Irrigation and Water Resource
1) Hydrology:
1. Coefficient of variation:
Cv = (100 * standard deviation)/mean.
2. Average echo power:
Pr = (CZ)/r2.
3. Radar echo factor:
Z = aIb.
4. Intensity of rainfall:
I = [r2Pr / (aC]1/b.
5. Average depth of precipitation over an area:
Arithmetic Mean Method:
Theissen Polygon Method:
Isohyetal Method:
Average depth of rainfall = (1/A) ∑ [Area between two adjacent isohyets] * [mean of the two adjacent isohyet values].
6. Optimal number of rain gauge stations:
N = (Cv/ε)2.
7. Standard deviation:
8. Missing annual precipitation:
Px= (1/M) (P1 + P2 +-------+ Pm).
9. Correction for precipitation values at station x and beyond the period of change:
Pcx= Px( Sc/ Sa.
10. Average cumulative depth of rainfall:
11. Actual rate of infiltration at any time:
f = fc when, i ≥ fc.
f = i when, i < fc.
12. Runoff by Barlow:
R = Kb P.
13. Runoff by Strange:
R = Ks P.
14. Runoff by Inglis and De Souza for Western Ghats:
R = 0.85 P - 30.5
For Deccan plateau, R= (1/254) P (P - 17.8).
15. Runoff by Khosla:
Rm = Pm - Lm.
16. Runoff by hydrologic water-budget equation:
R = P - Eet - ∆S.
17. Flow mass curve ordinate:
V = to∫T Q . dt.
18. Flow-duration curve:
Percentage probability:
Pp = [m/(N+1)] * 100.
19. Hydrograph analysis:
Time Interval: N (in days) = b A0.2.
20. Equilibrium flow rate:
Qe = [(A/D) * 104 m3/hr.
Qe = 2.78(A/D) m3/s.
21. Ordinate of a D-hour unit hydrograph:
U(t) = S(t) - S (t - D)
or S(t) = U(t) + S(t - D).
22. S-curve addition: S(t - D).
23. Rational Method:
Peak value of runoff = Qp = (1/3.6) C i A.
24. Time of concentration by Kirpich:
tc = 0.01947 L0.77 S-0.386.
25. Empirical methods:
Dicken´s formula:
Qp = CDA3/4.
Ryves formula:
Qp = CRA2/3.
Inglis formula:
Qp = (124 A)/ √(A + 10.4).
Envelope curve technique:
Qp = f(A).
Baird and McIll wraith:
Qp = (3025 A)/( 278 + A)0.78.
CWC for small to medium catchments (A < 250 sq. km):
Qp = A[a(tp)b.
26. Flood frequency method:
P = m/(N + 1).
27. Return period (or recurrence interval) Tr = 1/P.
2) Soil-water relations and irrigation methods:
1. Soil water relationships:
e = Vv / Vs.
n = Vv / V.
w = Vw / V.
S = Vw / Vv.
w = S n.
γ b = WT / V.
WT = Ws + Ww.
V = Ws/ (Gbγ w).
Vs/V = Gb/ Gs.
2. Volume of water in the root zone soil:
Vw = W Ad (1 - n) Gs.
3. Depth of water:
dw = Vw/A.
dw = Gs (1-n) Wd.
dw = w d.
4. Moisture fraction:
Wfc = (Ww / Ws.
5. Volumetric moisture content at field capacity:
wfc = Gb Wfc.
6. Total available moisture:
dt = (wfc - wwp) d.
7. Management allowed deficit:
Dm = fm dt.
8. Soil moisture deficit:
Ds =( wfc - w) d.
9. Potential evapotranspiration:
Det = K Ep.
10. Consumptive use of crop by Blaney-Criddle:
u = kf.
11. Consumptive use factor:
f= (p/100)(18 t + 32).
12. Field irrigation requirement:
FIR = [Det- (Dp - Dpl)]/ Ea.
13. Effective rainfall depth:
Dpe = 0.8 Dp - 25 when Dp>75 mm/month.
Dpe = 0.6 Dp - 10 when Dp<75 mm/month.
14. Frequency of irrigation = Allowable soil moisture depletion / Rate of consumptive use.
15. Depth of water to be applied =[ (wfc - w) d] / Ea.
3) Ground water and wells:
1. Darcy´s law:
Q = K A (∆H/L).
V = - K (dh/ds).
2. Flow along the three principal co-ordinate axes:
u = -Kx(∂h/∂x).
v = -Ky(∂h/∂y).
w = -Kz(∂h/∂z).
3. Reynolds number:
Re = (V d ρ)/ μ.
4. Boussinesq´s and Dupuit´s continuity equation of motion for confined and unconfined aquifers:
For steady flow:
5. Steady state well discharge for unconfined aquifers, using Dupuit´s equation:
6. u =(r2s)/(4Tt).
7. Q = -(4∏Ts)/W(u).
8. Well drawdown:
Sw = ho - hw = -(Q/2∏T) ln(ro/rw).
9. Total drawdown:
10. For steady flow conditions for two wells in a confined aquifer, drawdown in the two wells:
11. Electrical Resistivity Method:
Wenner arrangement:
ρa = (2πa)(V/I).
Schlumberger arrangement:
12. Pumping tests:
Discharge rate:
4) Canal irrigation:
1. Loss:
qa = (1/200) ( B + h )2/3 in m3/s per ki
1) Hydrology:
1. Coefficient of variation:
Cv = (100 * standard deviation)/mean.
