The characteristics of arid zones, Rainfall Patterns, Runoff formation

1. Introduction to
arid zone hydrology
Water Resources Research Institute
email: wrri@wrri.org.eg
Web: www.wrri.org.eg
Dr. Ahmed Adel Saleh
email: norahmed1@gmail.com
F.B. : ahmed.a.saleh.965
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2. Contents
• Introduction
• Data collection
• The geomorphologic characteristics of arid zones
• Rainfall Patterns
• Runoff formation
• Rainfall-Runoff relationships
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3. Introduction - Aridity
A little or no
rainfall
Low soil
humidity
Flooding and
erosions
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4. Introduction - Aridity..(2)
4
0-50
Hyper
Arid
50-250
Arid
250-500
Semi-
Arid
Mean annual precipitation

5. Introduction..(3)
http://semiaridvyd.weebly.com/major-weather-patters.html
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Populations
Management
Catchment vs. Wadi
Wadi hydrology
The more people the more
living in arid areas
Alternative resources Exploitation and management in
arid region

6. A complete understanding
Meteorology Soil cover Geology Hydrogeology
Hydrology
Satellite
images
Geographic
information
systems
Modeling
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7. Data issues
field
observations
rainfall records
Runoff
measurements
Infiltration
tests
Groundwater
level records
Aquifer tests
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8. Methodologies issues
▪ Field trips experiments,
▪ Empirical and rational
approaches,
▪ Numerical computer modeling.
Developed for humid
regions
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9. Mystery
•In general, in humid
regions, discharge
increases in the
downstream direction,
whereas in arid regions
just the opposite is valid.
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10. The geomorphologic
characteristics of arid zones
surface features in arid regions that play a significant role in the formation of runoff
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11. Topography
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12. Cross sections
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13. Alluvial fans
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14. Key terms
• water divide lines
• Time of concentration
• The main channel
• the outlet point.
• tributaries
• drainage pattern
• water divide lines
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15. Drainage Basin Features
Drainage
Area
the projected horizontal surface area
Stream
Slope
vertical drop per unit of horizontal distance
Drainage
Density
the total stream channel length per unit area of drainage basin
Centroid
Length
the distance between the nearest point to the drainage basin
centroid on the main channel and the outlet point
Time of
Concentratio
n
the time that a raindrop requires from the farthest upstream
point to reach the outlet
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16. Rainfall Patterns
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17. Rainfall types
Orographic
rainfall
Convective
rainfall
Frontal rainfall
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18. Rainfall frequency
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19. Rainfall spatio-temporal variation
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20. Rainfall spatio-temporal variation
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21. Relative anomalies of the annual rainfall
𝑟𝑟 =
𝑅𝑅 − ̅𝑟𝑟
𝑆𝑆𝑟𝑟
Relative anomaly of a year
Total rain of that year
Mean yearly rainfall
Standard deviation of yearly rainfall
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22. the internal independence
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23. Areal reduction factor
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storm

24. Intensity–duration–frequency relationship (IDF)
• Tells how rare a given rain storm is.
• A graphical representation of the
probability that a given average
rainfall intensity will occur
• In the arid regions is take an
exponential probability distribution
function
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25. Spatial distribution of rainfall
• A single point rainfall measurement
• Interpolation
• Arithmetic average
• Thiessen polygon
• Isohyetal map
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26. Runoff formation
Rainfall-Runoff relationships
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27. Hyetograph–Hydrograph relationships
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28. Rainfall-Runoff relationships
Water Resources Research Institute
email: wrri@wrri.org.eg
Web: www.wrri.org.eg
Eng. Ahmed Adel Saleh
email: norahmed1@gmail.com
F.B. : https://www.facebook.com/ahmed.a.saleh.965

30. {
Introduction
• Rainfall-runoff relationships find the volumetric loss of storm water.
• The most important looses are:
• evaporation,
• transpiration,
• interception,
• depression storage,
• soil moisture storage and
• groundwater recharge. Infiltration
No vegetation
Short period
Rare trees

31. precipitation losses
surface
runoff

32. Rational Method
• The rational method for determining flood peak discharges from
measurements of rainfall depths.
𝑄𝑄𝑝𝑝 = 𝐶𝐶𝐶𝐶 𝐶𝐶
C : coefficient depends on catchment characteristics [0.05 : 0.95]
i : mean rainfall intensity in the time of concentration [in / Hour]
A : catchment area [Acres]

33. Time-Area Method
𝑄𝑄𝑝𝑝 = �
𝑘𝑘=1
𝑛𝑛
𝑖𝑖 𝑛𝑛−𝑘𝑘 ∆𝐴𝐴 𝑘𝑘

34. The Unit Hydrograph

35. Depth(mm)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00 12:0
01Jan2016 02Jan2016 03Jan2016 04Jan2016
Flow(cms)
0
50
100
150
200
250
300
350
400
450
Subbasin "Ghoawiba" Results for Run "SCS-Type II"
Run:SCS-Type II Element:Ghoaw iba Result:Precipitation
Run:SCS-Type II Element:Ghoaw iba Result:Precipitation Loss
Run:SCS-Type II Element:Ghoaw iba Result:Outflow
Run:SCS-Type II Element:Ghoaw iba Result:Baseflow

36. ESTIMATION OF DESIGN NET RAINFALL

37. The Unit Hydrograph … (2)
φ index method with initial losses W index method with initial losses

38. The Unit Hydrograph … (3)
SCS-CN method Modified Horton method

39. References
Wadi Hydrology
• Chapter 1 Introduction
• Chapter 2 Wadi Characteristics
• Chapter 3 Rainfall Pattern in arid region
• Chapter 4 Runoff and Hydrograph Analysis
Hydrology of Wadi systems
• Chapter Two: Hydrological processes in arid and semi-arid areas
• Chapter Six: Rainfall-runoff analysis and modelling in wadi systems
• Chapter Nine: Sustainable management of wadi systems
Hydrological Modelling in Arid and Semi-Arid Areas
• 1.3 HYDROLOGICAL PROCESSES IN ARID AREAS
• 8 Calibration, uncertainty, and regional analysis of conceptual rainfall-runoff models
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