Time Area Curve (m2)

[mize_zl]

Dear Dr Quek,

How are you? Here I have a few question to you.:

1. While using a Time Area Method which follow Masma manual, I found that there are not clearly stated how to get the area for Time area curve,
Example below;

-------------------------------------------------------------------
TIME-AREA CALCULATION
Design ARI (yr) = 50
Tc (min) 55
Design I (mm/hr) = 61.91 Design P (mm) = 15.48
Pattern Type = 3
Time Interval (min) = 5
Duration (min) = 15
Location= Kuala Kangsar
Area = 260 Ha
1 2 3
A B1 B C D E F G H K
Time R.Ratio Rainfall Losses ER Time-Area
Curve Runoff
Hydrograph
(min) (mm) (mm) (mm) (m2) 3.45 7.74 2.79 (m3/s)
0 0.000 0.00 0.00 0.00 0 0.00 0.00
5 0.320 4.95 1.50 3.45 303,140 3.49 0.00 0.00 3.49
10 0.500 7.74 0.00 7.74 431,289 4.96 7.82 0.00 12.78
15 0.180 2.79 0.00 2.79 548,648 6.31 11.12 2.81 20.25
20 813,765 9.36 14.15 4.00 27.52
25 568,592 6.54 20.99 5.09 32.63
30 132,912 1.53 14.67 7.56 23.75
35 0.00 0.00 3.43 5.28 8.71
40 0.00 0.00 0.00 1.23 1.23
45 0.00 0.00 0.00 0.00

-------------------------------------------------------------------------

2, Actually how to determine the value for Time area curve?
is it base Tc and temporal time?

3. for my example, I'm using ratio from temporal pattern according to Tc is 55min ~` 60min. but when come to duration of 15min as this example, is it correct?

Your advice are very much appreaciate

TQ
Mize_zl

[drquek]

1. While using a Time Area Method which follow Masma manual, I found that there are not clearly stated how to get the area for Time area curve,
Example below;

-------------------------------------------------------------------
TIME-AREA CALCULATION
Design ARI (yr) = 50
Tc (min) 55
Design I (mm/hr) = 61.91 Design P (mm) = 15.48
Pattern Type = 3
Time Interval (min) = 5
Duration (min) = 15
Location= Kuala Kangsar
Area = 260 Ha
1 2 3
A B1 B C D E F G H K
Time R.Ratio Rainfall Losses ER Time-Area
Curve Runoff
Hydrograph
(min) (mm) (mm) (mm) (m2) 3.45 7.74 2.79 (m3/s)
0 0.000 0.00 0.00 0.00 0 0.00 0.00
5 0.320 4.95 1.50 3.45 303,140 3.49 0.00 0.00 3.49
10 0.500 7.74 0.00 7.74 431,289 4.96 7.82 0.00 12.78
15 0.180 2.79 0.00 2.79 548,648 6.31 11.12 2.81 20.25
20 813,765 9.36 14.15 4.00 27.52
25 568,592 6.54 20.99 5.09 32.63
30 132,912 1.53 14.67 7.56 23.75
35 0.00 0.00 3.43 5.28 8.71
40 0.00 0.00 0.00 1.23 1.23
45 0.00 0.00 0.00 0.00

-------------------------------------------------------------------------
The area for Time-Area Method- actually you are referring to the areas between successive isochrones. This can be determined as follows: a) Get a topo map, demarcate the catchment boundaries. b) Identify the main stream. c) Along the main stream length, mark out times of equal travel at regular spacing along the main stream length. d) Measure the areas between successive isochrones. This is the area you interested.

2, Actually how to determine the value for Time area curve?
is it base Tc and temporal time?
Compute the Tc using Rational Method. Divide Tc into less than 10 time steps.
3. for my example, I'm using ratio from temporal pattern according to Tc is 55min ~` 60min. but when come to duration of 15min as this example, is it correct?
For 60 min, try 10 minutes time steps.

[mize_zl]

Sir,

Thanks for your explaination.

Regards
Mize_zl

[drquek]

Hi Mize,

If you have any more questions, you are welcome to post here.

Regards,
Dr. Quek

[mize_zl]

Dear Dr Quek,

Can you please chek my calculation as per attached.

My catchment is too big, 2340hectare, is it my calculation for time area curve are correct? my tc is 303min. the Q are very big if I compare with Rational method, even it is not acceptable to use rational method in this case where the area are more than 80 Ha but the different are too big.

your help are very much appreciated

TQ

Mize :)

[drquek]

You computation for the Time-Area Method is wrong.

The Tc according to you is 303 min but the time interval you use is 5 min.

It seems you do not understand how to modify the spreadsheet.

I recommend that you learn more about the Time-Area Method before you attempt to apply the method.