Municipal solid waste and flooding in Lagos metropolis, Nigeria: Deconstructing the evil nexus

Municipal solid waste (MSW) has contributed significantly to flooding in the Lagos metropolis. This study examined the volume of MSW generated using per capita waste generation, projected population, quantity of MSW collected and deposited at six landfills sites from 2007 to 2013. One thousand and twenty-five copies of a structured questionnaire were administered to obtain data. The points where MSW blocked drainage channels in the metropolis were mapped. Multiple regression was used to establish the association between flooding and MSW at p<0.05. A total of 77,757,749.8 tons of MSW was generated, while 27.7% of it was collected and deposited at six landfill sites from 2007 to 2013. 11% of the municipal solid waste was collected by the Lagos State Waste Management Authority, 9.9% by private sector service providers, 29.2% by cart pushers and 49.7% dumped in canals/lagoons. Weekly collection of MSW was 58.5%. The sampled buildings were flooded at an average of nine times. Two hundred and twenty-two points where MSW blocked drainage channels were identified. The municipal solid waste indicators were statistically significant at F2, 1022 = 1034.2, R 2 = 0.669. The study recommends measures to enhance the strengths and address the weaknesses of the current approaches towards the attainment of global best practices in the management of MSW and flooding in the Lagos metropolis.


INTRODUCTION
The amount of municipal solid waste (MSW) generated in Nigerian cities keeps soaring as a result of increasing urban population and rapid urbanisation.This, in turn, presents greater challenges for disposal and management of MSW (Ojolowo and Wahab, 2011).
The volume of waste being generated continues to increase at a faster rate than the ability of the authorities to improve on the financial and technical resources needed to respond to this growth (Aderogba, 2012).The global generation of municipal solid waste in 1997 was 0.49 billion tons, with an estimated annual growth rate of 3.2 to 4.5% in developed nations and 2 to 3% in developing nations (Suocheng et al., 2001).An estimated 2.5 to 4 billion tons of waste was generated in 2006 globally, out of which municipal solid waste was 1.84 billion tons (Chandak, 2010).Municipal solid waste over 800 people (Jha et al., 2012).The situation is the same in Nigeria.
Floods in various parts of Nigeria have displaced millions of people, destroyed property, disrupted socioeconomic activities, contaminated water resources and facilitated the spread of water-borne diseases.Over 28 (80.0%) of the 36 states of Nigeria were devastated by flood in July 2012 (Wahab, 2013).Some of the states severely affected were Kebbi, Kogi, Anambra, Plateau, Oyo, and Bayelsa.The impact of the 2012 flooding was very high in terms of human, material, and production loss, with 363 people killed, 5,851 injured, 3,891,314 affected, and 387,153 displaced (The Federal Government of Nigeria (FGN), 2013).
The total value of destroyed physical and durable assets caused by the 2012 floods in the most affected states of Nigeria has been estimated at N1.48 trillion, or its equivalent of US$9.5 billion (FGN, 2013).The total value of losses across all sectors of the economy was estimated at N1.1 trillion, equivalent to US$7.3 billion, while the combined value of these damage and losses is N2.6 trillion, or US$16.9 billion (FGN, 2013).
This study, therefore, investigated the contributions of municipal solid waste to flooding in the Lagos metropolis by establishing the variations in the amount of municipal solid waste generated and collected from 2007 to 2013.It also examined methods of disposal and collection, frequency of collection, and number of times buildings were flooded.

METHODOLOGY
Primary and secondary data were used in this study.The primary data were obtained through questionnaire administration, personal observation and participatory mapping.The simple random sampling technique was employed to select 211 out of the 1403 streets prone to flood in the metropolis (Table 1).The number of the sampled buildings was calculated using a formula developed by Yamane (1967) (Equation 1) with the desired level of precision of ±3.The output was 1031 (7.2%) out of 14273 buildings as presented in Table 1.The systematic random sampling technique was used to select buildings where questionnaire were administered in each street.The starting point was randomly selected by using the table of random numbers.One household head was randomly selected from each building and a pre-tested structured questionnaire was administered to them.Each household was assigned a number and the number was written on a piece of paper, which was then wrapped and put in a box.After thorough shaking of the box, a wrapped paper was picked and the number on the paper represented the household head that was sampled.
(1) (Yamane, 1967) The The points along drainage channels where municipal solid waste had solidified and always prevented rainwater from flowing downstream were mapped with the assistance of one resident from each community who knew the geography of the community and could identify the points.The coordinates of the points were obtained with GPS Garmin 76, processed in Microsoft Excel 2007 and mapped in ArcGIS 10.3 environment.

