AGE 506 IRRIGATION ENGINEERING

1. AGE 506 IRRIGATION ENGINEERING Course Lecturer: Dr J.K. Adewumi Dept. of Agricultural Engineering UNAAB. Nigeria

2. Methods of Irrigation A. Surface Irrigation • Wild flooding • Border strip • Check Basin • Furrow • Sub- Irrigation • Natural sub-irrigation (Advantages & disadvantages) • Artificial sub-irrigation (Advantages & disadvantages) • Overhead Irrigation • Rotating head systems • Perforated pipe system • Furrow irrigation • Border Irrigation • Level Border • Graded Border

3. Water Measurement in Open channel • Water measurement in pipes • Volume • Velocity • Orifices Basin Flow Equations Hydraulic Radius Continuity Equation • Darcy-Weibach Equation • Bernoullis Equation

4. Measurement of Irrigation Water • Bucket and watch method • Float method • Flow from a vertical pipe • Flow from a horizontal pipe • Discharge from siphon tubes

5. Frequency and Amount of Irrigation • Methods of Frequency • Meteorological Method for determining CU or ETp for the plant Blaney Criddle method • Plant Index method (i) Crop itself (ii) indicator Plant (iii) change in leave colour (iv) Physiological Index • Soil Index method (i) Moisture content (ii) Soil potential by tensiometer • Methods of determining amount of irrigation • Tensiometer • C.U. • Available water moisture

6. Irrigation Efficiencies • Reservoir Storage Efficiency • Er = Ws/Wso X 100%,Ws = amount of water directed, Wso = amount of water stored • Water conveyance Efficiency • Ec= Wf/Wr X 100%, Wf = amount of water delivered into farm, Wr = water diverted from reservoir • Water application Efficiency • Ea = Wst/Wf X 100% Where Wst = water stored in root zone , • Overall Irrigation Efficiency • Ei = Er X Ec X Ea (100%) or Ei = Er/Wd where Wd = water stored or diverted for irrigation • Water distribution Efficiency • Ed = 1 – y where d = ave. depth of water stored along run during irrigation, y= ave. numerical deviation from d d

7. Design of Sprinkler system The following should be considered for design: • Area of land • Consumptive use of crop • Water holding capacity • Root zone depth • Effective rainfall • Water application efficiency • Antecedent moisture content • Net irrigation requirement • Gross irrigation requirement • Irrigation frequency • Maximum time needed to apply dg (hrs)

8. Quality of irrigation water • Depends on amount and kind of salt present • Total salt concentration • Relative proportion • Bicarbonate and boron contents Suitability of irrigation water can be expressed as SIW = f(QSPCD) Where Q= quality of irrigation water S = soil type P = salt tolerance characteristics of the plant C = climate D= drainage characteristics of the soil

9. Effects of poor drainage on plants and soil Reduces aeration in soil Water-logging Anaerobic decomposition Temperature fluctuation in soil Factors affecting rate of flow into drains Soil permeability Depth of soil Drain spacing Drain opening Drain diameter Distribution of potential at a flow boundary Drainage of Agricultural land

10. Factors affecting erosion by water Climatic factors Soil characteristics Topography Vegetation Phases of erosion Detachment Transportation Deposition Types of soil movement by wind Suspension Saltation Surface creep

11. Gully Erosion Aim of Gully Erosion Control • To reduce peak flow rate • To provide stable channel • Runoff reduction • Vegetative control • Structures Stages of Gully Development • Channel erosion by downward scour of topsoil • Upstream movement of gully head • Healing stage • Stabilization of gully

12. Terraces Terracing: An erosion control method Types are: • Bench terrace • Broad based terrace Functions of terraces • To decrease length of hill-side slope • To remove or retain runoff rate in area of inadequate rainfall Terrace Design involves: • Proper spacing • Location of terraces • Design of channel with suitable capacity • Development of farmable cross-section Terrace Spacing Location • Land slope • Soil condition • Proposed land use • Farm roads • Fences and outlet

13. Drainage and Reclamation Process and practice involved in bringing saline and alkali soils into productive condition Essentials of reclamation procedures: • Determine nature of the soil • Degree of salinity or alkalinity • Drainage Characteristics • Topography of the land • Presence of hardpan Reclamation Procedure Permanent reclamation • Lowering water table (if high) • Improving infiltration rate of soil • Leaching of salts in saline soils • Replacing excessive exchangeable Na by ca salts • Suitable management practice Temporary reclamation • Removing the salts crust from surface of soil (Biological) • Ploughing salt surface-crust (Physical) • Neutralizing effects of salts (Chemical) • Synergic effects

14. Class projects • Design a channel of rectangular cross-section to carry water at the rate of 0.3m3/s a distance of 5 km if the width is restricted to 1.5 m and the head loss along the length limited to 1 m. Consider lining to be of rough concrete (n= 0.015) • Determine the system capacity for a sprinkler irrigation system to irrigate 16ha of maize crop. Design moisture use rate is 5 mm/day. Moisture replaced in soil at each irrigation is 6 cm. Irrigation efficiency is 70%. Irrigation period is 10 days in a 12-day interval. The system is to be operated for 20 hours per day.