The Padma River is one of the largest rivers in Bangladesh, flowing through the centre of the country before joining the Meghna River and reaching the Bay o...

(a) Two uses of sand and gravel in the construction industry [1 each, max 2]:

1. Concrete production: Sand is mixed with cement and water to make concrete, which is used for building foundations, walls and floors.
2. Road surfaces: Gravel is used as aggregate for road surfaces and in the production of asphalt.

Other valid answers include: glass manufacture, land reclamation, drainage fill, or mortar.

(b) Using Fig. 4 to describe the locations of extraction sites:

1. The five extraction sites are spread along a 25 km stretch of the Padma River in the Faridpur District [1].
2. Sites A and B are in the upstream section near Goalundo, while sites D and E are in the downstream section near Daulatdia and Nagarbari [1].
3. Site C is positioned in the middle section near Rajbari. Eroded bank sections (shown with wavy lines on the map) are visible near sites B, D and E, suggesting that extraction has destabilised the river banks in those areas [1].

(c) Changes in sand extraction and river depth (Table 4):

1. Sand extraction increased steadily from 2.4 million m³ in 2010 to 9.8 million m³ in 2025, more than quadrupling [1].
2. Average river depth decreased from 12.5 m to 7.2 m, a decline of 5.3 m or approximately 42% [1]:

\[\text{Percentage decrease} = \frac{12.5 - 7.2}{12.5} \times 100 = 42.4\%\]

3. The increase in extraction corresponds closely with the decrease in depth, confirming that sand removal is directly lowering the riverbed [1].
4. The trend is consistent across the entire period with no sign of recovery in any year, indicating ongoing and unsustainable pressure on the river system [1].

(d) Effects of sand removal on the river ecosystem:

1. Benthic habitat destruction: Removing sand destroys the riverbed habitat where invertebrates and fish depend on stable substrate for shelter, feeding and breeding [1].
2. Increased turbidity: Dredging operations stir up fine sediment, reducing light penetration in the water. This affects aquatic plants that need sunlight for photosynthesis [1].
3. Altered flow conditions: Changes in river channel depth and flow speed alter the distribution of species adapted to particular conditions, reducing biodiversity [1].
4. Fish spawning disruption: Fish such as hilsa that require sandy substrates for spawning cannot breed in areas where the sand has been removed. Table 4 shows fish catch declining from 1,850 to 510 tonnes per year [1].
5. Noise disturbance: Vibration and noise from suction dredging equipment disturbs aquatic organisms, causing them to avoid areas near extraction sites [1].

(e) How sand mining increases flood and erosion risk:

1. Bank collapse: Mining lowers the riverbed, which undercuts the river banks and causes them to collapse. The bank erosion rate increased from 3.2 to 12.5 m per year (Table 4), destroying farmland and buildings along the shore [1].
2. Increased flow velocity: A deepened channel can increase water velocity during floods, meaning floodwater moves faster and with more erosive force against downstream settlements [1].
3. Weakened natural levees: Natural levees along the banks are weakened by extraction, making them more likely to breach during monsoon floods and allowing water to inundate low-lying areas [1].
4. Quantitative evidence: The number of flood events along this stretch increased from 2 in 2010 to 7 in 2025, directly corresponding with the increase in extraction [1].

(f) Three ways the government could manage sand extraction [max 4 marks]:

1. Licensing and quotas: Introduce a system that limits the total volume extracted per year to a level the river can naturally replenish through sedimentation. Crack down on the estimated 15 unlicensed operations [1+1].
2. Seasonal bans: Enforce a ban on extraction during the monsoon period (June to September) when banks are most vulnerable to erosion and flood risk is highest [1].
3. Alternative materials: Promote the use of manufactured sand from crushed rock and recycled building materials as substitutes for river sand in the construction industry [1].

Other valid suggestions include: buffer zones near villages, environmental monitoring, fines for illegal extraction, or relocation of sites away from vulnerable areas.

(g) Why demand for sand has increased rapidly in Bangladesh:

1. Population growth: Bangladesh has over 170 million people and a growing population, creating demand for housing, schools, hospitals and other buildings [1].
2. Urbanisation: Dhaka (population over 22 million) and other cities are expanding rapidly with rural-to-urban migration, requiring large-scale residential and commercial construction [1].
3. Infrastructure projects: Government investment in major infrastructure - roads, bridges, flood defences and the Padma Bridge - has increased demand for concrete and aggregate [1].