Socio-economic characteristics of the respondents
One thousand and twenty-five out of the 1031 respondents (Table 1) were successfully sampled and used for analysis.The socio-economic variables considered relevant to the issues under investigations were household size and income (Table 2).There is tendency that household size and income could affect volume of waste likely to be generated by household.However, this study did not measure the quantity of waste generated by each household, rather, it projected quantity generated per local government area.The information obtained on the size of households revealed that most of the respondents had large household size.By inference, they are likely to generate much waste.The majority (72.0%) had 3 to 6 members; 11.3% had more than 10; 9.7% had 7 to 9 members; while 7.0% had 1 to 2 members.More than a half of the respondents (51.4%) earned ₦19,000 and below monthly; 16.8% earned ₦40,000 to ₦59,000; 15.2% earned ₦80,000 to ₦99,000, 11.7% earned ₦20,000 to ₦39,000; 3.7% earned ₦100,000 and above; while 1.2% earned ₦60,000 to  ₦79,000 per month.This means that most of the people living in flood-prone areas earn below the national minimum wage of N18, 000 per month.

Municipal solid waste generation and collection rate
Column B of  3. The amount of municipal solid waste deposited at 6 landfill sites (MSWD@6LS) (Olusosun, Abule-Egba, Solous II and III, Ewuelepe and Epe) (Column E, Table 3), obtained from LAWMA, was regarded as the quantity collected in the last seven (7) years.The quantity of municipal solid waste probably generated (MSWPG) in the Lagos metropolis per year was calculated by multiplying the corresponding PCSWG by the projected population as presented in Column D of Table 3.The difference between the amount of MSWPG and quantity of MSWD@6LS was calculated to determine the quantity of uncollected municipal solid waste (QUMSW) in the Lagos metropolis (Column G of Table 3).This represents the amount collected by LAWMA and Private Sector Service Providers (PSP).
Table 3 reveals the gap between the quantities of MSW generated and collected from 2007 to 2013 in the Lagos metropolis.In 2007, the MSW generated was 8,287,126.5tons, but 2,222,745.50tons was collected, leaving 6,064,381 tons.In 2008, 2,814,543.45tons was collected and deposited at 6 landfill sites out of 8,552,304.5tons; while 5,737,761.05tons was not collected.However, 2009 recorded the highest volume of 3,831,708.00tons collection and the least volume of 7,299,465.6tons uncollected MSW.The story in 2010 was similar to 2007 and 2008, as only 25.8% of the municipal solid waste generated was deposited at landfill sites, leaving behind 74.2% .
The situation of municipal solid waste collection in 2011 was the worst because only 17.6% (the least in seven years) of the municipal solid waste generated was collected; leaving 82.4% uncollected.The situation of municipal solid waste collection improved in 2012, with a record of 32.6% collection out of 12,610,874.9 tons.However, the situation was still below expectation when we consider the fact that a total of 8,499,705.13tons (67.4%) was not collected.The year 2013 witnessed another poor performance, as the percentage of the collected municipal solid waste declined to 25.6%, leaving 74.4% uncollected (Table 3).
A total of 77,757,749.8 tons of municipal solid waste was generated between 2007 and 2013.However, only 27.7% was collected.This led to indiscriminate disposal of a substantial amount of MSW on open space, air

Municipal solid waste disposal and collection methods
This study revealed that only 9.9% of the respondents engaged registered PSP operators to dispose of their waste (Plate 2), while 29.2% patronised cart pushers (Plate 3).Only 11.2 % of them used LAWMA communal waste bins.There was no LAWMA communal waste bin in the following LGAs: Agege, Ajeromi-Ifelodun, Alimosho, Apapa, and Kosofe.About 1.3% of the respondents burnt solid waste in their yards; while 16.7% dumped their waste at communal waste dumps (Plate 4).
Those who buried their waste in yards were 4.6%, they were in Alimosho, Amuwo-Odofin, Ifako-Ijaiye, and Ojo LGAs only.Of all the respondents, 27.2% dumped solid waste directly into the canals/lagoons; owing to poor collection rate by authorised agencies.Over a half (58.6%) of the respondents had their waste collected once a week, while 27.0 and 14.4% had their waste collected twice a week and daily, respectively.Among the 101 of the respondents who indicated that registered PSP operators collected their waste, 66.3% indicated monthly collection, 20.8% indicated fortnightly, and 12.9% indicated weekly basis.Therefore, it can be safely assumed that only 21.1% of the respondents who disposed of their waste through the PSP operators and in LAWMA's communal waste bins managed their waste responsibly.The majority (78.8%) disposed of waste indiscriminately and was contributing to the incidence of flooding in the metropolis of Lagos.The "alternative" waste disposal channels were illegal and unhealthy and encouraged indiscriminate waste dumping in water bodies and wetlands, which eventually hindered free flow of water during the rain and caused flooding.

Frequency of flooding
Investigation on the number of times that the respondents' buildings were flooded revealed that 5.9% of the buildings had not been flooded (Table 4).However, 10.2% of the buildings had been flooded once; 7.2% twice, 4.8% thrice and 2.8% 4 times.About 3.4%, had been flooded 5 times, 1.9% 6 times, 3.3% 7 times, 3.2% 8 times, 7.6% 9 times, and 1.8% 10 times.It is noteworthy that 2.3% of the buildings had been flooded 21 times.The mean of the frequency was 9.3 times, the minimum was zero, and the maximum was 21 times.The standard deviation of 6.2 indicates that the frequency of flooding occurrence was close to 9 times across the communities sampled without significant outliers.

Proof of the intersection of municipal solid waste and flooding in the Lagos metropolis
Excessive rainfall and blockage of drainage channels by municipal solid waste caused flooding in 126 (60%) streets.The points where MSW blocked drainage channels were either where two or more drainages crossed (Plate 5) or at points of discharge into canals/lagoons (Plate 6).A total of 222 points were recorded (Figure 2).The LGAs with the highest concentration of blockage points were Shomolu (36), followed by Lagos Island (20).Apapa, Lagos Mainland and Surulere had 19 points each; while Kosofe had 18 points.Ajeromi-Ifelodun had 17.Alimosho and Mushin had 13 points each; Agege 12; Ojo had 9, Eti-Osa had 8; Oshodi-Isolo had 7; Ifako-Ijaiye had 6; while Amuwo-Odofin and Ikeja had the least points of 3. Plate 7 shows a section of the canal along Bakare-Faro Street, Ajeromi-Ifelodun LGA, which was flooded owing to blockage by solid waste.The names of the 126 streets along which municipal solid waste blocked drainage channels in metropolitan Lagos is presented in Appendix 1.

Municipal solid waste disposal methods and frequency of collection as predictors of flooding
Waste disposal methods and frequency of collection were subjected to multiple regression model to investigate their contributions to flooding.The result R 2 (Table 5) indicated that about 66.9% of the number of times that flooding was recorded could be explained by waste disposal methods and frequency of collection.The F-statistics showed that the overall regression model was a good fit for the data.It means that the independent variables statistically and significantly predicted the dependent variable (number of times sampled buildings were flooded), F ( 2, 1022 ) = 1034.219,p<0.0005.Therefore, municipal solid waste indicators play significant roles in the occurrence of flooding in the Lagos metropolis.
The coefficient of frequency of waste collection was 0.567.This means that 1% increment in the frequency of waste collection could lead to 56.7% in the number of  times the sampled buildings would be flooded.This assertion is owing to the fact that frequency of waste collected by agents who dumped in water bodies was higher than that collected by PSP and LAWMA agents who dumped in designated dump sites.
Also, waste disposal methods produced a coefficient 11.030.This translates into the fact that 1% increment in the number of existing municipal solid waste disposal methods could lead to 11.030% that sampled buildings would be flooded.The two methods approved by LAWMA, as discussed in this study, were dumping in LAWMA communal waste bins, for onward collection by its officials, and collection by PSP.Flooding was predicted from frequency of waste disposal and waste disposal methods.These variables significantly predicted flood, F ( 2, 1022 ) = 1034.219,p<0.0005,R 2 = 0.669 at p< 0.05.

CONCLUSION AND RECOMMENDATIONS
The study revealed that the quantity of municipal solid waste generated outweighed the amount collected in the Lagos metropolis from 2007 to 2013.Between 2007 and2013, 77,757,749.8 tons was generated, 21,550,809.73 (27.7%) was collected, while 56,206,940.07(72.3%) was uncollected.
The uncollected MSW was indiscriminately dumped in unauthorised places, such as road verges, wetlands, The study concluded that the rate and frequency of municipal solid waste collection was unable to keep pace with the rate of generation in the Lagos metropolis, as more solid waste was found in unauthorised places within the environment than designated sites.The unrestrained and indiscriminate disposal of municipal solid waste, particularly in the drainage channels, was identified as one of the major causes of flooding in the metropolis.Owing to the failure of the PSP and LAWMA to adequately collect generated waste, the residents resorted to patronising cart pushers.The cart pushers dumped waste on any available space, drainage channels, wetlands and canals/lagoons, thereby causing flooding.They avoided using LAWMA-designated dumpsites because they had been outlawed.
In order to increase the quantity of MSW collection, the LAWMA framework should be revised by the Lagos State House of Assembly to either include cart in the fleet of LAWMA to enable access to flood-prone areas in the metropolis or integrate cart pushers into formal MSW management systems.As revealed in this study, cart pushers enjoyed more patronage than LAWMA and its agents.Also, LAWMA and PSP should increase both the areal coverage and the number of times they collect waste weekly from residents in order to reduce the incidence of flooding in the Lagos metropolis.Solid waste deposited in communal dump grounds should be properly evacuated by LAWMA.The Drainage Department, Ministry of Environment should establish units in all the LGAs to manage storm water drainages and always keep them free of MSW of all descriptions.
After establishing effective modalities to reach all residents in flood-prone areas and improve areal coverage and frequency of waste collection, refuse guards should be reinvigorated and stationed at communal dump grounds.They should be given the mandate to arrest and subsequently prosecute recalcitrant residents to serve as a deterrent to others.If waste collection issues are handled properly, waste management would serve as a complementary and an effective measure to managing flooding.By this, every effort put forward to manage drainage channels in the metropolis will become meaningful.

Figure 1 .
Figure 1.The sixteen metropolitan local government areas in Lagos state (Source: Lagos state ministry of physical planning and urban development, 2014).
secondary data included: the list of the 1403 streets where floods had occurred, this was obtained from the Department of Drainage Services, Lagos State Ministry of Environment; the amount of solid waste deposited at six landfill sites and the per capita generation of municipal solid waste of 0.5, 0.6, 0.65 and 0.7kg/person/day for 2007/2008, 2008/2010, 2011/2012, and 2013, respectively obtained from Lagos State Waste Management Authority; and the 2014 projected population of the Lagos metropolis obtained from the National Population Commission of Nigeria.

Plate 1 .
A Section of canal at Oreofero Street, Shomolu LGA of Lagos state, filled with municipal solid waste of all descriptions Source: Authors' Field Survey, 2014.
A PSP operator collecting refuse from residents in sacks and plastic containers along Iganmu Road, Apapa LGA of Lagos State, Nigeria (Source: Authors' Field Survey, 2014).spaces of buildings, road verges and islands, and, in particular, drainage channels and water bodies.The flood incidence of the year 2011 coincided with when only 17.6% of the MSW generated was collected.The incident claimed more than 25 lives, displaced 5,393 households, and destroyed an estimated N100 billion worth of property.It is logical to deduce that indiscriminate deposition of MSW in drainage channels (Plate 1) and water bodies contributed significantly to flooding in metropolitan Lagos (Plate 1)

Figure 2 .
Figure 2. Points where solid waste blocked drainage channels in the Lagos metropolis (Source: Lagos State Ministry of Environment, Ikeja and Authors' analysis (2014)).

Table 1 .
Sample frame and size.

Local government areas *No. of Streets *No. of Streets prone to flood *No. of selected Streets prone to flood *No. of houses on the selected Streets **No. of houses sampled (7.2%)
Source: *Drainage department, Lagos state ministry of environment, Alausa Ikeja; **Authors' construct, 2014.

Table 2 .
Socio-economic and demographic characteristics of the respondents.

Table 3 .
Percentage of municipal solid waste generated and collected in the Lagos metropolis from 2007 to 2013.

Table 4 .
Total number of times buildings were flooded.
Source: Field survey, 2014.Plate 5. Drainage intersection blocked with MSW along Agege Motor Road, Agege Local Government Area of Lagos State, Nigeria Source: Authors' Field Survey, 2014.Plate 6.Municipal solid waste blocked a point of discharge into canal at Badia, Ajeromi-Ifelodun Local Government Area, Lagos State, Nigeria (Source: Authors' Field Survey, 2014).

Table 5 .
Municipal solid waste as predictor of flooding in the Lagos metropolis.