An estimated 2,100 kilometers of rivers and canals have been dredged in deluge-prone regions since March 2019 to prevent and reduce floodwater damage.
According to the Energy Ministry’s news portal, before 2018 close to 300 kilometers of rivers were dredged annually on average.
“That has now increased by about seven times so far this year.”
Streams in many provinces have been and are being dredged including Khuzestan, Lorestan, Golestan, Kermanshah, West Azarbaijan, Kerman, Khorasan Razavi, Gilan, Semnan, Markazi, Chaharmahal-Bakhtiari and Sistan-Baluchestan provinces.
Dredging covers a range of activities from the removal of material from the bed and sides of river channels through to the wholesale 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 the water over the 15 months, namely in Golestan, Lorestan and Khuzestan provinces.
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) leads to a reduction in water levels and hence to a reduction in fluvial flood frequency in the immediate area.
In the March 2020-21 budget $20 million has been allocated for river engineering, which shows a three-fold increase compared to $6.15 million in last year’s spending.
River engineering helps in optimizing rivers’ numerous benefits while providing protection against flooding.
Consequences
Mohammadreza Haj Rasouliha, managing director of Iran Water Resources Company, argues that dredging can play an important role in flood risk management in some cases, but is not a “standalone solution” as it has its own negative sides.
“Dredging should be considered in the context of a range of tools and the origins of different sources of flood water, and comes with significant risks that must be understood at a local and catchment scale.”
Dredging can have significant direct and indirect drawbacks for ecosystems. For example, it can lead to 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. This means 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.
