The disaster that hit Pakistan in the last days of July is seen to have been caused by heavy monsoon rainfalls that ultimately led to an overflow of its rivers. According to PMD (Pakistan Meteorology Dept) Pakistan experienced heavy rains around the 29th of July, with over 40 cm in Khyber ; 33 cm in Peshawar; 25 cm in Islamabad, whereas the normal monthly rainfall measures up to only 4.6 cm.
The downpour in the north flooded the upper Indus River which led to the bursting of its banks. The Indus, much like the Nile, rises in the highlands, watered by seasonal rains. It is Pakistan's longest river with a length of about 3180 km and the dam on the Indus, the Tarbela Dam, unlike Aswan Dam or Lake Nasser, is not positioned to curtail an overflow. Even though there are various low dams or "barrages" on the Indus these are only capable of directing any overflow into supply canals.
Read more about the Kingdom's assistance to Pakistan in the aftermath of the floods in The Diplomat, the bi-monthly magazine of the Institute of Diplomatic Studies.