TABLE OF CONTENTS
LIST OF DEFINITI DEFINITIONS ONS .......................................................................................................................... A 1.0
INTRODUC INTRODUCTION TION ..........................................................................................................................1
2.0
RAINFALL RAINFALL ZONES .......................................................................................................................2
3.0
INTENSITY - DURATION - FREQUENCY CURVES ................................................................6
4.0
DRAINAGE DRAINAGE DESIGN DESIGN PARAMETER PARAMETERS S .........................................................................................7
5.0 DESIGN FLOOD DETERMINATION FOR BRIDGES, BOX CULVERTS, ETC USING THE RATIONAL RATIONAL METHOD ....................................................................................................................8
5.1 6.0
6.1 7.0
GUIDELINES FOR DRAINAGE STRUCTURE PROVIS PROVISION ION.................................................... 11 EROSION EROSION CONTROL CONTROL MEASURES MEASURES ........................................................................................... 18
PROTECTION MEASU MEASURES RES ......................................................................................................18 CONSTRUCTION GUIDELINES GUIDELINES FOR DRAINAGE STRUCTURES ............ ...... ............ ............ ............ ............ ........ .. 20
7.1 REQUIREMENTS OF VARIOUS DRAINAGE STRUCTURE STRUCTURES S ................................................. 20 7.1.1 Mitre Drains Drains ....................................................................................................................... 20 7.1.2 Catch-w Catch-water ater Drains Drains.............................................................................................................21
List of Definitions Term
Definition
Catchment area
Total area contributing runoff to the inlet of drainage structure. This area is obtained from a topographical map by connecting the high and low points on the map to delineate the area contributing runoff to t he inlet of the drainage structure being designed.
Runoff Coefficient ( C)
This is is a factor that that is applied in the flood discharge discharge equation equation which is an integrated value representing many factors that influence the runoff relationship i.e. topography, soil permeability, vegetation cover and land usage.
Return Period
Refers to the time interval during which a given rainfall depth/intensity depth/intensity is likely to be equaled or exceeded once.
Rainfall Intensity
Refers to the depth of rainfall over a given period of time.
Design Storm
This is the Maximum Storm depth/intensity depth/intensity that is likely to be equaled or exceeded once or a little more (rarely) during the design period.
Design Discharge
This is the Maximum Discharge that is likely to be equaled or exceeded once or a little more (rarely) during the design period.
Contour Rate
Number of ground level contours per kilometer.
1.0 INTRODUCTION Drainage structures and associated works, such as scour protection, account for a considerable part of the total cost of road works mainly because of the purpose they serve to protect the investment in roads. To this end, the factors associated with drainage design must receive due attention. The design of drainage structures is based on the worst expected flood situation at the drainage structure's proposed location. The area of land draining to the structure site is the catchment and the drainage structure is located at the catchment exit. When rain falls on a drainage catchment, some of the water may be prevented from reaching the catchment exit, while some may be delayed en route. Other precipitation losses may also arise from infiltration, evaporation, storage in surface depressions and interception by vegetation cover. The excess precipitation then travels by the hydraulically shortest route to the catchment exit. The determination of the volume of this runoff and the rate at which it arrives at the
However, selection of a proper design storm does not preclude the possibility of a larger storm destroying the drainage structure immediately after it is built since the selection is based on statistical probabilities. The accuracy with which flood estimates can be made depends on the amount and quality of relevant information available. Practical experience under local conditions and the application of sound judgment are particularly important in determining the data needed for the design storm intensity.
2.0 RAINFALL ZONES Because of the variability of rainfall in Uganda, delineation rainfall zones have been adopted in this study using results of the t he study for Design of a Regional Minimum rain gauge network. network. The method method used was based based on the Principal Component Component Analysis (PCA).
The principal principal components components were rotated using the principal of orthogonal
varimax. The spatial patterns of the dominant principal components were used to classify
Table 1: Description of the Rainfall Zones ZONAL AVERAGE RAINFALL, STD AND EVAPORATION ANALYSIS Zone Districts, 2000 boundaries Annual Rainfall and its zonal Main rainy seasons variability NORTHEASTERN TO NORTH CENTRAL AREAS G Moroto, Kotido and Average of 745 mm, STD 145 mm. One rainy season of about 5½ Northeastern Kitgum High variability, from ~ 600 over the months, from April to early north and northeastern northeastern parts to ~ 1000 September with the main peak mm over the southern and western in July/August and a secondary parts. peak in May. H Kitgum, Eastern Lira, South Average of 1197 mm, STD 169 mm. One rainy season of about 7 Kotido, Western Moroto and Moderate variability, from ~ 1000 over months, April to late October Katakwi the north and northeastern parts to ~ with the main peak in 1300 mm over western and southern southern July/August and a secondary parts peak in May. I
Adjumani, Gulu, Apac, Western Lira and Eastern Masindi
Average of 1340 mm, STD 155 mm. Moderate variability, from ~ 1200 over northwestern and western parts to ~ 1500 mm over the southern parts.
