Low Cost Drainage for Emergencies | Surface Runoff

Please download to get full document.

View again

of 9
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information Report
Category:

Others

Published:

Views: 9 | Pages: 9

Extension: PDF | Download: 0

Share
Related documents
Description
Effective drainage is important in emergencies when there is a risk of flooding or there is a risk of poor environmental health conditions developing from standing water, muddy conditions, or erosion. It would not usually be the first priority in the initial stages of an emergency, but should be considered after the immediate water, sanitation and hygiene needs have been met. Sites which have natural slopes and drainage may not require additional work except in localised areas, such as providing cut off drains to prevent water from flowing into latrines or shelters. This Technical Brief provides an overview of the general principles of good drainage design and introduces a range of construction options for simple drainage channels, erosion control and road crossings. It focuses only on surface water drainage and does not cover the disposal of sullage or sewage. It has drawn heavily on early work by UNCHS (Habitat) and by the ILO in the area of labour intensive construction and low cost drainage.
Transcript
  OXFAM Technical Brief  –  Low cost drainage for emergencies 1 Low cost drainage for emergencies Effective drainage is important in emergencies when there is a risk of flooding or there is a risk of poor environmental health conditions developing from standing water, muddy conditions, or erosion. It would not usually be the first priority in the initial stages of an emergency, but should be considered after the immediate water, sanitation and hygiene needs have been met. Sites which have natural slopes and drainage may not require additional work except in localised areas, such as providing cut off drains to prevent water from flowing into latrines or shelters. This Technical Brief provides an overview of the general principles of good drainage design and introduces a range of construction options for simple drainage channels, erosion control and road crossings. It focusses only on surface water drainage and does not cover the disposal of sullage or sewage. It has drawn heavily on early work by UNCHS (Habitat) and by the ILO in the area of labour intensive construction and low cost drainage. Purpose of drainage The purpose of surface water drainage is: 1.To remove water safely and effectively from livingareas and hence improving the living environment.2.To prevent standing water, flooding and erosion.3.To ensure that vehicular and pedestrian access ispossible at all times, particularly for access inmedical emergencies.In turn effective drainage can prolong the life of simple structures, reduce breeding grounds for mosquitoes and reduce the build up of muddy stagnant pools. These can harbour dangerous pathogens which can cause a range of faecal oral related diseases, from which children playing around them can be particularly susceptible. They can also become breeding grounds for mosquitoes.  Attention to drainage is particularly necessary, but also most challenging, where the ground is either very steeply sloping (in the form of erosion control), or very flat. Simple earth drains being constructed to reduce the muddy conditions around the tents in Jabba tented village, IDP camp in Pakistan  During emergencies there may be particular needs for drainage in camp situations and in urban environments. In urban environments, it is possible that the work required will be limited to unblocking or repairing existing drainage networks, but in poor peri-urban environments, existing drainage may be non-existent.   Principles of good drainage design 1.Drainage design starts from the receiving water bodyor outfall. Drain inverts will need to be designedbackwards from this point and wherever possiblefollow the natural fall of the ground surface.2.Secondary drainage feeds into larger interceptordrains which connect into the receiving water bodyor outfall.3.Water should always be kept flowing and should notstop when reaching a crossing point. Drainage mustallow water to pass effectively across all roads (overor under) and road junctions, whilst also allowingvehicular and safe pedestrian access.4.Water should ideally flow fast enough that the solidsit is carrying will not be deposited in the drain.Drains with sloping sides and narrow bases help tomaintain a steady flow.5.When the fall along the bottom of the drain issteeper than 1% (falls greater than 1 unit in 100units distance), protection against scouring effectswill be needed, either by lining or providingprotection at particularly vulnerable points along thenetwork.6.Ground which slopes greater than 5% can beconsidered a steep slope. Drainage will requiredesign features to reduce the speed of the flow,such as turn-out-drains, constructing drainage alongthe contours, or including steps or check-walls intothe drain profiles.7.Effective drainage construction and operation andmaintenance are activities which benefit from theinvolvement of the local communities and / or theaffected populations.  OXFAM Technical Brief  –  Low cost drainage for emergencies 2 Tools for drainage construction Hand tools  –   The ‘hoe’ / ‘jembe’, ‘mattock’, ‘pick’, ‘half pick’, sometimes get confused –  Use these diagrams to determine the local names for the tools required for the particular task (Ref: World Bank, 1983)  Camber board for development of road camber (Ref: Tournee, J / Shaloba, S, PUSH Project, Zambia 1991)   The selection of hand tools, appropriate to the local users, is important for drainage construction. The pickaxe, mattock, hoe and shovel or spade are the tools which will be required in greatest numbers. Communities usually have a preference for the type of tool they feel most comfortable working with and local names can vary. The pictures at the top of this page have been provided so that they can be used when discussing the purchase of tools for drainage construction.  