INTRODUCTION
This report summarizes the methodology and results of an assessment of the current condition of trails, watercourses, soils, and redwood forest within Joaquin Miller Park, Oakland, California. This assessment was performed by William Lettis & Associates Inc. (WLA) of Walnut Creek, California and Natural Resources Management Corporation (NRM) of Eureka, California under contract with the City of Oakland, Office of Parks and Recreation. The purpose of the investigation was to provide baseline data on sediment sources and erosion associated with the trail network and watercourses and to determine the health of the redwood forest within the park. The investigation was focused on 11 specific areas of concern identified by the City of Oakland. An assessment of additional problem areas identified during field reconnaissance is also included. The motivation for this study arises from concerns over the perceived negative impact of increased recreational use in the park. The baseline data produced in this report will provide a framework for understanding the impacts of erosion and sedimentation on park resources and help land use planners evaluate watershed management plans.
This report summarizes the methodology and results of an assessment of the current condition of trails, watercourses, soils, and redwood forest within Joaquin Miller Park, Oakland, California. This assessment was performed by William Lettis & Associates Inc. (WLA) of Walnut Creek, California and Natural Resources Management Corporation (NRM) of Eureka, California under contract with the City of Oakland, Office of Parks and Recreation. The purpose of the investigation was to provide baseline data on sediment sources and erosion associated with the trail network and watercourses and to determine the health of the redwood forest within the park. The investigation was focused on 11 specific areas of concern identified by the City of Oakland. An assessment of additional problem areas identified during field reconnaissance is also included. The motivation for this study arises from concerns over the perceived negative impact of increased recreational use in the park. The baseline data produced in this report will provide a framework for understanding the impacts of erosion and sedimentation on park resources and help land use planners evaluate watershed management plans.
TRAIL EROSION PROCESSES
Several factors contribute to the erosion of forest trails. Fluvial erosion is a major natural process that acts on the landscape in the presence or absence of trails. It results from the concentration of surface water runoff and is often enhanced by groundwater seepage. Sheetwash, rilling, gullying, streambank erosion, and bed scour are all examples of fluvial erosion processes. When trails are constructed without adequate provision for surface and groundwater water drainage, trails become subject to fluvial erosion. Mass wasting is another natural process that can contribute to the erosion of trails. Landslides and streambank failures are examples that can be found in Joaquin Miller Park. Although natural, these processes can be exacerbated by human activities. Recreational use results in two types of human induced processes which can cause or exacerbate trail erosion. Abrasion, in which soil is physically loosened and moved downhill or to the side by feet, tires, or hooves, can move significant amounts of soil. Evidence of such movement can be seen in the form of steps, grooves, troughs, and skids on hillslopes or on trails. These features can then enhance fluvial erosion by providing pathways for concentrated water flow. On some trails the cumulative effects of trail use can lower the trail surface and create an outside berm. Outside berms prevent surface water from exiting the trail and encourage fluvial erosion by forcing surface flow downhill.Trampling is a second process
caused by recreational use. Trampling by itself does not erode the
soil; rather it destroys the vegetation and compacts the soil. Soil
compaction, in turn, makes the soil less permeable resulting in
greater runoff and subsequent fluvial erosion, and it prevents the
penetration of roots and reestablishment of vegetation.