NORTHWESTERN TO CENTRAL WESTERN AREAS J Moyo and Arua Average of 1371 mm, STD 185 mm. Moderate variability, from ~ 1200 over the eastern parts and highest ~ 1500 mm over the western parts. K
Nebbi, Southwestern Gulu and Western Masindi
Average of 1259 mm, STD 195 mm. High variability, from from ~ 800 within the Lake Albert basin to ~ 1500 mm over the western parts
L
Hoima, Kiboga, Western Luwero, Kibale, North Kabarole and Bundibugyo
Average of 1270 mm, STD 135 mm. High variability, from from ~ 800 over eastern L. Albert parts to ~ 1400mm over the western parts.
Main dry seasons
Evaporation verses rainfall
One long dry season of about 6 months, October to March. Driest months December to February.
Evaporation > rainfall by a factor of over 10 during the driest months, December to February. During the rainy season evaporation is slightly > rainfall.
One long dry season of about 4 months, midNovember to late March. Driest months December to February.
Evaporation > rainfall by a factor of over 10 during the driest months, December to February. During the rainy months, May; July and August rainfall is slightly > evaporation.
One rainy season, about 7½ months, April to about mid November with the main peak in August to mid October and a secondary peak in April/May.
One long dry season of about 4 months, midNovember to late March. Driest months December to February.
Evaporation > rainfall by a factor of up t o 10 during the driest months, December to February. During the rainy rainy months of May, May, August and September rainfall > evaporation.
One rainy season of about 7½ months, April to about mid November with the main peak August to October and a secondary peak in April/May. Mainly one rainy season of about 8 months, late March to late November with the main peak August to October and a secondary peak in April/May. Two rainy seasons, main season August to November with peak in October and secondary season March to May with peak in April.
One long dry season of about 4 months, late November to late March. Driest months December to February. One long dry season of about 3½ months, December to about mid March. Driest months December to February. Main dry season December to about mid March, secondary dry season is June to July.
Evaporation > rainfall by a factor of ~ 10 during the dry months, December to March. During the rainy season, July to October, rainfall > evaporation. Evaporation > rainfall by a factor of ~ 6 during the driest months, December to March. During the rainy season, July to October, evaporation > rainfall. Evaporation > rainfall by a factor of ~ 5 during the dry months, December to March. During the rainy months, March and August to November rainfall > evaporation.
4
Zone
Districts, 2000 boundaries
ZONAL AVERAGE RAINFALL, STD AND EVAPORATION ANALYSIS Annual and its zonal variability Main rainy seasons Main dry seasons
CENTRAL WESTERN AREAS TO CENTRAL REGION MW Kabarole, Kasese, Northern Average of 1223 mm. High Rukungiri, Bushenyi and variability, lowest ~ 800 mm Kasese Mbarara Rift Valley, highest over slopes of Rwenzori mountains, over 1500mm. ME
Mubende, West Mpigi, Sembabule, and Northern Rakai
Average of 1021 mm.
B
Luwero, Mukono, Kampala, and Mpigi.
Average of 1250 mm.
SOUTH WESTERN AREAS TO WESTERN SHORES OF CW Kisoro, Kabale, Ntugamo, Average of 1120 mm. Southern Rukungiri Bushenyi and Mbarara
CE
Rakai, West Masaka, and East Mbarara
Average of 915 mm.
A1_ W
Western shores of Lake Victoria and Western Masaka.
Average of 1057 mm.
Two rainy seasons, main season August to November with peak in September to November and secondary season March to May with peak in April. Two rainy seasons, main season March to May with peak in April and secondary season September to December with a modest peak in November. Two rainy seasons, main season March to May with peak in April and secondary season August to November with a modest peak in October/November. LAKE VICTORIA BASIN Two rainy seasons, main season September to December with peak in October/November and secondary season March to May with a peak in April. Two rainy seasons, main season March to May with peak in April and secondary season September to December with a peak in October/November. Two rainy seasons, main season March to May with peak in April and secondary season October to December with a peak in November.
