Technical Note About the Monitoring of Hydromorphological Restoration/Management of the Salzach River (Salzburg, Austria)

Case Studies 13: BAW-IWB; BOKU

Technical note about the monitoring of hydromorphological 1 restoration/management of the Salzach River (Salzburg, Austria)

Project: HyMoCARES Work package: WPC. Communication Activity: Web Site Deliverable: Case Studies 13 Status: 1st draft Date: 28-08-2017 Authors: BAW-IWB and BOKU Revision: All the PPs Approval: PP1 APC_PAB

1. General presentation of the study site

The river Salzach leaves the northern eastern Alps near the town Salzburg and flows along the Austrian and Bavarian border through the Alpine foothills. The river has its source in the Kitzbühler Alpen/Österreich at a height of 2300 m ü. A. and flows into the Inn at a height of 344 m ü. NN. The bed level difference is, thus, 1956 m over a length of 225 km.

1124 mm mean annual precipitation in Oberndorf/Laufen (Fkm 47,5) no glaciers

The concerned river section – called Untere Salzach – reaches from the Saalach river mouth (km 59,3) to the mouth into the Inn. This section can be divided into 2 basins (Freilassing Basin, Tittmoning Basin) and 2 Narrows

Case Studies 13: BAW-IWB; BOKU

(Laufen Narrow, Nonnreit Narrow). The bed level difference between km 59,3 and km 12,0 is 46,5 m.

Figure 1. Geographical setting 2

Pilot Sites Untere Salzach Drainage area (km²)* 6727,5 Location km 59,3 – 12,0 Length of the study reach (km) 59 Active channel width (m) 90-100 Channel slope (m/m) 0,001 Planform morphology straightened river alternate bars * At the monitoring reach Table 1. Main physical features of the pilot site(s)

Case Studies 13: BAW-IWB; BOKU

Figure 2. Fkm 51,9

2. Hydromorphological restoration/management

bed load input 20.000-40.000 m³/a bed load output appr. 100.000 m³/a

Case Studies 13: BAW-IWB; BOKU

Figure 3. Salzach 1817

Figure 4. Salzach 2002

 Originally a braided river  1820 State Treaty for improved flood protection, shipping, land reclamation  reduction of river width to 90 m  beginning erosion process, 5 m within 80 years, currently 4 cm/year  after 1959 construction of bottom sill Lehen, hydro power station Urstein, hydro power station Hallein

Case Studies 13: BAW-IWB; BOKU

Since bed erosion has progressed to such an extent that bank structures as well as bridge piers have become endangered, a couple of interdisciplinary studies were carried out.

Figure 5. riverbed breakthrough

Case Studies 13: BAW-IWB; BOKU

1 m

Graphik: WWA Traunstein

Graphic 1.

 WRS – Wasserwirtschaftliche Rahmenuntersuchung Salzach (1990-2000), interdisciplinary study (river and floodplains, ecology)  GUS – Gesamtuntersuchung Salzach (1991-1997) including a floodplain-concept  RAS – Risikoanalyse Salzach (2003-2004), risk, costs and consequences without restructuring of the river

Restauration measures:  2008-2009 construction of a rip rap-section/revetment (km 46,2) for stabilising the river bed

Case Studies 13: BAW-IWB; BOKU

Figure 6. rip rap-section/revetment

Case Studies 13: BAW-IWB; BOKU

Figure 7. rip rap-section/revetment

Case Studies 13: BAW-IWB; BOKU

Figure 8. step-pool-ramp

 2009-2010 construction of the step-pool-ramp (km 51,9) including an improved connectivity of river and floodplains

Case Studies 13: BAW-IWB; BOKU

Figure 9. Restauration measures

Case Studies 13: BAW-IWB; BOKU

see also online data storage of HyMoCARES\WPC\Pictures

3. Monitoring activities

11 currently no monitoring activities are planned, since there already exist a lot of long term data on gravel, bed levels, bed load transport, etc.