As with any tools for labour intensive work, care must be taken to ensure that the tools are sharpened on a regular basis and the handles are securely fixed into the heads without additional wood being fitted into the gaps. Loose heads or blunt tools can lead to accidents. A stock of spare handles for the key tools is also useful (if heavy use is expected then purchase an additional 10% of handles when placing initial orders). Other tools which may be required include: sledge hammers and crowbars for breaking rock, a tape measure for measuring distances and drain widths, string, pegs and lump hammer or lime powder for marking out the line of the drain, and a spirit level or  ‘line level’   (a spirit level which is hung on a line) to help determine the slope of the drain. Shovel Hoe Pick Mattock Camber board Drain profile Tools commonly used in the construction of road camber and drainage Mattock Jembe Pick Hoes Half pick  OXFAM Technical Brief  –  Low cost drainage for emergencies 3 Men and women may prefer different tools. For example, women sometimes prefer head-pans for earthmoving whilst men may prefer wheelbarrows. Wherever possible consult the users as to their preferred tools, particularly for extensive drainage works.  A     ‘camber board’ is a triangular board which can be used to form the slope or    ‘camber’   of a road surface or a drain slope. It is used in conjunction with a spirit level which makes sure the camber board is held level. A  ‘ditch or drain profile’   is a shape of the cross section of the drain which can be used as template during excavation. Large rocks which can not be removed by digging around them or by hitting them with a sledge hammer can be removed using the  ‘fire and water method’  . A fire is burnt on the rock and then when it is very hot, cold water is poured onto the rock. The heating and cooling process results in cracks in the rock which can then be forced apart using a crow bar. This method however is both time-consuming and expensive and can use up a large quantity of wood. Any work involving smashing rock with a sledge hammer must be undertaken with appropriate clothing and in particular with goggles to protect the workers eyes from flying pieces of rock. Simple drainage channel designs Composite channel to help prevent deposits during low velocity flows  Variations in simple drainage cross-sections (Refs: taken directly from UNCHS (Habitat), 1986; WHO, 1991)    A range of different low-cost drain cross sections are shown above. The choice of shape, size and lining of the drainage channels will depend on a number of factors. For example, it would not be appropriate to construct expensive lined drains in an IDP camp which is expected to only be in place for a short period of time and hence simple earth unlined drains may be adequate. However, if the site is on a steeply sloping where there is a risk of gulleys forming and damage to living areas, then simple unlined drains may not be appropriate on their own. Where there is limited space, a drain with vertical sides may be the only design possible, but unless the drainage is only required for a short period of time, the sides should ideally be lined to prevent erosion. The    ‘composite channel’   is a small drain within a drain and is designed for areas where there are likely to be a wide variation in flows and particularly where there may be sullage thrown into the drain as well as the drain collecting storm water. Without the smaller channel in the middle, the sullage water will deposit its solids as it  OXFAM Technical Brief  –  Low cost drainage for emergencies 4 would have a low velocity in the large channel. This could then pose an environmental hazard. For large or complex areas, for example in peri-urban environments where there are going to be many road crossings, detailed design of the drainage network will be required (see the final section below). But for a small area where it is clear in which direction the water will naturally flow, it may be appropriate to simply design the lines, sizes and fall of the drains by eye on site. Watching the flow of the water and any particular problem areas during a heavy rainfall can be a useful tool in determining the required routes of the drains. Self-cleansing flow ‘Roughly speaking, a channel of 10  -15cm wide will need a minimum slope of about 1% to achieve a self-cleansing speed of flow. A channel twice the size needs roughly half the slope’   (WHO, 1991). Such gradients will not always be possible however, so a regular drain cleaning regime will be required to prevent the drains from filling. Erosion protection Drainage on steep slopes Slopes of ground above 5% can be considered steep slopes and will require additional features to reduce the speed of the water and prevent erosion. These features can include: 1.Constructing  ‘turn -out- drains’  , which take thewater away from the main drainage route and directit into fields to soak away. These are usually onlypossible in rural environments or where there isopen space in urban areas.2.Constructing the drainage along the contours of theland.3.Construct  ‘check  - walls’   or  ‘erosion checks’   atregular intervals down a slope. These effectivelyform small walls across the drain and can beconstructed of stone, wooden poles, or masonry, orfor large drains from gabions (large baskets of wirewith large stones placed inside). As the water passesdown the drain it stops behind each check-wall anddeposits its solid load. After a while the solids buildup until a stepped effect is produced which reducesthe effective slope of the drain (see the diagramsopposite).4.In areas with a moderate drain slope (4-10%), thedrains can also be lined with concrete masonry orvegetation. Stone pitching for erosion protection alongside a road culvert and at the join of two drains For unlined drains, erosion protection may still be needed at particularly vulnerable locations where sour effects may be strongest, for example at bends, or at outlets to drifts or culverts, or where one drain feeds into another drain. Stone masonry known as  ‘stone pitching’,  uses stones of approximately 15cm thick and cement mortar to bind the stones together (see the photo above). Steepness Gradient Spacing of erosion checks  Very steep hill More than 10% 5m spacing Steep hill Between 5-10% 10m spacing Gentle hill Between 3-5% 20m spacing  Almost flat Up to 3% Checks are not required (Ref: Antoniou, J et al, 1990) Roads and drainage Roads are important to ensure access at all time. This is particularly important for medical related emergencies where vehicle access may be needed to take somebody to hospital. Drainage is the most important part of a road and if the drainage is correct and the road surface material reasonable, then the road should be passable for most of the year. Road surfaces The best surface for a simple road is compacted  ‘road gravel’  , which consists of approximately 50% stone, 40% sand and 10% clay. Its strength comes from the various sizes of stone locking together on compaction with water.
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks