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Cosumnes power plant (01-afc-19) data response, set 1A


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Attachment W&SR-116

November 26, 2001 “Will Serve” Letter



Attachment W&SR-133




project: Cosumnes Power Plant

job no.: 13561

discipline: Civil

subject: Drainage Volumes and Areas

calculation no.: 13561-C-1

originator: L. Gasparetti

date: 7/26/01

file no.:

checker:

date:

Sheet 1 of 5 Sheets



Purpose of Calculation

Determine the detention pond storage volume required to contain the total runoff from a 10-year, 24-hour storm.


Summary of Results and Conclusions Starts in Sheet No. _

Sources of Design Criteria


Sources of Formula and References:

FR-1 Rainfall Depth Duration Frequency for Eagles Nest (Department of Water Resources)

FR-2 Plot Plan, Drawing No. G1, Rev. by PB Power








Record of Issues


No.



Description



By



Date



Checked



Date



Approved



Date


Date Filmed








































































































































Preliminary Calculation

x




Committed Preliminary Design Calculation




Superseded Calculation







Final Calculation



project: Cosumnes Power Plant

job no.: 13561

discipline: Civil

subject: Drainage Volumes and Areas

calculation no.: 13561-C-1

originator: L. Gasparetti

date: 7/26/01

file no.:

checker:

date:

Sheet 2 of 5 Sheets

  1. PURPOSE

See cover sheet.


  1. METHODOLOGY

    1. The Rational Method determines the peak runoff:

Q = CiA, where

Q = peak runoff (cfs)

C = runoff coefficient

i = rainfall intensity (in/hr) (based on time of concentration)

A = contributing area (acres)


  1. Modify the rational method by using the rainfall depth for the 24-hour event to determine “i” rather than a shorter time period based on the time of concentration. This will yield a volume which is more realistic than using a higher intensity and assuming the storm maintains that intensity over a 24 hour period.




  1. DESIGN CRITERIA

    1. Use 10-yr frequency, 24-hour storm.

    2. Runoff coefficient, C:

C = 0.30 for crushed rock surfacing, landscaped, and undeveloped areas

C = 0.75 for compacted earth

C = 0.90 for paving and roofs


  1. Rainfall intensity for 10-year, 24-hr storm, i:

Rainfall depth = 2.60 in/24-hr (FR-1)

Therefore, i = 0.11 in/hr



      1. Storage volume required is the difference between the runoff from the developed site minus the runoff from the undeveloped site.




  1. SUMMARY

Required volume for detention pond is 100,000 cubic feet.


  1. AREAS

  1. Total site:

AT = 25.2 ac

  1. Paved areas, AP:

Ap = 13.5 ac

  1. Crushed rock areas, ACR:

Switchyard: ACR = 6.2 ac

  1. Landscaped areas, AL:

Entrance: AL = 1.1 ac

  1. Compacted earth, AE

Cooling towers: AE1 = 2.8 ac

O/W Separator: AE2 = 0.7 ac

Gas Metering Station: AE3 = 0.9 ac

AE = AE1-3 = 4.6 ac



  1. RUNOFF COEFFICIENTS

For developed site, CDEV:

AT, CDEV = X

AP, C = 0.90

ACR, C = 0.30

AL, C = 0.30

AE, C = 0.75

CDEV = [0.9(13.5) + 0.3(6.2+1.1) + 0.75(4.4)]/25.2 = 0.70

For undeveloped site, CUDEV: AT = 25.2 ac, C = 0.30



  1. VOLUME OF RUNOFF

From developed site, Q DEV:

Q DEV = CiA = 0.70(0.11)(25.2) = 1.94 cfs

For 24-hour duration:

VDEV = (1.94 ft3/sec)(3600 sec/hr)(24 hr) = 167,616 ft3

From undeveloped site, QUDEV:

QUDEV = CiA = 0.3(0.11)(25.2) = 0.83 cfs

For 24-hour duration:

VUDEV = (0.83 ft3/sec)(3600 sec/hr)(24 hr) = 71,712 ft3



  1. VOLUME OF DETENTION POND, VPOND:

VPOND = VDEV - VUDEV = 167,616 – 71,712 = 95,904 ft3, say 100,000 ft3


INSERT FIGURE W&SR-150






Attachment W&SR-159

EBMUD American River Diversion Analysis





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