It also extends from the mid-mountainous area of the northern Eifel Mountains in its upper reach to the lowlands of the Lower Rhine Embayment in its lower reach [ 71 ]. The springs of the km-long Rur River are located in the raised bog area of the High Fens in Belgium at an altitude of m above sea level [ 70 ]. In the Dutch city of Roermond, the Rur River flows into the Meuse River at an elevation of 30 m above sea level [ 70 ].
Approximately 6. After approximately 10 river-km in Belgium, the upper reach of the Rur River flows through the Eifel, a low mountain range in Germany [ 73 ]. The Eifel is one of the most rural areas in Germany [ 74 ]. The catchment is wholly anthropogenic, marked by forestry in the highlands and grassland and farmland on the plateaus [ 71 ]. The Lower Rhine Embayment is marked by agriculture [ 75 ] and lignite open cast mining [ 71 ]. Source: own illustration; DEM: [ ] ; river system: [ , ]; towns: [ ]; country borders: [ ].
North Rhine-Westphalia has a comparatively humid but cool climate due to its proximity to the Atlantic Ocean [ 71 , 76 ]. Precipitation in the Eifel Mountain region is significantly higher than that in the northern lowlands [ 71 ].
Due to its source region in Eifel, the year-round aquiferous and dam-regulated Rur River has a rain- and snow-influenced discharge regime and is affected by snowmelt from the low mountain range [ 43 ].
Related to climatic characteristics, the river regime is pluvio-nival with the highest discharge in winter and long periods of dry weather runoff in summer. Flood events occur mainly in spring and winter due to prolonged rainfall or snowmelt and in summer due to storm events. Due to the dams, the discharge of the Rur River is regulated; thus, runoff peaks are smaller [ 41 , 43 ].
In the last years, northern Eifel has been characterized by urbanization, grassland cover of arable land in the low mountain ranges and foothills, and reforestation measures in the Eifel forests [ 77 ]. Today, the Rur River is strongly anthropogenically influenced. Private companies, especially those in the paper industry, are still the largest water consumers in the Rur-Eifel region to date [ 76 , 78 ].
Most days of the year, various reservoirs in the upper catchment withdraw a reduced amount of water, which is morphodynamically ineffective [ 78 ]. The largest settlement on the Rur River in the low mountain range is Monschau, where massive bank protection characterizes the river cf. In the low mountain range, the Rur River is categorized as a German river type 9, indicating a silicate, low mountain range river rich in fine to coarse material.
The course of the river today in the upper catchment is partially similar to the ecological mission statement, which calls for stretched to slightly sinuous, natural sections existing with numerous characteristic longitudinal benches, sliding slopes and riffle pool sequences [ 79 , 80 ]. Side channels would be characteristic but are missing [ 79 ]. In the lowlands, the Rur River is categorized as a German river type 17, indicating a gravel-embossed lowland river [ 73 ].
Immense hydraulic engineering between the s and s led to a completely embossed straightened channel with strong incision [ 80 ]. Additionally, the flow is regulated by dams, and a large number of transverse structures restrict continuity [ 80 ]. Source: own illustration. The three focus regions cover one section each of the upper A , middle B and lower C reaches of the Rur catchment cf. Figure 5 ; Table 1.
Focus region A and focus region B cover the Rur segments that are siliceous, low mountain rivers rich in fine to coarse material German river type 9. In focus region C, the Rur River is characterized as a gravel-embossed lowland river German river type Focus region; source: own illustration; DEM: [ ]; River system and catchment area: [ , ]; towns: [ ]; country borders: [ ]; German river type: [ 71 ].
Focus region A is located upstream from the dams starting at the end of the village of Monschau. In the low Eifel mountain range around Monschau, large riverbed shifts are topographically not possible. Therefore, characteristic waterway bends are used to mark the start and end of the focus region. Focus region B, which is 20 km long, covers a typical agricultural area. As a transshipment point for rafted wood in the Middle Ages, it later became the main location for the paper industry, and afterwards, sugar cane factories cf.
The Wurm tributary marks the lower boundary of the 15 km-long focus region C. Impressions of the Rur River from the three focus regions. To analyze the river course development over the last years, historic maps and digital orthophotos are evaluated in three focus regions cf.
Development of industry and land use in the Rur catchment from to today; source: own illustration; river system and catchment area: [ , ]; towns: [ ]; Corine land use data: [ 77 , ].
Map sheets that were previously georeferenced by the Cologne District Council were used. Therefore, information on accuracy and rectification errors cannot be given.
