DEVELOPMENT OF DESIGN STORMS FOR URBAN RUNOFF ESTIMATION AND DRAINAGE DESIGN IN NIGERIA

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DEVELOPMENT OF DESIGN STORMS FOR URBAN RUNOFF

ESTIMATION AND DRAINAGE DESIGN IN NIGERIA

BY

AGUNBIADE, AKINYEMI OLUWASEYE

Ph.D/SEET/2013/502

DEPARTMENT OF CIVIL ENGINEERING

FEDERAL UNIVERSITY OF TECHNOLOGY,

MINNA

MAJOR SUPERVISOR: ENGR. PROF. O. D. JIMOH

CO-SUPERVISOR:

CO-SUPERVISOR:

SEPTEMBER, 2014


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TABLE OF CONTENTS

Page

1.0.INTRODUCTION 1

2.0.METHODOLOGY 7

3.0. WORK PLAN 8

References 9


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1.0INTRODUCTION

1.1Background

The concept of urban drainage management involves the use of Hydrologic and

Hydraulic principles to locate, design, size, and construct structures that will aid in the

timely capture and safe conveyance/dispersion of stormwater runoff. The essence of

performing these procedures is to prevent flooding due to urbanization. These hydraulic

structures within the built-up environment could include culverts, bridges, conduits,

channels, and detention/retention ponds.

In the process of drainage design, the idea of a design flood is introduced, which is

the flow peak or discharge hydrograph associated with a return period (frequency). This

design peak flow can be estimated by using the following procedures (WMO, 2009):

(a) Flood frequency based on a flow series of adequate length;

(b) Empirical equations based on a regional flood frequency analysis;

(c) A Design rainfall, which is fed into a rainfall-runoff model in order to estimate the

discharge.

Due to the relative scarcity of flow data compared to precipitation measurements, option

(c) is usually the most preferred choice. It is generally assumed that this design

rainfall/storm subsequently generates a design flood/flow of the same return period,

although this might not be true because of antecedent soil moisture conditions and other

hydrologic parameters.

The decision regarding design frequency is really a statement of acceptable risk of

system capacity being exceeded. An economic and/or political analysis by public

decision makers indicates that a prescribed risk level is acceptable, this risk level is then


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assigned to the design storm and the resulting design is assumed to preserve this risk

level. (Wenzel and Voorhees, 1981).

Design Storms can be gauged events or synthetic events. Since future rainfall

characteristics cannot be predicted, a convenient way of using rainfall data is to analyse

long gauge records to define the statistical characteristics of the rainfall, and then to use

these statistics to produce synthetic rainstorms of various return periods and durations

(Loucks, Van Beek, Stedinger, Dijkman, and Villars, 2005) .

The most widely used method for the determination of peak flows from the design

storm in urban drainage design is the Rational Method (WMO, 2009).

Q = 0.0278CAI (1.1)

Where:

Q= peak discharge in m3/s,

C = dimensionless runoff coefficient, which is a measure of the degree of

imperviousness of the catchment; this ranges from 0 to 1, higher values signifying

greater imperviousness.

A= the catchment area from the point of interest in km2.

I= average design rainfall intensity in mm/hr.

The duration used for the determination of the design precipitation intensity is the time

of concentration, t (minutes), of the watershed.

Of all the values to the right of equation (1.1), the hardest to determine is the design

storm intensity, and this is because of the unpredictable nature of rainfall. Typically,

rainfall intensities are determined from Intensity-Duration-Frequency (IDF) curves or

Depth-Duration-Frequency (DDF) curves; these are plots of average rainfall intensity


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(or depth) versus duration of the event rainfall. There are usually several curves plotted

on a single graph, one for each of the different rainfall frequencies (Figure 1.1).

Ideally, one or both of these graphs (or a tabular form thereof) are supplied by the local

governmental authority under whose auspices the work is being done.

Figure 1.1: Intensity-Duration-Frequency (IDF) Curve. Source: (DID, 2000)

First, the time of concentration is determined. Then, in the case of the IDF curve, the

graph is entered with time of concentration and the rainfall intensity or depth is read at

the intersection of the duration coordinate and the corresponding design frequency

curve.

