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Planning and design of urban drainage systems in

informal settlements in developing countriesJ. Parkinson

a, K. Tayler

b& O. Mark

c

aWS Atkins International Ltd, Woodcote Grove, Ashley Road, Epsom, Surrey, UK

bSchool of City and Regional Planning, Cardiff University, Glamorgan Building, King Edwar

VII Avenue, Cardiff, CF10 3WA, UKc

Urban Water - DHI - Water Environment Health, Agern All 5, DK-2970, Hrsholm,DenmarkPublished online: 13 Jul 2007.

To cite this article: J. Parkinson , K. Tayler & O. Mark (2007) Planning and design of urban drainage systems in informalsettlements in developing countries, Urban Water Journal, 4:3, 137-149, DOI: 10.1080/15730620701464224

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Planning and design of urban drainage systems in informalsettlements in developing countries

J. PARKINSON*{, K. TAYLER{ and O. MARKx

{WS Atkins International Ltd, Woodcote Grove, Ashley Road, Epsom, Surrey, UK

{School of City and Regional Planning, Cardiff University, Glamorgan Building, King Edward VII Avenue,

Cardiff CF10 3WA, UK

xUrban Water - DHI - Water Environment Health, Agern Alle 5, DK-2970 Hrsholm, Denmark

Many cities in developing countries are typified by large areas of informal settlements.These

often do not adhere to official planning guidelines, building regulations and construction

standards and, as they are not officially recognised by local authorities, are rarely provided

with adequate infrastructure and services. The provision of improved systems for drainage

of wastewater and stormwater runoff is an important component of urban upgrading

initiatives. This paper focuses on urban drainage as a component of urban upgrading and

discusses issues related to the integration of drainage systems serving informal settlements

into citywide stormwater management systems. Experiences from urban upgrading

schemes in different parts of the world are used to highlight innovative approaches towards

planning and design as well as illustrating examples of potential problems that may

be encountered during project implementation and subsequent operation.

Keywords: Informal settlements; Low-income communities; Drainage; Slums; Solid

waste; Stormwater runoff; Urban planning; Urban upgrading

1. Introduction

1.1 Informal settlements and growth of slums

Rapid urban growth in developing countries has resulted

in the proliferation of informal settlements. These are

opportunistic developments taking advantage of unused

land, both privately and publicly owned. In some cases, the

land may be earmarked for future development whereas in

others it is assumed to be inappropriate for construction

owing to physical or environmental factors. The housing

within informal settlements is virtually always built without

the consent of the official planning authorities and rarely

conforms to official planning guidelines, building regula-

tions and construction standards.

Many informal settlements form on the peri-urban

fringes of major cities. These settlements are usually in-

habited by a heterogeneous mixture of families from

various socio-economic backgrounds, and are oftencomprised of immigrants from rural areas (UN-Habitat

2003). Another type of informal settlement is the inner city

slum, characterised by high density and prevalence of

poverty. In some cities, many informal settlements are

slums, which are characterised by poor housing, squalid

living conditions and an almost complete deficit of basic

amenities.

By definition, all informal settlements are illegal

when they are formed and therefore not officially part of

the city and are excluded from urban services. However,

many subsequently gain recognition from the local

authorities, often as a result of political patronage. As a

result, they become legitimised and are subsequently

entitled to receive the same urban services as the rest of

the city. However, many remain marginalised and are

poorly served by municipal services. The provision

of drainage infrastructure is invariably inadequate

*Corresponding author. Email: [email protected]

Urban Water Journal, Vol. 4, No. 3, September 2007, 137 149

Urban Water JournalISSN 1573-062X print/ISSN 1744-9006 online 2007 Taylor & Francis

http://www.tandf.co.uk/journalsDOI: 10.1080/15730620701464224


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and a wide range of problems prevail related to flood-

ing and environmental health issues caused by poor

drainage.

In hilly cities, the location of informal settlements is often

predictable as they will invariably be found alongside exis-

ting drainage paths and on steep hillsides. It is, however,

less obvious where the topography of the city is flat, For

example, in Cairo and Faisalabad (Pakistan). The majority

of the informal settlements are located on erstwhile agri-

cultural land and their layout is therefore heavily influenced

by the path of irrigation canals and drains, which often

later become part of the urban drainage system. These

drains frequently become fetid, slow flowing open sewers

but the local farming community continue to abstract water

from the drains for irrigation even though this presents

significant health hazards.

In other cases, notably where water resources are scarce,

it is not uncommon for farmers to deliberately block

sewerage systems to divert wastewater onto adjacent

fields. As well as abstraction of wastewater from the

drainage system for irrigation, water in the drains is oftenused for various domestic purposes and commercial

activities (see figures 1(a) and (b)). These activities are

likely to result in transmission of a range of water-related

diseases.