However, since the analyses are based on quantitative data, for the purpose of this paper, an accurate cutoff of the focus regions in the various maps is more important than the accuracy of the georeferencing. To ensure that the focus regions in all time slices included identical river sections, their start points and end points were defined with the help of historic monuments and tributaries, which can be found in all historical maps and orthophotos.
Details on the pixel size and scale of different maps are shown in Table 2. River courses are digitalized manually with QGIS as line objects approximating the middle line of the riverbed. Quality parameters for the accuracy of digitalization were introduced to make the length of the digitalized river courses comparable.
The accuracy of a line object can be identified by its number of knots per length. Adding more knots leads to a better approximation of curved elements, but elongates the total length. With the criterion of 4 knots per m, river course comparability is ensured.
The consistent distribution of knots is controlled visually using the distance matrix function. For straightened river segments, a coarser resolution is sufficient, whereas highly sinuous segments need more knots for an adequate approximation. Additionally, morphodynamic structural elements of the Rur River are digitalized, which serve as indicators for morphodynamic activity and river straightening cf.
For this study, islands in the riverbed that are not part of a braided river section are digitalized as islands. They can quickly obtain vegetation [ 66 ] and are more permanent than bars [ 81 ]. Large islands that divide the channel into two approximately equal anabranches, causing the river corridor to widen, are not marked as islands but as anastomosing channels. Anastomosing channels are multithread channels in which the outflow is divided into a multitude of watercourses [ 59 ].
Braided channel structures are characterized by intertwined blurred shorelines and variable bedload deposits in the riverbed [ 59 ]. Braid bars are not vegetated [ 82 ]. Although anabranching channels can be braided [ 81 ], in this study, braided single-channel rivers and anabranching rivers are distinguished [ 83 ]. Oxbows are either permanently connected to the watercourse or separated former river sections [ 84 ], and hence are constantly or temporarily flowing through former watercourses [ 84 ].
Side arms are permanently flowing side waters, whose start and end are attached to the main course. Side arms differ from anabranches since they are smaller than the main channel. Source: own illustration; criteria according to [ 59 , 83 , 84 ]. Hand-sketched historic maps at a low resolution and vegetation in digital orthophotos lead to difficulties in digitalization, as also recognized by Roccati et al. The transition between islands and short sections of single braided channel or two anastomosing channel structures is fluent.
Therefore, some structural elements are digitalized with a possible alternative cf. Table 3. For the analysis, the first choice for the type of structural element is considered with a weight of 0. From the digitalized channels and its structural elements, indicators are computed for each time slice according to Table 4.
Inaccuracies reaching 20 m in historical maps of the nineteenth century lead to a variation in the results of less than 0. Focus regions are not affected by sheet lines or map edges. Therefore, the results can be specified without an error range. A change of 0. With this normalized approach, focus regions can be compared with each other in addition to covering unequally long river sections. To calculate the river sinuosity, the thalweg for each focus region is computed using a digital elevation model DEM with a grid resolution of 25 m DEM By using a relatively coarse DEM, it is ensured that the thalweg and not the river coarse is computed e.
Indicators are used to evaluate the development of river straightening Eq. Additionally, whether the structural diversity of rivers is increasing is evaluated Eq. If structural development is driven by fluvial processes it is very likely self-sustaining [ 98 ]. To evaluate whether the Rur River experienced significant straightening during the Industrial Phase 2 , the increase in river straightening Eq.
A positive value means, that the river has experienced straightening during a specific period. A negative value means, that straight river sections have been reduced.
Therefore, as a second outcome value, the increase or decrease in structural diversity within the five phases is evaluated. First, changes in river length and sinuosity in the three focus regions are evaluated. In focus region A, the river course was 2. The river section elongated from The length of the river section changed from Here, the length of the river section changed from Since the twenty-first century, the length of the river courses has remained static in all three focus regions.
Changes in river length and sinuosity in the three focus regions of the Rur River over its five phases of river management in the last years. Overall, the total river length changed the least in focus region A in the low mountain area. In the lowlands, greater changes in total river length occurred, whereby the greatest change occurred in focus region C, where the Rur River is categorized as a gravel-embossed lowland river. The sinuosity in focus region A slightly increased from 1.
According to the criteria of Brice [ 92 ], the Rur River in focus region A is classified as sinuous in all five phases. In focus region B, the sinuosity dropped from 1. The largest decreases in sinuosity occurred during the Pre-industrial 1 and Agricultural 3 Phases. With a sinuosity smaller than 1. The Rur River in focus region C changed its sinuosity from 1. Therefore, the river course changed from meandering to straight [ 92 ]. Since the early twenty-first century, river sinuosities have stabilized with a very slight tendency to increase.