2. Average echo power:
Pr = (CZ)/r2.
3. Radar echo factor:
Z = aIb.
4. Intensity of rainfall:
I = [r2Pr / (aC]1/b.
5. Average depth of precipitation over an area:
Arithmetic Mean Method:
Theissen Polygon Method:
Isohyetal Method:
Average depth of rainfall = (1/A) ∑ [Area between two adjacent isohyets] * [mean of the two adjacent isohyet values].
6. Optimal number of rain gauge stations:
N = (Cv/ε)2.
7. Standard deviation:
8. Missing annual precipitation:
Px= (1/M) (P1 + P2 +-------+ Pm).
9. Correction for precipitation values at station x and beyond the period of change:
Pcx= Px( Sc/ Sa.
10. Average cumulative depth of rainfall:
11. Actual rate of infiltration at any time:
f = fc when, i ≥ fc.
f = i when, i < fc.
12. Runoff by Barlow:
R = Kb P.
13. Runoff by Strange:
R = Ks P.
14. Runoff by Inglis and De Souza for Western Ghats:
R = 0.85 P - 30.5
For Deccan plateau, R= (1/254) P (P - 17.8).
15. Runoff by Khosla:
Rm = Pm - Lm.
16. Runoff by hydrologic water-budget equation:
R = P - Eet - ∆S.
17. Flow mass curve ordinate:
V = to∫T Q . dt.
18. Flow-duration curve:
Percentage probability:
Pp = [m/(N+1)] * 100.
19. Hydrograph analysis:
Time Interval: N (in days) = b A0.2.
20. Equilibrium flow rate:
Qe = [(A/D) * 104 m3/hr.
Qe = 2.78(A/D) m3/s.
21. Ordinate of a D-hour unit hydrograph:
U(t) = S(t) - S (t - D)
or S(t) = U(t) + S(t - D).
22. S-curve addition: S(t - D).
23. Rational Method:
Peak value of runoff = Qp = (1/3.6) C i A.
24. Time of concentration by Kirpich:
tc = 0.01947 L0.77 S-0.386.
25. Empirical methods:
Dicken´s formula:
Qp = CDA3/4.
Ryves formula:
Qp = CRA2/3.
Inglis formula:
Qp = (124 A)/ √(A + 10.4).
Envelope curve technique:
Qp = f(A).
Baird and McIll wraith:
Qp = (3025 A)/( 278 + A)0.78.
CWC for small to medium catchments (A < 250 sq. km):
Qp = A[a(tp)b.
26. Flood frequency method:
P = m/(N + 1).
27. Return period (or recurrence interval) Tr = 1/P.
2) Soil-water relations and irrigation methods:
1. Soil water relationships:
e = Vv / Vs.
n = Vv / V.
w = Vw / V.
S = Vw / Vv.
w = S n.
γ b = WT / V.
WT = Ws + Ww.
V = Ws/ (Gbγ w).
Vs/V = Gb/ Gs.
2. Volume of water in the root zone soil:
Vw = W Ad (1 - n) Gs.
3. Depth of water:
dw = Vw/A.
dw = Gs (1-n) Wd.
dw = w d.
4. Moisture fraction:
Wfc = (Ww / Ws.
5. Volumetric moisture content at field capacity:
wfc = Gb Wfc.
6. Total available moisture:
dt = (wfc - wwp) d.
7. Management allowed deficit:
Dm = fm dt.
8. Soil moisture deficit:
Ds =( wfc - w) d.
9. Potential evapotranspiration:
Det = K Ep.
10. Consumptive use of crop by Blaney-Criddle:
u = kf.
11. Consumptive use factor:
f= (p/100)(18 t + 32).
12. Field irrigation requirement:
FIR = [Det- (Dp - Dpl)]/ Ea.
13. Effective rainfall depth:
Dpe = 0.8 Dp - 25 when Dp>75 mm/month.
Dpe = 0.6 Dp - 10 when Dp<75 mm/month.
14. Frequency of irrigation = Allowable soil moisture depletion / Rate of consumptive use.
15. Depth of water to be applied =[ (wfc - w) d] / Ea.
3) Ground water and wells:
1. Darcy´s law:
Q = K A (∆H/L).
V = - K (dh/ds).
2. Flow along the three principal co-ordinate axes:
u = -Kx(∂h/∂x).
v = -Ky(∂h/∂y).
w = -Kz(∂h/∂z).
3. Reynolds number:
Re = (V d ρ)/ μ.
4. Boussinesq´s and Dupuit´s continuity equation of motion for confined and unconfined aquifers:
For steady flow:
5. Steady state well discharge for unconfined aquifers, using Dupuit´s equation:
6. u =(r2s)/(4Tt).
7. Q = -(4∏Ts)/W(u).
8. Well drawdown:
Sw = ho - hw = -(Q/2∏T) ln(ro/rw).
9. Total drawdown:
10. For steady flow conditions for two wells in a confined aquifer, drawdown in the two wells:
11. Electrical Resistivity Method:
Wenner arrangement:
ρa = (2πa)(V/I).
Schlumberger arrangement:
12. Pumping tests:
Discharge rate:
4) Canal irrigation:
1. Loss:
qa = (1/200) ( B + h )2/3 in m3/s per ki
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