Cover Image
close this bookStormwater Drainage and Land Reclamation for Urban Development (HABITAT, 1991, 94 p.)
View the document(introduction...)
View the documentFOREWORD
close this folderINTRODUCTION
View the documentA. Background
View the documentB. Purpose of the report
View the documentC. Scope of the report
close this folderI. URBANIZATION AND THE DEMAND FOR URBAN LAND
View the documentA. Current trends in urban growth
View the documentB. Increases in land prices and the use of marginal land
View the documentC. Specific problems of the urban poor
View the documentD. Urban health in marginal settlements
View the documentE. Conclusions
close this folderII. POTENTIAL IMPACTS OF STORMWATER DRAINAGE AND LAND RECLAMATION PROJECTS
View the documentA. Urban land-use planning
View the documentB. Urban health
View the documentC. Socioeconomic benefits
close this folderIII. TECHNICAL OPTIONS FOR STORMWATER DRAINAGE AND LAND RECLAMATION
View the documentA. Stormwater management
View the documentB. Drainage system components
View the documentC. Storage: detention and retention
View the documentD. Drainage system design
View the documentE. Land reclamation options
View the documentF. Land stabilization
close this folderIV. MAINTENANCE
View the documentA. Maintenance objectives
View the documentB. The maintenance programme
View the documentC. Review of maintenance
View the documentD. Institutional arrangements for maintenance
close this folderV. PROJECT APPRAISAL
View the document(introduction...)
View the documentA. Technical appraisal
View the documentB. Social and health impact appraisal
View the documentC. Economic and financial appraisal
View the documentD. Institutional appraisal
View the documentVI. CONCLUSIONS AND RECOMMENDATIONS
View the documentBIBLIOGRAPHY
close this folderAnnex I: STORMWATER DRAINAGE DESIGN PROCEDURES
close this folderA. INTRODUCTION
View the document(introduction...)
View the documentA.1 Drainage systems
View the documentA.2 Aims and principles
close this folderB. PLANNING
View the documentB.1 General
View the documentB.2 Multiple use
View the documentB.3 Natural channels
View the documentB.4 Transfer of problems
View the documentB.5 Storage and reserves
close this folderC. DESIGN CRITERIA
View the documentC.1 Procedures for design and analysis
View the documentC.2 Hydrological models
close this folderC.3 Data
View the document(introduction...)
View the documentC.3.1 Rainfall data
View the documentC.3.2 Runoff data
close this folderC.4 Standards of performance
View the documentC.4.1 Introduction
View the documentC.4.2 Selection of average recurrence intervals
close this folderC.5 Basic design criteria
View the documentC.5.1 Basis of design
View the documentC.5.2 Calculation of stormwater runoff
View the documentC.5.3 Design recurrence intervals
View the documentC.5.4 Calculation of capacity of stormwater drains
View the documentC.5.5 Drainage reserves
close this folderD. FLOOD ESTIMATION
View the documentD.1 General
View the documentD.2 Modified rational method
View the documentD.3 Design hydrograph
View the documentD.4 Partial areas effect
close this folderE. CHANNEL DESIGN
View the documentE.1 General
View the documentE.2 Flow computation
View the documentE.3 Lined channels
View the documentE.4 Vegetated channels
View the documentE.5 Natural channels
View the documentE.6 Unkerbed streets
View the documentE.7 Design calculations
close this folderF. DRAINAGE DESIGN FOR URBAN STREETS AND PIPELINES
View the documentF.1 General
View the documentF.2 Gutter capacity
View the documentF.3 Drainage inlets
View the documentF.4 Pipe flow
View the documentF.5 Pipe system design
close this folderG. PUMPING CAPACITIES AND STORAGE REQUIREMENTS IN POLDERS
View the documentG.1 Principles of drainage in a polder
View the documentG.2 Pumping capacity versus storage requirement

D. Institutional arrangements for maintenance

The drainage system in a city falls into a distinct hierarchy. At the lowest level is the initial drainage system, the small drains along the edges of the roads and paths, and the kerbs and channels where rain falling on the roads and buildings will slow first. These channels convey water through inlets in the kerb or road edge to the minor drainage network.

The minor network of pipes and open channels are the second level in the hierarchy where the stormwater is collected and transported to discharge into the next tier, the major drainage system network of natural streams and watercourses.

It is not possible to set one single strategy for the management of the whole drainage system which will be suitable for all cities. Much depends on the overall institutional structure in the city: is it one municipality or is there more than one municipality with a regional authority with metro-wide responsibilities for major drainage works? It is possible, however, to make some general assertions:

(a) The initial drainage system maintenance should be integrated with the maintenance of the local road network. These drains form an integral part of the road. Good drainage maintenance is an essential requirement of the protection of the road itself. The patrol gang responsible for the road maintenance should also ensure that the drains, culverts and entry points to the drains are clear, serviceable and able to function properly. In general, the public works department of the municipality would have this responsibility.

(b) Depending on the structure of the city government, the minor drainage system could also be maintained by this same public works agency. This will normally lead to efficient use of the agency's plant and equipment fleet and its labour force. In large cities this will be decentralized into districts where local depots would hold stores of materials, house equipment and provide servicing of the district's equipment. It also provides a local contact point for residents to lodge complaints. In some cities there is a division of responsibility for the construction and maintenance of the minor drainage system between the municipality and the metropolitan regional authority. For example, the regional authority might have responsibility for drains where the contributing catchment is greater in area than, say, 100 hectares. This has the advantage of locating the maintenance of these larger drains which frequently cross municipal boundaries with a single agency. This will lead to a consistent application of maintenance standards and design criteria.

(c) The major drainage system includes roads and landscape/park areas where excess stormwater from the minor system flows during heavy storms. These parts of the major drainage system are not formal drains and are used as overflows from the minor drains. Their maintenance needs careful attention so that they will properly fulfil this overflow role in times of excessive run-off, but they would fall within the ambit of the municipality for routine maintenance. The other components of the main drainage system, the watercourses, streams and rivers, are clearly regional, traversing municipal boundaries. These are not only used to carry excess stormwater but may be used for recreation, transport, irrigation or water supply. Only a metropolitan-wide organization can successfully integrate these functions with the drainage function of the watercourse. Maintenance should therefore be the responsibility of this organization. If no metropolitan agency exists, the role will most likely fall to a provincial level of government.

The following are some of the key functions related to drainage maintenance:

(a) Programming and implementation of a regular inspection and maintenance programme of the drainage system;

(b) Collection and recording of rainfall and run-off data for all catchments in the area, if this is not available through a central agency;

(c) The establishment and maintenance of records of all drains in the system and the inspection and repair programme;

(d) The training of staff and operators;

(e) The protection of the public and employees by the development of safety programmes;

(f) Public communications to increase the awareness of the public of the importance of good drainage and the community's role in achieving this;

(g) Liaison with other agencies who may be affected, or whose functions affect, the drainage system;

(h) Consultation with the drainage design and construction agencies to ensure designs incorporate details to facilitate maintenance.

The form of organization for maintenance of urban drainage systems will vary by country and the government structures established in each country. The structure shown in figure 4.1 is indicative only and is meant to show the levels of the organization and the sections which are required to provide a comprehensive maintenance programme.

The key sections are:

(a) Safety office - separate from the operations sections to ensure this aspect retains its priority and status in the organization;

(b) Operations and maintenance;

(c) Inspection, records and survey;

(d) Sub-districts in larger cities with mobile gangs;

(e) Plant maintenance;

(f) Stores.


Figure 4.1. Organization chart for drainage operations and maintenance