Low-Flow in 2018 Content Outline 3 Chronology … 4 Impacts of the 2018 low-flow 8 Lowest water level in recent years? New record? 13 Editor: Lower water levels do not always mean lower Federal Institute of Hydrology Am Mainzer Tor 1 • P.O. Box 20 02 53 water volumes 14 56002 Koblenz • Germany Mitigate effects by means of information: Tel.: +49 261 1306-0 • Fax: +49 261 1306-5302 the role of BfG 16 E-Mail: [email protected] • Internet: http://www.bafg.de Low-flow 2018 – a harbinger? 18 Effective: February 2019 DOI: 10.5675/BfG-Niedrigwasserbroschuere_2018 Water level – press reviews 21 Outline The year 2018 was marked by In many places, water levels at also impacted on the industry: persistent drought. In its wake, the gauging stations reached due to the high water temperatu- riverine water levels sank historically low levels. Runoff res in rivers, the discharge of dramatically in the course of the was also extremely low, but warm water into the rivers had year. After a humid winter with without breaking any records. to be limited. In addition to the large amounts of snow in the The runoff of the extreme low water quantities, notably Alps, average monthly rainfall year 2003 was reached or even high water temperatures and the had not been reached since undercut. In terms of the major inherent deterioration of water March 2018. From April onwards, federal waterways, the rivers quality gave rise to concern. The rainfall in Germany accounted Weser and Elbe were particularly summer heatwave of 2018 also for only about half the long-term affected: their water levels fell affected the riverine biology, mean. As a result, riverine water below the navigation-relevant entailing i.a. the blue-green levels first sank in the North and low level in 80 % resp. 90 % of algae bloom in the Moselle river East of Germany, and later on in all days between June and as well as major heat stress for the South and West. In the December 2018. numerous species of fish and Middle and Upper Rhine, snow invertebrates. It was not before and glacier melt water delayed a Notably the low water level of early December, that an improve- decrease of the water levels. the Rhine, causing lower cargo ment of the low-flow situation Therefore, low stages impeding tonnages on inland vessels, and came into sight. Information on navigation were not reached hence supply bottlenecks, had current water levels and multi- until mid-November. economic impacts. Low-flow day forecasts in all federal 3 waterways notably helped the cause a more frequent occur- boatmen and the logisticians to rence of such low-flow periods. determine or adapt the maxi- Towards the end of the century, mum cargo capacity or to find it is expected that earlier and alternative solutions. reduced snowmelt as well as absent glacier melt will pose Studies implemented by BfG new challenges to the manage- show that climate change may ment of the federal waterways. Chronology Overall, 2018 was marked and West of Germany. Persis- by low rainfall. In particular tent drought increasingly from June onwards, major impeded inland navigation in precipitation deficits were the course of the year. Smaller recorded. As a result, riverine amounts of rainfall failed to water levels decreased. The bring lasting relief. From late watercourses in the North and summer, progressive drought East were affected first, follo- caused new historical all-time wed by the rivers in the South lows. 4 June July August + 2,0° + 2,3° + 2,4° – 40 % – 52 % – 45 % As of: 29.06.2018 As of: 26.07.2018 As of: 31.08.2018 September October November + 2,6° + 1,5° + 0,8° – 36 % – 55 % – 70 % As of: 27.09.2018 As of: 25.10.2018 As of: 29.11.2018 precipitation anomaly [%] Mean water level Low water level High water level No current water level 1 25 50 75 100 125 Fig. 1: Water levels, deviations of monthly rainfall totals and mean monthly temperatures from the long-term average (1981–2010). Data: PegelOnline (WSV / Federal Waterways and Shipping Administration) and Deutscher Wetterdienst (DWD/German Meteorological Service) 5 June July August September October November 650 1 2 3 4 5 600 550 500 450 Upper Rhine/Maxau 41% days June – Nov below GIW* 400 350 300 500 450 400 350 Lower Rhine/Duisburg-Ruhrort 300 67% days June – Nov below GIW* 250 200 150 400 350 300 Danube/Hofkirchen 67% days June – Nov below RNW* 250 200 160 Water levels in cm at gauging station Water 140 120 Weser/Vlotho 83% days June – Nov below GIW* 100 100 90 80 93% days June – Nov below GIW* 70 Elbe/Magdeburg 60 50 Fig. 2: Temporal development of water levels (solid line) of selected rivers and the pertaining gauge-specific low-flow reference value (dashed line). Provisional data. Data WSV, graph BfG * GlW (equivalent water level) and RNW (regulation low-flow) are river-specific reference values. They