1.2 Poor drainage, flooding and impact on the poor

Poorer households are much more likely to inhabit pre-

carious areas that are at risk from flooding. Whole

settlements may be vulnerable and within settlements there

are likely to be areas that are at particular risk; often those

inhabited by the poorest households. These locations

include:

(a) low-lying areas that are liable to flooding;

(b) banks of drainage channels and natural water-

courses;

(c) steep hillsides that are at risk from landslides.

The residents of informal settlements, particularly slum

dwellers, also suffer from a wide range of environmental

problems related to a lack of drainage infrastructure. In

addition to health hazards related from microbial patho-

gens, they are often most vulnerable to flooding because

their dwellings are precariously located and poorly served

by urban infrastructure and services (Parkinson 2003).

The combination of direct and indirect impacts of poor

drainage has both social and economic implications for the

poor. To make matters worse, poor people have the least

resources to assist in the recovery from the negative impact

of floods. Figure 2 illustrates how a combination of greater

vulnerability to flooding and lack of resources to recover

from flooding compounds upon the poor and exacerbates

conditions of poverty.

It is important to recognise that, as well as providing a

range of other functions, the avoidance of large-scale

flooding may not necessarily be such a high priority for

people living in poorly serviced areas, compared with

other needs such as employment and access to health

services. In particular, residents who grow up with floodingas part of their lives and value the benefits of living in a

place that is cheap and close to city services and employ-

ment opportunities may have a fairly ambivalent attitude

towards flooding (Few 2003). Of greater importance is the

predictability of the flood event and the resultant depth,

duration and area of flooding. In addition, there is often a

high demand for sewerage or drainage to dispose of

unwanted wastewater and to drain runoff from more

frequent smaller rainfall events that otherwise result in

ponding.

2. Responses to the problem of informal settlements andprovision of services

2.1 Official responses from local authorities

Service providers in informal settlements are often

constrained by the fact that informal settlements do not

Figure 1. Local residents in Vientiane, Lao P.D.R. use drainage channels for (a) washing vegetables and (b) fishing (Photos:

Birgitte Helwigh).

138 J. Parkinson et al.


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meet formal planning regulations and, as mentioned above,

are often illegal. Thus, agencies responsible for the

provision of urban drainage infrastructure are often not

officially allowed to provide services to these areas.At the same time, irrespective of legal status of these

settlements, the same agencies frequently lack sufficient

resources to respond effectively to the scale of the problem.

Flooding problems in informal areas also present a com-

plex set of engineering challenges and potential difficulties

due to the haphazard nature of development and the fact

that the communities may not be accustomed to cooperat-

ing with government agencies.

Despite these difficulties, drainage improvements take

place in a number of ways as summarised below.

2.2 Locally based initiatives

In the absence of interventions from local government,

residents of informal settlements may work collectively to

try to solve communal drainage problems by digging and

installing drains and cleaning existing drains (see figure 3).

However, the effectiveness of these initiatives tends to be

dependent upon local leadership and the extent of social

cohesion within the community. Community-based

organisations can play a key role in encouraging collective

action but assistance from a non-governmental organisa-

tion (NGO) is often also needed to assist during project

implementation.In some situations, locally elected representatives use

their limited budget for small drainage improvements

projects as a form of political patronage. These initiatives

tend to be piecemeal and benefits are often constrained by

the lack of a secondary network with capacity to accept

increased runoff.

2.3 Urban upgrading

Informal settlements may be prioritised as part of

government supported slum improvement schemes often

with the support of development banks such as the World

Bank, various bilateral and multi-lateral agencies such as

the UK Governments Department for International

Development and UN-Habitat. Urban upgrading involves

a systematic approach to the improvement of basic

infrastructure and other services in informal settlements.

Upgrading projects generally target low-income, commu-

nities and include a range of activities, mainly focussed on

improving access and quality of essential services, which

Figure 2. Livelihood impacts of flooding reinforce conditions of poverty (adapted from Parkinson and Mark 2005).

Planning and design of urban drainage systems in informal settlements in developing countries 139


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are designed to improve the quality of life in thesesettlements.

Upgrading projects normally include a wide range of

activities but the main focus of activity involves efforts to

improve physical infrastructure. Thus, upgrading efforts

typically involve a package of improvements including

street paving and lighting, water supply and sanitation,

drainage and solid waste collection. As well as benefits in

environmental health, the provision of improved infra-

structure can be very important in improving the image of

the slum (Amis 2001).

3. Examples of approaches towards urban upgrading

This section briefly describes the experiences from three

urban upgrading projects, which highlight various practical

aspects related to urban drainage planning and design in

informal settlements. Each of these projects illustrates

drainage considerations in different types of urban envir-

onment characterised by specific topographies and ground

slopes.

