Rainfall-Runoff Modeling Of Wadi Zimar

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Rainfall-Runoff ModelingOf Wadi Zimar 
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• Prepared by
• Ahmad Tallal Abu-Hamed
• Mohamed Nemir Mohsen
• Osama Omar Nazzal
•  
• Under the direction of
• Dr. Sameer Shadeed

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Presentation Outline

• Introduction
• Study Area
• Literature review
• Analysis of Rainfall Data
• Rainfall Runoff Models

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• Introduction

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General

• The demand of water is increasing since the
  population of the world is increasing.
• Studies of water and its management in the
  Palestinian Territories are essential.
• Hydrology is the science that deals with the
  occurrence and movement of water on and over the
  surface of the earth.
• hydrology studies of precipitation and runoff
  linked with problems associated with design and
  management of water resources projects.

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Objectives

• The main objective of this project is to study
  the storm water drainage of Wadi Zimar.
• derive the unit hydrograph of catchment.

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Data collection

• Contour map of Wadi Zeimar.
• Nablus and Tulkarm Metrological stations.
• Other sources were consulted to collect
  information about the study area. This include
  Nablus and Tulkarm Municipalities.

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Study Area
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General

• The Wadi Zeimar catchment area is hilly,
  mountainous in the eastern side, and
  approximately flat in the western part.
• Surface and subsurface water drains towards the
  coastal aquifer in the direction to the
  Mediterranean sea.

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• The climate in the study area is Mediterranean,
  with moderate summers and warm winters.
• The annual rainfall is very unevenly distributed
  over the year.
• Land use in the catchment varies from
  agricultural area to Industrial area and Built up
  area.

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• Literature review

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Introduction

• The history of rainfall-runoff is believed to
  have begun about 335 years ago .
• The importance of rainfall-runoff Pa-Qa modeling
  has long been recognized
• several hundred perhaps thousands models of
  rainfall-runoff are exist.

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Rainfall-Runoff Modeling Methods
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SCS Method

• The SCS synthetic unit hydrograph is the
  dimensionless unit hydrograph developed by the
  soil conservation service.
• The SCS synthetic unit hydrograph was developed
  based on the analysis of a large number of
  natural unit hydrographs from a wide range of
  catchment sizes and geographic.

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• SCS method is used, since it requires
  geographical parameters which can very easily be
  obtained by using GIS techniques.
• Synthetic unit hydrographs are developed along
  two main concepts
• Each watershed has a unique unit hydrograph.
• All unit hydrographs can be represented by a
  single family of curves or a single equation.

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• The basic procedure of the SCS method for
  estimating runoff can be summarized as follows
• Determine the watershed area and slope in
  percent.
• The flow velocity could be estimated.

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• the time of concentration in hours
• Where
• L length of flow path in feet.
• V average velocity in feet per second.
• Tc time of concentration in minute.

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• The time of peak discharge Tp, in hour
• Where
• Tr duration of effective rainfall
• The peak discharge, m³/s.cm

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Snyder's Method

• Snyder's method is a very straight forward,
  mostly empirical method for deriving the time to
  peak and peak flow of a unit hydrograph.
• Snyder method was developed using the analysis of
  a large number of hydrographs from catchment
  region.

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• The basic procedure of Snyder's method for
  estimating runoff can be summarized as follows
• Basin lags in hours tp
• Where
• L is the main stream distance from outlet to
  divide (mi).
• Lc is the main stream distance from outlet to a
  point opposite the basin centroid (mi).
• Ct a coefficient representing variations of
  watershed slopes and storage.
• S is the weighted channel slope.

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• Peak discharge Qp(cfs)
• Where
• Cp the coefficient accounting for flood wave and
  storage condition.
• A watershed size (mi²).
• tp lag time.

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• To construct Snyder's unit hydrograph,W50 , W75
  are also considered
• W50 width of unit hydrograph at 50 of peak
  discharge in hour.
• W75 width of unit hydrograph at 75 of peak
  discharge in hour.

