The Twin Lakes (Upper & Lower Lake) historically have large variations in lake levels with about a 20 year water cycle – the aquifer and lakes are fed mainly by Horn Creek which originates from the overflow outlet of the “Top Lake” at 1555 meters above sea level. In 2019 no surface water reached the Upper Twin Lake due to a lower than normal snow pack and as a result the lakes in 2019 are both at a lower lake level. With use, seepage & evaporation each lake loses about 2 vertical feet of water in a year.
What happens in the Twin Lake affects the aquifer named #261 and all wells in this area. Likewise what happens in Aquifer #261 affects Twin Lake and the Willowbrook aquifer #260. Ground water and surface water are hydraulically connected.
Upper Twin Lake (UTL) & Lower Twin Lake (LTL) Water Facts
Summary of Critical LTL vertical waterway levels:
Normal high water is 17.6 ft. (must consider UTL stored water which is up to ~4 vertical ft.)
Tree line/ environmental flood level for LTL begins at 18.6 ft.
Built Infrastructure flood damage begins at 19.6 ft.
Terms
A Flood plain definition is “that area of land adjacent to a stream or river which stretches from the banks of the channel to the base of the enclosing valley walls and which experiences flooding during periods of high discharge”. Note there are two interpretations for flood: 1. The tree line – environmental/ nature water damage; and 2. The built environment water damage. High water discharge depends on the weather cycle, snow pack, and health of the watershed (tree growth/logging/erosion/cleared culverts), weather/wind patterns, temperature, and the timing/amount of spring rains.
The appearance of the shoreline of Twin Lake (TL) has changed some with the built environment (retaining walls, driveways & buildings), but basically according to the shoreline fir trees the natural tree line had been the same for at least the past 70-80 years until the flood of 2017 & 2018 when many fir trees with their roots in water died & several cottonwoods fell down due to the liquefaction of the soil. In the wet years of 1996 to 1999 the tree line did not change as ½ the spring freshet was diverted to a natural hollow in the next south White Lake Valley. Anecdotally, in the wet year of 1972 the LTL water flowed out to Twin Lake Road near TL Strata driveway area – no change occurred in the tree line.
Flood mapping of TL/Park Rill is now being completed by North West Hydraulic (NWH) and Caleb Pomeroy, Penticton Hydrologist. These hydrologists considered only the LTL datum marker (a concrete sill under the 325 Westview dock). They did not observe the quantity of water in the UTL.
The built flood was stated in 1973 by J. Botham in the BC Lands & Forest Report to be 19.6 ft. In 2017 & 2018 the flooding of buildings/built infrastructure did begin at 19.6 ft. In 2020 the lake level rose to 18.2 ft.
Full pool/tree line is defined as a high water flow event which in 2017 & 2018 was well beyond 18.6 ft. in LTL. Fir & pine trees do not survive if the roots are in water. After the floods of 2017 & 2018 many fir trees died & the roots of willows & cottonwoods will survive the water but because the soil becomes loose many fall into the lake as seen on Nature Trust of BC (NTBC) property. Fir trees which died after the 2 flood events were likely about 70 to 80 years old (confirmed by Verna Mumby). Thus, we do know that these trees had not been previously in water/flood – there had not been such a flood in at least 80 years. 1959 & 1971 were large spring run-off years of about 10 ft. but the lake was very low the year prior. The NTBC’s natural shoreline to gives a tree line measure.
The LTL main trigger point is the normal high water of 17.6 ft. as described by the Botham Report in Feb. 1973 according to the hydrometric station set in 1968. This data station is marked by a hollowed cement block (the old sill of the 1951 outlet works/pipe) under the dock of 325 Westview near to the pump well. The top of the pump well cement ring was surveyed in 2016 to be 18 vertical ft.
In 1970, a local rancher irrigated recklessly and drained LTL to a low level of 4.2 vertical ft. In 2009 LTL again had a very low lake level of 7.5 vertical ft. caused again by irrigation during a dry year cycle (9 years of low snow packs) which created low surface and ground water levels. In 2010 Summit stated that water-out of the aquifer should not be greater than 30 to 35% of the recharge/water- in. The area wells showed a dangerous water level drop in 2009 of 2 to 3 m. (Summit 2010). The lake level is connected hydraulically to the aquifer and the Twin Lake (TL) water level signals the aquifer level/health.
