A SYNOPSIS OF THE ROBERTS INTERNATIONAL AIRPORT(RIA) HIGHWAY IN LIBERIA
The Roberts International Airport (RIA) Highway is the major and most convenient route available for to and fro travel between the only international airport in Liberia and the capital city Monrovia. More so, the highway connects the southeastern part of the country, which hosts three major seaports and as well as access to major cash crops concessions such as Firestone Natural Rubber Company, the biggest contiguous rubber plantation in the World and the Indonesian owned Golden Veroleum Oil Palm Plantation. Interestingly, this highway currently serves as the most reliable road for movement of little over 34% of the total population of the country to the capital Monrovia, where centrally established authority, businesses, socially improved facilities are located. For international travelers entering the country, this highway provides the first perception of the country.
BRIEF DESCRIPTION OF THE PROBLEMS POSED BY THE CONTINOUS FLOODING ON THE RIA HIGHWAY
Over the past six(6) years, the Roberts International Airport Highway has experienced massive flooding. The flood over the years has affected the economy, the environment and social strata of the communities within the locality. Data gathered from the disaster assessment conducted by the Liberia National Red Cross Society, a technical assessment conducted on the environment and physical structures of the highway by the Ministry of Public Works and a social well-being survey conducted by the National Disasters Management Agency of Liberia, provided a combined figure converted to a financial loss of approximately $ 1,000,000 million this year due to the flood. Using mathematical extrapolation (an estimate about something extracted from known facts which extends or expands the given data into an area that is not known, in order to arrive at a conjectural knowledge of unknown area) method, a calculated figure for the past six(6) years of flooding summed the total cost to a financial loss of approximately $ 18,000,000 million. Considering a country of a yearly average fiscal budget of $ 500 million losing 18 million in six(6) years, which is 3.6% of the combined six years budget is dreadful and hinders priority spending. Liberia, as a financial resource-scarce country cannot afford to lose a little under 1% of its budget every year to flooding.
Based on the situational analysis conducted to determine the scope of intervention and the level of assistance to be provided by the Liberia National Red Cross Society, a total of Two Thousand Five (2,500) affected households, One Thousand Five Hundred (1500) residential buildings and over Three Hundred and Seventy-Five (375) farms and crops damaged within a year in eleven(11) communities within the locality.
The National Disaster Management Agency has conducted a year on year detailed Social-Situational analysis of the flooding within this region. Based on their analysis, a total of 52,036 individuals have been affected over the years with an array of social, environmental and health-related problems. Hospitals, Schools and normal ways of life have been constantly affected around this time every year. The flooding has led to occasional death of one or two persons. But most importantly, the social disturbance caused by the flood every year has created a deep fear and reduced the urgency of investment in the region.
THE GLOBAL CAUSES OF THE INCREASE IN FLOODING WORLDWIDE
The global increase in disasters is a phenomenon that has engulfed our planet and has been a major concern for humanity in general. Henceforth, there have been many theories concerning the rise in disasters such as flooding, hurricanes, tsunami etc. Many of the theories have shifted from terming these happenings as natural disasters to man-induced phenomena.
It is largely postulated by Earth Scientists (Environmentalists, geologists, climatologists etc.) that the changes in the climatic condition and sparks in temperature or long period of bad weather are driven by the continuous degradation of the environment by human’s daily activities. Popular of these postulates is the environmental degradation caused by the diesel and gasoline produced from oil and use by different engines. These products when combined with the mechanics of the working of engines spilled out harmful gases the destroyed the atmosphere and causes severe heating and heavy rainfall. As rainfall increases and human activities especially development with impermeable surfaces such as roads, building complexes, concrete street pavements, etc. are vastly implemented, flooding is triggered. More over, the destruction of natural floodplains by unplanned settlements cause flooding to become a global problem as the world moves more towards an intensive physical development era.
THE ASSESSMENT OF THE FLOODING ON THE RIA HIGHWAY
The cases of flooding in Liberia and especially on the RIA Highway may not be different from the global reasons for flooding as provided above. A team of Engineers from the Ministry of Public Works for the past years have conducted several assessments with the intent to remedy the situation. These situations have had environmental and physical effects, such as the damage of water points, alteration of the ecology of the region and reduction of the service life of the highway respectively.
This year(2018) a team comprising of a Structural Engineer, A Geotechnical Engineer, and Urban Habitat Engineer conducted a full assessment of the situation. The aim of the assessment was to provide an immediate solution to the flooding situation as it was impeding movement, damaging homes and farmlands and causing environmental and health-related problems as usual. It was also intended to proffer long-term solutions to the flooding at this section of the highway.
The scope of the assessment conducted during the peak of the flood on the RIA Highway took into consideration three fundamental engineering principles as a benchmark to mitigate the flood.
THE TOPOGRAPHY, ELEVATION AND RANDOM SETTLEMENT ANALYSIS
The team studied thoroughly the topography of the area as a means to understand the terrain, generate the geo-reference data and as well to understand the geological features, which are potential means of flooding (e.x marshland, low elevation, flat landform, etc.). As stated, a reference topography map containing the basic feature of the area was generated using google earth software. In addition to the map, physical observation, distance measurement, a low level, and high-level flood zones geo-reference data containing latitude and longitude were generated for eight(8) points at boundaries, the intermediate and inner locations of the flood zone. A sample of the soil was collected and taken to the laboratory for a porosity testing. The location which is identified as a floodplain based on the geological features is heavily encroached upon by random settlements. Eleven(11) human settlements are observed within and around the flood zone shown in the flood map below.
|Latitude||Longitude||Altitude||climate vulnerability type||climate vulnerability grade|
Based on the information collected and the study of the geo-reference data containing the latitude and longitude as well as the physical measurements, it was deduced by the team that the flooding in the area follows the topography and geological features of the landform and the soil respectively. On the west side of the road is a higher landform which contains all the features that aided flooding. Features such as a large area of mangrove marshland, low lying flat plain with little or no obstruction to water flow and as well as the limited porous ability of the silky marshland soil upon the reading of the test result from the laboratory.
THE BASIC CONCEPT OF GRAVITATIONAL FLOW AND TRIBUTARY ANALYSIS
The fundamental concept of the flow of water due to gravity is very essential in such an assessment. Water in a river or a floodplain will follow the quickest path downslope(the path of least resistance), normally, unless prevented by some obstacles, a rock, a buildup land etc. The water then eventually back up to a point, that the backup flow is equivalent to the downslope flow. At this point, the water will spread out into every possible direction of least resistance until all directions are filled and then the spillover starts to occur as the water continues to flow leading to flooding of elevated dry land. This concept explained clearly the flooding situation on the RIA Highway. West of RIA Highway, closed to the flooding location contained the Farmington river which, when filled overflow its banks into the low lying marshland and plains from the Marshall territory to the inland areas increases the risk of flooding. This overflow water follows the path of least resistance until it hits communities build within the floodplain and the elevated embankment of the highway. This phenomenon occurred in a record and unnoticeable time that leaves residents with limited time to evacuate with their belongings and government with no time for an intervention.
THE GEOTECHNICAL CONCEPT OF EARTH CHANNEL CONSTRUCTION TO EASE THE FLOW OF EXCESS FLOOD WATER
To mitigate the problems, as it has been well understood by the team through the assessment and research of the location, a two-fold solution was proposed. The first solution was the short-term intervention that proposed three(3) separate activities according to the observations and conclusion reached by the team.
- Based on the analysis of the least resistance flow in the gravitational flow concept, a conclusion sufficed that prioritized the removal of vegetation within the flow path of the water. This will allow the excess water to flow in line with the designated flow path instead of backing up;
- Drawing from tributary analysis and elevation concept, a tributary extension of the Farmington was located at a lower elevation 500m east of the highway. Based on this, a conclusion was reached to construct an earth channel 5m x 5m to 500m long to convey the excess flood to Farmington tributary;
- Lastly, a massive clean-up exercise for the drainage structures at the flooded location of the highway was proposed. Cleaning of both inlet and outlet were considered.
THE LONG-TERM MEASURES
The location like every flood-prone locations had the resembles of human-induced activities and provided enough of means for the flooding to continue every year. Considering this, the team proposed three major long-term solutions.
- Remove Settlement from the Flood Zone.
The relocation of the communities within and very close to the low lying land that host excess flood water should be strongly considered. Especially the five(5) smaller communities within the Joeblow Town that are directly situated within the water main.
2. Raise the Road Embankment
Considering the recent rate of recurrence interval (how many times the location has been flooded) and calculating the maximum rate of returns (100-year flood) using the knowledge of global trend of naturally changing phenomena, it is prudent to re-construct this section of the highway at a higher elevation.
3. Restrict farming and other man-induced activities within the floodplain
Using our knowledge of environmental degradation we can conclude that the breakdown of natural features of the land aid a lot more in erosion and subsequent flooding. It is recommended for a drastic reduction or total removal of man-induced activities, especially within the floodplain. This will restore natural features, build up the soil and crop the movement of excess water downstream of the plain.
GENERAL RECOMMENDATIONS FOR FLOOD PREVENTION
The critical changes in the climatical conditions in all region of the world present a harsh reality. Henceforth, Liberia should prepare herself for the road ahead by following some of the good case examples and recommendations of system planning and disaster prevention adopted in other places.
- Setup a research unit dedicated to disaster prevention research
- Dredge river bed to provide more space for excess water during high precipitation
- Construct breakwater at the bank of rivers closed to settlements
- Create canal to convey water at designated locations
The short-term intervention is completed at the section completed and it is expected to hold up for few years. Thanks to the Ministry of Public Works. However, it is important to continually asses and observe the changes in the environment and the water level at this location. If it turns out that the short-term solution does not mitigate the flooding for the expected time, implementing the long-term measures is an prudent decision that should be made sooner than later.
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