Sand is a crucial resource for society’s development. Among the most exploited sand quarries in the world are the lagoon and wetland sand. Although mechanical sand dredging is the most spread technique, manual and traditional techniques are still widely used in West Africa. The purpose of this paper is twofold: to describe traditional sand dredging (TSD), highlighting the procedure used and the structural organization of this activity, and to evaluate the total economic value of TSD in order to help decision making about wetland management. Therefore, TSD occurring in the coastal lagoon complex of Grand Nokoué (CLCGN) in Benin was investigated. Field surveys indicate that TSD is mainly dominated by men, about 93% of the actors. It required intense physical efforts including diving to the bottom of the lake and removing manually the sand in backed toward the surface of the water. TSD actors are organized in local associations which deliver extraction license and discuss with both the others actors and the local government. The total economic value of the benefits of TSD to the population, estimated using direct market value and replacement cost, was estimated at 2.44 million USD per year for 127,818 m3 of sand extracted. It is clear that introduction of mechanical sand dredging will increase the amount the sand removed and subsequently will increase some benefits such as reduction of flooding amplitude and mitigation of the filling of the lakes. However, mechanical sand removal will also considerably reduce the profit the local population makes from sand commercialization which currently represents 80% the total economic value of TSD.
The global assessment of the benefits that ecosystems offer to society clearly indicates the great dependence of human well-being on these benefits also known as ecosystem services (ESS) [
Economic valuation of ESS has been largely debated in the literature [
In Benin (West Africa), recognition of the role and importance of ESSw in the population well-being have been increasing, even though very few research studies have been done [
Based on information collected from literature, the ecosystem cascade diagram developed by [
CLCGN offers some unusual services including Acadja fishery [
ESS governance (as defined by [
Based on [
Only the anthropogenic values of TSD are considered and the possible intrinsic values of TSD are out of the scope of this study. Thus, based on the literature and on a contextual analysis of the CLCGN, five level of benefit provided by TSD have been identified and presented in
Lagoon sand dredging also present negative environmental impacts. The most recurrent consequence is an increase of the water turbidity which caused the decrease of photosynthetic activity, disturbance of feeding activity of some fish species and the increase of infestation risk for aquatic animals. Another consequence regarding the water quality is the change in the nutrient dynamics of the ecosystems through sediment resuspension. In addition, in many aquatic ecosystems, degradation of aquatic biota and alteration in fish population has been
Benefits as good, service or function | Value type | Valuation technique | Data needs | |
---|---|---|---|---|
1 | Profits through sand commercialization | Direct use | Market Price-Based Methods | Structural organization of the actors Volume of sand extracted per year Market price of lagoon sand |
2 | Mitigate the filling of the lakes | Indirect use | Benefit transfer: function transfer | Volume of sand extracted per season and per year. Total volume of the water body. Total area of the lakes |
3 | Deeping some area: improve pelagic habitat for fish reproduction | Indirect use | Benefit transfer: function transfer | Volume of sand extracted Geographic location of extraction points. Average density of fish in the lakes. |
4 | Moderate flood events | Indirect use | Benefit transfer: function transfer | Volume of sand extracted Area impacted by flooding |
5 | Decrease pressure on terrestrial sand mining | Indirect use | Cost-based Methods: replacement cost | Volume of sand extracted per year Market price of sand from other quarries |
data | ||||
---|---|---|---|---|
Volume of the water body m3 | Ouémé River: 9,200,000; L. Nokoué: 250,000,000 ; P. Novo Lagoon: 53,400,000 | |||
Fish production estimated in tonnes (based model from [ | Ouémé River: 192 tonnes; L. Nokoué: 12,920 tonnes; P. Novo Lagoon: 2380 tonnes | |||
Information on 2010 flood | Has caused the rise of water between 25 and 60 cm. More than 210 km2 of flooded land. Impact estimated at 262 million USD. Flood damage valuation per m2 was estimated to 1.21 USD | |||
Volume of sand extracted in m3 per year | 2013 | 2015 | 2016 | |
Ouémé River | 50,695 | 51,074 | 54,074 | |
P. Novo Lagoon | 43,442 | 42,511 | 43,963 | |
L. Nokoué | - | 28,576 | 29,781 | |
Market price of lagoon sand in USD/m3 | 15.7 | 16.8 | 17.0 | |
Average price of fish in USD/kg | 2.4 | 2.6 | 3.0 | |
Market price of land for terrestrial sand mining USD/m2 | 25 | 25 | 25 |
linked to sand dredging [
The CLCGN is located in the South-eastern of Benin in West Africa (
Geologically the study area is in the middle of three structures including the
sand barrier in the South, the lower basins of Ouémé and Sô River in the North, and the sub-horizontal plateaux of the Continental Terminal in the East [
The total economic valuation of TSD was made by adding all the benefits provided by this ESS.