The water level recommendations are from the hydrology available, lake level history, the land form, the ranching history/practices and water licences.
Land Improvement in the old BC Water Act was described as “drainage” but in the legal definition of land improvement involves the land along the water and the land under the water.
Similkameen Valley or Okanagan Valley – Twin Lake Area is the height of land at the interface of the 2 Valleys. Water from Manual Creek originating near the Orofino Mt. Keremeos Columns runs toward Keremeos, but water from the NW face of the 13 km Orofino Mt. runs in Horn Creek to the Okanagan Valley along with NE face Myers (Park Rill) Creek & Orofino Creek water. Lower Horn Creek, Park Rill and Orofino meet Kearns Creek at Willowbrook to enter the large wetland of Myers Flat & are joined by Victoria Creek at the Seacrest Rd. culvert which empties into Sportsman Bowl.
Clouds/snow prevailing winds are usually from the Cathedral Mts. in Keremeos but drop their water /snow on the northern face of Orofino Mt.
Apex snow melt moves down in Keremeos Creek & some in Sheep Creek.
Horn Creek originates from a “Top Lake” at 1550masl and moves through the deep, dark gully where the Old Growth Cedars are present and these large trees slow the melt which may happen earlier above. When the gully of the Old Growth Cedars thaws, back-up water could be released quickly.
The TL water course follows the land form and when Horn Creek originally met Parker Mt. is was slowed (to create TL) and as the water pushed further downstream it moved in 2 directions: 1. as surface water towards Willowbrook with Myers Creek and 2. under the moraine hill from TL as ground water under the Twin Lake Golf Resort [TLGR], and towards Trout & Marron Lake as ground/aquifer water. Marron Lake via the Marron River reaches Skaha Lake just N. of OK Falls.
LNID work is unique in BC and has been overwhelming for only a few volunteers. TL is a sensitive rural, upland lake with a small population and several seasonal residents. LTL is ~ 90 acre or .29 square km. with about 70 lakefront lots. The UTL is ~ 80 acre with no dwellings.
TL is very sensitive to: 1. Low water levels which will increase the salt concentration, and 2. Pollutants such as with flood since LTL does not turn and has no overflow outlet. There is no flushing of LTL– what goes into this lake stays in this lake. See the BC Lake Stewardship Monitoring Program of Twin (Nipit) Lake 1999-2003. This article informs us of the importance of an overflow outlet for water quality, clarity and dissolved oxygen. TL is a layered lake with a deep layer of salt & hydrogen sulphide. The hydrogen sulphide is present as a result of the decomposition of organic matter. Warm water temperatures decrease the O2 saturation. Shoreline modification, tree line flood, logging, erosion from watershed disturbance, septic systems and cattle all increase the nutrient & phosphorous loading to create algae and decreased clarity. Cattle have only been fenced out of the lake since 2016. Decomposition of organic matter (plants & animals) encountered in the deep layers of TL water uses the limited oxygen. The oxygen is limited since the lake does not turn due to the salt layer & has no flushing without an outlet. Whatever goes to the bottom, stays in the bottom layer and maybe toxic to fish & unsuitable for drinking and recreation.
We owe much to the hard work of the 1996 to 2000 past trustees Betty & Lloyd Purdy, Ken Hyland, Bill Wells, Michael Parsons, Rick Brown, Christa & Denton Black and Gordon Nickerson who worked together to dig in across DL 280 a 6 inch x 1200 ft. pipe which exits through a 3 ft. diameter concrete distribution box and an upright 3 ft. pipe without a lid as it caused back pressure. The LNID Board secured a SRW, a pump and divert ½ of the freshet for 2 years to the next south White Lake Valley.
The Twin Lake Water Level Procedure Management Plan describes the 3 purposes of the LNID:
a. To continue the Annual Twin Lake Level Report (monitoring, documenting & reporting).
b. To estimate a capacity forecast for the next Twin Lake freshet & manage the pump accordingly.
c. To investigate a mitigation strategy to decrease the flood & drought cycles, so to maintain/ improve water quality & quantity.