas. Lower Miller Creek in particular appears to function as a depositional zone for sediments delivered from upstream. Both riffle and pool environs had excessive silt loads.
Source and control of sediment loads should be critically evaluated for present loads and conditions to what would have been expected under historical (normative) conditions.
Large Woody Debris
Middle and upper reaches of Miller Creek, had marginal numbers of wood pieces for fish bearing streams (> 10 but < 20 pieces per 100-m stream length). Notably, Miller Creek had most wood pieces with 18.5 per 100-m stream length. Notably, although not optimal, Miller creek contains enough wood to provide a marginal level of protective cover; however, wood volume is low with less than 20.0-m3 per 100-m stream length, and no key pieces (> 60 cm diameter and > 10 m long) were documented in either of the three basins. However, wood clusters greater than 3-km (complex pools) are found in pools in the middle reach.
Wood is abundant, but volume is low and key pieces are rare, indicating that wood is falling into the system, but is not being retained. Note, riparian trees are large, hence should be providing large pieces into the system. The implications of this are not certain, but one could speculate that small to medium sized pieces are falling into the creek and forming clusters, but large boles and snags are not. Prolonged or acute peak flows and inadvertent (or planned) maintenance removal of large wood throughout lower Miller creek may have resulted in low large wood abundance and volume basin-wide. Additionally, the combination of high flows, incised channels and lack of in-channel complexity, may limit the amount of wood that is retained in-channel.
(Miller Creek Woody Debris Summary Table)