Sand commercialization (Benefit 1): was estimated by Market Price-Based Method. The sand extracted from the lakes were sold and contributed to profits through sand commercialization. The economic value of Benefit 1 was calculated by using the following formula:
Benefit 1 = Volumeextracted ∗ Marketprice
Mitigate the filling of the lakes (Benefit 2): was estimated by function transfer which is a Benefit Transfer Method. The function which was transferred here is the use of water as habitat for fish. The idea here was to estimate how much cost a decrease of about one unit length (here cm) the water depth in terms of fish population? The approach used considered that the filling of the lakes reduce the available volume of water for fish, and then the fish population. It was assumed the density of the fish population in a lake always adjust to a mean value which is the maximum density for the dominants species. [
Benefit 2 = Volumeextracted * fishdensity * priceofaunitweightoffish
Deeping some specific area (fish nursery) improve fish reproduction (Benefit 3). The transfer function used for Benefit 2 already considered fish habitat. Therefore a valuation of Benefit 3 was considered as part of Benefit 2. It is important to note that for Benefit 3, the location where sand removal occurs is very important compared to Benefit 2 which considered a homogenous removal across the lake. However, it was challenging to measure how this difference in function affects the financial estimation of Benefit 3 when compared to Benefit 2.
Moderate flood events (Benefit 4): was estimated by function transfer. The flood events of 2010 in Benin resulted in an overflow of 1000 m of the water bodies in CLCGN. The material damage and the production losses recorded were estimated at 262 million USD. On the basis of these values, the average cost of one square meter of overflow ( D P r i c e ) for each lake has been determined. Using QGIS (area and volume calculation plugin), the area which would has been flooded ( Area overflow ) if there was not TSD was estimated (
Benefit 4 = Area overflow * DPrice
Decrease pressure on terrestrial sand mining (Benefit 5): was estimated by replacement cost. It was assumed that the volume of sand extracted each year from CLCGN could be replaced by terrestrial sand quarries. Terrestrial sand quarries would have requested land cost and road accessibility cost. The cost of sand quarries and road cost associated have been used as the replacement cost of TSD. Based on the volume of lagoon sand extracted, the area of land needed ( Area needed ) for terrestrial sand extraction was calculated. The additional transportation cost related to terrestrial sand quarry was calculated based on the distance from the quarries to CLCGN.
Benefit 5 = Area needed * priceof 1 m 2 ofland + Transportation
The data needed for the valuation of each benefit was listed in
A Socio-Economic Survey was conducted from November 2016 to April 2017, in order to collect the data to understand TSD and its economic importance in CLCGN. The data collected from this field survey concerned: the ecosystem services description (organization of ecosystem service implementation and actors involved), the identification of actor’s characteristics (sex, age, main activity, secondary activities, role in TSD), and the financial revenue from the activity (possible variation in market price, volume extracted, additional cost). An exploratory survey was first organized since almost no literature exists on TSD in CLCGN. It allowed designing survey questionnaire and indicated that 80% of the activity occurs around Porto Novo Lagoon and Ouémé River against 20% around Lake Nokoué. After this exploratory survey, snowball sampling method was used to identify the actors to be questioned [
Since all the required information for financial evaluation of TSD could not be collected from field survey, the additional information was collected from published research papers, administrative documents provided by decision makers and municipalities’ libraries, and the National Institute for Statistic (secondary data collection). These documents included municipal action plans, study reports financed by the municipalities, the monitoring reports of the TSD activity and soil and occupation maps of the study area.
TSD in the CLCGN covers the entire Porto Novo Lagoon (PNL), the northern part of Lake Nokoué (LN) near the entrance of its tributaries and the long the Ouémé River in the deltaic zone (
In the early 1960s, the increased need of the population of Porto Novo to build their house in concrete has led to the search for nearby building material. Thus, local communities living nearby PNL (at Djassin Daho;
Following the ban of marine sand extraction on March 4, 2009, by the government of Benin, TSD for the commercial purpose have been amplified. Several markets developed rapidly around the CLCGN. A total of 13 (formal) sand markets were identified by this study in 2017, including 6 markets around the PNL, 3 around Lake Nokoué and 4 along the Ouémé River. Also, two mechanical sand dredging companies were created around Porto Novo Lagoon, but the functioning and economic valuation of two mechanical sand dredging are out of the scope of this research.
TSD involves a succession of step with most of the tasks requiring some physical energy. The first step is the preparation of dredging equipment consisting mainly of aluminum buckets, wooden ladders, shovels and motorized boats. Then, the extractor’s team explore the lake to identify an extraction site which is the second step. The identification of the site is done intuitively and requires experience from the extractors. An operator embedded a wooden post in the bottom sediment, to identify first the nature of the sediment (since they are looking for sandy sediment), and second whether the depth at the point is safe. Sometimes water hyacinth cover the surface of the water at the identified sites, and it is necessary to clear them to facilitate the inking of the boats. The third step consists of the implementation of the preliminary tasks before the actual sand extraction. This consist of inking the boat by fixing it to 2 to 4 stilts, then the ladder is set up for the descent of the divers to the bottom and their climb to the boat. If necessary, the divers proceed to the removal of the layer of mud and detritus (generally consisting of dead hyacinths) covering the layer of sand to be extracted. The fourth step is the actual sand extraction. The divers pick up the bottom sand using aluminum buckets and climb up to the surface using the wooden ladder. When the boat is considered full, the extraction team proceeds to the regrouping point on the shore (the market). There, women unload the sand from the boat and form the piles on the sand storage platforms. Finally, the sand is loaded into trucks and delivered to customers.
The procedure described above is the same whether the dredging is done in PNL, in LN or in Ouémé River. The procedure has not changed since the establishment of TSD in early 1960. However, some improvements have been done regarding the material used especially the boat which is wider to limit the risks of capsizing once on the water.
About 1206 persons are the number of people directly involved in TSD. The low representation of women, only 7%, could be explained by the nature of the tasks since the perception of the local society some tasks are exclusively for men (
Direct actors | Society perception | Number (%) |
---|---|---|
Sand extractors, | Only men | 26.7 |
Boat unloader | Only women | 06.7 |
Truck loader | Only men | 26.7 |
Truck owner | Only men | 15.5 |
Promotor (owner of sand storage platform) | Both sex | 24.4 |
residence places of the actors indicates that 73% are the indigenous living in the local community and whose families are the predecessors of TSD. They are present in all the groups of actors and have the monopoly of the activity.
Surveys revealed that 62% of the extraction sites identified in the CLCGN are privately owned. In other words, the families which are in the activity since its creation, have divided the surface of the water bodies on the basis of seniority and heritage, bringing a concept of private ownership on a public resource. This ownership concept about TSD is very similar to the one observed in Lake Nokoué about acadja fisheries [
The volume of sand extracted was the major information needed in the economic valuation of TSD. It was calculated from the number of trucks delivered to customers and the volume of the different type of trucks used. It was found that 127,818 m3 of sand are extracted per year with 42% from Ouémé River, 35% from Porto Novo Lagoon and 23% from Lake Nokoué (
The total value of TSD generated by CLCGN is estimated at per year or 2.44 million USD per year (
Benefit | Value | |
---|---|---|
Benefit 1 | Profits through sand commercialization | 1,950,505 USD |
Benefit 2 | Mitigate the filling of the lakes | 17,659 USD |
Benefit 3 | Deeping some area: improve pelagic habitat for fish reproduction | ------- |
Benefit 4 | Moderate flood events | 230,903 USD |
Benefit 5 | Decrease pressure on terrestrial sand mining | 229,084 USD |
largest contribution (80%) of TSD followed by flood moderation (10%), a decrease of the pressure on terrestrial sand mining (9%), and mitigation of the filling of the lakes (1%). About 9% of the profits from sand commercialization go to the municipalities as the tax on TSD. An analysis of the activity from 2013 to 2016 indicated an average yearly increase of 2.9% on the profits made from sand commercialization. The actors reported that sand extraction is a function of the sand demand on the market. They estimate that they can dredge up to 1.5 times the current demand which will result in an increase of the economic value of TSD.
