Rational Module description

Thursday, April 16, 2020 2:58:00 PM

User will input “Maximum length of flow from remote point to the point of concentration (m)” and “Difference in elevation between the remote point and the point of outlet (m)” using Texbox.
System will fetch information related to Soil texture, Slope, Landform (Black, Red / lateritic) from the Parcel characteristics table for the respective survey number.
A query will be executed to find current Land use for the selected survey number.
A query will be executed to find the hourly rainfall for last 24 Hours (rainfall value will be reset at 08:30 am daily).
A query will be executed to find current Land use for the selected survey number.
A query will be executed on below table to find the runoff Coefficient (C) using Land use, Soil Texture, Slope.

Land_Use	SLOPE	Texture	runoff Coefficient
Cultivated Land	1-3	Clay	0.6
Cultivated Land	3-5	Clay	0.6
Cultivated Land	5-10	Clay	0.7
Cultivated Land	10-15	Clay	0.82
Cultivated Land	15-25	Clay	0.82
Cultivated Land	25-33	Clay	0.82
Cultivated Land	33-50	Clay	0.82
Cultivated Land	>50	Clay	0.82
Cultivated Land	<1	Sandy Loam	0.3
Cultivated Land	1-3	Sandy Loam	0.3
Cultivated Land	3-5	Sandy Loam	0.3
Cultivated Land	5-10	Sandy Loam	0.4
Cultivated Land	10-15	Sandy Loam	0.52
Cultivated Land	15-25	Sandy Loam	0.52
Cultivated Land	25-33	Sandy Loam	0.52
Cultivated Land	33-50	Sandy Loam	0.52
Cultivated Land	>50	Sandy Loam	0.52
Pasture Land	<1	Clay	0.4
Pasture Land	1-3	Clay	0.4
Pasture Land	3-5	Clay	0.4
Pasture Land	5-10	Clay	0.55
Pasture Land	10-15	Clay	0.6
Pasture Land	15-25	Clay	0.6
Pasture Land	25-33	Clay	0.6
Pasture Land	33-50	Clay	0.6
Pasture Land	>50	Clay	0.6
Forest Land	<1	Clay	0.4
Forest Land	1-3	Clay	0.4
Forest Land	3-5	Clay	0.4
Forest Land	5-10	Clay	0.5
Forest Land	10-15	Clay	0.6
Forest Land	15-25	Clay	0.6
Forest Land	25-33	Clay	0.6
Forest Land	33-50	Clay	0.6
Forest Land	>50	Clay	0.6
Pasture Land	<1	Sandy Loam	0.1
Pasture Land	1-3	Sandy Loam	0.1
Pasture Land	3-5	Sandy Loam	0.1
Pasture Land	5-10	Sandy Loam	0.16
Pasture Land	10-15	Sandy Loam	0.22
Pasture Land	15-25	Sandy Loam	0.22
Pasture Land	25-33	Sandy Loam	0.22
Pasture Land	33-50	Sandy Loam	0.22
Pasture Land	>50	Sandy Loam	0.22
Forest Land	<1	Sandy Loam	0.1
Forest Land	1-3	Sandy Loam	0.1
Forest Land	3-5	Sandy Loam	0.1
Forest Land	5-10	Sandy Loam	0.25
Forest Land	10-15	Sandy Loam	0.3
Forest Land	15-25	Sandy Loam	0.3
Forest Land	25-33	Sandy Loam	0.3
Forest Land	33-50	Sandy Loam	0.3
Forest Land	>50	Sandy Loam	0.3
Cultivated Land	<1	Clay Loam	0.5
Cultivated Land	1-3	Clay Loam	0.5
Cultivated Land	3-5	Clay Loam	0.5
Cultivated Land	5-10	Clay Loam	0.6
Cultivated Land	10-15	Clay Loam	0.72
Cultivated Land	15-25	Clay Loam	0.72
Cultivated Land	25-33	Clay Loam	0.72
Cultivated Land	33-50	Clay Loam	0.72
Cultivated Land	>50	Clay Loam	0.72
Cultivated Land	<1	Silt Loam	0.5
Cultivated Land	1-3	Silt Loam	0.5
Cultivated Land	3-5	Silt Loam	0.5
Cultivated Land	5-10	Silt Loam	0.6
Cultivated Land	10-15	Silt Loam	0.72
Cultivated Land	15-25	Silt Loam	0.72
Cultivated Land	25-33	Silt Loam	0.72
Cultivated Land	33-50	Silt Loam	0.72
Cultivated Land	>50	Silt Loam	0.72
Pasture Land	<1	Clay Loam	0.3
Pasture Land	1-3	Clay Loam	0.3
Pasture Land	3-5	Clay Loam	0.3
Pasture Land	5-10	Clay Loam	0.36
Pasture Land	10-15	Clay Loam	0.42
Pasture Land	15-25	Clay Loam	0.42
Pasture Land	25-33	Clay Loam	0.42
Pasture Land	33-50	Clay Loam	0.42
Pasture Land	>50	Clay Loam	0.42
Forest Land	<1	Clay Loam	0.3
Forest Land	1-3	Clay Loam	0.3
Forest Land	3-5	Clay Loam	0.3
Forest Land	5-10	Clay Loam	0.35
Forest Land	10-15	Clay Loam	0.5
Forest Land	15-25	Clay Loam	0.5
Forest Land	25-33	Clay Loam	0.5
Forest Land	33-50	Clay Loam	0.5
Forest Land	>50	Clay Loam	0.5
Pasture Land	<1	Silt Loam	0.3
Pasture Land	1-3	Silt Loam	0.3
Pasture Land	3-5	Silt Loam	0.3
Pasture Land	5-10	Silt Loam	0.36
Pasture Land	10-15	Silt Loam	0.42
Pasture Land	15-25	Silt Loam	0.42
Pasture Land	25-33	Silt Loam	0.42
Pasture Land	33-50	Silt Loam	0.42
Pasture Land	>50	Silt Loam	0.42
Forest Land	<1	Silt Loam	0.3
Forest Land	1-3	Silt Loam	0.3
Forest Land	3-5	Silt Loam	0.3
Forest Land	5-10	Silt Loam	0.35
Forest Land	10-15	Silt Loam	0.5
Forest Land	15-25	Silt Loam	0.5
Forest Land	25-33	Silt Loam	0.5
Forest Land	33-50	Silt Loam	0.5
Forest Land	>50	Silt Loam	0.5
Cultivated Land	5-10	Silty Clay	6.7
Cultivatedc Land	3-5	Sandy Clay	NULL

