Libby VARQ Flood Control Impacts on Kootenay River Dikes Hamish Weatherly, Hydrologist C R E S TO N VAL L E Y, B R I T I S H C O L U M B I A
Creston Valley Dikes 2
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Dam Construction • Increased control of flooding on the Kootenay River and Kootenay Lake was achieved through the construction of three dams – Corra Linn Dam (at Nelson) – 1932 – Duncan Dam – 1967 – Libby Dam – 1973 • Libby Dam has had a major impact on Kootenay River and Kootenay Lake water levels – it regulates 70% of the flow at the US-Canada border 5
Porthill, Idaho 2000 1800 pre-Libby Dam (1929-1971) 1600 Average Discharge (m 3 /s) post-Libby Dam (1973-2011) 1400 1200 1000 800 600 400 200 0 Jan-01 Feb-01 Mar-01 Apr-01 May-01 Jun-01 Jul-01 Aug-01 Sep-01 Oct-01 Nov-01 Dec-01 6
7 Peak Annual Discharge (m 3 /s) 1000 1500 2000 2500 3000 3500 4000 500 0 1929 1933 1937 Kootenay River Peak Flows 1941 1945 1949 1953 1957 1961 1965 Year 1969 1973 post-Libby Dam 1977 1981 1985 1989 1993 1997 2001 2005 2009
Kootenay Lake 535 pre-Libby Dam (1938-1971) 534 post-Libby Dam (1973-2010) Average Lake Level (m) 533 532 531 530 529 Jan-1 Feb-1 Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 8
Kootenay River 540 538 Reclamation Farm Diking District 536 534 Elevation (m) 532 530 528 526 2-year flood level 524 200-year flood level ground elevation 522 no topographic data 520 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Distance (km) 9
Libby Dam Operation • 1973 to 1992 – Standard Flood Control regime with operation of the dam driven almost exclusively by flood control and power • 1993 to 2002 – Standard FC continues and flood control remains a top priority. However, operations for downstream fisheries has a higher priority than power operations. Ramping rate restrictions were also adopted in the late 1990’s. • 2003 – present – Variable Flood Control is adopted. With this regime there are higher flood control curves for most water conditions, although flood control remains a top priority. 10
Load Following • Prior to the late 1990’s, Libby Dam was operated with the practice of load following – Refers to fluctuations in dam releases that correspond to changes in power demand – Load following was typically employed during the late fall and winter 11
Load Following 1000 1980 900 800 Dam Release (m 3 /s) 700 600 500 400 300 200 100 0 Jan-1 Feb-1 Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 12
Water Level (m) 13 12.0 12.5 13.0 13.5 14.0 14.5 15.0 15.5 Jan 1989 Feb 1989 Mar 1989 Load Following - 1980 Apr 1989 May 1989 Jun 1989 Jul 1989 Aug 1989 Sep 1989 Oct 1989 Nov 1989 Dec 1989 Jan 1990
nhc (1999) • nhc was retained by Kootenay Diking Districts to investigate bank erosion “It is considered probable that the development of this notch is more pronounced now that the river level is controlled by Libby Dam in comparison to pre-Libby Dam, when the river level fluctuated over a wider range and the short duration releases from Libby Dam did not occur. The more limited range of water levels, greater fluctuations in flows during the winter season, and more frequent cycles of wetting and drying appears to induce a weakening of the banks resulting in toppling of soil wedges.” 14
Dike Erosion • The US Army Corps of Engineers (2006) have also concluded that past practices of load following contributed to the erosion of the toe slope of much of the levee system in the Kootenai Valley • Lack of riparian vegetation is also likely a factor • Maximum ramping rates were therefore prescribed in the late 1990s – implemented not only for fisheries but also to help minimize dike/levee erosion along the river 15
Prescribed Ramping Rates 1000 1980 900 2010 800 Dam Release (m 3 /s) 700 600 500 400 300 200 100 0 Jan-1 Feb-1 Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1 Sep-1 Oct-1 Nov-1 Dec-1 16
17 Water Level (m) 12.5 13.5 14.5 15.5 16.5 17.5 11.5 01-Jan 01-Feb Load Following 01-Mar 01-Apr 01- May 01-Jun 01-Jul 01- Aug 01- Sep 01-Oct 01- 2008 2006 Nov 01- Dec
Standard vs VARQ FC • In December 2000, the USFWS and the National Marine Fisheries Service (NMFS) each issued a Biological Opinion outlining measures to protect endangered species including sturgeon, bull trout, salmon and steelhead • Recommended measures included VARQ FC • Intent of VARQ FC is to provide additional flows for downstream fish while continuing to provide adequate downstream flood protection 18
Standard vs VARQ FC • Dam began discharging less water during the fall/winter period and more water during the spring/summer to benefit downstream fish. • Standard and VARQ FC have the same storage space for flood control when then water supply forecast is 120% of normal • In practice, there is only a difference in the two methods when the inflow forecast is between 80% and 120% of normal 19
Standard vs VARQ FC 537 pre-Libby Dam (1937-1971) 536 Average Water Level (m) Standard FC (1973-1992) Standardl FC (1993-2002) 535 VARQ FC (2003-2011) 534 533 532 531 530 Jan-01 Feb-01 Mar-01 Apr-01 May-01 Jun-01 Jul-01 Aug-01 Sep-01 Oct-01 Nov-01 Dec-01 20
Standard vs VARQ FC 1.2 Standard FC ( 1973-1992) Average Daily Velocity (m/s) pre-Libby Dam (1938-1971) 1 VARQ FC (2003-2012) Standard FC ( 1993-2002) 0.8 0.6 0.4 0.2 0 Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 21
Conclusion • Implementation of VARQ FC has not had a significant impact on diking infrastructure adjacent to the Kootenay River • The past practice of load following did have a significant negative impact on diking infrastructure • High flows in 2011 and 2012 may be contributing to perception of impacts – highest lake level on Kootenay Lake in 2012 in 38 years – also record June and July rainfall 22
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