Kincaid Ravine Hydrology Restoration Options and Recommendations
Aaron D. Clark Ph.D. (Stewardship Partners/ 12,000 Rain Gardens Campaign)
Daniel J. Hintz (University of Washington)
Matthew B. Schwartz (University of Washington/ EarthCorps)
Kristine A. Kenney ASLA, LEED®AP (University of Washington)
University of Washington Grounds Management
University of Washington Transportation Services
University of Washington Restoration Ecology Network
University of Washington Campus Sustainability Fund (CSF)
Site History/ Story
Restoration efforts have been ongoing in Kincaid Ravine since the winter of 2013/14. The roughly 4 acre ravine was overgrown with invasive species and littered with trash when Martha Moritz (MEH ’14) began to plan restoration work to transform the ravine into an asset for the university and its community. In the two years since work began, myriad partnerships have developed around Kincaid Ravine that have led to high quality restoration work and continued plans to restore and enhance the campus connection with Kincaid Ravine for years to come. The student project management is now under the guidance of its third master’s student and stakeholders include the Society for Ecological Restoration – UW Chapter, Campus Sustainability Fund, Office of the University Architect, UW Grounds, UW Transportation Services, UW Restoration Ecology Network, EarthCorps and Stewardship Partners. The wide array of project partners and the time, money and energy already committed to restoration of Kincaid Ravine clearly demonstrate that this is not a project destined to fizzle out, but one that can and will be sustained. While there is much work still to be accomplished, Kincaid Ravine is well on its way to becoming a healthy urban forest oasis that not only provides ecological functions, but also opportunities for education, research and connection to nature for those in and around the UW community.
The existing topography and hydrology of the Kincaid Ravine include a small stream that is fed by 2-3 small springs or seeps. At the lower end of the ravine the creek area spreads into a flatter area and creates a 2,087 square foot category III wetland (delineated “Wetland 2” in Raedeke Associates, Inc report March 2014—see attachment B). The stream exits the ravine via infiltration along an existing ditch that becomes a 2,980 square foot category III wetland flowing north along the west side of the Burke Gilman (B-G) Trail under the 45th Street viaduct (delineated “Wetland 1” in Raedeke Associates, Inc report March 2014—see attachment B). Where this the stream turns north and enters the northbound ditch, it is filled with fine sediments allowing water to overtop the B-G Trail and also to flow south into a previously dry ditch and infiltrating into the native soils. Flooding of the B-G trail commonly inundates half of the trail’s width at the location where the stream reaches the trail. Between March 3 and June 11, stream flow was relatively consistent in volume based on visual observation in spite of significant variations in precipitation (including at least one >1 inch/day storm on 3/16/15), temperature and humidity. Visually estimated surface water flow rates are in the range of 1-3 gallons per minute. Water chemistry was tested from a sample collected 4/21/15 (no rain that day or for 6 days previous) showing non-detectable levels of oil. The tests showed relatively low levels of copper (19.7 ug/L or 1.3% of allowable drinking water levels) and high levels of lead (91.6 ug/L, 6.1 times the allowable level for drinking water).
Within the ravine, along the stream course uphill of the B-G Trail, there are areas of erosion and stream incising that could be mitigated with check dams and/or course woody debris (CWD) to slow flows and decrease erosive force and further reduce sediment loads in the stream. Introducing CWD into the stream course was identified as a potential strategy to reduce erosion, increase infiltration, increase potential wetland habitat, and reduce downstream sedimentation and thereby reduce trail flooding and related ditch maintenance. In areas of steeper stream gradients CWD can be used to create pools and pour-overs, while in flatter sections of the stream CWD can encourage broader dispersion and better infiltration and retention times, potentially leading to increases in future wetland area and habitat. A check dam designed with a V-notch weir could serve a double function in a higher gradient section of the stream by slowing flows and providing additional benefits of research, monitoring, and educational opportunities for multiple disciplines within the university to utilize as an outdoor classroom and laboratory (see attachment C for approximate placement of each enhancement).
