Strategies Addressing Hydromodification in Channels Through Unstable Terrains John Gartner Barry Hecht Shawn Chartrand Edward Ballman, P.E. BALANCE HYDROLOGICS, INC.

Field Problem Incision by streams draining urbanized areas

Channel dredging, Mowry Slough, Fremont, California Field Problem

(Leopold, 1968)  Semi-permanent hydrologic change to which the channel must adjust  Decreased lag time  Increased peak  Increased volume  More frequent erosive flows Erosion threshold?? Understanding Hydromodification LOGARITHMIC AXIS!

Regulatory context Downstream impacts are becoming unacceptable CEQA and NEPA Endangered Species Act County permits per Bay Area RWQCB

Role of geomorphologist Recognize disturbed landscapes and importance as sediment sources Understand channel form, function Comprehend channel adjustments to environmental change

Outline Site Assessment Solutions Summary

Case study: Coyote Gulch

560 acres Site Ridgetop Downstream Steep Disturbed

“Orinda” Formation –Tightly folded –Mass movements –Beds with varying resistance Geology

Clay Soils Low Infiltration Millsholm Soils

Larger watershed context Downstream Hydromod Biota Network Barbed

Flow monitoring and baseline Host of info Lag time Calibrate model Seasonal effect saturation – baseflow steps Date Discharge (cfs) WY 2004

Sediment monitoring, baseline Mostly suspended Regional context Baseline Assess success

Stream walks Channel Stability

Presentation is continued in: Gartner GSA talk hydromodification part 2.pdf