Floods in Bangladesh are a complex phenomenon, with various causes and effects in different places. Traditional settlement patterns and economic activities are well adapted to seasonal flooding. Floodplain settlements are on the highest available ground. Houses are on raised mounds and mainly made of locally available wood, bamboo and jute sticks with straw thatching material. Damage occurs when floods are abnormally high, breaches occur in embankments or land is eroded by shifting river channels. Following severe floods in 1987 and 1988, families raised house plinth levels, and galvanized iron sheets widely supplemented traditional materials in rebuilding and repairs. Some NGOs promoted more costly rigid frame houses. Aid donors supported a $150 million Flood Action Plan mainly comprising studies to identify long-term mitigation measures. Settlement related studies include flood response, flood proofing and resettlement studies.