delta cross channel gates
DESCRIPTION
Delta Cross Channel Gates. A “gate” formulation ——— Q = g A 3 √ 2 g D h. X. Matthai,H.F. 1967. Measurement of peak discharge at width contractions by indirect methods. Chapter A4 in Techniques of water-resources investigations of the United States Geological Survey. - PowerPoint PPT PresentationTRANSCRIPT
Delta Cross Channel Gates
A “gate” formulation ———
Q = A3 √ 2gh
Matthai,H.F. 1967. Measurement of peak discharge at width contractions by indirect methods. Chapter A4 in Techniques of water-resources investigations of the United States Geological Survey.
Figure III.2.i-1. Delta Cross Channel and gates, circa 1950’s. Sacramento River is in the foreground.
Photo courtesy of Lloyd Peterson, USBR.
Figure III.2.i-3. USGS Monitoring locations in the vicinity of Delta Cross Channel, Sep 2003 to Nov 2004.
Sacramento River above DCC
Sacramento River below GS
Georgiana Slough
Delta Cross Channel
Sn
od
gra
ss S
lou
gh
Mo
kelu
mn
e R
iver
Nor
th F
ork
Sout
h Fo
rk
Dead
Horse
Cut
Figure III.2.i-4. Comparison of field measurements (blue rhombuses) in Delta Cross Channel and simulated flow (solid lines) based on gate equation for two gate coefficients. Flow estimates at maximum and minimum water depth are also shown as dashed lines.
USGS flow measurements are 15-minute averages. Stage measurements are instantaneous values. The stage difference in this plot is the average of two time-steps.
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
11,000
12,000
0.0 0.1 0.2 0.3 0.4
Stage difference (feet)
flo
w (
cfs)
w = 120'
= 0.65
= 1.00
Mass balance (continuity) and energy balance (Bernoulli equation) give
vd = [1 + f – (Ad / Au)2)]-½ [2 g (hu - hd)]½
where the friction loss term is assumed to take the form
hf = ½ f vd2
Binomial expansion about mean water level (and dropping h.o.t.s) give
Qd = Ad [2 g (hu - hd)]½ [1 + f – o2 (1 + d hd - u hu)]-½
where the ratio of cross-sections is assumed to take the form
= Ad / Au = o [1 + d hd - u hu + higher order terms (h.o.t.s)]
and
d ≈ wd / Ado and u ≈ wu / Auo
Semi-empirical coefficients to be calibrated: f, o2, u,d, Ado
Alternative Formulation
Figure III.2.i-5. Simulated flows in the Delta Cross Channel using open channel hydraulic formulation. Values of coefficients in Equation III.2.i-6 are given in Table III.2.i-2. Field data at 15-minute intervals span over 50 M2 tide cycles, from July 24 to August 18, 2004.
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2,000 4,000 6,000 8,000 10,000 12,000
Measured (cfs)
Sim
ula
ted
flo
w (
cfs)
1 + f 2 au ad Ado
1.400 0.200 0.030 0.075 2732 sq.ft.
Figure III.2.i-6. Comparison of simulated flows in the Delta Cross Channel using gate-type formulation and open channel hydraulics formulation shown in Fig.III.2.i-4. Field data at 15-minute intervals span over 50 M2 tide cycles, from July 24 to August 18, 2004.
0
2,000
4,000
6,000
8,000
10,000
12,000
0 2,000 4,000 6,000 8,000 10,000 12,000
Measured (cfs)
Sim
ula
ted
flo
w (
cfs)
Gate coefficient = 1.00 Gate coefficient = 0.65
Open channel hydraulics
= 0.65
= 1.00
Figure III.2.i-7. Range of simulated flows in the Delta Cross Channel for a stage difference of ±¼” that estimated. Simulated flow are computed using the open channel hydraulics formulation (equation III.2.i-3). Only a small fraction of the data shown in Figs.III.2.i-4,5 are shown in this plot for better clarity.
(b) At high flow rates
0
2,000
4,000
6,000
8,000
10,000
12,000
4,000 5,000 6,000 7,000 8,000 9,000 10,000 11,000
Measured (cfs)
Sim
ula
ted
flo
w (
cfs)
Figure III.2.i-7. Range of simulated flows in the Delta Cross Channel for a stage difference of ±¼” that estimated. Simulated flow are computed using the open channel hydraulics formulation (equation III.2.i-3). Only a small fraction of the data shown in Figs.III.2.i-4,5 are shown in this plot for better clarity.
(a) At low flow rates
0
1,000
2,000
3,000
4,000
5,000
6,000
500 1,000 1,500 2,000 2,500 3,000 3,500 4,000
Measured (cfs)
Sim
ula
ted
flo
w (
cfs)
Observations – DCC gates formulation
• Current formulation is inappropriate
• An alternate formulation appears to simulate measured flow more closely
• Uncertainty in stage difference leads to large scatter at low flows