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IMPACT OF SAND AND GRAVEL DREDGING ON THE ENVIRONMENT

ABSTRACT

For thousands of years, sand and gravel have been used in the construction of roads and buildings. Today, demand for sand and gravel continues to increase. Mining operators, in conjunction with cognizant resource agencies, must work to ensure that sand mining is conducted in a responsible manner. Excessive in-stream sand-and-gravel mining causes the degradation of rivers. In-stream mining lowers the stream bottom, which may lead to bank erosion. Depletion of sand in the streambed and along coastal areas causes the deepening of rivers and estuaries, and the enlargement of river mouths and coastal inlets. It may also lead to saline-water intrusion from the nearby sea. The effect of mining is compounded by the effect of sea level rise. Any volume of sand exported from streambeds and coastal areas is a loss to the system.

CHAPTER ONE

1.1  BACKGROUND TO THE STUDY

For thousands of years, sand and gravel have been used in the construction of roads and buildings. Today, demand for sand and gravel continues to increase. Mining operators, in conjunction with cognizant resource agencies, must work to ensure that sand mining is conducted in a responsible manner. Excessive instream sand-and-gravel mining causes the degradation of rivers. Instream mining lowers the stream bottom, which may lead to bank erosion. Depletion of sand in the streambed and along coastal areas causes the deepening of rivers and estuaries, and the enlargement of river mouths and coastal inlets. It may also lead to saline-water intrusion from the nearby sea. The effect of mining is compounded by the effect of sea level rise. Any volume of sand exported from streambeds and coastal areas is a loss to the system.

Excessive instream sand mining is a threat to bridges, river banks and nearby structures. Sand mining also affects the adjoining groundwater system and the uses that local people make of the river. Instream sand mining results in the destruction of aquatic and riparian habitat through large changes in the channel morphology. Impacts include bed degradation, bed coarsening, lowered water tables near the streambed, and channel instability. These physical impacts cause degradation of riparian and aquatic biota and may lead to the undermining of bridges and other structures. Continued extraction may also cause the entire streambed to degrade to the depth of excavation.

Sand mining generates extra vehicle traffic, which negatively impairs the environment. Where access roads cross riparian areas, the local environment may be impacted. Sand and gravel are used extensively in construction. In the preparation of concrete, for each tonne of cement, the building industry needs about six to seven times more tonnes of sand and gravel (USGS, 2013b). Thus, the world’s use of aggregates for concrete can be estimated at 25.9 billion to 29.6 billion tonnes a year for 2012 alone. This production represents enough concrete to build a wall 27 metres high by 27 metres wide around the equator. Aggregates also contribute to 90% of asphalt pavements and 80% of concrete roads and the demand for aggregates stems from a wide range of other sectors, including production of glass, electronics and aeronautics. Added to this are all the aggregates used in land reclamation, shoreline developments and road embankments (for which the global statistics are unavailable), plus the 180 million tonnes of sand used in industry. This sand and gravel are mined world-wide and account for the largest volume of solid material extracted globally and the highest volume of raw material used on earth after water (about 70-80% of the 50 billion tons material mined/year). Formed by erosive processes over thousands of years, they are now being extracted at a rate far greater than their renewal. Despite our increasing dependence on the colossal quantities of sand and gravel being used and the significant negative impact that their extraction has on the environment, this issue has been mostly ignored by policy makers and remains largely unknown by the general public. Indeed, the absence of global data on aggregates mining makes environmental assessment very difficult and has contributed to the lack of awareness about this issue. As a consequence, a large discrepancy exists between the magnitude of the problem and public awareness of it.

1.2  STATEMENT OF THE PROBLEM

The impact of sand and gravel dredging or mining on the environment is enormous; this is so because when they see is dredge Excessive in stream sand-and-gravel mining causes the degradation of rivers. … Any volume of sand exported from streambeds and coastal areas is a loss to the system. Excessive in stream sand mining is a threat to bridges, river banks and nearby structures. With advancement in technology and infrastructural development, the need for sand and gravel is on the high side, and dredging happens to be the only solution to meet this needs. However if dredging and is not control it impact on the infrastructure can be very fatal.