Evaporation verses rainfall
Main dry season December to late March, secondary dry season is June to July.
Evaporation > rainfall by a factor of ~ 5 during the dry months, December to March. During the rainy months, March, and August to November rainfall > evaporation.
Main dry season June to August, secondary dry season is January to February.
Evaporation > rainfall by a factor of ~ 6 during the dry months, June to August. During the main rainy months, April and May rainfall ~ evaporation.
Main dry season December to February, secondary dry season is June to July.
Evaporation > rainfall by a factor of ~ 2 during the dry months, December to February. During the peak peak of the rainy seasons rainfall is greater and or equal to evaporation.
Main dry season June to August, secondary dry season is January and February.
Evaporation > rainfall by a factor of ~ 3 during the dry months, June to August. During the rainy seasons rainfall is greater and or equal to evaporation.
Main dry season June to August, secondary dry season is January and February.
Evaporation > rainfall by a factor of ~ 5 during the dry months, June to August. During the main rainy season rainfall is greater and or equal to evaporation.
Main dry season June to September, secondary dry season is January and February.
Evaporation > rainfall by a factor of ~ 3 during the dry months, June to August. During the main rainy season rainfall is greater and or equal to evaporation.
These climatological zones are very useful for the presentation and analysis of features of the hydro-climatic regime and derivation of the Intensity - Duration - Frequency relationships in an area.
5
3.0 INTENSITY - DURATION - FREQUENCY CURVES In the design process, two important characteristics of the 'design' stor m are considered: considered: -
The duration, and
-
Intensity Intensity o f rainfall.
To assist in arriving at the 'intensity of rainfall' ra infall' for the design storm duration, IntensityDuration-Frequency relationships have been derived using the 'Watkins and Fiddes' approach which uses the following relationship: Equation 1
T
it
Where a, b and n are coefficients,
a t b
n
4.0 DRAINAGE DESIGN PARAMETERS The table below provides a guide towards the design of rural transport drainage structures in terms of choice of return period and duration of design storm. Table 2: Drainage Structure Design Return Periods Drainage
Return
Design Storm
The intensity of rainfall (mm/hr) is
feature
Period (Yrs)
duration
equivalent to the indicated value or is
(min)
to be determined from the indicated graph All Demarcated Zones
Side
drainage
and
5
10
relief
storm from the t he Intensity-DurationIntensity-Duration-
culverts. Drifts Bridges
Read off the 5-year Return period 10min
Frequency Curves in Annex 1 10
10 (Tc)
IDF
IDF
IDF
25 or 50
T
IDF
IDF
IDF
5.0 DESIGN FLOOD DETERMINATION FOR BRIDGES, BOX CULVERTS, ETC USING THE RATIONAL METHOD The following step-by-step approach will be used by designers intending to determine the design discharge from a catchment of interest as delineated from a topographical map. Most of the parameters to be used are explained earlier. Design Assumptions
The main assumptions inherent to this method are: (i)
The design storm produces a uniform rainfall intensity over the entire catchment
(ii)
The relationship between rainfall intensity and rate of runoff is a constant for a particular catchment.
(iii)
Time of concentration ( Tc) is the time taken for rainwater to flow from the hydraulically must remote point to t he catchment catchment exit.
Table 3: Runoff Coefficient Parameters
Runoff coefficient (C) = Cs + Ck + Cv Cs (topography) Very flat < 1%
Ck (soils) 0.03
Sand
&
Cv (vegetation) 0.04
Forest
0.04
gravel Undulating 1 – 1 – 10% 10%
0.08
Sandy clay
0.08
Farmland
0.11
Hilly 10 – 10 – 20% 20%
0.16
Clay & loam
0.16
Grassland
0.21
Mountainous > 20%
0.26
Sheet rock
0.26
No
0.28
vegetable Step 3:
Estimate the time of concentration (Tc) For larger catchments: -
Determine the Length (L) of t he mainstream, mainstream,
-
Estimate the Slope (S) of the main stream,
Determine the corresponding corresponding rainfall intensity ( I)
Step 4:
In order to determine the corresponding design rainfall intensity, the following has to be done: -
Determine the drainage feature return period from table 2 above,
-
Using the return period above determine the intensity of rainfall from the Intensity – Duration – frequency curves (figures B - D) at the time Tc. This is the rainfall duration expected to yield a maximum flood at the t he drainage drainage structure entry point.
NB.