The trailside ditch that the stream began to overflow into in 2015 (south of the delineated wetland ditch) and a parallel ditch approximately 12 feet further west and slightly uphill appear to have the potential to infiltrate significant volumes of surface water and were assessed for bioretention capacity (see attachment H for bioretention concept design). Both ditches are approximately 100 ft in length (see attachment E). Infiltration tests were conducted at two locations in each ditch yielding variable but generally high infiltration rates (2.89-6 inches per hour under simulated saturation conditions achieved by successive infiltration tests). Input from University Landscape Architect, Kristine Kenney, as well as observational data shared from EarthCorps staff detailing the results of a previous redirecting of the stream into one of these ditches prevented this team from pursuing that option further. Ms. Kenney informed our team that the University would prefer to see the trailside ditch filled in to improve safety for pedestrians and cyclists on the trail. EarthCorps staff recounted that directing the stream into this ditch in the previous year (approximately March 2014) had led to poor infiltration and eventual overflow of the ditch and flooding of the trail. The cause of the poor infiltration was unknown but may have been due to fine sediments washing down from areas of the ravine where erosion has been observed and leading to reduced pore space and infiltration rates within the ditch.
The primary path for the stream as it exits the ravine is a trailside ditch that runs parallel to the B-G trail running northbound. The ditch extends over 1,000 feet before the bottom of the ditch approaches the same elevation of the B-G trail itself (see attachments B and D). This northbound ditch has not been observed to overflow at any point except the point where the stream turns and initially enters the ditch in over 1,000 direct observations by Aaron Clark as a cyclist on the B-G trail between 2003 and 2015. The northbound ditch has not been tested for infiltration, however it has no known manmade drain within its length, therefore implying that infiltration is generally sufficient to handle the full volume of the stream flow.
Improvement of Hydrology in Kincaid Ravine Toward a Reference State Approximating a Natural Woodland Ravine and Wetlands
In line with ongoing restoration efforts for the Kincaid Ravine by multiple stakeholders, the primary identified goal for hydrological restoration of the ravine is to approximate a reference state of an undisturbed natural woodland ravine and wetland system. Such a reference state is typified by abundant coarse woody debris, a forest canopy of heterogeneous structure that includes deciduous and evergreen species (e.g. big leaf maple, western red cedar) in areas more frequently inundated, as well as evergreen species (e.g. Douglas Fir, Western Hemlock) in adjacent, less saturated soils. The understory reference state would include wetland species as well as other typical Western Washington forest understory species (e.g. indian plum, red flowering currant, salmon berry, pacific willow, Oregon grape, salal, sword fern, red-osier dogwood, skunk cabbage, and a diversity of emergent vegetation including common rush, slough sedge etc.). Animal diversity of the target reference state would include avian, amphibian, mammal, and aquatic and terrestrial invertebrate species inhabiting, migrating through and reproducing within the ravine. Native amphibian species that could utilize Kincaid Ravine include: Pseudacrys regilla (Pacific chorus frog), Rana aurora (red legged frog), Ensatina escholtzii (ensatina salamander), Plethodon vehiculum (Western redback salamander), Ambystoma macrodactylum (long-toed salamander), and Ambystoma gracilie (Northwest salamander). A few avian species that would be indicative of the reference state include: Melospiza melodia (song sparrow), Calypte anna (Anna’s hummingbird), Selasphorus rufus (Rufous hummingbird), Pipilo maculatus (Spotted towhee), Sitta canadensis (Red-breasted nuthatch), Colaptes auratus (Northern flicker), Hylatomus pileatus (Pileated woodpecker), Picoides villosus (Hairy woodpecker), Picoides pubescens (Downy woodpecker), Contopus sordidulus (Western Wood-Pewee), Poecile atricapilla (Black-capped chickadee), Poecile rufescens (Chestnut-backed chickadee), Troglodytes troglodytes (Winter Wren), Cistothorus palustris (Marsh Wren), Regulus satrapa and calendula (Golden and Ruby-crowned kinglets respectively), and Caltharus ustulatus and guttatus (Swainson’s and Hermit thrush respectively).
