1. Estimation of areal recharge for the Spokane Valley-Rathdrum Prairie Aquifer J.R. Bartolino U.S. Geological Survey Idaho Water Science Center SVRP Aquifer Summit May 8, 2007—Spokane, WA

2. Bartolino Magnitude of areal recharge ► Areal recharge is second- largest single inflow component  233 ft 3 /s: 16% of total ► Includes permeable and impermeable surfaces   Permeable surface assumes no overland runoff   Impermeable surface excludes impervious cover that drains directly to the Spokane River or other water body 1,471 ft 3 /s inflow 1,468 ft 3 /s outflow

3. Bartolino Four methods identified Runoff based: assumes Runoff = Recharge ► Langbein (1961): Raft River, ID  Annual only  Precipitation and PET ► ESPAM (Contor, 2004)  Based on Rich (1951, 1952) and calibrated to previous GW flow model.  Three soil types: thin and thick soils, lava rock  Precipitation ET based: assumes Precipitation - ET c = Recharge ► USDA (1970)  Effective rainfall calculated  Precipitation, PET, and temperature ► FAO Penman-Monteith (Allen and others,1998)  Reference ET (ET o ) calculated—requires many meteorological data; most can be approximated  Single coefficient approach: ET c = K c ET o r e = 0.70917 r t 0.82416 -0.11556(10) 0.02426u (f) P a / L a vs R a / L a curve Precipitation vs Runoff curve

4. Bartolino Active NWS stations within 20 miles ► ► Bayview Model Basin ► ► Coeur D’Alene 1E ► ► Newport ► ► Sandpoint Exp. Station ► ► Priest River Exp. Station ► ► Spokane WSO Airport ► ► Mean annual precipitation   16.1 in—Spokane   32.0 in—Sandpoint ► ► Mean annual temperature   50.3°F—Bayview   53.4°F—Coeur d’Alene ► Closest AgriMet station is Seven Bays Marina, Washington, (SBMW) 50 mi west of Spokane

5. Bartolino Mean monthly recharge ► Langbein:  Annual only ► ESPAM:  Recharge 1-57% of monthly precipitation  Lava rock > Thin > Thick ► USDA:  Recharge 53-73% of monthly precipitation ► FAO Penman-Monteith single coefficient (Spokane only):  Recharge 0-93% of monthly precipitation Mean monthly precipitation

6. Bartolino Mean annual recharge ► Langbein:  Recharge 0-11% of annual precipitation ► ESPAM:  Recharge 2-52% of annual precipitation  Lava rock > Thin > Thick ► USDA:  Recharge 64-69% of annual precipitation ► FAO Penman-Monteith single coefficient (Spokane only):  Recharge 30% of annual precipitation All problematic conceptually or in water budget

7. Bartolino What’s wrong with these estimates? ► ► Single coefficient FAO: no recharge for summer months—unlikely ► ► Monthly time steps assume that there is always sufficient soil moisture to satisfy ET, but:   Daily soil moisture will occasionally be insufficient to meet ET c demand, thus actual ET will be less than the calculated ET c ► ► For recharge to occur soil moisture has to be replenished:   Depends on the amount and timing of individual precipitation events ► ► The FAO Penman-Monteith dual-coefficient approach with daily time steps addresses this temporal variation ► ► Mass-balance to determine soil drainage/deep percolation/recharge ► ► Spreadsheet based ► ► Used wind speed from Spokane WSO Airport for all stations ET cd = (K cb + K e ) ET o

8. Bartolino Recharge with 1990-2005 daily values ► Daily calculations show timing of precipitation can be more important than the amount ► Is this important? It depends on the model and purpose…

9. Bartolino Comparison and application ► Realistic and defensible ► Calculations are for points:  Triangular network-linear interpolation

10. Bartolino Recharge from impermeable surfaces ► ► Precipitation on an impermeable surface that runs off to:   a recharge well   an infiltration basin   adjacent permeable surfaces ► ► Assumed that 85% recharges and 15% lost to ET

11. Bartolino Reports and links ► Report available from the USGS Publications Warehouse at URL: http://pubs.usgs.gov/sir/2007/ 5038/ ► Rick Allen’s site:  Includes spreadsheets and links to the FAO report http://www.kimberly.uidaho.edu/ water/fao56/index.html http://www.kimberly.uidaho.edu/ water/fao56/index.html