The effect of the Four Major Rivers Restoration obviously turned out. Even though there was record-breaking torrential rainfall from the late June to mid-July, the sites of the Four Rivers perfectly withstood. As the damage figure turned out merely one tenth comparing to before, the Project proved to be effective to the whole world.
One month with half of ‘annual’ rainfall
According to the data from National Meteorological Administration, this year’s jangma (Korean rainy season in early summer) has been increased more than a week comparing other years with more amount of rainfall. Deluges of more than 30mm per hour were observed even 65 times nationwide, with tripling than usual. The case of continual rains in more than 10 days also broke the record. Average precipitation from June 22 to July 16 was recorded as 642mm, the 2.5 times more than usual. It was the second largest one since record began. While annual average precipitation of Korea is 1,245 mm, the record of 642 mm is surprisingly more than the half of yearly amount. Summarizing the data of Meteorological Administration and National Emergency Management, the amount of rainfall during this July 22 and June 16 is equivalent to the 50% of average annual precipitation, and with 70% more amount than usual. At Chungju, for instance, 876 mm of rain downpoured during the period, it is 67% of annual average.
Buyeo (810.5mm), Gunsan (793mm) and other areas also had more than 700 mm rainfall. Wonju, Yangpyeong, Cheonan and Suwon had unprecedented heavy rainfall with half of annual amount just only within 10 days. In case of Seosan in Chungnam Province had 899 mm of rainfall (more than 4.5 times than usual); Sancheong, Gyeongnam Province, had 923 mm. Seoul and Chuncheon recorded in triple amount than other years. Some people who have suspicion insist that flood damage counts how it was concentrated in short period, not by simple comparison of precipitat ion. However, the data f rom Meteorological Administration obviously shows this rainfall was record-breaking than before.
Notwithstanding, the damage throughout the Four Rivers was unbelievably slight. Not a single place was flooded or being formed lake out of inundation as the past. Though some agricultural lands were experienced slight waterlogging, any other damages out of countercurrent or collapse did not happen. Particularly, from the areas prone to flooding every year, Haman, Changnyeong, Goryeong, Hapcheon Counties in Gyeongnam Province, no news of inundation was delivered.
Dredging and farmland remodeling block inundation
Despite copious amount of rainfall comparing to other years, there was no worrying inundation damage. This is because of lowered riverbed out of dredging works during the Project resulted in lowered flood level too, experts analyze. “As dredging lowers riverbed, flood level also went down. So we could prevent severe inundation damage like before. Now we came to see remarkable results from the Project as expected”. Shim Myung-pil, the head of National River Restoration Office, evaluated. To piece together data from Office of National River Restoration, flood level around Sangju (the Nakdong River) got lowered to 3.78m with other regions (Yeoju-the Han: 2.54 m, Yeonngi-the Geum: 3.36 m, and Naju-the Yeongsan River: 2.13 m). In case of the Nakdong River, it had the largest amount of dredge (320 million ton) amid the other rivers. It means the capacity of holding water has increased so that floods buffering effect increased together. 320 million ton is equivalent to the water amount kept in the Andong Dam.
Another key purpose of the Project besides dredge was farmland remodeling; it surely worked for stable flood control. The agricultural areas (217 ha) of Sinchon District of Changwon, Gyeongnam Province, was inundated in July, last year 2010 after torrential downpour with 137 mm. However, the precipitation of June this year was 136 mm; farmlands mounded with dredged soils were turned out inundation-proof. Jeungsan District in Buyeo County, Chungnam Province, had 24 hectare inundated in July 2005 because of 129 mm’s annual precipitation. However, this year of 2011, almost doubled amount of 253 mm was downpoured just from June 22 to 25, no place was waterlogged. Effectiveness of farmland remodeling could be found many places where once were prone to be inundated. Okseong-myeon (Gumi city), environs of Sangju Weir, farmlands of Changnyeong County and Hapcheon County (Gyeongnam Province) have been those of most frequent inundation areas, but from now on it could be a thing of the past.
Damages of Tributaries also reduced
This heavy rainfall proved it is right that enhancement on mainstream should be prior to those for tributaries. Lowered level of mainstream naturally caused tributaries to be lowered. The Seom River (tributary of the Han) became lowered 0.5m; Hwang River (tributary of the Nakdong) 1.3m; Miho Stream (in the Geum River) 0.5m; Hwangryong River, the branch of the Yeongsan River 0.6m. Lowered flood level of tributaries proved government’s prediction was correct.
Amount of damage shows rapid decrease up to 1/10 of before the Project
Although record-breaking cloudbursts persistently downpoured from late-June for a month, damage on Four Rivers and environs was reduced sharply than usual. According to the estimated damage of Four Rivers by National Emergency Management in July 20, the total damage amount was turned out KRW 104 billion (June 22 – July 19). That was aggregated from every damages reported by each local municipalities. It is merely correspondent to the half of the damaged amount of typhoon Gonpas in 2010, when the damage reached to KRW 195.1 billion. Surprisingly, it shows that the status has remarkably reduced up to one tenth comparing to that of year 2002 (Rusa, damage amount KRW 2,872.7 billion), 2003 (Maemi, KRW 2,020.9 billion) and 2006 (Ewinia, KRW 1,535.6 billion)