In the absence of pre-existing IDF or DDF curves, the engineer must develop the

information that is required from local or nearby rainfall data. However, for all practical

purposes, the necessary rainfall data are seldom available, and if they are available, the


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cost of developing the rainfall frequency relations is seldom justifiable in terms of any

design project where the Rational method is applicable (e.g. drainage design for a

subdivision, an industrial park, a shopping centre, etc.). (Mays, 2001)

1.2Statement of the Problem

Prior to 2013, the only authoritative official document published for the design of

Hydraulic Structures was the Nigerian Highway Design Manual (FMWH, 1973). Chief

among the inadequacies of this document were:

a)

The IDF charts and equations are developed for only three (3) locations in Nigeria,

namely Lagos (Apapa), Kano, and Ikeja. Calculations of intensities for other

locations are highly subjective because it depended on the ability of the design

engineer to determine areas of similar rainfall regimes, and make calculations based

on the assumption of direct proportionality between the desired locations total

annual rainfall and compared rainfall intensities.

b) The IDF curves and equations were also derived from only 7 years of data (1938-

1944), and are presented for storm durations of 15mins to 24hrs, and recurrence

intervals of up to 25yrs.

c) Units of measurements used in the manual were all in unfamiliar imperial units, this

necessitates the conversion of units back and forth.

Between the years 1973 and 2013 however, numerous research and several papers were

published by eminent Nigerian academics and professionals in attempts to deal with the

inadequacies therein and develop design storms for various locations in Nigeria.

(Ayanshola, Salami, Olofintoye, and Abdulkadir, 2014; Isikwue, Onoja, and Laudan,

2012; Nwoke and Okoro, 2012; Ogunlela, Adewale, and Adamowski, 2012; Okonkwo


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and Mbajiorgu, 2010; Olofintoye, Sule, and Salami, 2009; Oyebande, 1982; Oyegoke

and Oyebande, 2008; A W Salami and Sule, 2009; Adebayo Wahab Salami, Bilewu,

Ayanshola, and Oritola, 2009; Sule and Alabi, 2013; Uzoigwe, Mbajiorgu, and

Alakwen, 2012)

By year 2013, an official update to the Nigerian Highway design manual was released

(FMW, 2013), this included significant improvements to the 1978 edition. The IDF

locations had been increased to 35, with durations from 6mins to 24hrs and return

periods up to 100yrs.

Although this research topic was conceived before the unveiling of this recent

document, there is still need for an independent analysis of the available rainfall data

and subsequent comparisons to determine the adequacy of the results presented therein.

The main reason for the absence of a standard national document to this effect, despite

the presence of seasoned academics and professionals, can be attributed to the lack of

widespread gauged rainfall data at the required resolution. Most precipitation records

are available at daily (24hr) totals, meanwhile urban storm events of concern are dealt

with at a sub-daily timeframe (especially in minutes). There is therefore need to

research proven methods for rainfall disaggregation to enable extraction of sub-hourly

data from these daily totals.


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1.3Aim and Objectives

The aim of this study is to undergo a rigorous analysis of available up-to-date

rainfall data for Nigeria, and generate design storms suitable for urban drainage

design. The specific objectives include:

a) To develop IDF curves, tables, and equations for available data locations using

standard global procedures and local constraints.

b)

Production of Isohyetal/Isopluvial maps of the computed storm durations and

return periods.

c)

Comparison of completed works with the current authoritative document in the

country and other academic/professional works in the field.

d) Performance of a sample urban drainage design to demonstrate the procedure

for use of the finished works.

1.4Justification Of Study

This study will assist engineers to perform more objective hydrologic designs for

urban drainage management. Indeed from field experience, it has been observed that

at best, engineers use the obsolete IDF charts presented in FMWH (1973); at worst

they use existing rules of the thumb to size hydraulic structures, which would likely

lead to costly over-design or dangerous under-design of these structures.


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2.0METHODOLOGY

2.1Data Collection: This will involve sourcing of national precipitation data from all

available agencies and private organizations, including satellite rainfall estimates.

Quality control and data infilling procedures will be performed on the received data

to ensure integrity.

2.2Climate Review and Regionalization: due to foreseen scarcity of nationally

representative results, regionalization of the rainfall data will be performed based

on spatially similar rainfall patterns and average depths.

2.3

Storm Disaggregation: This will involve the temporal downscaling of daily

rainfall totals to hourly and sub-hourly values. It is envisaged from previous

experience that the highest widely available rainfall resolution for the country is

typically daily/24hr totals.

2.4Statistical/Frequency analysis: this includes the extraction of annual maximum

series for the selected rainfall durations (see 2.5), parameter estimation, distribution

fitting, and tests for goodness-of-fit.

2.5IDF charts:production for standard durations of:

1, 2, 3, 4, 5, 10, 15, 30 minutes

1, 2, 3, 6, 12 hours

1, 2, 3, 4, 5, 6, 7 days,

For 1, 2, 5, 10, 20, 50, 100 years return periods.

2.6GIS analysis and Isohyetal/Isopluvial map production:for Nigeria for all given

durations and return periods.

2.7Sample Design: of storm drainage system to demonstrate the uses of the final

product.