It should be noted at this stage that figures B, C and D provide IDF curves for zones I, G and H respectively. Therefore, the particular zone for which the drainage structure is being design should be taken note of at this stage so that the correct intensity is obtained from the right IDF curve.
Step 5:
Estimate the Area Reduction Factor ( ARF)
5.1
GUIDELINES FOR DRAINAGE STRUCTURE STRUCTURE PROVISION
1. For road sections with Unlined side drains in situations where only Turnouts or
Mitre drains can be provided for the longitudinal drainage system the table 4 below provides guidelines on the maximum frequency of turning off water using mitre drains or turnouts. Table 4: Mitre Drain spacing for Unlined Side Drainage Channels Contour Rate
Slope or gradient
MAXIMUM Spacing of Mitre drains (m)
(%) (5m ground contours) contours )
2
1
200
4
2
150
6
3
100
>6
>3
Line with stone masonry or concrete lining or
Table 5: Mitre Drain spacing for Lined Side Drainage Channels Contour Rate
Slope or gradient
MAXIMUM
MAXIMUM
(%)
Spacing of Mitre
Spacing of Mitre
drains (m)
drains (m)
Stone Pitching
Concrete Lining
(5m ground contours)
Type of Lining 2
1
450
950
4
2
650
1350
6
3
750
1700
8
4
900
1950
10
5
1000
2150
12
6
1100
2400
14
7
1200
2600
16
8
1300
2750
18
9
1350
2950
Table 6: Considerations for Provision of Scour Checks (table Dwg No. WWP 001 Sheet 1/1) Contour Rate
Slope or
Level difference between
gradient (%)
Sour Checks ( mm)
MAXIMUM
(5m ground
Spacing of Scour Checks
contours) contours )
( m)
2
1
60
25
4
2
30
12
6
3
15
7
8
4
10
5
10
5
10
4
>10
5
Line side drainage system
Other considerations need to be taken into account when providing for culverts
4. For the Design of single barrel culverts table 7 shows guide discharge
values and corresponding culvert diameters that can convey the discharge. The assumption made is that 95% efficiency of discharge is achieved due to inlet and outlet friction and other losses. For the design of multiple barrel culverts the table 7 shows guide discharge values and corresponding culvert diameters that can convey the discharge. The assumption made is that 80% efficiency of discharge is achieved due to inlet and outlet friction and other losses Table 7: Capacity and Inlet Velocities for Piped Culverts
Diameter
Number of Pipe Barrels
of Culvert 1
(mm)
2
3
4
5
V
Q
V
Q
V
Q
V
Q
V
Q
(m/s)
(m /s)
3
(m/s)
(m /s)
3
(m/s)
(m /s)
3
(m/s)
(m /s)
3
(m/s)
(m /s)
3
5. For the design of both vented and normal drift crossings will be based on
the over-flow peak discharge as determined d etermined from the contributin contr ibuting g catchment during the wet weather. The drift will be defined by the DIP (h) designed to suit the overflow discharge and also prevent the flood flows spreading. Figure E below provides a graphical guide for determining the Plan length (L) of the approach slab for different DIP (h) values of 300, 500 and 700 mm and also deck slab lengths (B). The Engineer will have to use his judgment of the maximum clearance acceptable for the drift crossing depending of the traffic using that particular route. The maximum DIP (h) = 700mm can be used for routes where the most common traffic type are Heavy trucks, Lorries and other Heavy Goods Vehicles which have high chassis clearances. The normal DIP (h) value should be 300mm for small design flood discharges with high flood design discharge taking on DIP (h) values of 500mm. Therefore, in the design for drifts, the main variables will be three i.e. DIP (h), deck slab length and slope of the approach slab.
Figure B: Variation of Discharge (Q) with Approach Slab Plan Length (L) for Drift DIP value = 300mm
Figure D: Variation of Discharge (Q) with Aproach Slab Length (L) for Drift DIP value = 700mm
6.0 EROSION CONTROL MEASURES Roads interrupt the internal drainage of an area by concentrating water discharge through culverts and drains often leading to soil erosion if the drainage is not carefully planned and constructed. Good erosion control should preferably start from the top of the rainfall catchment with the objective of reducing water run out towards the road. Along the road, sufficient numbers of drifts, vented drifts, culverts and mitre drains must be installed to avoid large concentrations of water discharging through the structures. The best approach to date is “Land husbandry” using good land management practices especially biological control measures measures The most important soil erosion control measure is the careful selection of sites for structures and and mitre drains. A guiding principle principle should be the discharge discharge of water of water “little and often”, to avoid potentially harmful concentrations co ncentrations of flow.
