Water Management in Bamenda and the Netherlands

1.Issues in water management

2.Water in the Netherlands

3.Water in Bamenda

4.Possible solutions

5.Planning considerations

Water Management Problems Generally summarised as…

1.Too much water or too little

2.In the wrong place or wrong time Too little also includes too little of good quality.

 

In the Netherlands

•The Netherlands is very densely populated.

•All land is ‘developed’.

•Many water ‘users’.

•A wet country with several large rivers.

•20% lies below sea level and 50% is less than 1 metre above sea level.

•We have very large drainage and flood problems!

In the Netherlands

•We employ an ‘integrated’ approach.

•Account for all stakeholders or ‘water users’.

•Upstream farmers need their land to be well drained.

•But we need to keep downstream urban areas dry as well.

•Need to keep the rising sea levels out as well.

So where do we put all this water?

The old approach was to have lots of pumps and dykes!

•But it is too expensive.

•Can fail spectacularly.

•Not designed for Climate change.

•Need a more sustainable and cheaper approach.

•Integrate spatial planning with water management.

•The aim in the Netherlands is no longer ‘prevent all floods’ but ‘reduce the risk and learn to live with water’.

•Employ a three-layer safety (and sustainability) approach to optimise basin hydrology called : “Vasthouden-Bergen-Afvoeren”.

•“Vasthouden-Bergen-Afvoeren” Approach… or

•“Capture” and keep water within the higher subbasin

•“Store” excess water in open water or green areas that may be inundated.

•“Discharge” the water the rivers.

 

•“Vasthouden-Bergen-Afvoeren” Approach… or

•“Capture” and keep water within the higher subbasin

•“Store” excess water in open water or green areas that may be inundated.

•“Discharge” the water the rivers.

 

In Bamenda

We have done a little research on the water situation in Bamenda…

Bamenda’s climate

In Bamenda

1.Extreme rainstorms in rainy season.

2.Steep escarpment above the city which has been developed (roads, etc).

3.Deforestation in the upper catchment.

4.Loss/degradation of wetlands.

5.Solid waste management problems causing drainage systems to be blocked.

6.Uncontrolled urban development increasing the people at risk.

 

In Bamenda

1.Urban flooding (actual and increased risk)

2.Landslides

3.Soil erosion Are there any water management issues that we have missed?

•But it is not possible (or fair) to stop farming in the upland areas.

•Nor is it easy halt all deforestation or road development.

•Nor relocate large numbers of people.

•So we need solutions that are feasible and locally appropriate in terms of the environment, social acceptance and cost.

“Capture”, “Store” and “Discharge”

•Consider this three step approach.

•Look at how to keep the water in the upland areas for longer.

•Look at how water can be stored in and around the city.

•Look at how to ensure water is discharged to the rivers and flows away.

Conceptualising this for Bamenda

•Guiding the water - Look at the topography to find ways to route water away from the urban areas.

Conceptualising this for Bamenda

•From the maps there are possible alternative routes for storm water.

Conceptualising this for Bamenda

 

Planning for extremes

•Important to understand the maximum probable rainfall events and river flows.

•What amount of water shall we plan for?

•Increasingly we need to account for the quantifiable impact of climate change on these extremes.

Climate change and Cameroon

•Limitations ….

•Current climate model predictions poorly represent precipitation.

•But better at simulating temperature.

•Model predictions are based on coarse resolution global models.

•Regionally based models provide a better resolution for water planning.

Planning for extremes

•Encroachment on flood ways

•Unregulated urban expansion.

•Increases the flood risk considerably.

Capture

•The easiest way to capture rainfall in the upper catchment is to maintain the natural soils and vegetation.

•But this is not always possible. Roads, settlements and agricultural land is already there.

•Therefore important to identify the hydrological role of the remaining ‘natural’ areas and augment them.

Capture

•Protected thick vegetated strips and contour ploughing of fields are all measures that farmers can carry out.

•Farmers have a self interest in protecting their soils so should see the benefits if consulted.

•Careful design of road drainage. •Implementation of simple ‘SUDS’ measures in the settlements

•It is also important not to capture water in the wrong places.

•Consider the escarpment with its landslide prone soils. If these soils are too wet then they loose their strength and can slide.

•Therefore good drainage on the hillsides is important but not too good that the water floods the city = A balancing act.

•Better keep the water on the land above the escarpment for longer.

“Capture” and “Storage” measures

•Sustainable Drainage Systems (SUDS or SuDS)

•The philosophy of SUDS is to replicate, as closely as possible, the natural drainage

 

Why do we need SUDS?

•Urban Creep –Typical Example

•1984 Impermeable surfaces

 

Urban Creep –Typical Example

•1984 Impermeable surfaces

•2011 Impermeable surfaces

Why do we need SUDS?

•Urban Creep –Typical Example

•1984 Impermeable surfaces

•2011 Impermeable surfaces

•2034 Impermeable surfaces?

Water Quantity in SUDS? 

•The urbanisation/development process means that surface flows are larger, quicker and shorter lived than the pre-urbanisation situation.

•SUDS attempts to recreate the slow discharge by holding the water for longer and allowing infiltration to groundwater.

 •Quality (Treatment)

•How clean is surface water? Water Quantity in SUDS?

 

Ecology in SUDS?

•Green Areas in urban settings can provide an aesthetic value but also act as flood retention.

•Urban parks are increasingly being designed along the banks of restored urban rivers which have a recreational use but also act as flood ways and rainwater storage areas in the rainy season.

 

Examples of SUDS?

•Green SUDS examples –Green Roofs (Source Control)

 

Discharging storm water

•Not only new infrastructures.

•Maintenance of existing storm drains.

•Clearance of solid waste prior to rainy season.

 •River / drainage channels may need to be enlarged for increased larger storms

•Dredged to remove eroded sediment.

•Additional channels to move the water away from the city.

  •Water velocities in drains and rivers can be increased or decreased according to needs.

•Constructed weirs or check dams can slow flows as can encouraging bankside vegetation.

•Cleared, straightened and dredged channels will speed up flow but have little aesthetic value.

•It greatly depends on which areas you want to hold water back and which areas you need to make it flow faster away from flood areas.

Important considerations

•It is important to realise that SUDS measures are very effective in Europe…

•BUT there are considerations that need to accounted for in Bamenda when selecting appropriate measures.

•e.g. will storm water retention ponds increase malarial risk or water borne disease?

•e.g. can ‘Swale’ vegetation strips be maintained and kept waste free on the available budget?

•Important to consider the current hydrological conditions.

•What impact will climate change have?

•Carry out a proper assessment of different solutions (both engineering and economic)

•Consult local residents (they may propose their own solutions or identify flaws in your plans).

•The simplest approach to risk mitigation is to remove the ‘receptor’.

•If the people and critical infrastructure are not in flood or landslide prone areas then there is no risk.

•Easier said than done as the people and critical infrastructure are already there.

 •The simplest approach to risk mitigation is to remove the ‘receptor’.

 

 

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