1. RUNOFF

2. LECTURE OBJECTIVES Understand the runoff generation processes
Know measures that can be used to regulate runoff rate

3. LECTURE OBJECTIVES
Know the applications of runoff data in hydrology, water management and agriculture
Know methods that can be used to measure river runoff and field runoff

4. INTRODUCTION What is runoff?
What are the other terms that can be used to describe runoff?
Units of measurement?

5. INTRODUCTION Define the following terms: Inter flow
Antecedent soil moisture
Stage / head
Weir / flume

6. INTRODUCTION 2 runoff generation processes:
Hortonian Overland Flow (HOF)
Saturation Overland Flow (SOF)

7. INTRODUCTION HOF occurs when i > f, i – f = rainfall excess
Common in tropical regions

8. INTRODUCTION HOF – A result of saturation (prolonged rain)
Water returned to the surface through exfiltration
Rising water table intersecting soil surface

9. INTRODUCTION FACTORS AFFECTING RUNOFF Rainfall properties
Surface properties
Soil / geological properties

10. INTRODUCTION
What are the rainfall properties that affect runoff generation? Explain how each of the factors affect runoff generation.

11. WHY QUANTIFYING RUNOFF
Preparation of water budgets
Identification of major sources of pollutant loads in a catchment
Quantification of discharges from tributaries or other sources

12. WHY QUANTIFYING RUNOFF
Design of water conservation structures
Design of dams
Flood control and monitoring
Soil erosion and sedimentation studies

13. RUNOFF MEASUREMENT
Refers to flow measurement in open channels (natural streams / artificial channels) or field runoff

14. USE OF MEASURING DEVICES
RUNOFF MEASUREMENT
USE OF MEASURING DEVICES
Weirs and flumes
Used for long term discharge measurement

15. RUNOFF MEASUREMENT Referred to as primary measuring devices
Creates critical flow through a control section of known dimensions
Q = f (section shape, head of water)

16. RUNOFF MEASUREMENT
Weir – A “dam” built across an open channel over which water flows through or over a specially shaped opening or edge
Flume – specially shaped open channel flow sections that restrict the channel area resulting in a change in water level as water flows through it

17. V – notch, rectangular, chipoletti / trapezoidal
RUNOFF MEASUREMENT
Each weir / flume has an associated equation linking stage (depth) to discharge (Q)
Examples of weirs are:
V – notch, rectangular, chipoletti / trapezoidal

18. Parshall, H – flume, Montana, Palma Bowlus
RUNOFF MEASUREMENT
Examples of flumes are:
Parshall, H – flume, Montana, Palma Bowlus
Flumes are often used to measure field runoff

19. RUNOFF MEASUREMENT

20. RUNOFF MEASUREMENT

21. RUNOFF MEASUREMENT

22. RUNOFF MEASUREMENT

23. NEXT LECTURE Rating a gauging station The dilution method
Runoff estimation (equation of continuity, Manning’s equation, the Rationale method, Soil Conservation Service method, COOK’s method)