b)
Drains & waterways -
Grass
Should be established as soon as possible on the sides and inverts of new drains and waterways. -
Scour checks
Such as wooden pegs, stones or grass sods to assist establish vegetation (low growing creeping grasses are must suitable) -
“At -level” scour checks
For gently sloping channels in erodible soils. c)
Gullies -
Establish vegetation
7.0 CONSTRUCTION STRUCTURES
GUIDELINES
FOR
DRAINAGE
Various drainage measures measures are needed to satisfactorily satisfactorily deal with rainwater ra inwater falling on or near the road. Rainwater Rainwater is the main cause of damage to district district roads and as such such a good drainage system will significantly reduce rainwater damage and in the long run minimize maintenance requirements. Water damages district roads in two principal ways: -
Weakening road materials hence reducing traffic heavy bearing capacity.
-
Erosion and silting which damages and reduces effectiveness of drainage system.
An efficient drainage system must therefore collect all rainwater and dispose of it quickly to minimize minimize road damage. This enables the road materials materials to rapidly dry out after the rains and regain traffic t raffic bearing strength. The major components of the drainage system are the following:-
-
Discharge should be channeled to garden/shamba/field boundaries and not into farmland to course nuisance or damage,
-
Minimum width of mitre drains should be 0.60m and x-section should have at least same capacity as side drain,
-
Some excavated soil should be used to block the downhill side of drain to ensure water flows into mitre drain.
7.1.2
Catch-water Drains -
To be provided only for roads situated on hillsides with significant amount of rainwater flowing from hill towards road,
-
Catch-water drain should be constructed to intercept this surface water and carry it to a safe discharge point usually a natural water course,
-
Catch-water drain should have a satisfactory gradient throughout its length (>2%),
-
Catch-water drain should not be so close to the cut face because that will increase the danger of a land slip,
-
Grass sods should be placed against the upstream face of scour check to prevent water seeping through scour check and to encourage silting behind scour check,
7.1.4
7.1.5
Table 6 provides guidelines for the frequency of providing scour checks.
Grass Planting -
To be used for effective prevention of erosion,
-
Should be planted on all slopes where scouring is likely to occur,
-
Grass type should be strong, fast growing and provide good coverage.
Turfing -
Excavating an area of live grass and lifting the grass complete with about 50mm of topsoil and roots root s still attached forms a grass turf. The turfs are then replanted in another location,
-
Grass turfs give a faster and more effective protection protection to slopes than planted grass. They can be cut in the grubbing activity,
-
The size of the turfs should not be smaller than 0.20x0.20m. Wooden pegs
7.1.7
Drainage for Roads with a 'Sunken' Profile
Roads with a “sunken profile” refers to roads that have been trafficked for many years, subjected to poor grading practices or suffering from severe erosion such that they are situated below the surrounding ground level for a considerable length. This situation presents serious drainage problems as even after improvement operations, operations, they can still be impossible to drain. They will simply act act as channels in wet weather creating continuous maintenance problems. Where a road with a sunken profile exceeds 200m in length without any possibility to take away water to surrounding ground, the following drainage options should be considered: considered: a)
Raise the level of the road, at least in some locations so that it may drain to the adjoining land,
b)
Where option (a) is difficult to achieve or where the earthworks involved would be excessive and the road has a noticeable longitudinal
correspondingly. correspo ndingly. The soakaway ponds need to be desilted in the dry season. Smaller but deeper ponds filed with rocks and larger stones may be more appropriate appropr iate in some situations. situat ions. located at least 10m from the side drains.