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3.0WORK PLAN

J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

1 Introduction & L iterature review

2 Proposal Preparation

3 Proposal Submission

4 Methodology Design

5 1st PhD Seminar & Proposal Defence

6 Annual Progress Report 1

7 Apply For Research Grant

8 Data acquisition & Fieldwork

9 Model Development

10 Data Analysis

11 Modelling & Results Presentation

12 2nd PhD seminar Presentation

13 Annual Progress Report 2

14 Calibration, Validation, & Review

15 Discussion & Conclusion

16 Thesis Draft Presentation

17 Thesis Review & Corrections

18 Paper Preparation

19 Conference presentation/ publishing

20 3rd PhD Seminar Presentation

21 Final Corrrections & Production

22 Thesis Submission

ID

YEAR 2014 YEAR 2015 YEAR 2016

TASK / MONTH


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REFERENCES

Ayanshola, A., Salami, A., Olofintoye, O. & Abdulkadir, T. (2014). Development of

Storm Hydrographs for three rivers within Drainage Network in Kwara State, Nigeriausing Snyders Method.Nigerian Journal of Technological Development, 7(1).

DID. (2000). Urban Storm Water Management Manual for Malaysia (MSMA)(First

Edition.). Department of Irrigation and Drainage, Malaysia.

FMW. (2013).Nigerian Highway Manual Part 1: Design(Second Edition.). Federal

Ministry of Works.

FMWH. (1973).Nigerian Highway Manual Part 1: Design(First Edition.). Federal

Ministry of Works & Housing.

Isikwue, M. O., Onoja, S. B. & Laudan, K. J. (2012). Establishment of an empirical

model that correlates rainfall-intensity-duration frequency for Makurdi area, Nigeria.

International Journal of Advances in Engineering & Technology, 5(1).

Loucks, D. P., Van Beek, E., Stedinger, J. R., Dijkman, J. P. & Villars, M. T. (2005).

Water Resources Systems Planning and Management: An Introduction to Methods,

Models and Applications. UNESCO.

Mays, L. W. (2001). Stormwater Collection Systems Design Handbook(First Edition.).

McGraw-Hill New York.

Nwoke, H. U. & Okoro, B. C. (2012). Rainfall Intensity-Frequency Regime For Warri,

South-South Nigeria.Journal of New Clues In Sciences, 2, 4249.

Ogunlela, A., Adewale, P. & Adamowski, J. (2012). Developing Design Storm

Hydrographs for Small Tropical Catchments with Limited Data.Ethiopian Journal of

Environmental Studies and Management, 5(4), 356365.

Okonkwo, G. & Mbajiorgu, C. (2010). Rainfall intensity-duration-frequency analysis

for Southeastern Nigeria.Agricultural Engineering International: CIGR Journal,

12(1).

Olofintoye, O., Sule, B. & Salami, A. (2009). Best-fit Probability distribution model for

peak daily rainfall of selected Cities in Nigeria.New York Science Journal, 2(3),

2009.

Oyebande, L. (1982). Deriving rainfall intensity-duration-frequency relationships and

estimates for regions with inadequate data.Hydrological Sciences Journal, 27(3),

353367.

Oyegoke, S. & Oyebande, L. (2008). A new technique for analysis of extreme rainfall

for Nigeria.Environmental Research Journal, 2(1), 714.


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Salami, A. W., Bilewu, S., Ayanshola, A. M. & Oritola, S. F. (2009). Evaluation of

synthetic unit hydrograph methods for the development of design storm hydrographs

for Rivers in South-West, Nigeria.J Am Sci, 5(4), 2332.

Salami, A. W. & Sule, B. F. (2009). Establishment of Rainfall Intensity Model for

Selected Towns in Nigeria Based on Sherman Equation. 1st Annual CivilEngineering Conference University of Ilorin, Nigeria.

Sule, B. & Alabi, S. (2013). Application of synthetic unit hydrograph methods to

construct storm hydrographs.International Journal of Water Resources and

Environmental Engineering, 5(11), 639647.

Uzoigwe, L., Mbajiorgu, C. & Alakwen, O. (2012). Development of Intensity Duration

Frequency (IDF) Curve for Parts of Eastern Catchments using Modern Arcview GIS

Model. Special Publication of the Nigerian Association of Hydrological Sciences,

2444.

Wenzel, H. G. & Voorhees, M. L. (1981).An evaluation of the urban design storm

concept. University of Illinois, Water Resources Center.

WMO. (2009). Guide to Hydrological Practices: Management of Water Resources and

Application of Hydrological Practices(Sixth Edition., Vol. 2). World Meteorological

Organization.

DEVELOPMENT OF DESIGN STORMS FOR URBAN RUNOFF ESTIMATION AND DRAINAGE DESIGN IN NIGERIA

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