Chapter 2.0    Watershed Assessment

	2.1	Introduction
	2.2	Watershed Description
		2.2.1	General Location and Size
	2.3	Jurisdictions and Sub-watersheds
	2.4	Landscape Factors
		2.4.1	Topography
		2.4.2	Soils

2.1      Introduction

Johnson Creek Watershed Council (JCWC) Watershed Assessment compiles, synthesizes, and summarizes the most relevant information on existing conditions within the Johnson Creek Watershed. Subsequently, the assessment is used to meet the main goals of the Action Plan; namely to identify, prioritize, and sequence specific projects and actions necessary to address factors limiting watershed health. The overall goal is to protect, restore, and enhance the health and function of the Johnson Creek watershed. To accomplish this goal, the action plan must also:

1. Raise awareness of the issues and constraints facing the watershed and the JCWC.
2. Identify key problems that are most detrimental to watershed health.
3. Identify key opportunities that are most important to protecting watershed health.
4. Build support for its implementation through public input, ensuring the plan is accessible and useful to the multiple local jurisdictions and stakeholders who will be involved in its implementation.
5. Provide the JCWC with priorities to focus efforts and provide direction for partnering and plan implementation.
6. Serve as a marketing tool to obtain future grants and implementation funding.

This watershed assessment highlights and summarizes the most important and up-to-date information available for this basin. More detailed information on various elements and functions of the Johnson Creek Watershed can be obtained in the following key studies or reports: Johnson Creek Resources Management Plan (Johnson Creek Corridor Committee, 1995); Salmon Restoration in an Urban Watershed: Johnson Creek, Oregon (Meross, 2000); Aquatic Inventory Project Physical Habitat Surveys (ODFW, 2000); the Johnson Creek Master Plan (City of Gresham, 2003); and the Johnson Creek Restoration Plan (Portland Bureau of Environmental Services (BES), 2001).

The JCWC Watershed Assessment summary is an introductory chapter in the Action Plan and identifies the key problems or factors limiting watershed health. The watershed assessment also initiates discussion about sources of these problems and conditions and suggest opportunities that could lead to actions for protecting, restoring, and enhancing watershed functions. 

It is important to note that while there is a focus and attention placed on fish and restoring conditions for their recovery and sustainability, they were selected as an indicator species for this watershed assessment. Improving conditions for both resident and anadromous fish species will improve overall watershed health, including water quality for human contact and conditions for other fish and wildlife species. In addition, flooding and factors that are contributing to flood conditions in the watershed are extremely important. Flooding elements are being addressed in the Action Plan and through recommended projects that pertain to watershed functions. Restoring watershed functions will aid in reducing the frequency and magnitude of floods.

As an introduction to the Watershed Action Plan, this assessment provides a general description of the watershed, highlights the human and built environmental conditions, and summarizes the current conditions and four main attributes for watershed and river health. These attributes are: 1) stream flow and hydrology; 2) physical habitats; 3) water quality; and 4) biological communities. The watershed assessment concludes with a summary of the problems and opportunities, highlights the key functions and processes, outlines the major limiting factors, and focuses on specific reaches and sections of Johnson Creek which would most benefit from protection and restoration actions.

2.2       Watershed Description

2.2.1       General Location and Size

Located on the east side of the greater Portland Metropolitan region, Johnson Creek originates in Clackamas County, east of Boring, Oregon, and flows westerly approximately 25 miles to its confluence with the Willamette River. The Johnson Creek drainage basin encompasses approximately 34,000 acres or about 54 square miles. 

2.3       Jurisdictions and Sub-watersheds

The mostly urban watershed is contained within six local jurisdictional entities including Clackamas and Multnomah Counties, and the cities of Gresham, Happy Valley, Milwaukie, and Portland. Portland, Clackamas County (outside of Milwaukie and Happy Valley), and Gresham have the greatest portion of the watershed at 38 percent, 24 percent, and 23 percent respectively. The remainder of Multnomah County (outside of Portland and Gresham), Milwaukie, and Happy Valley has the least land acreage as a percentage respectively and are highlighted below (City of Portland BES, 2000). The general watershed location and jurisdictional boundaries are included in Figure 1 (PDF, 249 KB).

