Poster zum Projekt "S2m"

From source to mouth: the sediment budget of the river Rhine
Roy Frings1, Nicole Gehres2, Gudrun Hillebrand2, Stefan Vollmer2, Holger Schüttrumpf1
of Hydraulic Engineering and Water Resources Management, RWTH Aachen University, Aachen, Germany
2Department of Groundwater, Geology and River Morphology, Federal Institute of Hydrology, Koblenz, Germany
Objective
The objective of this research project is to
establish a sediment budget for the entire
Rhine catchment, starting at the source in
Switzerland and extending to the mouth in
the Netherlands (Fig. 1, 2). This implies
quantification of the downstream fluxes of
clay, silt, sand, gravel, cobbles and boulders
through the river Rhine and identification and
quantification of their sources and sinks.
Itributary
Onet dredging
Isediment feeding
Ofloodplains/
groyne fields
Iupstream
Oabrasion
∆S (Bed level change)
Fig. 3. The sediment budget approach, representing the balance between the sediment amounts entering the study area (I, Mt/a), leaving the
study area (O, Mt/a) and being stored in the study area (ΔS, Mt/a). ∆z = total bed level change (m), ∆zt = tectonic bed level change (m), ∆t =
time (a), W = river width (m), L = river length (m), ρs = mineral density (Mt/m3), p = porosity (-) (Frings et al, in prep).
Study Area
The Rhine has a drainage basin of 197,000 km2,
covering 5 geological zones (Fig. 2). Its length is
1230 km and its discharge regime partly snow-melt
and partly rain dominated. The mean discharge at
the German-Dutch border is 2300 m3/s. For most
of its length, the Rhine is heavily engineered (Fig.
1): banks are protected with groynes, shipping
routes are constantly being dredged and
embankments prevent flooding of the densely
populated areas near the river.
e
f
Fig. 1. The Rhine river from source to mouth: (a,b) Alps,
(c) Upper Rhine Graben, (d) Rhenish Massif, (e,f) Delta.
(Photo courtesy: H Krapf, Cinedoku Vorarlberg, BfG, F
Geller-Grimm, Rijkswaterstaat, M Minderhoud).
Fig. 2. Topography and geology of the Rhine basin (Frings et
al, in prep, modified from CHR, 1976). Major tectonic units: 1.
Alps with Molasse, 2. Upper Rhine Graben, 3. Rhenish Massif,
4. Lower Rhine Embayment, 5. North Sea Basin.
Contact information
[email protected]
[email protected]
Methods
During the project duration (2012-2015) existing
data on sediment fluxes, sources and sinks will be
reanalysed, whereas essential, but hitherto missing
data on the sediment input from tributaries and
the exchange of channel sediment with floodplains
and groyne fields will be gathered. We focus on the
time period 1991-2010.
Preliminary Results
Up to now, a sediment budget analysis has been
carried out for the German Lower Rhine, a 225 km
long reach of the Rhine (area 4 in Fig. 2), focusing
on gravel and sand. Echosoundings indicate an
average bed degradation of 3 mm/a between 1991
and 2010 (Fig. 5a). This bed degradation
represents a major term of the sediment budget
(Fig. 4). Sediment sources are: the sediment supply
from upstream (Fig. 5b) and the artificial feeding
of sediment (mostly gravel) by river managers to
reduce bed degradation (Fig 5c). Sediment inputs
by tributaries and bank erosion are assumed
negligible. Sediment sinks include net dredging
activities (Fig. 5d), abrasion and the sediment
output to the downstream area (Fig. 5b). Although
no data on floodplain deposition exist, a
significant deposition of sand on the floodplains
and in the groyne fields has to be assumed in
order to close the budget (Fig. 4).
Invitation
International cooperation is a prerequisite for success in this project.
If you are interested in cooperating with us, please feel welcome to contact us.
The sediment budget analysis shows that
although the Rhine is a gravel bed river (Fig.
5e), sand is the dominant morphological
agent, which implies a high morphological
process rate. The budget also shows that the
sediment exchange between the river bed,
floodplains and groyne fields, which is usually
neglected by river managers, is highly
relevant. It may be clear that budget analyses
provide new insights into the Rhine system. In
future more insight into the sedimentary
coupling of the several Rhine reaches, as well
as a better understanding of the long-term
(climate change) and short-term (floods) river
development are expected.
Sand & Gravel
Budget
44%
Sediment feeding
1
0
-1
-2
25%
0.4
1.3 Mt/a
(100% )
Floodplains/
Groyne fields
Downstream
41%
54%
Fig. 4. Sediment budget for gravel and sand for the studied
part of the Rhine (the German Lower Rhine) for the Period
1991-2010. 100% equals 1.30 Mt/a. Source: Frings et al.
(2012).
Project Funding
The Ministry of Transport, Building and
Urban Development, Germany
Sand (bed-load)
650
700
750
800
850
700
750
800
850
75 c
50
25
0
650
50 d
x 103 m3/hm
Dumping
25
0
Dredging
650
750
700
32 e
8
2
50
1%
4%
850
Gravel
0
0.5
Net dredging
Abrasion
Sand (suspended)
0.2
Upstream supply
Bed degrad.
800
750
700
0.6
-25
31%
650
0.8 b
Sediment load (Mt/a)
Ibank erosion
Sediment feeding (kt/hm)
For sound river management, information is
needed on (1) the size of the sediments that
are moving, (2) the sources and sinks of these
sediments, (3) the mechanism and magnitude
of the sediment transport. This information
can only be obtained through sediment
transport measurements in combination with
a sediment budget analysis (Fig. 3).
∆z − ∆zt
∆S =
WLρ s (1 − p)
∆t
2 a
30
650
800
850
1992-2010
sand gravel
d
Odownstream
Onet .dredging − O floodplains / groynefields − Oabrasion = ∆S
Dredging/Dumping
c
Iupstream + Itributary + Ibank.erosion + I se dim ent . feeding − Odownstream −
Discussion & Conclusions
The causes for the bed degradation in the
study area are a.o. the river training works
from the past, an insufficient sediment supply
from upstream and subsurface sediments
consisting of fine Tertiary sand (Fig. 5f). The
erosion of sand leads to bed coarsening (Fig.
5e) or armouring, which is likely to reduce
erosion rates in future.
Mean bed grain size (mm)
b
Background
The Rhine (Fig. 1) is the most important
waterway in Europe. It is subject to severe
erosion and sedimentation, causing problems
for e.g. navigation, flood safety and ecology.
Elevation (m a.s.l.)
a
Bed level change (cm/a)
1Institute
1981-1983
750
700
River bed
800
850
f
Quaternary
10
-10
Tertiary
800
750
650
700
850
Distance downstream along Rhine axis (km)
Fig. 5. Downstream variation in bed level change (a),
sediment transport (b), artificial sediment supply (c),
dumping and dredging (d), bed grain size (e) and
geology (f) (after: Frings et al 2012).

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