Introduction of mechanical sand dredging in CLCGN is suspected to considerably increased benefit 2 to 5 since more volume of sand will be extracted. The objectives defined by decision maker for mechanical sand removal suggest an increase of more than 100 times of the benefit 2 to 5. However, mechanical sand removal is expected to negatively impact the direct profits that population make from TSD. The proposed mitigation plans currently suggest the conversion of TSD actors into mechanical dredging. However, it is recalled that most TSD actors may have difficulties in the operation of machines. In addition, 78% of the people interviewed rejected the idea of working for a dredging company. They defined TSD as a business inherited from their families and want to legate it to their child in turn. An option that could be developed by decision maker is to reserve some area for traditional dredging. This will require many meeting with TSD actors with currently are not associated with the discussion and the introduction of mechanical sand dredging. It is also important to note that mechanical dredging will have a higher environmental impact on both water quality and biodiversity of CLCGN. More research should be done on the environmental impact of TSD, even though from the perspective all the user of CLCGN including fishermen, TSD has a minor effect on the lakes water quality.
TSD is susceptible to influence positively and/or negatively others ESS. Based on the focus groups and on observations from the field the linkage between TSD and the others activities occurring around CLCGN were established (
From the fishermen perspective, sand extraction creates deepwater areas which promote fish reproduction. In Porto Novo Lagoon it clearly appeared that there is a continuous communication between fishermen and sand extractors about where to extract and where to do not extract. More research needs to be done in order to quantify the impact of such arrangement on the real reproduction of fish. Despite this non-institutionalise communication between fishermen and sand extractor, several cases of conflict have been recorded including the destruction of acadja by extractors and installation of new acadja on the space reserved for sand extraction. The concept of ownership on the lake developed by the families of the first users is increasingly being questioned by the new actors, both at the level of the “TSD” and at the level of the acadja fishery. About 75% of
the conflicts recorded were between old (more than 10 years in TSD or Fishery) and new (less than 2 years) users. Conflicts management is ensured by municipalities and local associations.
Boat transportation is very dense in CLCGN. The fact that the water complex is in the middle of the most important cities of the countries contribute to the high use of boats for the transportation of people and good. However, transporters and extractors are regularly in conflicts. The field survey revealed that on average one case of extractor’s boat capsizing is recorded per day because of the waves generated by transport boats moving very fast. Decision makers tried to impose a speed regulation of some part of the boat traffic but this measure didn’t work. Boat transporters accused extractors to overload their boats and then to be more vulnerable to water waves. Usually, financial compensation is required in case of boat capsizing but TSD actors reported this compensation does not cover their losses. There is no apparent relationship between TSD, tourism, vegetal production and breeding activities.
The economic value of TSD in CLCGN is about 2.44 million USD per year. Even though this activity is traditional, many advantages are derived from it including substantial incomes for the population, mitigation to a certain extent of lake’s filling by sediment and slight reduction of flood event amplitude. In addition, field investigation indicated a possible benefit of TSD for the fishery as most of the fishermen believe that sand removal to very particular locations in CLCGN enhances fish reproduction. Further studies should investigate the environmental impacts of TSD which could help decision makers to manage the balance between mechanical and traditional sand dredging. In addition to the value TSD determined in this research, a complete economic valuation of all the ESS in CLCGN should include the interaction between TSD, fishery, and transportation. An interesting concept of ownership on lake’s services has occurred in CLCGN and needs to be investigated for a suitable management of the resources.
The authors gratefully acknowledge the International Foundation for Science (IFS), Stockholm, for supporting the present work under the IFS Grant W/5840-1.
The authors declare that there is no conflict of interest regarding the publication of this paper.
Djihouessi, M.B., Aina, M.P., Kpanou, B.-V. and Kpondjo, N. (2017) Measuring the Total Economic Value of Traditional Sand Dredging in the Coastal Lagoon Complex of Grand-Nokoué (Benin). Journal of Environmental Protection, 8, 1605-1621. https://doi.org/10.4236/jep.2017.813099