Sediment budget
Topic: Landforms and their Evolution: Rivers, Groundwater, Glaciers, Waves and Wind · NCERT: Class 11, Ch 6 "Landforms and their Evolution"
Meaning
The sediment budget of a coast is the balance between the sand brought to it and the sand taken away. Rivers and longshore currents bring sand. A longshore current is a current that flows along the shore. Waves and currents also carry sand off. When supply equals loss, the coast stays stable. Dams trap river sand, sand mining removes it, and harbours block its flow along the coast. When this happens, the coast loses more sand than it gets. Protective bars, beaches and dunes then wear away, and losing mangroves makes things worse. Settlements are left open to storm and tsunami waves. About a third of India's mainland coast was eroding between 1990 and 2018 (NCCR).
Example
In Puducherry, a harbour blocked the sand moving north along the coast. Beaches to the north of it began to wear away, and the town has had to protect its shore with rock walls.