Braided channels only occur in small areas, whereby anastomosing channels can be found more often cf. In the Pre-industrial Phase 1 , the length of anastomosing channels increased from 1.
During the Industrial Phase 2 , anastomosing channels almost vanished approx. In focus region B, anastomosing channels had significant lengths during the Pre-industrial Phase 1 approx. During Phase 2, the length of the additional channel declined to approx. However, braided channel sections were at their longest, with approx. Since the Agricultural Phase 3 , anastomosing channels have expanded slightly approximately 1 km of additional channel length , and since the early twenty-first century, braided channel sections have disappeared again.
Change in indicators over the five phases of river management in the last years in the three focus regions of the Rur River, a changes in the length of anastomosing and braided river structures in comparison to the total river length, b changes in the length of side arms in comparison to the total river length, c changes in the average number of oxbows per river-km, and d changes in the average number of islands per river-km. Side arms are not present in focus region A, which can be explained by the steep thalweg cf.
Later, a third channel occurs, marking the section as an anastomosing river. Due to dense vegetation, the channel width cannot be determined. Today, side arms total approximately 2 km in focus region B. In focus region C, side arms were of significant length during Phase 2. Four side arms had a total length of approximately 2. In focus region A, oxbows rarely occur, with less than one oxbow per river-km; however, they increased in the late twentieth century, when two small oxbows occurred cf.
In focus region B, oxbows occur more often. In the nineteenth century, 12 to 48 oxbows were counted in hand-sketched maps. After Phase 2, the number of oxbows per km dropped from approximately 2. Since the twenty-first century, approximately five oxbows have been counted in orthophotos. In focus region C, a maximum of 24 oxbows occurred in Phase 2. Afterwards, numbers have been declining, reaching three oxbows today.
Overall, the number of islands per river-km has decreased in the last years in focus region A from four to one island cf. In focus region B, the average number of islands varies heavily between 12 islands map of Tranchot and one island DOP After a decrease in islands during Phase 1 in focus region C from six to two, the number of islands stayed low. In focus region C, between three and one islands were counted in the first topographical map and orthophotos.
The greatest changes in river sinuosity occur at the Rur River in focus region C during Phases 2 and 3 cf. In focus region B, the decrease in river sinuosity is almost as significant as that in focus region C. The largest changes in braided and anastomosing channel sections occur in focus region B.
During Phases 1 and 2, anastomosing channels decreased and braided river structures increased. During Phase 3, both braided and anastomosing channels as well as the sinuosity of the Rur River decreased in focus region B. Additionally, the number of islands varied during this time, but for both indicators, a significant increase during the Industrial Phase 2 can be observed.
Since the general focus shifted towards improving the water quality and sustainability in river management Phases 4 and 5 , the number of oxbows slightly decreased and the number of islands slightly increased in focus region B, whereas both small-scale indicators decreased in focus region C. Development of indicators for morphodynamic activity and river straightening in the three focus regions over the five phases of water management in the last years.
With these indicators cf. Aquatic life forms and vegetation have been decreasing. These life forms require a specific temperature and speed of water flow to survive. But the modification of rivers has increased the temperature of water. The velocity of water has increased making it difficult for the survival of aquatic life.
Pool rifle patterns have been eliminated and substrates keep shifting. Vegetation along the riverbanks has been removed. This reduces the food for the aquatic life forms.
It also reduces the natural shade, increasing the temperature of the water. Hard engineering Hard engineering management of rivers involves the construction of structures, built to control the flow of water and reduce flooding. Dams and reservoirs A large wall is built across a river, usually in the upper stages. Flood defences at Cockermouth. Related Topics Use the images below to explore related GeoTopics.
Please Support Internet Geography If you've found the resources on this site useful please consider making a secure donation via PayPal to support the development of the site. Top Posts and Pages Home. Log In. What are the impacts of migration? What factors affect population density and distribution? How does flooding affect humans and the environment? Geography Case Studies. Dams serve many different functions like provision for drinking water, irrigation, power generation, flood control, and recreation.
For good volume of water at very swift speeds, it is customary to make a dam at the downstream of a straightened river. The above reasons obviously impact positively on the economy of the country and also have some positive impact on the environment. However, there are also negative impacts which must be weighed carefully before such projects are commissioned.
Some of them are:. Ground water recharge is a major contribution of total volume of water in a river among others. When straightening occurs, the river is diverted away from its natural course thereby cutting off the contribution of ground water recharge.
This causes an overall shortage in the total volume of water. The effect of this may not be noticeable in the rainy season but during dry seasons, it may.
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