Monitoring of Groundwater and Surfacewater Interactions on the Walla Walla River

1. Monitoring of Groundwater and Surfacewater Interactions on the Walla Walla River Graduate Student: Starr Silvis Major Professor: John Selker Field Coordinator: Bob Bower

2. Presentation Outline • Location and features of the basin • Background • Goals • Methods • Chemical Signature • Mini-piezometers • Temperature Profiling • Results • Discussion

3. Location of the Walla Walla River Basin

15. Water Resources for the Basin • Surface water • North Fork and South Fork • Groundwater • Alluvial aquifer • Basalt aquifers

16. Monthly Mean Flows 22 years of data 1969 - 1991

17. Walla Walla River Returns! • All river water above levied section (~100 c.f.s.) diverted for irrigation since turn of the century from June – September • 1998 American Rivers lists Walla Walla River as one of the top 20 most endangered rivers in the U.S. • Bull trout and Steelhead E.S.A. listed in 1998 and 1999 • Irrigation districts pledge to leave flow in the mainstem of the Walla Walla River; sign agreement with U.S.F.W. • 2000 – 13 c.f.s • 2001 – 18 c.f.s. • 2002 – 25 c.f.s • 2003 - ?

18. Summer 1999 Summer 2002

19. Low Flow Limitations • 2000 - all 13 c.f.s. percolated from the surface • Possible causes • In-stream gravel mining • Naturally high hydraulic conductivity (Schälchli, 1995,1992) • Large hydraulic gradients due to low aquifer levels

20. Aquifer Recharge • Irrigation ditch losses • Primarily unlined ditches • Stream losses • Winter recharge • Now – summer recharge too

21. Study Goals • Provide quantitative framework for the surface and groundwater exchanges • Determine influent / effluent nature of levied section • Quantify river losses • Identify seasonal patterns • Estimate alluvial aquifer recharge

22. SW/GW Overview Water flows from the stream into the subsurface Water flows from the subsurface into the stream

23. Methods • Chemical Signature • Mini-piezometers • Temperature profiling • Ditch loss

24. Chemical Signature Requirements • Conservative and naturally occurring • Chloride and Sulphate • GW/SW must have distinctly different concentrations • Ease of analysis • Ion chromatography

25. Chemical Signature • Grab Sampling • Mainstem Walla Walla River • Shallow aquifer wells • 10% duplicate sampling • Data Analysis • Mixing space diagrams • Linear Regressions • Mass Balance

26. Qgw Cgw Qsin Qs Cs Csin Upstream sampling point Downstream sampling point Accumulation = In – Out Accumulation = 0 In = Out Chemical Signature; Mass Balance

27. Groundwater Sampling Sites Red dots are wells Hwy 11 Tumalum Bridge Walla Walla River Nursery Bridge Milton-Freewater

28. In-Stream Sampling Sites Tumalum Bridge Nursery Bridge Milton-Freewater

29. Mini-Piezometers Vertical Hydraulic Gradient = dh/dl Stream surface dh Streambed surface dl Mid-point of perforations

30. Temperature profiling device Mini-piezometer

31. Temperature Profiling

32. Temperature Profiling Analytical Methods • HYDRUS-2D (Šimůnek et al., 1999) • Computer model using inverse processes to solve for vertical flux • Sine Wave Fitting • Stallman’s (1965) equation for a sine wave fit to the data

33. Temperature Profiling • HYDRUS-2D • Sophocleus (1979) Conduction Convection

34. Temperature Profiling • Sine Wave Fitting • Stallman (1965) • Solution for diurnally heated and cooled boundary condition Tz (t) = ΔT e-az sin (2πt/τ – bz) + Taz

35. Temperature Profiling; No Flux HYDRUS-2D no flux simulation R2 = 0.95

36. Ditch Loss Study Installed dam Covered with plastic Allowed to fill to capacity Shut off water supply Measured time and depth of draining for 6 hours

37. Chemical Signature; GW R2 = 0.89

38. Chemical Signature; SW R2 = 0.96

39. Chemical Signature; Mass Balance Filled symbols correspond to left axis, open symbols correspond to the right axis GW dominates Tumalum Bridge SW dominates Qgw Qsin

40. Mini-piezometers Nursery Bridge Tumalum Bridge duplicates duplicates

41. Temperature Profile

42. Temperature Profiling; Sine Wave M 5.5 August 14

43. Temperature Profiling; HYDRUS-2D

44. Temperature Profiling; Sine Wave vs. HYDRUS-2D Pink are results using loggers 3 to 2 (15 cm) Blue are results using loggers 3 to 1 (30 cm)

45. Mini-piezometers

46. Seasonal Patterns; Mini-Piezometers K = -Q / (A dh/dl)

47. Seasonal Patterns; Temperature

48. Ditch Loss • Infiltration estimate 204 cm/d

49. Conclusions • Effluent river on section studied • Estimated flow loss • 0.3-0.76 m3/s using temperature estimates • 0.43-0.63 m3/s using in-stream flow measurements • Seasonally hydraulic conductivity decreased • factor of 2-4 using temperature profiling estimates • factor of 2-100 using mini-piezometer estimates

50. Implications for GW recharge of the shallow aquifer • Assuming only 50 km of ditches with an average infiltration rate of 204 cm/d • 2 * 107 m3 / yr • On an area of 538 km2 and a porosity of 0.27equivalent to 23 cm of water • Assuming 5 months at max infiltration rate of 310 cm/day using temperature profiling estimates • 1.8 * 108 m3 / yr • On an area of 538 km2 equivalent to 1.2 meters of water