Licca Liber - the free Lech

Licca Liber - the free Lech

Source: W. Schilling WWA Donauwörth

The river Lech an overview Hydrography / Hydrology catchment area 4000 km² Length 256 km Delta H 1100 m Slope Ø 0,4 % discharge in Augsburg with Wertach MQ 114 m³/s HQ100 1600 m³/s Source: wikipedia.org

Cross sections and lateral view

Area of interest Augsburg Gersthofen Lechkanal Staustufe Ellgau Staustufe 23 Gersthofener Wehr Hochablass Thierhaupten Sector 2 (south) Sector 1 (north)

Historical situation and after the correction Lech, heute Lech, 1924

Correction: length reduction 1819 1983 Aims of the correction: Improved flood protection Land gain Reduction of groundwater level Patches against the progressive erosion (Canyon creation): hydraulic structures weirs, ground sill hydro power plants (diversion in Lechkanal north Augsburg) Problem increased: downstream erosions no sediment continuity reduction in ecological variety barriers for the aquatic fauna Source: W. Schilling WWA Donauwörth

Hydro power plant chain from the Forgensee to Augsburg Source: W. Schilling WWA Donauwörth

HPP 23 total sediment trap Source: W. Schilling WWA Donauwörth

Consequences of the Sediment deficit (Wertach) Collapse of the Bobinger bridge Endangering of the Inningen barrage Source: W. Schilling WWA Donauwörth

Sister river: Wertach Erosion to a canyon river Sinking ground water level Source: W. Schilling WWA Donauwörth

Actual situation at the Lech

Visualization of erosion from 1993 to 2010 (south sector)

Volume balance Sector 2

Hydraulic problem at the old hydraulic structures HW99 structure Rip rap Gravel / river bed

And other design problems Source: W. Schilling WWA Donauwörth

Visualization of erosion from 1986 to 2010 (north sector)

Volume balance Sector 1

Bank erosions in the north sector

Different studies from water management office Donauwörth came to same results Lech is a morphological intensive active river (Station 56.7 to Danube) Sediment transport (eroded) 15-20 000m³/a Transport capacity from around 42 000m³ /a Average erosion between 1cm and 3.5 cm per year Local erosions between 1m and 3m in 3 decades Source: W. Schilling WWA Donauwörth

Photos from the Lech south Augsburg At 1908 and today Possible width for restoration and stabilization Source: W. Schilling WWA Donauwörth

Look around for an successful restoration Source: W. Schilling WWA Donauwörth

Widening combined with open armored layer Source: W. Schilling WWA Donauwörth

Source: W. Schilling WWA Donauwörth

Regime - Lech original actual continuative branched No manipulated discharge Natural sediment flux Separated /interrupted habitats restricted Controlled discharge No sediment inflow from upstream future?

Cover layer - armoring?

Grain size distribution (south sector) River bed material Bank material Natural armoring layer

Regime Classification (Zarn) Grain diameter: d m ~ 0,02 m verzweigt slope: 1,0 < I < 2,0 width: 80 m < B < 180 m alternierende Bänke Alternierende Bänke / Mäander Mäander

Can we go back to this regime?

Cross section (regime sustainability?) Formed by flood Natural bank fixation (manipulated hydrograph) -> forced erosion in main channel -> concentrated discharge -> no new sediment from upstream -> cut branches off over widening is no solution

Find a solution Flora - Fauna Protection Morphological Stabilisation Human Morphodynamic sustainability Solution Actual situation

Variation parameter for morphological stabilization Slope Cross section design Roughness Iterative process manipulated hydrograph Flood protection, ground water level

Stabilization concepts slope Cross sectional design Roughness (bed and bank)

Possible stabilization concepts Slope of the river bed I Topography Technical construction I Stability I Stability < I Topography Morphological stability level Technical construction. Weirs, ramps and so on

Possible stabilization concepts Widening Alternierende Bänke Verzweigtes Gewässer

Possible stabilization concepts Open armored rip rap layer I topogr. = I Stability_New I stability, existing Increase erosion defense Existing situation: I stability < I Topography new concept: I stability. = I Topography Width [m] Stone diameter [cm] Number of stones per m² 80 29 6,9 100 26 8,4 120 23 10,5

Stabilization Sector 2 south Augsburg scope Flood area between dikes: 190 250 m width Connect existing lakes to Lech Recreate 1999 bed level (before flood event)

Stabilization Sector 2 south Augsburg Lateral view existing design - 1,1 1,8 Downstream protection of Lechstaustufe 23 2,1 1,6 1,7 1,5 2,264 missing stabilization 2,2

Stabilization Sector 2 south Augsburg Lateral view H L = 3450 m 50% - 75 % of H must be stabilizated

Stabilization Sector 2 south Augsburg H (OK HX ) I (Hochablass Schwelle 6) H Soll 488, 85-489,25 3,0 3,5 2,24-2,13 H 1976 486,76 5,5 1,52 Original design H 1999 486,19 6,1 1,35 H 2010 485,40 6,9 1,13 Av. level 1999 Talweg

Sinking groundwater level? development Sinking rate: ~. 0,65 cm/a Sinking rate: ca. 0,36 cm/a Weir structure 6

Connection of existing lakes to the Lech Ecological connection Improvement of water quality Initialization of a flushing No over-widening Diverted discharge? How much should be diverted from the Lech? How to connect? Technical construction Nature like connection (maybe not perfect controllable)

Weidmannsee level: 501,2 m asl Change in levee positions

Auensee level 493,10 m asl

Kuhsee level: 484,30 m asl

Sediment management Area for sediment compensation Directly downstream Storage reservoir 23

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