Introduction

Drainage systems require a global planning at the different scales of a settlement, and a comprehensive understanding of the surrounding areas and (existing) drainage networks (see introduction “Surface Water Management”). Drainage networks can take many forms and include several techniques and materials such as :

1) Natural drains (primary canals) are based on restorations of riparian vegetationand planting of trees and other shrubs. This nature-based measure comprises natural canals with low gradients where the water runs slowly.
2) Low-tech drainage systems can include interventions like bamboo drains (primary, secondary, tertiary drainage) and geotube/geobag embankment drains (primary, secondary, tertiary canals).
3) Medium and high-tech drainage systems describe measures such as masonry and precast concrete drains (secondary, tertiary canals). When using concrete ditches, re-infiltration through holes in the drainage bottom should be used wherever it is possible.
4) Other interventions include ridgeline and cascade drains, silt and waste traps, and microsoak pits.

Benefits & Risks

In general, if the drainage is not properly maintained and cleaned or the slope and infiltration effectively planned, there is a risk of stagnant water where mosquitos and will grow and transmit diseases.

Natural drains: Natural drainage is low in cost and eco-friendly. However, it is not recommendable in congested locations and there is the risk of erosion.

Bamboo drains: Bamboo drains are quickly installed and efficient during emergency situations, where this material is easily available. However, the bamboo does not last long and needs to be replaced frequently, so over time more durable solutions should be developed.

Geotube/geobag embankment drains: This low-tech measure is cost-and labor-effective. The base is made from well compacted earth which supports infiltration. However, the drains do not benefit highly dense areas.

Masonry drains: Masonry drains are beneficial for densely populated areas. In addition, their maintenance and cleaning are comparatively simple. However, the measure is costly and complex to install and repair. Also, the base (concrete/brick-based) may cause flooding downstream since there is no infiltration in the soil.

Precast concrete drains: The installation of precast concrete drains is best at road sides, ridge lines, or vehicular roads. Although they are installed relatively quickly, the material costs are high. Precast concrete drains are also at risk of accelerating the flow velocity and thus causing downstream flash floods. In general, very high-tech solutions are comparatively expensive and complex to build. That is the reason why they are seldom applied in refugee camp settings.

Environmental Impact

Bamboo drains include sustainable materials and support infiltration. Geotube embankments foster infiltration, but the earth base can increase siltation and erosion. Masonry and concrete drains may prevent waterlogging but can disrupt habitats through excavation and vegetation removal before the implementation. 

Good Practice

Suds Management Train in the Gawilan Refugee Camp, Kurdish Region of Iraq

The community of the Gawilan Refugee Camp in the Kurdistan Region of Iraq designed a SuDS-management train (SuDS: Sustainable Drainage Systems) which includes a range of drainage techniques. Adjacent to the shelter area, a gardening patch, native tree pits, endemic vegetation, wet areas, and trickle trenches were installed. In addition, the implementation of two concrete greywater channels took place. One greywater channel joined a pond for biofiltration and the other flowed “through a broken pavement of aggregates to trap solids carried in the greywater” (Charlesworth et al. 2019, p.3505). Since the beginning of the construction in 2018, the site, pits and trickle trenches added around 2000 trees and grapevines. The co-creation with the inhabitants of the refugee camp included workshops and site walkovers. The ideas and design from the community (represented by a committee) were then elaborated by a professional landscape architect, implemented by local and WASH engineers, and coordinated by the UNHCR.

References

Score Card

Criteria

Scale of Intervention

Shelter-Plot-Block Settlement Supra-settlement

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Type of Intervention

Engineered Nature-based Hybrid Non-structural

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Targeted Natural Hazard

Pluvial Flood Coastal/Riverine Flood

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Strategy Type

Relocate Reduce Hazard Magnitude Reduce Asset Vulnerability Reduce Casualties

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Implementation Time

Short (1 day ‐ 1 month) Medium (1 month ‐ 1 year) Long (> 1 year)

  Bamboo drains: short (1 day – 1 month)
Geotube embankments: short (1 day – 1 month)
Masonry and Concrete Drains: medium (1 month - 1 year)

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Effect Duration

Short‐term ( <1 year ) Medium‐term (1 year to 10 years) Long‐term (>10 years)

  Bamboo drains: short-term (10 years)
Geotube embankments: medium-term (1 year to 10 years)
Masonry and Concrete Drain: medium-term (1 year to 10 years), long-term (>10 years)

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Targeted Vulnerable Assets

Buildings Transport Technical Infrastructure Land Cover

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Investment Costs

Low Medium High

  Bamboo drains: low
Geotube embankments: low, medium
Masonry and Concrete Drains: medium, high

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Maintenance Costs (yearly)

Low (<10% investment costs) Medium (10-50%) High (>50%)

  Bamboo drains: low
Geotube embankments: low
Concrete Drain: low

Materials

Bamboo drains: (Borak) bamboo, bamboo mats, basha bera mats, geotextiles, earth base (can be complemented with cement screed or trapaulin for better waterflow) Geotube embankment: Geotube/bags, sand, Alternatively: Jutebags, seeds Masonry Drain: Bricks, jute/geotextile bags filled with brick chips, concrete, beams Concrete Drains: Concrete, compacted earth

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