WORKSHOP #2 [Modeling and Sediment Transfers Review of alternative solutions] Bucharest 07 October 2015

Transcription

1 STUDIU DE FEZABILITATE PENTRU SOLUŢII TEHNICE ALTERNATIVE/COMPLEMENTARE PRIVIND LUCRĂRILE CE SE VOR EXECUTA ÎN PUNCTUL CRITIC 01 BALA DIN CADRUL PROIECTULUI ÎMBUNĂTĂŢIREA CONDIŢIILOR DE NAVIGAŢIE PE DUNĂRE ÎNTRE CĂLĂRAŞI ŞI BRĂILA, KM 375 KM 175 WORKSHOP #2 [Modeling and Sediment Transfers Review of alternative solutions] Bucharest 1

2 Chapter A Project objectives & requirements 1. AFDJ 2. NGOs 2

3 A1. AFDJ A I xxxx P1: Ensure navigation on Old Danube (MWD = 2.5 m) all over the year P2: Preserve river eco-system, including in particular sturgeons migration P3: Reduce maintenance costs (e.g. dredging) by ensuring sediment continuity in the long run P4: Ensure navigation on Bala branch (MWD = 2.5 m), as a safety alternative to Old Danube fairway 3

4 A2. NGOs A I xxxx N1: No disruption of fish migration (e.g. sturgeons) N2: No destruction of sturgeons habitats N3: Preservation of ground water level in floodplain downstream of Bala branch sill N4: Evaluation of sediment dynamics by modelling predictions 4

5 Chapter B Technical solutions reviewed by the work group 1. Alternatives 1 to 8 5

6 B1. Alternative 1: main features Source: IAD (2013) 6

7 B1. Alternative 1: main features No bottom sill at Bala branch inlet Diversion structures on left bank U/S Bala bifurcation (groynes, chevrons and possibly guiding walls) Complementary maintenance dredging works Construction (eventually) of sturgeon passage across Turcescu Island tip Source: IAD (2013) 7

8 B1. Alternative 1: remarks Longitudinal connectivity restauration is the main concern Solution based on upstream flow diversion (dynamic effects) No direct action on initial cause of Bala branch incision questionable efficiency regarding bed-incision control Bala inlet narrowing = obstacle to navigation Source: IAD (2013) 8

9 B1. Alternative 1: analysis Analysis regarding the objectives of the project: Extra roughness on the guiding wall: reduction of Bala inlet P1 attractiveness? Hypothesis: no more incision in Bala inlet P2 Maintain of longitudinal connectivity on Bala branch (N1) (N2) Fish passage through Turcescu Island: restauration of fluvial appendices? Fish passage efficiency has to be established? Poaching concern with the fish passage Dredging to maintain the solution P3 Hypothesis: stopping of incision in Bala branch and restauration of the? channel downstream Old Danube P4 Chevrons upstream Bala inlet N3 Maintain of longitudinal connectivity on Bala branch [?] to be evaluated 9

10 B2. Alternative 2: main features Source/ WWF (2014) 10

11 B2. Alternative 2: main features Redesign of diversion (bifurcation angle, low-water breach ) Deflection of thalweg toward Old Danube using groynes, bed shift (by dredging?) and chevrons Additional large bypass for ecological continuity (2 locations suggested Source/ WWF (2014) Local reduction of fairway width in Old Danube for reducing maintenance costs by dredging 11

12 B2. Alternative 2: remarks Solution based on upstream flow diversion (dynamic effects) No direct action on initial cause of Bala branch incision questionable efficiency regarding bed-incision control Increase of sediment flow towards Bala branch is supported both by the low-water breach and by the change in bifurcation angle Low-water breach effect is Source/ WWF (2014) questionable due to the velocity increasing possibly induced. Especially on: Fish migration Navigation 12

13 B2. Alternative 2: analysis Analysis regarding the objectives of the project: P1 Bed shift has no impact on upper Old Danube navigation as long as structures on the right side preserve the channel width? The construction phasing has to take into account navigation P2 (N1) (N2)? Longitudinal connectivity on Bala branch Fish passage through Braţul Turcescu: restauration of fluvial appendices? Longer upstream fish passage: efficiency compared with Braţul Turcescu bypass?? Fish passage efficiency has to be established? Poaching concern with the fish passages P3 Yearly dredging reduction by local narrowing of the fairway Additional sediment take at Bala inlet will reduce sediments in the lower Old Danube, but without other action on lower Old Danube, long term sediment deposit may go on P4? Stream concentration by low-water breach, in the entrance turn N3 Maintain of discharge (water and sediment) on Bala branch [?] to be evaluated 13

14 B3. Alternative 3: main features 14

15 B3. Alternative 3: main features Bottom sill with crest at 4.2 mbsc Fish pass for (upward) migration: 4 locations suggested Lock for the Bala branch connection. 15

16 B3. Alternative 3: remarks Based on corrections of current solution No direct action on initial cause of Bala branch incision questionable efficiency regarding bed-incision control Limited feedbacks on fish passage facilities for sturgeons Lock = very complex structure requiring safe foundations 16

17 B3. Alternative 3: analysis Analysis regarding the objectives of the project: P1? Hypothesis: no more incision in Bala inlet, which is very doubtful P2 (N1) (N2) Longitudinal connectivity on Bala branch Fish passage through Braţul Turcescu: restauration of fluvial appendices Fish passage on left Puiu Turcului: restauration of fluvial appendices; additional stream attractiveness thanks to the lock Fish passage across the tip of Turcescu Island may be the shortest fish pass The Serban tunnel is considered not to be feasible (IAD 2014)? Fish passage efficiency has to be established? Poaching concern with the fish passages P3 Without any action on lower Old Danube, long-term sediment deposit should go on New maintenance costs for Bala lock P4 Lock construction before sill crest elevation, in order to maintain navigation as far as possible? External energy is needed for lock operation N3 Maintain of discharge (of water; to be evaluated for sediment) on Bala branch [?] to be evaluated 17

18 B4. Alternative 4: main features 18

19 B4. Alternative 4: main features Lowering of the bottom sill for meeting velocity requirements regarding fish migration Total or partial decommission of guiding wall (optional) to reduce water head at Bala entrance. 19

20 B4. Alternative 4: remarks Longitudinal connectivity restauration is the main concern No direct action on initial cause of Bala branch incision: Questionable efficiency regarding bed-incision control Bala branch predominance regarding water flow is likely to exacerbate As the new guiding wall contributes significantly to Bala bed incision, question of structure removal or adaptation is thus raised 20

21 B4. Alternative 4: analysis Analysis regarding the objectives of the project: P1 The current situation should worsen P2 (N1) (N2) Maintain of longitudinal connectivity on Bala branch Aging worsening on lower Old Danube P3 Without any action on lower Old Danube, long-term sediment deposit should go on P4 Ok for navigation in Bala branch but it might become the main (unique?) route N3 Maintain of longitudinal connectivity on Bala branch [?] to be evaluated 21

22 B5. Alternative 5: main features 22

23 B5. Alternative 5: main features Bottom sill kept in its initial state (crest level at 0.0 mbsc), or at another level to be determined (bed incision prevention), and enhancement of structure foundations. Groyne field on the right side of Old Danube: Notched type with downstream orientation should be favored for preventing sedimentation and vegetation development as well as preserving good biodiversity conditions Total length between m including m long notches and crest level close to annual flow level 23

24 B5. Alternative 5: remarks Incision in Bala branch is counteracted by: Promoting erosion & transport processes in lower Old Danube Bed incision blockage by Bala branch bottom sill. Development of a deep waterway in the vicinity of the groynes Main interests of notched type groynes: Hinder a development of permanent vegetation Prevent extra flooding hazards Enhance biodiversity (compared to classic solutions) 24

25 B5. Alternative 5: analysis Analysis regarding the objectives of the project: P1 Long term solution No navigation restriction is needed during the construction period P2 (N1) (N2)? Longitudinal connectivity on Bala branch Positive impact for habitats over the groyne field, in the long term P3 Long term solution for sediments Dredging costs reduction as soon as the system reaches its morphological equilibrium P4 Close to initial situation N3 Maintain of discharge (water and sediment) on Bala branch [?] to be evaluated 25

26 B6. Alternative 6: main features 26

27 B6. Alternative 6: main features 1/3 Bottom sill in its initial state (crest level at 0.0 mbsc), or at another level to determine Groyne field on the right side of Old Danube (notched type+d/s orientation) 27

28 B6. Alternative 6: main features 2/3 Fish pass to ensure migration (upward passage of sturgeons). Different locations are suggested. Guiding Wall roughness increasing by short perpendicular structures aiming at moving away main flow from GW 28