3.1 North-east Lahore urban upgrading project

The north-east Lahore Upgrading Project was a World

Bank-funded project which ran from 1987 through to 1994.

The project had a target beneficiary population of approxi-

mately 100 000 inhabiting an area of about 270 ha which

were targeted for upgrading, The project adopted an

integrated approach to infrastructure improvement; cover-

ing water supply, street paving, solid waste management

and street lighting in addition to drainage and sewerage.

Designs were prepared by consultants on behalf of the

Lahore Development Authority, which was the implement-

ing agency.

The overall area is flat and was characterised by high

housing densities, narrow streets and lanes, and poor

services. Prior to the project, a system of open drains had

developed in a piecemeal fashion over the years. Initially

local systems had been constructed; draining to depres-

sions and open land and these had gradually been

combined into larger systems. The drains serving the

northern part of the area discharged to open farmland atthe periphery of the built-up area whereas a larger area

in the south discharged to the Shalimar Escape Drain, one

of the main city drains, which formed the western

boundary of the project area. The drains were constrained

in places by undersized culverts and narrow sections

passing between houses. In some recent developments,

there were no drains and wastewater was discharged to

the nearest open plot.

Replacing the existing system with combined sewers laid

with sufficient fall to prevent settlement of solids with dry

weather flows would have required considerable pumping

of storm water and so an early decision was made to

develop separate storm and foul water drainage systems.The project adopted an innovative response to the lack of

household connections to foul sewers, which is a wide-

spread problem in developing countries.

Foul water was collected by replacing existing drains

along the sides of lanes with covered drains connecting to

sewers. Storm water was allowed to run on the surface of

lanes for as long as possible and was eventually discharged

into covered drains running along the larger streets. Inlet

grills were provided at intervals to allow water to enter the

drains. Based on early experience with blockages in small

covered drains, the minimum covered drain size was

450 mm by 450 mm. Drains were covered because it was

felt that this reduced the ingress of silt and solid waste

and because covering drains increased the area available

for vehicular and pedestrian access. Paving consisted

of bricks laid on edge for lanes and asphalt for through

roads.

The project was heavily engineered in the sense that

levels were carefully determined to ensure that there was

always a fall towards the nearest drain while road surfaces

Figure 3. Local residents in an informal settlement in

George Compound in Lusaka remove solid waste from the

drainage channel passing through their settlement (Photo:

Dr Martin Mulenga, International Institute for Environ-

ment and Development, London).



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were kept below the plinth levels of most existing houses.

Raising the level of existing roads and lanes was generally

avoided. As shown in figure 4(a), lanes that had sufficient

fall were dished towards the centre to form a shallow

channel, but these were not used when the gradient was flat

(less than 0.33%) in order to reduce ponding in the centre

of the lane (see figure 4(b)).

Problems were experienced during the course of the

project as residents made cross-connections from sewers to

storm drains in response to sewer blockages. North-east

Lahore has experienced problems related to storm drains

gradually silting up over the years and people making

cross-connections between sewers and storm drains to

solve sewer blockage problems. A recent inspection of the

project area by one of the authors revealed that the storm

drains have become heavily silted, reducing their capacity

to deal with high-intensity storms.

3.2 Slum networking, Indore, India

The slum networking approach was developed in India as aninnovative approach to the upgrading of low-income settle-

ments; exploits the linkages between slums and natural

drainage paths in the city (Diacon 1997, Parikh 2001). The

approach aims to mitigate problems of flooding in the city

as a whole, whilst concurrently providing services for

the slum-dwellers in low-lying areas adjacent to natural

drainage paths. Thus, the approach was designed to be

mutually beneficial for the both slum dwellers and other

city residents.

The natural drainage paths are the most obvious places

to construct drainage channels as the storm drains and

sewers in adjacent settlements can be laid to natural

gradients, thus reducing construction costs. These are often

the areas where poor communities reside; a major problem

for conventional project designs. In the slum networking

approach, problems of land acquisition and demolition

normally encountered during implementation are reduced

because the local residents are involved in the planning

process and have an interest in the successful completion of

the project.

The other important innovative feature was the use of

the roads to act as drainage conduits for larger storm

events and the installation of a sewerage system, which was

designed to drain lower runoff volumes and domestic

wastewater. This was considered to offer a more cost

effective sanitation solution than the improvement of on-

site sanitation. However, as in Lahore, experiences from

Indore highlighted problems with blockages, arising partly

because of ineffective solid waste management systems,

which meant that it has been difficult to keep the drains free

from refuse (Verma 2000).

3.3 Participation and partnerships in urban environmental

rehabilitation in Santo Domingo

This pilot project focused on slum upgrading in Santo

Domingo in the Dominican Republic an area charac-

terised by sleep slopes and landslides during the rainy

season. The project was supported by the World Bank and

involved an NGO (Insituto Dominicano de Desarrollo

Integral), which worked in partnership with various

community-based organisations. The project adopted an

integrated approach to urban upgrading, including storm-

water drainage, in combination with the design and

implementation of a local environmental management

plan. As well as drain construction, paving, latrines,

drinking water supply, and collection of solid waste, the

Figure 4. Lane paving in North-East Lahore Urban Upgrading Project: (a) the lane is dished to enable the flow to be

channelled; (b) the lane is not dished as the fall of the lane is low (Photos: Kevin Tayler).



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project included in an important disaster-mitigating infra-

structure component which involved the installation of

slope-stabilizing concrete-reinforced walls in order to

secure the terraces where people had built their homes.

A socio-economic and environmental survey of the entire

settlement was undertaken with the community to help

plan and prioritise investments. Once the integrated envi-

ronmental rehabilitation plan was accepted, the NGO/

community-based organisation (CBO) team encouraged the

community to offer volunteer unskilled labour for tasks

such as clearing garbage heaps and digging trenches. Local

masons were hired to build sewers and stormwater drains

along the bottom of the ravines and covered them with

walkways in collaboration with the water company who

installed a water supply system. Concrete pedestrian paths

and stairs with tracks for bicycles, carts and motorbikes,

located above the storm drainage system up the side of

gullies, were also constructed. Grills over drains were

installed to prevent solid waste from clogging the system

and polluting the river downstream. The CBO and NGO

also jointly established a community micro-enterprise tocollect solid waste on order to ensure that the drainage

system did not suffer from blockages (Chavez 2002).

4. Design of urban drainage in informal settlements

Although there is considerable experience in urban up-

grading there is surprisingly little literature on issues related

to the provision of urban drainage in upgrading projects.

Therefore, this section aims to identify the main issues and

suggest ways in which drainage systems may be planned

and designed most effectively given the specific character-

istics of informal settlements.

4.1 Rainfall runoff relationships

Based upon experience of drainage design and runoff

modelling in developing countries, runoff from informal

settlements is often lower than would be expected under

similar conditions for well planned/engineered city areas.

This may be a result of a combination of:

(a) lack of paving and surfacing of open areas; resulting

in higher depression storage and greater infiltration

(and evapo-transpiration in vegetated areas);

(b) incomplete stormwater drainage systems, which

means that a considerable volume of runoff remains

ponded in open low-lying areas.

Runoff from informal settlements is therefore difficult to

predict, particularly as the data required for standard

computations (e.g. rational, unit hydrograph, time-area

methods) are often not readily available. The rational

method is the simplest approach to estimate peak runoff

based upon rainfall and catchment surface characteristics.

It may be applied during the design of urban drainage

systems for small urban developments, but in larger areas

the relationship between rainfall and runoff is more

complex and cannot be approximated by such a simple

relationship. A key constraint is that the rational method

does not allow for surface storage which, as noted above,

can be considerable in informal settlements.

According to Heaney et al. (2002), the rational approach

is archaic and should be replaced by data-centred appro-

aches using sophisticated technologies and computer

simulation software such as MIKE URBAN, InfoWorks

and SWMM. However, these models require considerable

amounts of data and experienced staff with considerable

skills. Consequently in reality in many cases the rational

method may be the only option. In addition, care should be

taken when using models before using default values (many

of which have been derived in developed temperate

countries) as the use of erroneous values or inaccurate

design parameters in hydrological models may lead tolarge-scale errors in the design of drainage systems

(Packman 2000).

4.2 Capacity of drainage conduits

The return period of flooding is the most important

parameter used for design of urban drainage systems since

it determines the size and therefore the costs of the drains

required. The choice of return period depends upon the

land use and the potential consequences of flooding. In

theory, designs should take account of an acceptable

frequency of flooding and this should be linked to attitudes

of local communities towards flood risks, but in practicethese are rarely taken into consideration.

Design of drainage systems to cater for the runoff from

all storm events is impossible without very high expenditure

and often requires demolition of properties, both of which

act as constraints. Therefore, provided the proposed level

of service is accepted by community members, it may be

appropriate to design systems on the basis of short-return

period storms. As many urban communities in developing

countries are accustomed to regular flooding during the

rainy season, they may accept flooding on the streets, as

long as it does not damage their property.

Another important factor affecting the capacity of

drainage conduits is the build-up of sediment and solid

waste. The parameter of self-cleansing velocity is widely

used for the design of channels and pipes, which in theory is

used to ensure that drains are free of sediment. However, in

reality very few drains in developing countries are self-

cleansing due to the excessive solids loading, long dry

periods and flat gradients.



8/14

4.3 Combined versus separate systems

Conventional wisdom on the design of sewerage and

drainage systems is that combined systems carrying both

foul and stormwater, should not be used (Taylor and

Cotton 1993). However, there are situations in informal

areas where a combined system may be the best option.