1.3  OBJECTIVE OF THE STUDY

The main objective of this study was to ascertain the impact of sand and gravel dredging on environment. However at the completion of the study, the researcher seeks to achieve the following objectives:

The impact of gravel dredging on the Lagos bar beach coastal area

The impact of sand dredging on Nigerian waters

To ascertain the consequences of gravel dredging in coastal area

The challenges of dredging on Nigeria coastal area

1.4 RESEARCH QUESTION

For the successful completion of these studies, the following research question was formulated:

What is the impact of dredging on Lagos coastal area?

What is the impact of sand dredging on Nigerian waters emphasis on Lagos coastal area?

What are the consequences of gravel dredging on infrastructural development in Lagos coastal area?

To what extent has dredging affect the infrastructural development of the region?

1.5 SIGNIFICANCE OF THE STUDY

It is conceived that at the completion of the studies, the findings will be beneficial to the environmental agency and coastal guard who is saddle with the responsibility of protecting the region, the study will also be of benefit to the NIMASA who are responsible for protection of Nigerian water ways. Finally, the study will also be useful to academia, teachers, lecturers, researchers and the general public.

1.6   SCOPE AND LIMITATION OF THE STUDIES

The scope of this studies covers the impact of sand and gravel dredging on Lagos coastal area, however, the studies have some constrain which are:

a) AVAILABILITY OF RESEARCH MATERIAL: The research material available to the researcher is insufficient, thereby limiting the study

b) TIME: The time frame allocated to the study does not enhance wider coverage as the researcher have to combine other academic activities and examinations with the study.

c) FINANCE: The finance available for the research work does not allow for wider coverage as resources are very limited as the researcher has other academic bills to cover.

1.7 DEFINITION OF TERMS

DREDGING

Dredging is an excavation activity usually carried out underwater, in shallow seas or freshwater areas with the purpose of gathering up bottom sediments and disposing of them at a different location. This technique is often used to keep waterways navigable. It is also used as a way to replenish sand on some public beaches, where sand has been lost because of coastal erosion. Fishing dredges are used as a technique for catching certain species of edible clams and crabs.

SAND

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles. It is defined by size, being finer than gravel and coarser than silt. Sand can also refer to a textural class of soil or soil type; i.e. a soil containing more than 85% sand-sized particles by mass. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz. The second most common type of sand is calcium carbonate, for example aragonite, which has mostly been created, over the past half billion years, by various forms of life, like coral and shellfish. For example, it is the primary form of sand apparent in areas where reefs have dominated the ecosystem for millions of years like the Caribbean.

GRAVEL

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule– to boulder-sized fragments. Gravel is categorized by the Udden-Wentworth scale into granular gravel (2 to 4 mm or 0.079 to 0.157 in) and pebble gravel (4 to 64 mm or 0.2 to 2.5 in). One cubic metre of gravel typically weighs about 1,800 kg (or a cubic yard weighs about 3,000 pounds). Gravel is an important commercial product, with a number of applications. Many roadways are surfaced with gravel, especially in rural areas where there is little traffic. Globally, far more roads are surfaced with gravel than with concrete or tarmac; Russia alone has over 400,000 km (250,000 mi) of gravel roads.[1] Both sand and small gravel are also important for the manufacture of concrete

1.8 ORGANIZATION OF THE STUDY

This research work is organized in five chapters, for easy understanding, as follows Chapter one is concern with the introduction, which consist of the (overview, of the study), statement of problem, objectives of the study, research question, significance or the study, research methodology, definition of terms and historical background of the study. Chapter two highlight the theoretical framework on which the study its based, thus the review of related literature. Chapter three deals on the research design and methodology adopted in the study. Chapter four concentrate on the data collection and analysis and presentation of finding.  Chapter five gives summary, conclusion, and recommendations made of the study.