The current rains have continued for the last two weeks in most parts of the Country. As earlier predicted by the meteorological department, though occurring during the normal heavy rain season of March to May in the region, the rains have turned to be unusually heavy, tending to El-Nino-like weather conditions across the region.
The size and storm intensity seem to vary every passing day, as almost accurately predicted. While the rains and weather patterns have been predicted, the effects and resultant destruction/damage/havoc have not been accurately projected. The rains have, therefore, caused Flooding, leading to the destruction of property, loss of life, and the disestablishing of the entire environment to different levels and extents.
We are going to discuss the flooding situation in relation to catchment stormwater hydrology and the existing natural and man-made drainage systems, and the effect of Flooding on the socioeconomic aspects to human life in a brief and concise format outlined in point form for both urban and rural land use..
- Flooding: This is overflowing of water or any other liquid submerging land or surfaces that are normally dry. In this presentation, we shall be specific about flooding due to stormwater.
- Current Flood Situation: The current rains have caused flooding in Nairobi City and several other urban and rural settlements, leading to loss of life and property damage. The entire Nation has been thrown into an emergency situation and a very challenging disaster management crisis.
- Causes of Flooding: Sudden heavy rainfall usually overwhelms existing natural or man-made water channels,, including the outfall/receptors.
- Source and quantity of flood waters: Stormwater Run-off is the rainwater that is not absorbed into the ground depending on the existing Catchment Characteristics. The quantity and rate of discharge/storm run-off will, therefore, be a function of the watershed area, intensity of the falling rain, slope and longest length of the catchment, rate and capacity of water percolation into the ground depending on soil types, density of vegetative cover, extent and quality of paving/ground interference on developed areas.
Accordingly, the different land-use patterns, including farming, forestry, wildlife activities, and other forms of physical development and land-use planning, will determine the flood size, duration, and effect of any particular region.
- National Drainage Basins. To study, assess and manage the flood situation in Kenya, we must demarcate the drainage basins accordingly. The Drainage Basins include the Ewaso Ngiro Basin, Tana River, Athi-Sabaki River, The Rift Valley and Lake Victoria North/South Basins. These drainage basins have different catchment characteristics and, therefore, are all unique in storm run-off quantities and effects of Flooding both within and outside the basin, where the run-off gets into the water receiving bodies like oceans, lakes and swamps or finally percolates into the ground recharging the groundwater reservoirs.
- Main Rivers in Nairobi: -Due to the tremendous socioeconomic importance and values attributed to the City of Nairobi, it would be necessary to also identify broadly the major drainage basins for purposes of studying the flood patterns, physical planning, monitoring and controlling the floods, etc for any future endeavour.
The drainage basins include Mathari, Getathuru and Kibagare, Nairobi River, Ngong River, Mbagathi River and Athi River. Mapping of flood spots will, therefore, be isolated according to these flood basins.
There are Negative and Positive Effects of Flooding.
- Negative Effects of Flooding: Human and Animal disease Outbreaks, loss of human and animal life, animal migration and disturbance to wildlife habitats, destruction of forest cover, damage to crops and other farming activities, destruction to properties and infrastructure (Human settlements, Commercial/Industrial development, Energy & Power/Dams, Water Supply/Sewerage and drainage channels, natural and man-made, Communication and transport infrastructure among others)
Floods also affect surface and subsurface geological formations, causing landslides and the development of subsurface gullies and other ground environmental degradation, disruption of social activities and development programmes, pollution, and contamination of land surfaces whenever flooding occurs.
- Positive Effects of Flooding: Allows development of water reservoirs and water pans for irrigation, farming, water supply and power generation. It makes land fertile through the transfer of soil nutrients, recharges groundwater, rejuvenates rivers in flora and fauna, and cleans natural and man-made water channels of deposited silts and debris and other obstructions and pollutants, among others.
Floods have continued to wreak havoc and destruction in both rural and urban settlements. We hereby review and outline briefly the significant causes of flooding in these forms of settlements, Urban and Rural.
- The Nairobi and Other Urban Settlements Flood Disaster Case- (Causes)
- Unplanned Human Settlements and Development of Unplanned Structures across waterways and on the flood plains/river riparian areas obstructing the free flow of river and storm waters. This could include river crossing structures and undersized bridges
- Inadequate information by planners during the design of private or public development ventures, including plantations, stadiums, buildings/estates and other infrastructure development, including commercial and industrial enterprises. (This leads to inadequate sizing of drainage facilities and structures like bridges and culverts)
- Dumping of waste materials and debris from all sorts of sources, including excavated black cotton soil and other construction/quarry waste, Solid waste from settlements and commercial activities, illegal dumping by solid waste disposal handlers, disposal of debris into constructed storm water drainage channels, natural water drains including the flood plains and receptor water bodies.
