Course Forum

Gauging

Gauging

by Leela G -
Number of replies: 9

Dear Sir Greetings to all !

In a contour canal of 49.20 km length,we have four interstate gauging points viz 0.165km,12.56 km,25.10km.,49.20 km Entire canal has intercepted catchment during rainfall seasons.one outlet is there above 12.56 km which will supply that water to a dam.while taking water through outlet back water effect will be for 3kmThe canal loss is 3%..In this condition. we are gauging @ 12.56 & 25.10km (during non raifall period). to calibrate chart But the discharge  @ 25.10 is lower than 12.56km we are working out in a ordinate method using cup currentmeter. velocity is 1.5m/sec. we are iterating  taking gauging.how to fix it sir.

In reply to Leela G

Re: Gauging

by Sidhartha Mitra -
I want to know a little bit more on the interesting problem posed by you. Can you please name which canal is it? 4 interstate crossover points in 50km reach.... ?


The dimensions of the canal like bed width, FSL, bed slope, side slopes etc. may be given just for some calculation. However, as per your statement discharge at d/s gauge point is lower than u/s in non monsoon season, which seems logical due to losses enroute. Still may be you can correct me. Whats the discharges at various chainage points?

Looking forward for an interesting discussion.

Sidhartha Mitra, Director, NWA and Course Facilitator.

In reply to Sidhartha Mitra

Re: Gauging

by Arasu A Meenakshi Sundara -

Sidharth ji,

i have already requested Ms. Leela to post the problem with a drawing so that understanding of the problem is easier and addressing the issue will be fruitful. hope she will be doing it at the earliest.

i am also waiting for the post


In reply to Sidhartha Mitra

Re: Gauging

by Leela G -

Sir, Greetings!


Contour Canal Details-after rehabilitation

0.165km 12.56km 25.10km 49.20km
Bed width 6.14m 4.36m 6.10m 4.36m
Bed fall 12mm in 30m 12mm in 30m 12mm in 30m 12mm in 30m
Length of left side slope vertical 3.96m vertical 2.94m
Length of rihgt side slope vertical 3.92m vertical 2.94m
Depth of water 3.62m 3.89m 2.85m 2.05m
The inflow to the canal is tail race water of a power house,The currentmeter is recently calibrated and the Velocity eqn is V=.0.6621R+.0059 which is used for LS 12.56 &25.10km.Yet another calibrated instrument with the equation V=0.6664R+.0047 is used for LS 0.165 km &49.20km.

Currentmeter reading in comparison with old chart

.165 12.56 25.10 49.20
Depth 3.62m discharge(currentmeter) 
            1036

 chart
901		 Depth
3.89		 discharge(currentmeter)
950.69		 chart
1000
Depth
2.85		 discharge(currentmeter)
839		 chart
809		 Depth
2.05		 discharge(currentmeter)
836		 chart
830
The issue is the difference between 12.56km and 25.10 km is 191c//sas per  old chart, currentmeter difference is 111.69 c/s  @0.165 km the discharge is 1036c/s but in the tail end it is 836 c/s only.The contour canal empties into another dam.



In reply to Leela G

Re: Gauging

by Arasu A Meenakshi Sundara -

Madam

I think the canal is a lined one.

at 0.165 the discharge is 1036

at 12,56 the discharge is 950.69

at 25.10 the discharge is 839

so the loss between 0.165 and 12.56 is 85.31

and the loss between 12.56 and 25.10 is 111.69

if the bed width is decreased there will be an increase in the velocity and the flow will not be uniform. that may be the reason of this kind of difference. again the bed width is increased. so this problem is to be addressed with hydraulics. more over the side slope will be in the form of 1:1 or 1.5:1 like that. this needs more information. (i think i am not wrong..... mitra ji)

In reply to Arasu A Meenakshi Sundara

Re: Gauging

by Pankaj Sharma -

Usually, there is a widespread practice of lifting water from canal directly using pumps (free electricity) to irrigate the fields (against gravity) on higher areas  or areas not covered by minors etc near to main canal. Has it been taken care of.

In reply to Leela G

Re: Gauging

by Sidhartha Mitra -

Dear Madam Leela G,

I am really getting interest in the practical issue posed by you. Actually, after getting such an elaborate data from your side i started some calculations off hand.

Firstly, if we see chainage 12.56KM, cross sectional area is around 32 Square metre (please point out if there is any mistake) and velocity of water is around 1.5 m/sec, so the discharge comes out as 48 cumecs and not 950.69. Is the data correct or i got it wrong?

Secondly, i wanted to know the discharge going out through the outlet before chainage 12.56Km as you pointed out in the first write up.

Please feel free to point out any ambiguities and let us learn together through some beautiful issue in hand.


Sidhartha Mitra.


In reply to Sidhartha Mitra

Re: Gauging

by Leela G -

 Sir Greetings to all ! Thank you Mitra ji,Arasu ji and Pramod ji.

S as Pramod ji mentioned the  i missed to give one more data. sorry for the mistake .top width is 5.33m(water) @12.56 km. top width of water is 6.20m @25.10km.top width of water is 8.66m @ 49.20km. 

wetted perimeter of 0.165 km section =3.62+6.14+3.62=13.38m

wetted perimeter of 12.56 km section =3.96+4.36+3.92=12.24m

wetted perimeter of 25.10km section =2.85+6.10+2.85=11.80m

wetted perimeter of49.20km section =2.94+4.36+2.94=10.24m

with regards

Leela.G

In reply to Leela G

Re: Gauging

by Parmod Kumar -
Greeting to all, 

I have also worked out some calculations I also feel same as pointed out by Mitra sir, there seems some error in the data given above. I think the data should be looked at again so that we can have a good discussion.