DOES CAUSATION MATTER? CHANNEL INCISION AND ENGINEERED STREAM RESTORATION IN MONTANE MEADOWS OF CALIFORNIA'S SIERRA NEVADA RANGE

My poster will present preliminary field research on a prominent restoration technique in California's montane meadows, the "Plug-and-Pond." Fundamentally, the technique re-channelizes the meadow by blocking flow into incised stream channels. Spoils dug from meadow sediments plug the incised channel, creating ponds as a by-product. One of three approaches to re-channelization ensues: (1) construct a new shallow and sinuous channel, (2) redirect flows into a remnant channel, (3) or allow the channel to define itself over the meadow floodplain. Re-channelization aims to support overbank flows at 1.5 to 3 year recurrence intervals.

A field-based post-project appraisal will assess twelve "Pond and Plug" projects constructed between 1995-2009. My guiding research question is: Does the scale and character of processes instigating incision in Sierran meadows affect the long-term viability of re-engineered channels?

Hypothesis: The spatial and temporal scale of the stressors that initially caused the incision will affect the restored channel’s ability to maintain bed elevations that support bank overflows and groundwater levels. Because low order montane channel forms are tightly coupled to basin-scale hydrologic and sediment flows, diffusive impacts to sediment transport regimes, vegetative cover and/or drainage density across the meadow’s catchment will continue to induce erosive forces on re-channelized beds during high flows, leading to incision over decadal time scales. Degradation caused by meadow-scale changes to channel slope (i.e. culverts concentrating flows, channel straightening, meadow grazing) will be more conducive to restoration.

Observations and analysis inform the development of a conceptual model of meadow degradation and restoration trajectories that include multi-scaled geomorphic feedbacks with consideration of geology, climate, vegetation, and hydrology.