Engineering Geology

Representative Engineering Geology Projects

O’Connor Environmental, Inc.

Geomorphology ▪ Hydrology ▪ Engineering Geology

P.O. Box 794, Healdsburg, CA 95448 (707) 431-2810

Landslide Hazard Evaluation and Hydrological Analysis, Cavedale Road, Napa County

An evaluation of potential change in landslide hazard associated with a proposed vineyard, and an assessment of potential cumulative runoff change was performed for County review. An estimate of the magnitude increase in runoff was developed and used to assess the impact of increased runoff.

Hydrological Assessment and Sediment Budget, Annapolis, Sonoma County

A hydrological assessment was performed to determine the impact of a THP and conversion to vineyard on erosion and sedimentation processes. A sediment budget was constructed from site scale field measurements, available landslide inventory data, and applicable sediment TMDL’s to place vineyard erosion in context with watershed erosion.

Effectiveness Monitoring of Forest Practice Regulations, Washington

Surveyed over 1400 landslides in southwest Washington to determine the effectiveness of the state’s forest practice regulations with respect to slope stability. Directed field crews visiting 22 randomly selected four square mile clusters (over 56,000 acres) and mapped and collected site data on all landslides present. By analyzing storm-related landsliding in areas that contained a variety of management treatments, the study compared the effectiveness between various treatment categories. Aerial photo interpretation, geodatabase design and maintenance, creation of detailed field maps and data forms for use with Trimble Nomad GPS units.

Landslide Investigation and Erosion Control Plan

A landslide investigation was prepared as a component of long term erosion control plan for a large forest and ranch property near Booneville, California to address regulatory requirements of the NCRWQCB. The report was based on field observations, aerial photo interpretation, and review of available geologic maps, including unpublished maps produced by California Geological Survey (CGS) staff related to THP Pre-Harvest Inspections (PHI’s). OEI represented the property owner at hearings of the NCRWQCB.

Erosion investigation, Mayacamas Mountains, Geyserville, Sonoma County, California

An erosion investigation was performed on ranch property disturbed by grading and storm runoff. Volumes of sediment that eroded and delivered to stream channels was quantified, as required by the North Coast Regional Water Quality Control Board (RWQCB) and CDFG.

Vineyard Erosion Assessment, Santa Rosa Creek, Sonoma County

Assisted landowner in resolving erosion enforcement action by Regional Water Quality Control Board. Utilized sediment budget and erosion source analysis to place vineyard erosion in perspective of total watershed erosion.

Erosion and Landslide Assessment, Santa Rosa Creek, Sonoma County

Assessed past erosion and future erosion hazards related to existing landslides and gullies on the subject ranch in the headwaters of Santa Rosa Creek watershed.

Ranch Road Erosion Control Plan, Dutch Bill Creek, Sonoma County

Assisted landowner in resolving erosion enforcement actions by Regional Water Quality Control Board; prepared an erosion site inventory with recommended erosion control treatments, including a quantitative prioritization of erosion source area.

Site Sediment Budget, Occidental, Sebastopol and Peteluma

Developed a sediment budget for three separate 400 acre ranches to provide quantitative assessment of potential vineyard erosion and water quality impact.

Forsythe Creek Watershed Assessment

OEI prepared a geology report as part of the Forsythe Creek Watershed Assessment conducted by Bioengineering Associates, Inc. The report included a literature review of the watershed geology, geomorphology and channel characteristics. An aerial photo landslide inventory was prepared to estimate sediment sources at the sub-basin scale for habitat restoration planning.

Sonoma Creek Floodplain Analysis

OEI conducted two hydraulic analyses for a project located within a 100-yr floodplain. The first analyses entailed importing HEC-2 data that was used to delineate the Sonoma Creek 100-yr floodplain. Once this data from the original study was imported, cross section topography was modified to assess the impact from the proposed project on flood elevations. Another HEC-RAS model was created for a small unnamed tributary to Sonoma Creek.

Hunter Creek Road Surface Erosion Assessment

Conducted forest road erosion assessment according to Washington DNR watershed analysis methodology for the 10,000 acre Simpson Timber Co. ownership in Hunter Creek, Del Norte County, California. Assisted in preparation of sediment budget for project area in association with Tim Best, CEG, including long-term estimate for historic road surface erosion.

West Fork Satsop River Watershed Analysis

Conducted Mass Wasting and Stream Channel Assessments for a 60,000 ac. forest watershed in the southern Olympic Mountains, Grays Harbor County, Washington for Simpson Timber Company under guidelines for Level 2 Watershed Analysis in the State of Washington. Inventoried landslides on aerial photographs and quantified sediment production for the past 50 years. Developed a map identifying mass wasting hazards to minimize risk to aquatic habitat posed by forest practices that affect hillslope stability. Surveyed and analyzed stream channels to determine likelihood, character and extent of effects of forest management on physical stream processes and aquatic habitat.

North Fork Calawah River Watershed Condition Assessment

Cooperative investigation of a 13,000 ac. forest watershed in the western Olympic Mountains, Clallam County, Washington, funded by University of Washington and Olympic National Forest. Inventoried landslides over a 37-year period of aerial photo records and quantified sediment production from mass wasting. Monitored stream channel response over 37 year period by measuring depositional areas on historical aerial photographs using a computer-driven analytic stereo plotter (Model AP190). Bedload transport rates were calculated by mass balance techniques. Sediment conditions were characterized using pebble counts and q-star analysis. Measured current LWD load and character and extrapolated past LWD load through correlation with aerial photo observations.

South Fork Eel River TMDL

Lead Fluvial geomorphologist (employed by Stillwater Sciences) assisting development of sediment budget for the South Fork Eel River under a technical support contract with U.S.E.P.A. San Francisco, CA. Analyses developed for Clean Water Act 303(d) listed watershed impaired by sedimentation.

Garcia River Watershed Assessment

Conducted Mass Wasting and Surface Erosion modules of Washington DNR Watershed Analysis procedure (Level 1) for a 72,000 ac. Coast Range watershed in Mendocino County, California. Prepared for Mendocino County Resource Conservation District and California Department of Forestry and Fire Protection in association with Forest, Soil & Water, Inc., for use in development of TMDL regulations under the Clean Water Act.

Office Location: 447 Hudson St. Mailing Address: PO Box 794, Healdsburg, CA 95448 Ph (707) 431-2810 Fax (707) 473-9050

Text Box: OEI investigations of erosion processes address regulatory requirements and environmental impact assessment relating to effects of development or management activities on water quality and aquatic habitat. Investigations typically include one or more of the following: quantification of past erosion, assessment of future erosion potential, and development of erosion control plans. OEI frequently joins existing project teams providing specific skills in hydrology and geomorphology. Typical projects include ranch and vineyard erosion control plans, hydrological and geologic assessments for timber harvest plans, and landslide investigations.