are of major importance as reference values for the maintenance of free-flowing waterways and for navigation, especially during low-flow. If the water level falls below these reference values, the ships’ potential draught and hence cargo capacity decreases, depending on the type of ship. 6 1 Mild and rainy autumn and winter seasons in 2017 were followed 4 The very dry weather in by a warm and dry spring in 2018. The months from March to October clearly escalated the June 2018 were continuously too dry and mild all over Germany. situation: historically lowest levels were reached at some At the beginning of the year, the rivers still carried larger amounts gauging stations. The Upper of snowmelt. A low-flow situation soon occurred on the rivers Rhine’s water level constantly Elbe and Oder, as rainfall in these regions had been below average dropped below the reference since 2014 and natural reservoirs were depleting fast. Therefore, value GIW that is crucial for the Elbe’s water level reached a low that impeded navigation navigation. already in June. 5 After short rainfalls, briefly 2 The outstandingly warm and dry weather persisted in July and easing the situation on Middle August. Regional, short rainstorms brought no relief. Riverine water Rhine and Danube, the sixth levels continued to drop on a large scale: On Weser, Danube and driest November since 1901 Lower Rhine they dropped below the river-specific reference values. caused another decline of the Merely the partly impounded Upper Rhine and the Middle Rhine water levels. It was not before initially maintained an adequate water level. early December that rising water levels were recorded again. Persistent rainfall must now fill 3 Rainfall, primarily in Southern Germany, slightly improved the empty groundwater and soil the low-flow situation, especially on Danube and Upper Rhine. water storage, before more stable Water levels on Elbe, Weser and Lower Rhine remained low. water levels can be expected. 7 The impacts of the 2018 low-flow Deteriorated water quality and discharges, e.g. from to rise to the second highest Low discharge impacts in sewage treatment plants and temperature values after the different ways on the water industry, are less diluted. The 2003 heat wave. A water quality in federal waterways: above-average air temperatures temperature of 25°C is a critical i.a. algae growth is stimulated caused the water temperatures value for many of the fish and invertebrate species living in Discharge /s the Rhine. 3 Turbidity In 2018, this value was exceeded Turbidity E/F Turbidity Discharge m in the Rhine near Koblenz on 31 consecutive days (fig. 3); this is un ul Aug Sep Oct Nov normally only true for 9 days in a year. 17 respectively 16 days ritical water teperature above 25°C were measured in the Elbe and Oder rivers, setting ritical oxygen concentration a new record value for the last Oxygen mg/l Oxygen 20 years. In the Rhine and Temperature temperature C Water further federal waterways, un ul Aug Sep Oct Nov Lorem ipsum Fig. 3: Temporal development of discharge (blue), turbidity (grey), oxygen content (green) however, oxygen values (blue) and temperature (red), on a daily basis during low-flow period June – December 2018. remained clearly above the Discharge from Kaub gauging station, data WSV (Federal Waterways and Shipping Ad- ministration). Remaining values from the Rhine at Koblenz: data BfG, graph BfG critical level for fishof 4 mg/l. 8 Inland vessel on the Rhine carrying containers. Photo by Dr. Sebastian Kofalk, BfG During a short period, however, critical values (up to 3.5 mg/l) Restrictions to inland were recorded on the rivers Oder, Lower Havel and tidal Elbe. navigation The summer low-flow on the Rhine and Moselle rivers featured a Due to low flow, inland vessels special phenomenon, i.e. the occurrence of algae blooms. These were unable to utilize their full algae caused an increased turbidity of the Rhine water in August. loading capacity and had to Usually, high turbidity values occur when discharge, and hence travel with low cargo volumes. sediment transport, are higher. In August alone, freight figures dropped by 21 %1. Hence, many In the Moselle river, a blue algae bloom lasting more than two ports (e.g. Mannheim –42 %) months caused restrictions for water sports, as these organisms may suffered losses from reduced present a risk to health. handling2. 9 Large-scale power station at Mannheim. Photo: Immanuel Giel, CC BY 3.0 According to the Federal Waterways and Shipping Administration amounted to almost 1 million €. (WSV)3, clearly less cargo was shipped in the locks at Iffezheim In some instances, ferry services (–23.6 %), on the Wesel-Datteln Canal (–24.9 %) and on the Main on Rhine and Elbe had to cease river (Kostheim lock –21.8 %) than in the previous year.