Wetland Habitat Restoration and Expansion
Wetland habitats in Kincaid Ravine are degraded but retain many of the biophysical traits of the reference state of an undisturbed wetland. Invasive species including Himalayan Blackberry, reed canary grass and bindweed are abundant and likely to recolonize with high frequency throughout the foreseeable future without regular maintenance work. With vigilant restoration effort and ongoing stewardship and maintenance, however, the goal of creating and maintaining an approximate representation of the reference state is achievable and considered to be particularly worthwhile given the surrounding matrix of a developed and urbanized landscape where wetland and natural woodland habitats are exceedingly rare. Existing wetland habitat occupies primarily small areas within a few feet of the primary stream. In addition to restoring the existing wetland habitat to the reference state, the relative expansion of wetland areas for both habitat and hydrological purposes (i.e. reduced flashiness of the stream system) is desirable. It is recommended that wetland expansion be achieved using CWD to slow and spread the flow of the stream in the flattest/ lowest gradient sections of the ravine (see attachment C).
As the largest intact natural area on the central portion of the main University campus, Kincaid Ravine represents a unique opportunity to connect the University community with nature. With a year-round stream and mature vegetation and forest/woodland canopy as well as wetland habitats and a major pedestrian and cyclist thoroughfare adjacent to it, the amenity and education value both have untapped potential. The placemaking goal as defined by our team is to create a space where the natural systems of the ravine can be viewed and appreciated, where opportunities to learn about the history of the ravine, the restoration and stewardship processes, and the ecosystem service values provided by this and other natural areas and wetlands are inviting and accessible. Educational signage has recently been installed near the B-G trail within the ravine as well as two benches. Improving access by filling in the southbound ditch, a portion of it or creating a small bridge/boardwalk across the ditch would significantly increase utilization of the bench and observation area.
Human Use Alignment with University and SDOT (B-G Trail) Visions
Some of the current human use activities in the Kincaid Ravine are harmful to the community, environment and the placemaking goals and a design that strategically reduces such uses is an additional goal for this project. Expansion of wetland habitat that makes social trails less inviting or even unpassable is a strategy that achieves multiple goals. Likewise, increased CWD in the ravine also can discourage foot traffic as long as long logs are kept to a minimum or retain enough branches as to not be walkable features themselves. Accessibility to the ravine’s “viewshed” by way of a short walking path at the location where two current educational signs have been placed may also provide benefits of greater public visibility. Public visibility in turn is a further deterrent for any undesired or illegal activity. A small foot bridge that invites foot traffic to the intended trail and viewshed would significantly enhance access and visibility of the overall ravine and educational and research goals.
Reduction/ Elimination of Burke Gilman Trail flooding
A primary human use goal for the Kincaid Ravine is reduced flooding of the B-G trail where the stream reaches the trail and turns (as of November 2015 the stream currently diverts both North and South into the trailside ditches described above). Flooding of the trail at this location appears to be due to a gradual increase in the grade of the soils in the stream system, presumably due to a gradual process of sediment build up. Flooding is exacerbated by heavy rain events. The goal of simultaneously reducing current flooding as well as reducing the rate of sediment deposition and avoiding future flooding or delaying required re-ditching are both of high priority. The previously described addition of CWD and increased wetland area are the primary recommendations that can be combined with excavation of the area where the stream turns at the B-G trail to enter the northbound ditch.
Opportunities and Options Summary
- Swale Directions North vs. South
- North is better for infiltration capacity. Opportunity to improve wetland quality of that wetland ditch (plantings, invasive removal. Probably no opportunity to expand area of this wetland ditch). North ditch has a length of approximately 650 feet vs. South ditch which is approximately 140 feet in length (see Attachment D). The substantially longer length of the North ditch provides greater opportunity for infiltration and evapotranspiration.
- Wetland area expansion below power line corridor. (See attachment C)
- Invasive removal
- Check dams and CWD further uphill from powerlines: increase wetland habitat, storage capacity, reduced flashiness, micro floodplain expansion, reverse trend of erosion and scouring. Opportunity to include a weir to measure flows rates/volumes for student research and education and demonstration of how forests and wetlands moderate stormwater flows relative to impervious urban surface flows (See attachments C and I).
- Educational signage, view point development, trail/ boardwalk/ bridge.
- Sightlines for reduced attraction of illegal activities as well as aesthetic appreciation. If path and viewpoint are essentially surrounded by wetland and foot traffic would have to get wet to travel deeper into the ravine that makes a great disincentive. A wider wetland around the stream all the way to the trail and Northbound ditch could reduce foot traffic and development of social trails.
Appendix A: SER Restoration Site Map
Appendix D: Northbound Ditch
Appendix E: Southbound Ditch
Appendix I: Notch Weir Design