Over 911,000 cubic meters of Karkheh River in the southern Khuzestan Province have been dredged since the beginning of the current fiscal year (March 21) not only to help prevent potential flooding but also to help cattle breeders bathe their cattle in the river, head of the provincial agricultural organization said.
“The plan is also aimed at reducing the exposure of fish, wildlife and people, as well as other areas to contaminants, in addition to increasing the depth of the navigation channel,” ISNA also quoted Khodarahm Amirizadeh as saying.
Karkheh River, one of the largest and most important rivers in Iran, has potable water and runs through the city of Andimeshk, north of the oil-rich province.
“Dredging needs to be undertaken regularly in deluge-prone regions, such as Khuzestan, Lorestan, Golestan, Chaharmahal-Bakhtiari and Sistan-Baluchestan, as they were all hit by floods in 2019 and 2020,” he said.
Dredging is the removal of sediments and debris from the bottom of lakes, rivers, harbors and other water bodies. It is a routine operation in waterways around the world because sedimentation — the natural process of sand and silt washing downstream — gradually fills channels and harbors.
Amirizadeh noted that in the past 20 months, rivers in many provinces have been dredged, including Khuzestan, Golestan, Kermanshah, West Azarbaijan and Khorasan Razavi provinces.
In the fiscal 2021 budget, about $20 million were allocated for river engineering, which showed a threefold increase compared to $6.15 million in the 2020 budget.
River engineering helps optimize rivers’ numerous benefits while providing protection against flooding. It involves modifying the natural river conditions, including stabilization, bank revetments, dredging, diversions, cofferdams, channelization, levees and flood control works.
Dredging covers a range of activities from the removal of material from the bed and sides of river channels through to straightening (canalization) and/or deepening of watercourses.
There is no denying the fact that flooding has shaped rivers and landscapes for millennia in Iran, but because its power has been underestimated, it has brought misery to large numbers whose homes, possessions, businesses and land have been lost to floodwater over the last two weeks, especially in Tehran, Alborz, Markazi, Isfahan, Fars, Hormozgan, Sistan-Baluchestan, Yazd and Chaharmahal-Bakhtiari provinces, due to unprecedented torrential rainfall.
Viable Solution
According to the Energy Ministry, although dredging is not the best long-term and economically-viable solution, in the past 13 months it has helped (to some degree) prevent flood damage in 2020 compared to 2019 when deluge caused loss of lives and widespread destruction in the northern and southern regions.
Dredging of a reach (length of channel) reduces water levels and fluvial flood frequency in the immediate area.
The strategy can play an important role in flood risk management in some cases, but is not a “standalone solution” as it has its own negative aspects.
Dredging should be considered in the context of a range of tools and the origins of different sources of floodwater, and comes with significant risks that must be understood at the local and catchment scale.
The removal of mud or sand from the bottom of a river can have significant direct and indirect drawbacks for ecosystems. For example, it can lead to the loss and degradation of natural habitats and features such as pools and riffles. It can also impact a range of protected species.
The removal of vegetation from within channels and along channel banks during dredging operations can increase water temperature by reducing shade. Warmer temperatures result in lower oxygen concentrations, making fish and invertebrates in dredged channels more vulnerable to stress during hot weather.
In a nutshell, floods, the deadliest, costliest and most common form of natural disaster, are not always easy to predict. Hence, all contingencies must be in place at all times.
Despite the fact that clearing the bed of a harbor, river, or other areas of water as well as building dams, seawalls, floodgates and levees are important in containing floodwaters, these cannot always serve the purpose effectively (as they have their own constraints). Nevertheless, they are still needed.