If the land use or soil types are different for the area in such situations, weighted average value of C can be calculated as indicated below:

Cw = A1 CI + A2 C2+ ……An Cn / A

Where,

A is the total area of the watershed,

C1, C2….,Cn are the coefficients of runoff for the different homogeneous areas (equivalent of soil map unit areas) of size A1, A2 ….. An in ha respectively.

Calculate Time of Concentration (Tc)
- It is the function of the length of the main channel (L, in m) and fall in elevation from the remotest point to the outlet (H, in m).
- Alternatively, the Time of concentration (Tc) can also be calculated from the empirical formula

T_C=0.0195K^0.77

Where K is the square root of L3/H

Where,

L - Maximum length of flow from remote point to the point of concentration (m).

H - Difference in elevation between the remote point and the point of outlet (m)

Tc - Time of concentration (hours)

Calculate Rainfall Intensity (I): Wherever the data on rainfall intensity is not available, it can be calculated as indicated below. Intensity of rainfall (I) for the desired frequency or recurrence interval and for duration equal to time of concentration can be worked out as follows;

Where,

K₁, a, b and n are empirical constants to be selected from the Master_Empirical_Constant.

Tc = Time of concentration in hours

T = Recurrence interval or frequency (years) to be selected from Master_Recurrence_Interval depending Land user, slope and texture

Peak rate of runoff can be estimated by rational method as below.

Where,

Q - Peak rate of runoff (Cubic meters per second, m/S)

C - Coefficient of runoff (Table)

A - Area of watershed (hectares)

I - Intensity of rainfall (mm/hour) for the duration equal to time of concentration

Display the result in a table showing the information such as Survey No, Farmer Name, Areain Hectare, Interval, Runoff(mm).

Rainfall intensity – duration – return period relationship &Empirical constants

Meteorological Station	Agro-climatic Zone	K₁	a	b	n
1. Bangalore	1. Southern Dry zone 2. Eastern Dry Zone	6.275	0.1262	0.5	1.1280
2.Hyderabad	3. Northern Dry Zone 4. North eastern Dry Zone 5. Central Dry Zone	5.250	0.1354	0.5	1.0295
3. Mangalore	6. Coastal Zone	6.744	0.1395	0.5	0.9374
4.Other Zones	7. Southern transition Zone 8. Northern transition Zone 9. North eastern transition Zone 10.Hilly Zone	6.311	0.1523	0.5	0.9465