Soakaway pond should be
8.0 COST EFFECTIVE DRAINAGE DESIGN The design and appraisal of rural transport infrastructure drainage interventions is field that is not always properly articulated in most rural transport manuals. Whereas the poor condition of rural roads will hinder poverty reduction efforts and stifle economic growth, the poor condition of rural transport drainage systems often precludes development altogether. The concept of low cost structures has often been misused as we seek to spend as little as possible on rural transport network infrastructure. It is in this regard that we should adopt the new notion of "Least Life Cycle Cost" which means the option that will cost least in the life of the infrastructure taking into account construction, maintenance, all-weather operability and access. It has often been the norm in Uganda to associate the provision of cross drainage infrastructure with only culverts, bridges or box culverts even where it is inappropriate. It should be noted at this stage that other drainage infrastructure exists which is even more amenable to the notion of Least Life Cycle Cost options by providing pro viding reliable and efficient all-weather access. Therefore, for cost effective design options such as drifts
poverty reduction cannot be sustained. Therefore, spot drainage improvements to the rural network using long-term drainage solutions especially drift and vented drifts crossings are a viable alternative available to the District Engineers and should be taken into account. Effective transport as a complementary input to nearly every aspect of rural activity is an essential element of poverty reduction. The removal of surface water is crucial for the success of rural networks because weather causes more damage that does traffic. This means that adequate side drains and carefully designed cross drainage structures are required. Usually, stone or concrete drifts are viable alternatives and substitutes for culverts. It is always essential to remember that very limited resources will be available for maintenance. As such, the use of structures that can be overtopped without damage e.g. drifts or vented drifts, at minimal maintenance in the place of culverts, will most likely be economically economically justified especially especially for areas prone to flooding. flooding. For small rivers and streams with wet-weather flow only, a simple drift is usually adequate to secure vehicle access. However, for continuous flows, vented drifts can be designed to pass
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE J) 250
200
) r h / m m ( Y T I S N E T N I
2 yr
150
5 yr 10 yr 25 yr
100
50 yr
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
I
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE I) 350
300
250 ) r h / m m ( Y T I S N E T N I
2 yr
200
5 yr 10 yr
150
25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
II
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE G) 300
250
) r h / m m ( Y T I S N E T N I
200 2 yr 5 yr 150
10 yr 25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
III
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE K) 350
300
250 ) r h / m m ( Y T I S N E T N I
2 yr
200
5 yr 10 yr
150
25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
IV
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE H) 250
200
) r h / m m ( Y T I S N E T N I
2 yr
150
5 yr 10 yr 25 yr
100
50 yr
50
0
10
20
30
40
50
60
70
80
90
1 00
110
1 20
DURATION (min)
V
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE E) 300
250
) r h / m m ( Y T I S N E T N I
200 2 yr 5 yr 150
10 yr 25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
1 00
1 10
1 20
DURATION (min)
VI
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE F) 250
200
) r h / m m ( Y T I S N E T N I
2 yr
150
5 yr 10 yr 25 yr
100
50 yr
50
0
10
20
30
40
50
60
70
80
90
1 00
1 10
1 20
DURATION (min)
VII
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE L) 200 180 160 140 ) r h / m m ( Y T I S N E T N I
2 yr
120
5 yr 100
10 yr 25 yr
80
50 yr 60 40 20 0
10
20
30
40
50
60
70
80
90
1 00
110
1 20
DURATION (min)
VIII
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE MW) 180 160 140
) r h / m m ( Y T I S N E T N I
120 2 yr 100
5 yr 10 yr
80
25 yr 50 yr
60 40 20 0
10
20
30
40
50
60
70
80
90
10 0
1 10
12 0
DURATION (min)
IX
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE ME) 250
200
) r h / m m ( Y T I S N E T N I
2 yr
150
5 yr 10 yr 25 yr
100
50 yr
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
X
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE B) 300
250
) r h / m m ( Y T I S N E T N I
200 2 yr 5 yr 150
10 yr 25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
11 0
12 0
DURATION (min)
XI
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE A1) 600
500
) r h / m m ( Y T I S N E T N I
400 2 yr 5 yr 300
10 yr 25 yr 50 yr
200
100
0
10
20
30
40
50
60
70
80
90
1 00
110
1 20
DURATION (min)
XII
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE A2) 300
250
) r h / m m ( Y T I S N E T N I
200 2 yr 5 yr 150
10 yr 25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
1 10
12 0
DURATION (min)
XIII
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE D) 300
250
) r h / m m ( Y T I S N E T N I
200 2 yr 5 yr 150
10 yr 25 yr 50 yr
100
50
0
10
20
30
40
50
60
70
80
90
10 0
1 10
12 0
DURATION (min)
XIV
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE CE) 250
200
) r h / m m ( Y T I S N E T N I
2 yr
150
5 yr 10 yr 25 yr
100
50 yr
50
0
10
20
30
40
50
60
70
80
90
1 00
1 10
1 20
DURATION (min)
XV
Intensity – Duration – Frequency Curves for all the Demarcated Rainfall Zones
Annex 1
INTENSITY - DURATION - FREQUENCY CURVES (ZONE CW)
200
) r h / m m ( Y T I S N E T N I
150 2 yr 5 yr 10 yr 100
25 yr 50 yr
50
0
10
20
30
40
50
60
70
80
90
10 0
1 10
12 0
DURATION (min)
XVI
