This file is
http://riolinda.info/flood/sorento051231.html
Sorento Road, 28 through 31 December
2005
pictures and text by Erwin Hayer, eeh625@hotmail.com
DECEMBER
31, 2005
The Steelhead Creek (formerly Natomas East Main Drainage Canal - NEMDC)
D15 pump upstream gage sensor, A44-2771, crested at 28.87 feet around
1:00 pm local time on December31, 2005.
At that same time the water elevation at the Sacramento County Bench
Mark (SCBM) No. 6-20 (33.04 feet) on east side of Sorento Road just
south of Rio Linda Blvd had already crested and had receded about 6
inches or more. When the water crested, it was less than 10
inches below the SCBM 6-20 or about 32.3 feet and much of the section
of Rio Linda Blvd that runs east and west was under more than 6 inches
of storm water and many homes had water almost up to their front steps.
From this I calculated the water level at the SCBM 6-20 would crest
before the D15 pump upstream sensor would crest and could be as much as
3.5 feet higher than the D15 pump upstream sensor.
NEMDC WATERSHED
The NEMDC watershed is 17,366 acres with about half in Placer
County. All of Placer county area south of Curry Creek and north
of Dry Creek watersheds and all of Elverta and Rio Linda area north of
Dry Creek watershed drains into the NEMDC upstream of the D15
pump. Natomas Reclamation District 1000 Pumping Plant Number 6 on
the NEMDC north of Elkhorn Boulevard can add 220 CFS to the NEMDC
Watershed during major storms.
Reference: http://riolinda.info/flood/watershed.html
DECEMBER 31, 2005 STORM WAS A 10 TO 50 YEAR STORM?
This storm was rated as a 10-year event on the American River Watershed
by Pete Ghelfi, SAFCA’s Director of Engineering (Sac
Bee, “New weir
rules sought”, 20 Jan 06) and as a 40 or 50-Year flood in the Linda
and
Cirby Creek watersheds by Rhon Herndon, Senior Civil Engineer for the
city of Roseville (Sac
Bee, “Flood control project helped in
Roseville”, 6 Jan 2006).
ELVERTA SPECIFIC PLAN
1,744 plus or minus acres with 4,950 dwelling units
The Elverta Specific Plan (ESP) Revised Draft Environmental Impact
Report (RDEIR), dated Jan 2006.
CUMULATIVE DOWNSTREAM FLOODING
The ESP-RDEIR states on page 1-21 and 2-4 that the
D15 pump station, constructed in 1997, reduced 100-year water surface
from 33.0 feet down to 31.0 feet which is substantially below the
observed high flood level of 36.5 feet in 1986 and 35.3 feet in
1995. I am assuming these figures are on the upstream side of the
D15 pump.
Then the DWR indicates on page 1-21 that, even with
provision of detention to mitigate peak flows, the increased runoff
volumes from NEMDC watershed development would cumulatively increase
the 100-year water surface elevation in the NEMDC from 31.0 to 32.3
feet or 1.3 foot. It was already at 32.3 feet on December 31,
2005 at SCBM 6-20 which exceeded the FEMA Flood Insurance Rate Map
(FIRM) 100-year flood elevation of 31.0 feet in that area.
It continues on to say that the ESP is roughly 15% of
the overall watershed and it would contribute 0.2 feet of the 1.3 foot
increase.
If the 100-year water surface elevation is increased to
32.3 feet at the upstream side of the D15 pump, then the water level
could rise to 35.8 feet during a 100-year event at the SCBM 6-20.
The stormwater elevation in the area of SCBM 6-20 could place homes at
risk because of the difference of the data in the ESP-RDEIR and what
actually happened on 31 December 2005. Something is wrong with
the water models and the figures at SCBM 6-20 area are not even
mentioned. This area is just north of NEMDC Tributary F and G or
about 4.8 miles upstream of the D15 pump or just north of Burr
Avenue. Reference Thomas Guide page 237-E4. Homes in this
area have been raised since the 1995 flood due to flooding in 1986 and
1995. If the water level could rise to 35.8 feet during a
100-year at the SCBM 6-20, then the homes that have been raised could
again be at risk.
I am asking the Sacramento County Department of Environmental Review if
the water elevations stated in the ESP-RDEIR take into account the
Placer Vineyards proposed development for 14,000 residential units with
SACOG recommending 6,500 additional residences for a total of 20,500 on
approximately 5,200 acres just north of the Sacramento/Placer County
Line that drains into the NEMDC. Also, were the drainage pumps at
the Reclamation District 1000 Number 6 that pump into the NEMDC
included in the water elevations.
I am also requesting the Sacramento County Department of Environmental
Review to ensure that the flood water elevations at the SCBM 6-20
location be added to the ESP-RDEIR.
Will additional pumping capacity need to be added to the D15 Pump
Station to meet the increased flows?
Erwin Hayer