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Analysis of Rainfall Data
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Analysis of annual rainfall

• The average annual rainfall data are obtained
  from the meteorological station in Nablus for the
  years from 1954 to 2008. The average of the
  average annual rainfall of Nablus data is
  calculated at 584.0684 mm. The standard deviation
  equals 233.26 and the maximum and minimum annual
  rainfall is 1195 mm (1992), 149.7 mm (1970)
  respectively.

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This figure shows the annual rainfall and its
average of Nablus
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• From the figure, it is noted that the deviation
  of the annual rainfall from the average varies
  from year to year and that the relatively wet
  year are 26 years out of 55 studied years.
• The dry years are 29 years out of the 55 studied
  years.

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Frequency Analysis

• The return period for each rainfall was
  calculated using the following plotting position
  formula
•  
• Where
• Tr return period
• m rank of event
• n number of events

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This figure plots the return period with rainfall
for Nablus station
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• Rainfall Runoff Models

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SCS Method

• The dimensionless hydrograph and triangular
  unit hydrograph of the SCS Method are shown in
  the following figure.
• Dimensionless hydrograph

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triangular unit hydrograph
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The following figure shows the Stream, contours
and centroid of Wadi Zeimar.
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• For Wadi Zeimar catchment, the following
  consideration and calculations can be done
• The total area of Wadi Zeimar which is under
  study is about 172.5km².
• tr 1 hour (assume one hour unit hydrograph).
• Description of water course is natural channel
  not well defined.
• the length, slope and velocity for the rainfall
  bath was found. The following table shows the
  results

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Velocity ft/s Slope Length of main stream (ft)
1 0.874 18766.2
1 0.339 16896.1
1 1.58 25918.3
1 0.0577 34874.9

By using this formula the time of concentration
can be calculated 1/60(18766.216896.1
25918.334874.9)1607.6 min 26.79 hr
0.5 0.6 26.79 16.57 hr
2.08(172.5/16.57) 21.65 m³
/s.cm
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• By applying the calculation we get the following
  results

q (m³/s.cm) t (hr) q/qb t/Tb
0.0 0.0 0.0 0.0
10.825 8.285 0.43 0.5
21.65 16.57 1 1
6.928 33.14 0.32 2
1.515 49.71 0.07 3
0.541 66.28 0.025 4
The SCS hydrograph for Wadi Zeimar catchment.
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Snyder's Method

• Applying the Snyder method to the catchment of
  the Wadi Zeimar, taking in consideration the
  following assumptions
• The total area of Wadi Zeimar under consideration
  is about 172.5 km².
• For the mountain drainage area the coefficient Ct
  is 1.2, and n is 0.38.
• For the mountain drainage area and for the
  minimum Ct the coefficient Cp is 0.7
• For one hour unit hydrograph tr 1.
• The following table shows the area, slope, main
  length and mean length for the catchment

Mean length, (mi) Main length, (mi) Slope () Area (mi²)
10.92 18.27 2.794 107.2
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• 1.2((18.2710.92)/2.794½)0.38
• 7.386 hr
• 18.125 0.7 107.2/7.386
• 184.15 m³/s
• 7.386/5.5
• 1.343 hr this is the duration of
  unit hydrograph.

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• To obtain one unit hydrograph, the adjusted
  formulas become
• 7.386 0.25(1 1.343)
• 7.3
• Qp 184.15(7.386/7.3)
• 186.32 m³/s.
• Tp 3 tp
• 3 7.3
• 21.9 hr

W75 (hr) W50 (hr) Qp (m³/s) tp (hr) Tp (hr) Mean length (mi) Main length (mi) Slope () Area (mi²)
3.08 5.4 186.3 7.3 21.9 10.92 18.27 2.794 107.2
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Recommendation

• Install an instrument at Wadi Zeimar to measure
  the flow and to estimate the real hydrograph.
  This will enable the measurement of actual flow,
  and thus the evaluation of the applicability of
  the UH model on the catchment.
• Develop a model to estimate the relationship
  between rainfall and runoff in semiarid region.
• Develop the available GIS-system in the
  Palestinian Authorities and justification to
  account for catchment characteristics.

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• Thanks for your attention