The important consideration, where sewers discharge to a

treatment works or a nominally separate trunk sewer, is

to be able to provide a storm overflow at some point

downstream.

As seen in Indore and Lahore and in the majority of

situations in developing countries, separate sewers and sur-

face drainage systems are rare, even where they have been

designed to be separate. In many cases it is not possible to

construct separate systems and, as shown in figure 5, open

channel surface water drains inevitably receive discharges

of untreated wastewater, which ends up in natural water-

courses. The situation is generally worse in informal

settlements where there is less control over ongoing

construction activities and new building drains are con-

nected to the most conveniently located drain.

Illegal discharge of domestic sewage into the storm

drainage system leads to increases in pollutants loads from

faecal sources and from other domestic activities. Owing to

the nature of these solids, they do not have significant

implication on hydraulic capacity, but they do have impli-

cations for environmental health conditions mainly result-

ing from the high concentrations of pathogens (Parkinson

and Goldenfum 2007).

An important consideration is therefore to reduce the

inflow of excreta, particularly faeces, which contain the bulk

of the organic load and pathogens, into the stormwater

system. However, considerable expense and disruption may

be required at the household level to separate systems

that are already combined. For instance, in Phnom Penh,

Cambodia, it is common for householders to discharge

rainwater runoff from back yards and roofs to the same pipe

as their kitchen and toilet wastes. This runs under the house

before discharging to a drain in the road.

Another possible way of separating black and grey waterwithin houses is to install pour-flush latrines with leach pits

for blackwater and to allow the greywater to enter the

drainage system. Aswater in storm drainsis nottreated,this is

not an ideal solution from an environmental perspective but

can be a pragmatic and low-cost solution for urban upgrad-

ing. This approach wasused in some schemes implementedin

the early 1990s through the Calcutta Slum Improvement

Project (CSIP) in Kolkata, India which was financed by the

UK Governments Overseas Development Agency (now

Department of International Development (DFID)).

4.4 Pipes or open drains

The majority of existing drains in informal areas are desi-

gned as open channel systems, but in reality, drains often

become covered by local residents in order to maximise the

amount of land available for building or for access. In

general, they are less prone to blockages due to the fact that

it is easier to see when drains are becoming choked and it is

easier to clean them with rudimentary equipment. However,

on the other hand, open drains act as recipients of solid

waste dumped by local residents, which reduces flow

capacity. There are other disadvantages. They may smell

more than closed drains and there is a risk that children may

fall into them or play next to or in them. In addition, they

may be more likely to provide breeding grounds for Culex

mosquitoes than closed drains.

4.5 Control of solids entering closed drainage systems

For covered/closed systems to be efficient at draining

stormwater runoff, they need to have inlets in order to

Figure 5. Combined drainage system in Peshawar,

Pakistan carries foul wastewater as well as stormwater

(Photo: Kevin Tayler).



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allow for the inflow of runoff but to avoid the ingress of

solids into the system. These inlets must be:

(a) large and numerous enough to allow for the inflow;

(b) not so big that they become dangerous;

(c) effective at stopping the ingress of solid waste.

Solid waste traps may be installed at strategic locations in

the drainage system to collect and remove solid waste from

the flow. Various designs for these inlets exist including a

range of devices such as grids or gully pots. The majority of

them rely on screening of runoff in order to remove floa-

ting debris, but the efficiency for solids removal is highly

variable. However, all inlets need to be cleaned at times.

Access for cleaning and maintenance is therefore crucial

and it is important that there is a routine programme of

maintenance especially before and during the rainy season

(Armitage and Rooseboom 2000).

4.6 Paving and road construction

The easiest way to pave/rebuild roads is to build on top of

the previous road surface. This leads to road surfaces being

raised above house plinth levels, so that any flooding

affects houses rather than public rights of way. Raised

streets may also obstruct runoff and impound floodwater

on private property. To overcome this, road levels should

be designed to be as low as possible. It is also important

that roads are not constructed in a way that fills in and

builds upon existing drainage channels or constructed on

elevated embankments, which will cause floodwater to be

impounded.

5. Wider considerations and problems related to city-wide

drainage provision

There has been a tendency for drainage improvements to

be implemented in a fragmented manner, often without

enough attempts to identify the boundaries of different

catchments and the linkages between the local area and the

city-wide drainage system. In addition, as paving and

drainage system are improved as part of urban upgrading,

runoff inevitably increases, which may exacerbate down-

stream drainage problems and lead to increased flooding.

This suggests a need to take a city-wide perspective on the

management of stormwater.

