Delta restoration and farm system function
This topic includes the ways that modification of delta landscapes affects farm functions primarily through the configuration and timing of groundwater fluctuation.
- Subsidence results in increasingly low farm field elevations compared to groundwater over time. This statement is obvious, but has not been rigorously observed. Subsidence rate and change over time has been haphazardly documented. The risks have not been quantified.
- The Port Susan Restoration resulted in the restoration of a farm field where the costs of pumping made farming uneconomical. The project design includes a flood gate that reduces flood impacts to adjacent farm land which has subsided.
- The Fisher Slough Restoration team learned that spring water levels are critical to farm operations because they can delay the time of spring tillage. Fisher slough incorporated drainage system enhancements into restoration, and made estimates of how the project would reduce flooding on Carpenter Creek (Weinerman et al 2012).
- The Wiley Slough Restoration team is working to resolve claims from adjacent land owners that restoration modified farm field drainage, and increased spring flooding. Downstream shoaling on the delta flats have be affecting conveyence, due to the very low slope of channels, suggesting that the function of farm drainage systems fluctuates.
- The Fir Island Farms Restoration team is evaluating the effect of restored tidal inundation and changes to drainage infrastructure on agricultural lands. The monitoring strategy includes multiple parameters related to drainage and water levels.
- Subsidence and sea level rise are likely to compel abandonment of some delta farm lands, unless river sediments can be brought in to raise subsided lands.
Delta Strategy Analysis
The uncertainties in how this topic affects delta restoration has resulted in its inclusion in the ESRP River Delta Adaptive Management Strategy. This three criteria analysis should build off the analysis above, and supports development of learning projects.
Larger scale planning may reduce project by project costs and result in solutions that improve agricultural viability.
The availability of land for restoraiton may be contingent on understanding and planning for the effects of restoration on agricultural functions, in the context of subsidence and sea level rise.