Cross Section Surveyed 11/19/03
On Wednesday November 19, Mono Lake Committee staff surveyed the following cross section from the highway to Mono Lake. This is south of Tioga Lodge and north of Old Marina near the north end of Segment 3 of the proposed project.
Note spring and wetland area labeled "brush" in Caltrans map.
The following graphs show the interaction between future lake levels and the proposed highway project. Alternatives 1 and 2 are the same at this location. The red lines assume an 11.5 foot alignment shift toward the lake, 12 foot lanes with 8 foot shoulders, and a 4 foot dirt shoulder that contains the guardrail on the lake side. While a 2:1 fillslope is not mentioned in the DEIR, during project development that is what was discussed and it matches the maps and figures that show the size of the fillslope in the DEIR.
Hydrologic models show that after transition to an average lake level of 6392.6 feet above sea level, the maximum expected lake level will be 6400 feet and the minimum expected lake level will be 6388 feet. It is expected to be below 6398 feet 95% of the time.
As Mono Lake rises, it cuts terraces. "The waves of a rising lake thus create a relatively broad platform that, depending on the erodibility of the substrate, may widen until the transgression ceases." (Stine, 1992, p.7) The lowest wave cut that you see in the profile is from the 6385.1 foot highstand in 1999. The next one is at 6390 feet and was cut during wet years in 1967 and 1969. "Should the lake rise above 6390 feet, the shoreline will not simply 'climb' this cliff; rather, it will beat the cliff-base landward, effectively widening the existing wave-cut platform. There is no apparent reason why this process should halt as long as the lake continues to rise." (Stine, 1992, p.19) Stine goes on to say the cliff at Navy Beach could retrograde 400 feet at 6395' and as much as 2000 feet at 6415'. The highest wave cut in the graph is just below 6400 feet. The graph below projects in yellow terracing that should be reasonably expected to occur from the future lake rise. It is almost certain that this proposed fillslope would be eroded by future lake waves at this location. Wave energy will also be greater than now due to a larger lake surface.
The spring that is shown in the graph above is coming out of the hill at the first large break in the slope above the current lake level--the 6390 wave cut. The spring has no tufa towers around it, which indicates it wasn't there the last time the lake submerged that area. It is likely that this spring will move back uphill to the next large break in slope as the water table is influenced by the rising lake (there may be a time lag as the groundwater recharges). In the graph below, a projected new emergence location is shown in yellow based on the projected wave cutting also shown in yellow. While nothing in yellow is exact, something close to this occurring is certain.
Stine, Scott, 1992. Past and Future Toppling of Tufa Towers and Sand Tufa at Mono Lake, California. Report to Jones and Stokes, Associates, Sacramento, 20pp.
NOTES
HIGHWAY PROJECTIONS
The projected highway in red is the result of the following. 11.5 foot
alignment shift to the east of the western white line, two 12-foot travel
lanes, one 8-foot shoulder, and a 4-foot unpaved shoulder including the
guardrail. This adds up to 47.5 feet from the existing westerly white line
to the new easterly edge of roadway. From this point, the 2:1 slope was
projected east. The height of the fillslope matches the 54 feet cited in
the DEIR, and the extent of it to near the 6400 high water line matches
what is shown on the maps in appendix F of the DEIR.
LAKE LEVEL PROJECTIONS
The lake level projections in blue are based on State Water Resources
Control Board Decision 1631 (1994) and the 1993 Mono Basin Water Rights
EIR. The cutting and spring movement shown in yellow is the result of the
following. A slope close to the existing terrace slopes was projected
landward from the 6389 foot elevation. The slope was steepened slightly
from the existing terrace at that elevation, and thus is on the
conservative side. Where that slope intersects 6392, the slope increases
and is parallel to the existing wavecut slope at 6396. Where that slope
intersects 6398, it increases again and is parallel to the existing
wavecut slope at 6390. Where this slope reaches the existing ground
surface, it continues a little way into the projected fillslope and
finishes with an even steeper slope to the fillslope surface that would
eventually lessen over time. This projection results in a roughly 3-foot
cut, similar to the existing wavecuts, and consistent with descriptions of
cutting found in Stine, 1992. The large spring and wetland that is
currently at the base of the 6390 wavecut is projected to move upward to
the next large break in slope at about 6398. This is not intended to be
exact--if the break in slope is at 6393, for example, then the large
spring and wetland should be expected to occur there.
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