5.1 Source control of runoff

Source control approaches involve infiltration and poten-

tially reuse of rainwater or groundwater recharge as a

means to reduce runoff (Reed et al. 2001). These appro-

aches are becoming increasingly common in developed

countries and also in some middle-income countries such as

Malaysia and Chile (Parkinson and Mark 2005), which are

promoting infiltration as part of a strategy for the control

of urban runoff. However, to date there have been few

attempts to apply these technologies in low-income

developing countries, which are the main focus of upgrad-

ing projects.

The potential role of rainwater harvesting in reducing

runoff is influenced by a range of factors related to urban

layout (population density, open space and housing type,

etc.), which will influence the amount of runoff and the

feasibility of introducing collection systems. Although

individual household roof area may be small (as low as

9 m2 in urban Bangladesh), which reduces the potential

benefits of collection of roof runoff (DTU 2002), total roof

coverage in dense urban informal settlements is usually

high. This suggests that storage of roof runoff at the

household level may help to reduce downstream drainage

problems and flooding as well as concurrently contributing

towards domestic water supply. According to Gould

(2000), it is possible to make do with a relatively small

tank if one accepts that not all of the household waterdemand will always be met. However, small tanks may fill

up during the early part of the storm and therefore fail to

reduce runoff in later rainfall events. In addition, tanks may

become used for other purposes during the dry season and

not reinstalled properly prior to the wet season.

5.2 Detention ponds and rainwater reuse

From a runoff control perspective, rainwater harvesting

from detention points may offer greater perspectives than

individual installations at the household level. The possi-

bility of using localised storage of runoff was considered in

north-east Lahore but it was found, as in many informalareas, that there was little publicly owned land and so no

obvious locations in which to hold storm water.

Two specific problems relate to land ownership and the

price of land. Informal developments may be constructed

on government land, but areas within them are often con-

trolled by private individuals. This means that efforts to use

land for runoff detention is dependent on reaching agree-

ment with the local land owners. It is important to con-

sider ways in which flood control areas can be used for

alternative purposes such as recreational activities and

agriculture. However, there will always be a problem such

as in Indore where detention ponds failed because over-

loading and poor maintenance led to them becoming

heavily polluted.

With a view to managing water holistically and reducing

flooding, an integrated approach toward stormwater mana-

gement based on a strategy of source control and reuse in

combination with a programme of cleaning and rehabili-

tation of the drainage system has been promoted by

Bangalore, India (see Box 1).



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11/14

catchment boundaries is relatively straightforward.

However, in cities with flat topographies, there is usually a

need to check the existing drainage situation in the field.

In addition, the relationship of the project area to natural

drainage basins needs to be established during the initial

stages of drainage planning.

In areas where flooding is expected, it is important to

gather data on the levels at which water will start to enter

houses, together with information about water levels

during past flood events. In order to define the catchment

in detail, it will be necessary to obtain elevations at road

junctions, roads and roadsides (noting whether the adjacent

land is above or below the ground) and general topography

of open land (low and high spots).

A combination of survey techniques can be required to

map the drainage area and provide a comprehensive view

of in the form of a map, combining some or all of the

following as appropriate.

6.2.1 Land based topographical surveys. Conventional

surveying methods are traditionally the most common formof mapping and more advanced surveying methods using

total station methods are now available. These are much

quicker and more accurate than traditional methods and

reduce the cost of mapping. Geographical positioning

systems (GPSs) use satellites to locate ground positions and

heights and there are various technologies available; some

of which may not provide sufficiently accurate data. Hand-

held GPS offer up to 10 m horizontal error and 20 m of

vertical error, which is unsatisfactory for the purposes of

drainage ground surveys. However, Differential GPS,

which uses two receivers simultaneously, offers a much

greater level of accuracy (less than 2 4 cm error horizon-

tally and 4 6 cm error vertically) and is therefore moreuseful for the purposes of drainage planning.

6.2.2 Aerial remote sensing. Although in some countries,

access to aerial images is not possible for security reasons;

remote sensing (including different types of aerial-based

photography and satellite imagery) provides an alternative

or complement to traditional ground surveys. Remote sen-

sing images are also a particularly good way of estimating

the degree of development and urbanisation in informal

settlements (Sartori et al. 2002) and may be used to cal-

culate impermeability. They may prove to be particularly

useful in cities in developing countries where the avail-

ability of good maps and data is so poor, that the

production of base maps is the first stage in the preparation

of urban drainage plans (see figure 7).

Aerial remote sensing can provide details for assessment

of contributory catchment area and land use, which can

then be used to calculate runoff. It can also identify some of

the large open drainage channels in the catchment, but

cannot provide the detailed data that are required to

describe the whole of the drainage network. Supplementary

ground-based survey will therefore normally be required to

provide additional information on drain and ground levels

because aerial photography does not provide accurate data

about ground elevations.