- Rapid and unpredictable change in land use patterns in both urban and rural areas which is uncoordinated. (Suddenly, most residential development areas have been converted to commercial business facilities and workshops, shops for vendors of vegetable and grocery, small scale businesses all over) Where there is road frontage in major towns throughout the entire country, makeshift structures to access residential and business premises have been erected. Traders and residents always block the drains meant for the road and catchment drainage, leading to back-flow and flooding to the entire upstream and surrounding region.
- Original and Revised Physical Planning Urban Master-plans have been disregarded due to emerging and conflicting ignorant selfish interests. The changing socioeconomic and political manifestations and interests have negatively impacted planned land use and settlement patterns. Commercial property development and land dealers have carried out land subdivisions and changes of users without control or approval by relevant authorities. Where genuine approval has been granted, the planning and approving authorities may not have considered current and future changes in the adjacent land use due to scanty information or sheer negligence by the planners or developers.
- Lack of engineering/planning expertise and capacity in both city and other county units
- Changing administrative structures in the county set-ups leads to uncoordinated development by various players, including private, local communities, and county and national development programmes.
- Changing Land Use without respective expansion of drainage facilities and river channels
- Diversion of Stormwater into Sewerage/Foul Water Pipelines
- Lack of Regular Cleaning and removal of Debris from the surface drains and river channels
- Dumping of Debris from the road pavement and swept loose soil into the drains
- Deliberate/Ignorant Blocking/Damage of the Road Drainage Channels by Developers to access private property.
- Lack of River Channel and Flood Plain maintenance initiatives.
- The Rural Flood Disaster Case(Causes of Flood Disaster)
- Human interference with natural vegetation cover through farming and other human activities like settlements
- Establishment of national parks interfering with wild animal feeding behaviour that leads to interference with vegetative cover
- Climate Change leading to loss in vegetation cover and change in surface soil erosion patterns
- Lack of coordination between rural agricultural and forestry activities with the downstream land users. (Farming methods and good catchment development practice affect the performance of dams and other water-holding structures, especially in sediment deposits, overflow and spillway characteristics, downstream flora and fauna quality etc.)
- Destruction of Forest and Vegetation Cover by negligent and accidental fires
- Lack of application of modern farming methods for erosion control
- Unpredictable Storms and Climate Change phenomenons.
- Uncoordinated Catchment development programmes
- Recommendations to Mitigate Flood Disaster
- Establish, determine, analyse, and coordinate the meteorological data available from all the existing national and private weather stations.
- Review the accuracy and reliability of weather forecast facilities and methods available in comparison to international practice.
- Establish and analyse the flood flows from all the installed river gauging stations, including overflows from the installed dam spillways.
- Determine the capacity of all existing man-made and natural drainage channels against various storm sizes and establish the shortfall.
- Outline a phased drainage infrastructure development master plan depending on planned changes of land use for current and future programmes.
- Settlements on river and drainage channels can be closed through the development of human settlements and commercial activities.
- Develop a river reclamation programme through a designed and defined strategy.
- Clear and demolish all illegal structures on the flood plans
- Carry out a detailed assessment of the flood risk areas, marking them in the comparative format as Low, medium and high risk, detailed assessment of the damage caused, estimating the commercial and socioeconomic losses,
- Preparation of a flood prediction and damage mitigation matrix to avoid current and future flood damage incidents
- National and Local authorities to identify and prepare an immediate and long-term investment programme and funding for the repair of the damaged infrastructure and other related facilities
- Carry out a re-afforestation programme, including the introduction of forest cover areas with special forest species that are drought-resistant in the rural catchment
- Further Medium and Long-Term Measures
- Carry out a resettlement action plan for all affected persons
- Enforce and keep reviewing the Physical Development Planning Act
- Review the infrastructure projects already planned or as identified in the national water master plan for water supply, irrigation, power generation and flood control purposes.
- Establish a River Riparian Management Authority for all the rivers in the entire country, from the source to the final outfalls. This could be done administratively by reviewing and integrating the existing Water Development Institute acts using a multi-agency approach.
- Need for frequent and regular revision of design standards and Codes to cope with the first changing environmental aspects and climate change.
- Establish a CENTRAL DRAINAGE TASK FORCE/COMMITTEE with all relevant stakeholders. This may include water resource and water infrastructure development departments, Power and Energy, Transport Infrastructure(Road/Railway/Water/Air), Agriculture, Wildlife and Forestry Development, County Departments and all the 3 arms of Government representatives.
Establish and maintain good housekeeping practices in all environmental management programmes under various organisations like UNEP and Global Environmental Initiatives like Green Concepts Initiatives. These will cover sustainable development, good and sustainable living standards, and healthy and safe environments that ensure long life expectancy for the entire society. As a non-governmental programme, this will be faster in programme implementation and more efficient and effective in coordinating various stakeholders without the challenges of the Complex Administrative and Legislative Acts.
Lastly and most importantly, ALL stakeholders must immediately come together through the central government and address the current precarious situation. The authorities are required to engage the experts in all relevant fields during the activities and management of the current DISASTER.
Eng. Karimi FRANCIS
Consulting Engineer, Registered Water Professional and Lead Expert(Environmental Assessment and Audit)
