Tag Archives: #stormwatermanagement

8 important Facts About Stormwater Drainage Systems

By Engr. John Cee Onwualu

“Stormwater drainage systems are essential to our health and safety – they help protect us from flooding and prevent water pollution, making them an important part of our infrastructure.” Engr. John Cee Onwualu

What is a Stormwater Drainage System?

A stormwater drainage system is an infrastructure constructed to receive and evacuate precipitation from rainfall runoff on the road surface and from the surrounding environment.

A stormwater drainage system can be made of concrete or steel structures and come in different shapes and sizes. It could serve as a surface drainage system or conduit (sewer) drainage system.

Why are Stormwater Drainage Systems Needed?

A stormwater drainage system is needed to evacuate excess floodwater from the environment that could not be absorbed by the soil due to the soil pores attaining a supersaturated state, thereby preventing damage to life and properties by conveying this excess floodwater to the streams or rivers.

How does a Stormwater Drainage System Work?

A stormwater drainage system is an infrastructure constructed as a receiver of precipitated rainfall runoff from the surface of the road or environment, which it efficiently and safely conveys to a bigger waterbody or river.

How do you fix or clean a Stormwater Drainage?

For the fact that stormwater drainage conveys flood water, it contains suspended debris or loose soil particles as it flows along its path which it drops as silt deposit as the flow velocity reduces.

These deposits are manually or mechanically excavated periodically. A stormwater drainage system can be constructed as a precast member or cast-in-place concrete member.

What is the difference between a Drainage System and a Drainage Pattern?

A drainage system is defined as a channel that conveys surface water from precipitation into a waterbody or wetland while a drainage pattern is a pattern created on the surface of the earth by erosion, stream, or river flow over a particular area.

Drainage patterns are more noticeable in areas with steep gradients and poor topography.

How do you drain a Stormwater Runoff?

A stormwater runoff is a result of precipitation from excessive rainfall, which the soil is not able to absorb by infiltration. It is drained by the construction of earth drain channels, concrete drain channels or steel sheet channels.

How do you design a Stormwater Drainage System?

Stormwater drainage systems can be designed through the following procedures:

  1. Having a good knowledge of the topography of the area
  2. Identification of the drainage basin
  3. Collection of surface ground data for rainfall modelling
  4. Knowledge of imperviousness and soil types
  5. Identification and location of underground services
  6. Creation of drainage boundaries or catchments
  7. Computation of peak discharges from each Sub-catchment or catchment areas using the Rational formula: Q = CiA
  8. Design and selection of channel sections, using the continuity equion of Manning-Che’zy equation: Qp = (AR2/3S1/2)/n

Read Also: Considerations in the design of stormwater channels

What is a Barrage?

A barrage, by definition, is a wire structure fitted with gates to regulate the water level in the river in order to divert the water to a canal situated at the bank of the river for the purpose of irrigation, domestic use, power generation, and flow augmentation to another river.

Read Also: 7 Ways To Handle Flooding in Any Part of Nigeria


By Engineer John Cee Onwualu (FNSE)

Storm Water Project in Delta State, Nigeria.

In my last post, I took a deep dive into the details of the findings and observations for Storm Water Management and Control Measures for Asaba, Warri, Effurun, and the environs.

It is clear that the topography of Asaba and its environs and that of Warri, Effurun, and its environs have similarities in their flood management and control approaches.

There were recommendations for optimal and efficient Pre-cast Open and Closed (underground sewers) concrete systems put forward for consideration and implementation for these project areas.

This article enumerates the merits to be derived from the use of these recommended pre-cast concrete structural elements of rectangular, square, and circular channels.

1) The use of precast primary receivers for the construction of the downstream channels to receive storm water discharges from the streets’ right-of-way will reduce the construction time required for evacuation of the current flooding menace that is being encountered in the environment, since non-functioning drains will now have discharge points.

Storm Water Construction at Effurun, Delta State.

2) There are savings in project delivery in terms of time, handling, and cost optimization during fabrication and execution of the project, since all these various types of channels with different operations will run simultaneously.

Construction of Drains at Okpanam, Delta State.

3) There is reduced construction risk to workers and passers-by during deep execution works since earth-moving equipment will be deployed for the placement of heavy precast concrete elements in deep excavations. This will improve the overall safety rating of the project.

Okpanam Drainage Construction, Delta State, Nigeria

4) There will be reduced exposure time to the excavated sections with the use of precast structural elements over cast-in-place concrete types, as the works are in built-up areas. This will improve the overall safety rating of the project.

Construction Work at Effurun, Delta State, Nigeria.

5) There is no need for long-exposed excavated trenches, as is the case with cast-in-place concrete, since smaller segments of work excavation are needed to place the precast elements.

6) The use of precast concrete structural elements will reduce in situ construction errors, which would create greater quality control on the project.

Storm Water Construction at Effurun, Delta State.

7) Finally, with adequate funding, the State government would complete the project within a short time, which would save her citizens the agony of economic and human losses occasioned with the hazardous and devastating flood water.

I hope that the state governments of different nations can take a keen look at the merits of these recommendations, and execute them where necessary.

Flooding: A Global Warming Aftermath by Engr. John Cee Onwualu

Climate change which is a direct effect of global warming has brought extreme weather changes to our environment, such as sea-level rise, more frequent rainfall with its associated flooding. The effects of these extreme changes have brought more flooding in our Cities, especially Asaba, Warri, Effurun, and Environs since they lie within the Niger Delta region of Southern Nigeria.

Despite these extreme weather changes from global warming, less attention is being given to the management, and control of stormwater by the government. The excess stormwater leads to the loss of agricultural farmlands, contamination of groundwater and rivers, and loss of lives and property of immeasurable values.

Today, due to the global climate change, Asaba, Warri, Effurun, and its environs are experiencing more months and frequent rainfall rather than the old known pattern of six months dry and six months rainy seasons. The effect on these cities and environs has defied the efficacy of existing drainage systems put in place by government and corporate bodies over the years. Hence, there was an urgent need by the government of Delta State to study and construct sustainable drainage systems for the management and control of Stormwater in Asaba, Warri, Effurun, and Environs.

This desire led to the Engineering Study and Design conducted in Asaba, Warri, Effurun, and Environs. Using interviews of locals, participatory meetings, and engineering surveys more in-depth knowledge of the flooding and causes was gathered.

The study looked at how overland drainages can be incorporated into nature-based gifts, such as Valleys, Waterways, and Rivers for the safe evacuation of the excess runoff generated from the environment.

Results obtained showed that improving the efficiency of these Natural Watercourses and Rivers would bring better management and control of the outfalls of both existing and new drainages into these Natural Watercourses. For this to be successful, the inhabitants must be aware of the environmental hazards associated with blocking of Valleys and Waterways with structures and dumping of waste materials into Storm Sewers and Drains, which would create blockages for the efficient evacuation of the Stormwater generated from the Environment.