Initially, satellite imagery was only possible for mapping

at scales between 1:25 000 and 1:250 000 using existing

systems such as Landsat and SPOT, but these systems do

not provide the same level of detailed information as

aerial photography at large scales. However, in recent

years a number of very high-resolution satellite systems

(QuickBird, Ikonos and Orbview 3) have become available

and these can produce a level of detail that is much closer to

traditional land-based terrestrial surveys.

In addition to these, the introduction of free software on

the internet such as Google Earth and NASA World Wind

can assist engineers estimate the extent of impermeable and

permeable areas and to plan routes of drainage channels

but at lower resolutions than the satellite systems men-

tioned above.

7. Approaches towards implementation

As mentioned above in the discussion of the Indore Slum

Networking project, upgrading in a dense and highly con-

solidated slum is more difficult than in a new settlement

since the settlement layout is already determined by the

existing housing and infrastructure (Imparato and Ruster

2003). Installing drains in informal areas can be proble-

matic owing to the fact that rights of way are often limited

while local residents continue to live and work in the area

while the construction takes place.

Figure 7. Satellite picture of Monrovia in Liberia showing

a mixture of formal and unplanned informal settlements

(Resolution 0.6 m, original image in colour) (Photo: DHI).



12/14

The conventional approach towards project implementa-

tion for drainage construction usually involves the con-

tracting of engineering companies under supervision by

engineers from the local government agencies responsible

for drainage in the city. For larger-scale infrastructure, the

need for specialist skills and equipment necessitates the use

of experienced contractors. However for small-scale com-

munity level infrastructure, the use of local contractors and

labour can reduce costs and facilitates transfer of skills into

the community as described in the example from Vietnam

in Box 2. The involvement of local business and micro-

contractors, especially those based within low-income

communities also has the added benefits that it generates

economic activity and stimulates local interest in the

project.

Box 2 Provision of local sewerage infrastructure in

Hanoi, Vietnam

For sewerage and drainage network in small roads

and alleys (see figure 8), where the total project cost is

less than US$1250, the community proposes the

project and can secure up to between 33 50% of the

capital requirement from the ward Peoples Commit-

tee (PC), which can be in the form of construction

materials. The ward PC may take the full decision

without referring to the District authority for

authorisation and the project costs are paid directly

from the ward PC account, which includes the annual

state subsidy budget and the local Labour Fund for

Public Interest. The local community is expected to

raise the remaining additional balance and thehousehold contribution can be in the form of labour

in kind instead of cash (Nguyen et al. 2005).

The community contracting approach involves the

award of contracts for implementing infrastructure works

to local community organisations or groups. The contract

is given to a group representing the beneficiaries and the

competitive tendering process is avoided. In this approach,

any profits go to the community and not to a contractor or

middleman. The concept is promoted as a more efficient

alternative to expensive, top-down, contractor-driven

urban upgrading projects (Cotton et al. 1998). However,

the approach presents some potential problems. In

particular, the community contractor may have limited

skills and thus need considerable supervision.

Another option is to engage community members as a

collective group to help manage the construction. In this

option, community representatives are partly or wholly

responsible for overseeing the quality of the work and

mobilising the community to contribute towards the cost of

construction. Community representatives may also help to

negotiate with the local contractors and the suppliers of

building materials. However, the increased involvement

and interactions between different stakeholders required by

this approach may result in potential complications and

increased transaction costs.

The mechanisms of participation and social interactions

in urban upgrading projects are highly variable and

complex and often it is not possible to work directly withlocal level stakeholders. It will therefore be necessary to

promote a structure to encourage social interaction

between the various actors involved in the project. In

many projects involving community participation, local

non-governmental organisations take on the role of the

intermediary in order to mobilise communities and assist

them in organising fund-raising (Kyessi 2001).

8. Operation and maintenance

Although many municipal authorities remove solids from

storm drains before the onset of the wet season, experience

and observation suggests that this is not always done

systematically. As a result, many urban stormwater drains

become blocked or partially- blocked by refuse, silt, sand

and other solids. This is especially the case in informal

settlements where this is ongoing construction and a lack of

effective services for solid waste collection (Parkinson and

Goldenfum 2007). Although drains tend to continue to

function and drain runoff from low-intensity rainfall

Figure 8. Upgrading of tertiary sewerage in Hai Ba Trung

district in Hanoi (Photo: Dr Nguyen Viet Anh, CEETIA,Hanoi University of Civil Engineering).



13/14

events, there is a considerable loss of hydraulic capacity,

which means that large-scale investments in drainage

infrastructure are wasted. For example, surveys in cities

such as Mumbai in India have shown that most of the

trunk sewers have become structurally unsafe and have had

their hydraulic capacity reduced by 40 60% (Gupta 2005).

Therefore, all drainage systems, irrespective of their

design and construction, require attention to maintenance.

