The Declining Raymond Basin and the Arroyo Seco Canyon Project Tim Brick, Arroyo Seco Foundation Ken Kules, PE Arroyo Seco Eaton Spreading Canyon Verdugo Dam Basin Basins • !949-98: LACDPW • 1998 to present: Pasadena MONK HILL BASIN Eaton Spreading Devil’s Basins Gate Dam PASADENA AREA SANTA ANITA SUBAREA
Main San Gabriel Basin HowHow waterwater flowsflows inin thethe RaymondRaymond BasinBasin
Surface Flow Path
MONK HILL BASIN
Devil’s Groundwater Flow Path Gate Dam PASADENA AREA SANTA ANITA SUBAREA
Main San Gabriel Basin BASIN HILL MONK Bedrock is 450’ to 750’ below ground surface Arroyo Seco Basin Hill Monk AREA PASADENA Bedrock is more than 1,200’ below ground surface Main SanGabrielBasin Pasadena Area Dam Canyon Eaton SUBAREA ANITA SANTA Basin Gabriel San Main THE RAYMOND BASIN JUDGMENT DWR (1954): “…it is probable that future • First adjudicated basin in California lining of stream channels and extension of • Safe yield calculated by DWR (Referee, WM) sewerage facilities, which factors tend to • Initial 1944: Safe Yield = 17,660 AF/Y* decrease ground water recharge, will • Amended 1955: Safe Yield = 25,332 AF/Y* overbalance compensating factors such as • Amended 1974: Parties allowed to recharge expansion or artificial spreading operations, using surface water rights to earn additional MONK and the net result will be a decrease in the pumping credits for 80% of recharged waterHILL present safe yield…” BASIN • Amended 1984: Replaced DWR with Raymond Pasadena’s Rights Safe Yield Surface Basin Management Board as Watermaster Monk Hill 4,464 AF/Y (60%) 25 cfs * Monk Hill Basin + Pasadena Area (not including Santa Anita Subarea) Pasadena Area 8,343 AF/Y (47%) 8.9 cfs PASADENA Safe Yield: “ …the average annual amount or ground water that could be AREA SANTA artificially extracted from the basin over an indefinitely long period of ANITA years…without causing a net lowering of ground water levels…” SUBAREA Inflow: Outflow: • Rainfall (mountains, in‐basin) • Groundwater pumping • Underflow (mountains, Verdugo Basin) • Channelized streams • Imported water • Sewerage exports Main San Gabriel Basin • Irrigation return flow • Underflow (MSGB) • Septic systems • Evapo‐transpiration • Artificial recharge safe yield objective: stabilize GW levels
~250’ (3.3’/year)MONK HILL 2009 30% safe yield reduction Main San Gabriel Basin 2016 wet year Amended Judgment BASIN Judgment
PASADENA AREA SANTA ANITA “Production at SUBAREA 1944 Rights” 1955 Monk Hill Basin
pumping LACDPW spreading basins resumed
Dry period LACDPW Stopped Pumping Credits drought
Behner closed ~30’ ~80’ pumping Judgment amended (80% credit) curtailed Behner WTP (25 cfs surface water right) How do you measure percolation/ infiltration? Percolation capacity in cfs (cubic feet per second)
Equilibrium: water in = water out Arroyo Seco diversion & spreading
Proposed: 100 cfs Arroyo limiting Diversion dam factor Existing: 25 cfs Seco Hume Canyon JPL pipeline Hahamongna 25+ cfs Project Watershed Proposed: 7 cfs expansion Park Spreading basins Existing: 18 cfs limiting factor
Devil’s Gate Dam ARROYO SECO CANYON PROJECT Pasadena Water & Existing 25 cfs Diversion Proposed 25 cfs Diversion Power: the increment of 18 cfs 25 cfs Water in the stream water captured by the Water diverted/spread Streambed infiltration ASCP would not have New pumping New spreading percolated behind Devil’s Gate Dam 7 cfs 0 cfs 5.6 cfs Key factors: 6.5 cfs 0 cfs 7cfs • Streambed infiltration capacity: 6.5 cfs* Change from existing (cfs) New water spread 7.0 • New pumping ‐5.6 Ponding infiltration capacity: Streambed infiltration loss ‐6.5 25-29 cfs** Ponding loss ‐0.5 Net basin replenishment ‐5.6 • “Big Dig” settlement: ponding 0.5 cfs at Devil’s Gate through June
* Philip Williams Associates (2000) ** PWA (2000) & PWP’s 2011 WIRP (CDM) HowHow doesdoes thisthis translatetranslate toto groundwatergroundwater impacts?impacts?
USGS Operations Model Gage Operating assumptions 1990 thru 2019 Spreading basins Modeling Operations Numbers of days affected by routing considerations is 2.2% of total days analyzed Devil’s Gate Dam Diversion dam Reservoir Routing Spillway • Operations rules • Area/Capacity curve • Flood hydrograph Mid-level 5 cfs/mile drain (tunnel) Modeling Opw x Low-level 6.5 cfs drain
Grout curtain 24 cfs
• 2020 “BIG Dig” settlement: ponding at Devil’s Gate through June • Grout curtain blocks subsurface flow past Devil’s Gate Dam HowHow doesdoes thisthis translatetranslate toto groundwatergroundwater impacts?impacts?
Existing Proposed Description (AF/Y) (AF/Y) Diverted & replenished at spreading basins - Existing 1,973 1,973 - ASCP increment N/A 1,104 Percolation behind Devil’s Gate Dam (Stream-bed & ponding) 1,206 433 New groundwater pumping (depletion) _N/A_ (-)883 Net effect on groundwater: 3,179 2,627 552 AF/Y (7.4% of safe yield) will be lost from the Monk Hill basin! DEIR Appendix F HEC-RAS Model Pasadena Area: ~33 feet/decade Monk Hill: ~80 feet/decade*
Direct Impacts • Reduced water supply • Increased pumping cost • Water quality impacts magnified • Cost of well replacement Indirect impacts • Land subsidence • Infrastructure damage • Harm to groundwater- dependent ecosystems • Economic losses from a more unreliable water supply
Pasadena Wells • Elevated TDS & nitrates * • Wells require replacement(?) https://waterinthewest.stanford.edu/groundwater/overdraft/ Recent ASCP History/Projected Schedule* • DEIR circulated June 15, 2020 • DEIR comments deadline July 31, 2020 • FEIR status report to MSC October 27, 2020 • WSRP EAC briefing October 27, 2020 • Met with PWP November 13, 2020 • FEIR (w/ responses to comments) December 23, 2020 • CUP/FEIR hearing January 6, 2021** • FEIR certification mid-January 2021** • WSRP to MSC January 26, 2021 • WSRP to City Council February 8, 2021 * All projected dates tentative ** Hearing & FEIR certification by a Hearing Officer (not the City Council) Existential questions…
• Is it Pasadena’s policy to continue drawing the Raymond Basin down? • If not, what is the plan for “healing” the Raymond Basin? • Is moving forward with the ASCP without a plan for the Raymond Basin responsible stewardship of the groundwater?