The characterization of the Johnson Creek watershed is based on sub-watersheds and reach areas.  A recent City of Portland assessment of the watershed divided the basin into reaches defined as the main stem Johnson Creek (lower, middle, and upper); and the following major tributaries: Crystal Springs Creek; Kelley Creek; Butler Creek, Hogan Creek; Sunshine Creek, and Badger Creek (City of Portland ESA, 2002). Crystal Springs Creek and Kelley Creek are the largest tributaries in terms of flow contribution. In addition, Minthorn or Spring Creek discharges into Johnson Creek within the city of Milwaukie. Most of the tributaries are located south of Johnson Creek. Crystal Springs Creek is largely groundwater-fed and originates from springs on the north side of Johnson Creek.

2.4       Landscape Factors

2.4.1       Topography

Elevations in the watershed generally range between 0 to 1,100 feet above mean sea level (msl). Slopes are highly variable and range generally between 1 to 25 percent. Mt. Scott and Powell Butte, which rise to approximately 1,000 feet, and have relatively, moderate to steep slopes ranging from 10 to 30 percent. Gresham and Hogan Buttes have the highest slopes, with a few approaching or exceeding 50 percent. 

The highest point in the watershed is in the Boring Hills at approximately 1,100 feet above msl.  The Boring Hills are of volcanic and erosional origin. Several of the hills reach an elevation of more than 1,080 ft. This is more than 800 feet higher than the terraces to the north and west. The Boring Hills are divided into three main sections by their characteristically broad and gently rolling hills (Laenen, 1980). 

The Kelso slope is a dissected northwestward-sloping surface west of the canyon of the Sandy River. It slopes from an altitude of approximately 1,000 feet near Sandy to around 400 feet east of Gresham. The ancestral Columbia and Willamette Rivers formed the east-side terraces. The terraces do not have a well-developed stream system in all areas and are underlain mostly by permeable sand and gravel. Although the precipitation is abundant, most of it percolates down to groundwater and leaves these areas by underflow (Laenen, 1980). Three isolated hills – Rocky Butte, Mount Taber, and Kelly Butte – rise about 200 to 400 feet above the surrounding terraces (Laenen, 1980). With the exception of the Powell Butte area, the terrain on the north side of Johnson Creek is less steep than the south side of the creek, which includes both Mt. Scott and the Boring Lava Domes. 

2.4.2       Soils

Soils in the watershed are primarily either Multnomah and Latourell-Urban Land Complex (Type B hydrologic group) or Cascade Silt Loam (Type C hydrologic group). Type B soils are predominant (71 percent), followed by type C soils (21 percent).  The Urban Land Complex classification refers to areas largely covered by impervious surfaces; these soils have been graded, cut and filled, or otherwise disturbed to the extent that their soil identification is not feasible.  Soil erodibility varies throughout the watershed. The northwest part of the watershed mainly within Portland is characterized by Latourell soils, which have a medium-high risk of erosion. Maximum erosion for this type of soil is approximately 5 tons per year per acre. The potential for erosion is not a large threat however, due to the area being relatively flat and developed. Multnomah soils, which have a low-medium erosion factor, dominate in the northeast portion of the watershed. The southeast portion of the watershed is dominated by Cascade soils, which have a medium risk of erosion.  Soils surrounding the Powell Butte and the Boring Lava Domes have an extremely high erodibility factor and are sensitive to ground disturbance.

The soils within the watershed also have varying ranges of permeability and water retaining capacity.  In areas where soils are relatively undisturbed, permeability is moderate, and available water capacity is 4 to 12 inches per hour. The areas south of the creek and at the eastern end of the watershed consist mostly of clay soils that tend to have a high runoff potential and are incapable or are only minimally capable of absorbing water through infiltration. Northern areas of the watershed are generally porous, with moderate to high permeability, and are suitable for infiltration type facilities.

In summary, the Johnson Creek watershed is a relatively large and diverse watershed. A mix of land use is present varying from large areas of urbanization and associated impervious surfaces to areas of undeveloped land and rural uses and activities. The mostly urban watershed is contained within six local jurisdictions. Elevations are highly variable and stream systems are either well defined or are not well developed in all areas depending in part on ancestral river formed terrace locations. Soil erodibility varies as does permeability and water retaining capacity.