Irrigation Related... formula, etc.

Question 1

Parameters needed in designing an open channel

Answer 1

1. Design Discharge or Flow Capacity
2. Flow Velocity
3. Roughness Coefficient
4. Canal Cross Section
5. Bottom Slope
6. Freeboard

Question 2

CROP WATER REQUIREMENT

Answer 2

𝐶𝑊𝑅 = 𝐸𝑇𝑎 + (𝑆 & 𝑃)𝑓𝑖𝑒𝑙𝑑

where:
CWR is the crop water requirement (mm/day)
ETa is the actual evapotranspiration (mm/day)
(S & P)field is the seepage and percolation in the field (mm/day)

Question 3

FARM WATER REQUIREMENT - Lowland

Answer 3

FWR = CWR - ER + LPWR + farm ditch losses
FWR = (CWR - ER + LPWR)/Ea

where:
CWR is the crop water requirement (mm)
ER is the effective rainfall (mm)
LPWR is the land preparation water requirement (mm)
Ea is the application efficiency (mm)

Question 4

FARM WATER REQUIREMENT - Upland

Answer 4

FWR = CWR - ER + farm ditch losses
FWR = (CWR - ER)/Ea

Where;
Ea is the application efficiency (mm)
CWR is the crop water requirement (mm)
ER is the effective rainfall (mm)

Question 5

DIVERSION WATER REQUIREMENT

Answer 5

DWR = FWR + conveyance losses
DWR = FWR/Ec

where:
DWR is the diversion water requirement (mm)
FWR is the farm water requirement (mm)
Ec is the conveyance efficiency

Question 6

Duration of the Penman-Monteith Method

Answer 6

daily, monthly, seasonal

Question 7

Accuracy/ Reliability of the Penman-Monteith Method

Answer 7

reliable for any length period

Question 8

Methods that are less precise than Penman-Monteith and with a duration period of 5 days or more

Answer 8

Radiation Method

Blaney-Criddle Method

Question 9

Accuracy/ Reliability of the Pan evaporation Method for a period of 10 days or longer

Answer 9

less reliable for short-term estimates than other methods

Question 10

Accuracy/ Reliability of the Pan evaporation Method if little previous history is available for a pan, caution should be exercised even for computing ETo for longer periods

Answer 10

can be accurate if evaporation pans are well maintained and properly located

Question 11

Data needed for Penman-Monteith Method

Answer 11

maximum temperature 
minimum temperature 
wind speed at 2m 
dewpoint temperature 
maximum relative humidity 
minimum relative humidity 
actual duration of sunshine

Question 12

Data needed for Radiation Method

Answer 12

maximum temperature
minimum temperature
solar radiation

Question 13

Data needed for Blaney-Criddle Method

Answer 13

maximum temperature

minimum temperature

Question 14

Data needed for Pan evaporation Method

Answer 14

pan evaporation

Question 15

Minimum length of record required for Irrigation Scheduling

Answer 15

Daily

Question 16

Minimum length of record required for Irrigation System Design

Answer 16

historical record of at least 10 years

Question 17

Minimum length of record required for Reservoir Design, Water Right Determination

Answer 17

monthly water use estimates

Question 18

Actual Evapotranspiration

Answer 18

𝐸𝑇𝑎 = 𝐸𝑇𝑜 × 𝑘𝑐

where:
ETa = actual evapotranspiration (mm/day)
ETo = reference evapotranspiration (mm/day)
kc = crop coefficient

Question 19

Land Preparation Water Requirement

Answer 19

𝐿𝑃𝑊𝑅 = 𝐿𝑆𝑅 + 𝑆𝑊 + 𝐸𝑇𝑜

where:
LPWR is the land preparation water requirement (mm)
LSR is the land soaking requirement (mm)
SW is the standing water (mm)
ETo is the reference evapotranspiration (mm)

Question 20

Farm Ditch Losses

Answer 20

𝐹𝑎𝑟𝑚 𝑑𝑖𝑡𝑐ℎ 𝑙𝑜𝑠𝑠𝑒𝑠 = (𝑆 & 𝑃)𝑓𝑎𝑟𝑚 𝑑𝑖𝑡𝑐ℎ × 𝑃 × 𝐿

where:
(S & P)farm ditchis theseepage and percolation rate (mm/day)
P is the wetted perimeter (m)
L is the length of farm ditch (m)

Question 21

Land Soaking Requirement

Answer 21

𝐿𝑆𝑅 = {[𝑛 − (𝑅𝑀𝐶 × 𝐴𝑠)] × 𝐷𝑟𝑧} / (100)

where:
LSR is the land soaking requirement (mm)
n is the soil porosity
RMC is the residual moisture content
As is the apparent specific gravity
Drz is the depth of root zone (mm)