Watersheds, Baylands and the Bay: Putting Landscapes Back Together or Rethinking Drainage around SF Bay Josh Collins, San Francisco Estuary Institute The Bay, Baylands, and Watersheds The Bay is an extension of local Watersheds, and the Watersheds are extensions of the Bay. The Baylands are transitional between the Bay and its Watersheds. Convention and convenience have conspired to subdivide regional environmental science and planning into three parts of the whole. Its time to starting putting the parts back together. The Bay, Baylands, and Watersheds The Bay is needed to receive our effluent, link us to maritime commerce, and accommodate our recreation. Watersheds are needed to flush the Bay, supply it with nutrients and sediment, give the Bay someplace to grow, provide us with water. Baylands restoration projects are ultimately watershed projects. The Bay, Baylands, and Watersheds ,000 Red Tailed Hawk SMHM Clapper Rail ,000 Red-legged Frog Gray Fox & Coyote Coho, Chinook, Steelhead Yellowthroats People Backshore Distance (meters) As physical systems, watersheds have two basic functions: move water and move sediment. Lets Consider the Consequences of Historical Land Uses Historical Improvements Drainage meant moving water to use it or get it out of the way. Historical Improvements Hydro-connectivity: ditching of alluvial fans and wet meadows to drain the land linked natural channels together and increased channel density (amount of channel per acre). Historical Improvements Channel re-alignment: moving creeks aside for agriculture straightened the channels and promoted incision (down-cutting) and thus headward extension (creeks lengthened uphill). Historical Improvements Channel Engineering: designing flood control channels and stream crossings for flood flows but not sediment transport caused chronic aggradation, reduced flood control capacity, increased maintenance costs, decreased sediment delivery to marshlands, and otherwise generally decreased linkages between the Bay and its watersheds. Historical Improvements Reclamation: diking and draining marshlands for agriculture or other land uses reduced the tidal prism (volume of tidal water) and thus promoted shoaling of remaining tidal channels and oxidation (burning) and subsidence of diked marshlands. Headward Gully As Source Ditch Across Alluvial Fan Channel Incision As Source Choked Culvert Reclaimed Tidal Marsh Reclaimed Baylands Old Marsh Now Salt Pond Old Channel As New Marsh Reclaimed Baylands Old Marsh Now Salt Pond Old Channel As New Marsh Reclaimed Baylands Loss of Subtidal Channel Historical Drainage Systems Valley Bottom Fan Wet Meadow Modern Drainage Systems Sediment Drainage Model Sediment Sources Zone 1 Transport Zone 2 Deposition Zone 3 Historical Condition Head Cuts Incision Aggradation Land Use Effects Subsidence Sediment Drainage Model Head Cuts Incision Aggradation Land Use EffectsModern Condition Subsidence Key Local Consequences of Historical Land Uses Much greater channel density More tributaries reaching main streams Chronic main stream incision Lower water tables Less seasonal wetlands Shorter perennial stream reaches Lowed and warmer stream base flows Increased flood hazards Shoaling of the estuary Land subsidence Key Regional Consequences of Historical Land Uses Dams and undersized crossings starve Bay and Baylands of sediment. Reclamation isolates intertidal landscape from fluvial and subtidal landscapes. Unnatural hydro-connectivity alters timing and location of freshwater influences. Rethinking Drainage Reconnecting the Bay, Baylands, and Watersheds Restore alluvial fan functions to recharge near-surface aquifers, reduce flood hazards, and recover mainstem base flow. Eliminate ditches that connect tributaries to main streams at valley bottoms. Restore tidal marshland and re-size stream crossings to increase tidal prism and ability of system to move sediment through intertidal zone and into subtidal zone. Reconnecting the Bay, Baylands, and Watersheds The process to establish baylands habitat goals should be matched by a process to set Riparian Habitat Goals. Setting riparian goals could serve to integrate the science and policy of watersheds, wetlands, and estuarine protection. Thank You