Since
the completion of the first pour in early July, each week has
essentially been a repetition of preparation for making concrete pours on
Tuesday and Thursday.
Good progress continues to be made production wise. The sidewalls
notwithstanding, two complete rows of concrete panels are complete and
a third approximately 40% complete. The plan view of the dam below
shows the progress made so far.
The Contractor has nearly completed the demolition of the remainder of the
existing concrete slab. Work has begun on the excavation of the soil behind the
existing retaining walls to allow them to be demolished, as well as provide room to
construct the new walls in their place.
Finally, it Rains!
Over the past 10 days we have recorded
about 3¾” of rainfall at the water plant. On
th
August 6 the lake level was recorded at
59” below full pool. The rain resulted in a
recovery of 5” as the recorded level was 54”
th
down on August 13 . The graph to the right
shows how the lake levels have changed
over the past 6 weeks. The shaded area
between -48” and -72” shows the location of the upper gate in the intake
structure. Any time the water level is in the shaded area, a portion of the
upper gate is exposed, limiting the amount of water that can be
withdrawn through that particular gate. The arrow represents the
projection of levels in the future, in absence of additional rainfall. On
average, the lake drops about three-eighths of an inch per day due to water pulled from the lake for water production. Although the rainfall is a welcome
sight, it can result in some minor detrimental effects as the colder rainwater forces the lake to turn-over stratified water layers as the heavier cold water
sinks to the bottom and forces warmer water up. The extremely hot weather in July heated the lake waters up. Warm water is lighter than cold water
which results in the lake stabilizing in the summer with cool water on the bottom and warm water on the top. In the absence of currents created by rivers
and streams, the lake doesn’t tend to mix. As a result, cool rain on the surface and/or the surface layer being cooled at night results in the top layers
getting heavier and sinking to the bottom. This activity is monitored since the result can be higher levels of the nuisance minerals manganese and iron
increasing in the water being treated. Neither are harmful, but can result in a discolored water.
Over the past week work has continued on schedule on the spillway
construction. Altogether the water plant recorded about 1.3” of rain over
the weekend. The lake levels rebounded a little and the lake is currently
settled at 56” down. The resulting rain had little, if any, impact to the
construction progress. The slab construction has progressed far enough
along to allow for the sidewall construction to begin. The sidewalls are
being constructed in three distinct stages. The first stage is to pour a mud
mat directed on the compacted subgrade. The mud mat serves to provide
a firm working surface for the rebar placement to help prevent the soil
from getting on the rebar and separates the structural portion of the pour
from direct contact with the ground. The second stage is the pouring of
the base slab, in which the wall steel rebar is embedded. The final stage
will be the forming and pouring of the vertical wall. One big difference is
that the sidewalls do not have a drainage system beneath them, that all
occurs out in the spillway itself.
The main item of concern remains the progress of the job overall. The Contractor
has completed three of the eight rows making up the core slab and is well into the
completion of the fourth row. All in all, everything at this point is moving very well.