29 B6. Alternative 6: main features 3/3 Chevron system for Parjoaia rock effect attenuation Chevron in front of Epuraşu inlet for reducing incision nearby existing breach 29

30 B6. Alternative 6: existing examples Source: PLATINA 30

31 B6. Alternative 6: existing examples Source: PLATINA (Pilot Project Witzelsdorf) 31

32 B6. Alternative 6: existing examples Source: PLATINA Restoration measures at the Rhine river Waal branch near Nijmegen. B. Boekhoven, NL,

33 B6. Alternative 6: remarks Incision in Bala branch is counteracted by: Promoting erosion & transport processes in lower Old Danube Bed incision blockage by Bala branch bottom sill. Development of a deep waterway in the vicinity of the groynes Main interests of notched type groynes: Hinder a development of permanent vegetation Prevent extra flooding hazards Enhance biodiversity (compared to classic solutions) Fish upward migration handled by a specific fish pass (alternative to passage through bottom sill) Chevrons should protect against local stream effects than can destabilize the system. Arrangement proposed allows navigation during work phase 33

34 B6. Alternative 6: analysis Analysis regarding the objectives of the project: P1 Long-term solution No navigation restriction is needed during the construction period P2 (N1) (N2) Restauration of longitudinal connectivity on Bala branch by additional fish pass Positive impact for habitats over the groyne field, in the long term? Fish passage efficiency has to be established? Poaching concern with fish passage P3 Long-term solution for sediments Dredging costs reduction as soon as the system reaches its morphological equilibrium P4 Close to initial situation N3 Maintain of discharge (water and sediment) on Bala branch [?] to be evaluated 34

35 B7. Alternative 7: main features 35

36 B7. Alternative 7: main features Elevation of existing bottom sill at Bala branch inlet to redesign so as to divert AMAP discharge toward Lower Old Danube (Bala branch incision prevention) Series of sills in D/S part of Bala branch so as to control channel conveyance (exact number, location and elevation to be optimized). Main constraints are as follows: General slope of Bala branch kept No influence of last sill on Borcea Water depths compliant with navigation Velocity compliant with fish migration Preservation of existing fish (sturgeons) habitats in Bala branch 36

37 B7. Alternative 7: A I Understanding of the river evolution in Critical Point 1 Bala Bala-Borcea branch slope steeper than Old Danube slope meaning: Higher flow velocity Higher exposition to erosion and incision hazards 37

38 B7. Alternative 7: evolution of longitudinal profile after works Current state Alternative 7 38

39 B7. Alternative 7: remarks Corrections of the current solution. No direct action on the initial cause of Bala branch incisio, no guarantee: neither that the incision will stop on Bala nor that Caragheorghe sand bar development will stop River works affect only Bala branch. Sills construction should start from downstream to upstream Higher level downstream sill #1 should limit downstream scour pit development. Additional river works (dykes) might be necessary if the water level raise, upstream of each sill, overtops Bala banks. 39

40 B7. Alternative 7: analysis Analysis regarding the objectives of the project: P1? Hypothesis: no more incision in Bala inlet (should be ok with sill #1 crest level high enough) No navigation restriction is needed during the construction period P2 (N1) (N2) Sills are designed to meet fish migration velocity requirements? Impact of several sills on fish migration has to be evaluated? Impact on habitats has to be evaluated (deep waters are ok for wintering sites) P3? Hypothesis: stopping of incision in Bala branch and restauration of the channel downstream Old Danube (should be ok with sill #1 crest level high enough) P4 Sills are designed to meet water depths requirements for navigation Navigation restriction on Bala branch during the construction period N3 Maintain of discharge (water and sediment) on Bala branch [?] to be evaluated 40

41 B8. Alternative 8 (as a reminder) Source: survey performed in Russia (St Petersburg) in the 1950 s Shifting the mouth of Bala upstream of Parjoaia rock. Execution of a guiding dyke on the left bank of Bala branch. Execution of a dyke in order to block Bala branch and shifting the mouth downstream in the area of Turcescu arm. Removal of Parjoaia rock 41

42 B9. Complementary measures Onboard digital maps regularly updated from bathymetric measurements with multi-beam echo-sounder Quick mini-dredging as soon as a critical situation is locally observed on the fairway Traffic management according to hydrological conditions Adaptation of ship to river and flow characteristics 42

43 B10. Synthesis: solutions favored by consortium Alternative 7 Alternative 6 43