Maintenance requirements are increased by high silt

loads and the ingress of solid waste to the drainage

system. The removal of solid waste from drains consumes

the major annual operating budget of urban drainage

operations and, if not managed, neglecting maintenance

can result in deterioration of infrastructure, a need for

premature replacement and loss of asset life (UNCHS

1993). In addition, most drains discharge via outfalls and

these may become heavily silted to such an extent that in

some cases the storm drains that are connected to them

may become embedded in silt as has been the case in

Kolkata (Gupta 2005).

The extent of maintenance required depends upon thequantity and types of solids on the catchment surfaces,

combined with climatic factors that affect the duration of the

wet season and the accumulation of sediment. It may be

beneficial to adopt maintenance strategies that remove the

waste from the drains more frequently throughout the year

rather than a major operation once per year, which requires

significant resources in both human and financial terms.

8.1 Solid waste management operations

Although municipal agencies often make an attempt to

clean and improve the operation of the system prior to the

onset of the wet season, this tends to be only a partialresponse to the scale of the problem. Owing to the fact that

maintenance strategies are not required for everyday

operations, they are often not planned or implemented

effectively.

Cheaper labour costs mean that operation and main-

tenance (O&M) strategies for urban drainage systems in

developing countries can be much more labour intensive

than those in developed countries. As solid waste manage-

ment is often poor in informal settlements, the focus on

improved solid waste collection becomes more important, as

shown by the example from Santo Domingo described

above. However, solid waste still frequently ends up in the

stormwater drains, and refuse collection services are

generally not well co-ordinated with drain cleaning activ-

ities even where different sections of the same municipal

department are responsible for these different activities.

Potentially the most effective approach is to adopt a

preventative approach towards solids waste management.

Box 3 describes a drain cleaning and solid waste manage-

ment project in Lahore, Pakistan, which emphasises the

importance of raising awareness about the need to manage

solid waste to prevent future problems related to drainage

blockages. The effective implementation of this project was

dependent on community awareness and participation in

solid waste management as in Santo Domingo.

Box 3 Drain cleaning and solid waste management in

Lahore, Pakistan

The project was initiated in 1992 to alleviate drainage

problems by reducing the accumulation of the solids

in the drainage system. It was combined with an

initiative to improve solid waste management in

order to reduce the potential for reoccurrence of the

problems in the future. Drain cleaning was carried

out by Lahore WASA staff with advice provided by a

Danish consulting firm. Larger drains and sewers

were cleaned by hand and specialist drain cleaning

equipment. Although the cleaning of the sewersthemselves posed a challenge from a technical

perspective, there were many difficulties presented

by the fact that it was impossible to undertake the

cleaning activities during the daytime due to the

amount of activity on the streets. The only time it

was possible to carry out the work was during the

night, but the disturbance and disruption during the

cleaning of sewers and open drains (nullahs) would

inevitably cause complaints amongst the local

residents. The role of the local NGO (YCHR) was

important in liaising with the community about the

project and communicating the reasons why the

remedial work would be undertaken during the night.In addition to this, the NGO implemented an

awareness-raising campaign to promote the impor-

tance of improved solid waste management in order

to encourage residents to understand the linkages

between poor solid waste management and blocked

drains. In addition, the awareness raising campaign

was complemented by the introduction of a new

system for collection of domestic refuse on a house-

to-house basis. This involved development of a

handcart, which had the mobility to access the

narrow, crowded streets in the old walled city area.

(Personal communication, Yasin 2004)

9. Concluding remarks

There is a need to consider the development of city-wide

drainage system in order to maximise the effectiveness and

efficiency of investments in drainage and to mitigate



14/14

downstream flooding and pollution problems. However,

urban upgrading projects rarely include provision of off-site

infrastructure requirements and this is a key constraint for

effective drainage provision. In addition, although some

examples were presented above, a component for operation

and maintenance is frequently not included in project

design.

The issue of land water interactions are particularly

problematic in developing countries because of the impacts

of uncontrolled growth and the constructions on flood

plains and even in drainage channels. The concept of source

control should be adopted wherever feasible in order to try

to solve problems locally but will often be difficult because

of weak planning controls. Regardless of this, it will always

be important to define drainage areas and the boundaries

between catchment areas.

Drains are often used for purposes other than those

assumed by their designers. For example, drains are often

used as sources of irrigation water. Therefore, drainage

engineers need to consider whether the ways in which

people use facilities will have an unexpected impact on theoperation of the drainage system and on the health and

living conditions.

It will therefore be important for engineers to talk to

local residents in order to both understand their concerns

and learn from their local knowledge. As well as good

technical skills, staff working on urban upgrading schemes

need to have a willingness to look, listen and learn from the

people and activities around them. However, too much

emphasis on social development and the softer aspects of

community participation, may lead to problems related to

the basic engineering aspects of drainage design.

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