Flood risk management works in the catchment of Cesenatico G.Cassani

Transcription

1 Provincia di Forlì-Cesena Autorità dei Bacini Regionali Romagnoli Provincia di Ravenna Flood risk management works in the catchment of Cesenatico G.Cassani

2 The 6-8 oct 1996 flood Extreme precipitation in the plains of Bologna, Ravenna, Forlì - Cesena & Rimini 1400 Km2 flooded area 500 persons evacuated citizens affected buildings affected. The main sources of floods were not rivers, but the drainage canal network on land originally occupied by agricultural activities, that has witnessed intense urban development during the last decades.

3 aerial picture of the town center of Cesenatico and neighbourhood, october 1996

4 aerial picture of the mouth of the Cesenatico canal, october 1996

5 State of emergency declared by the President of the Ministers Council (11 oct 1996). Plan of priority works for the recovery of hydraulic safety Multi-annual financing scheme. First two phases: urgent action with works for the rehabilitation and fitting of pumping stations, levees and point hydraulic works Third phase : a large scale system of strategic hydraulic works

6 The Cesenatico catchment

7 Protection from sea surge The town centre of Cesenatico suffers from high sea levels Flooding during sea surge is the most frequent cause of flooding and causes high costs Protection from surge has been designed through a system of along-shore levees and the closing of the harbour mouth with sluice gates ( porte vinciane ) The Autorità dei bacini regionali romagnoli has proposed the construction of sluice gates for funding in This was considered a strategic priority for the catchment, and was as such financed by the Minister of the environment.

8 sea surge, november 1999

9 Porte vinciane

10 The Cesenatico catchment is drained by 4 main canals (Canale Allacciamento, Rio Granarolo, Rio Mesola del Montaletto, Canale Vena Madonnina) discharging in the harbour ( Porto Canale ) of Cesenatico. When sea surge blocks discharge through the harbour mouth, it is necessary to let a flow of 190 cms (with a return period of 200 years) be discharged to the sea somewhere else. An alternative is to retain the corresponding flow volume in detention areas for the duration of the surge. A possible solution is to combine the two options: allow a smaller discharge while enabling partial detention. 190 m3/s

11 The Leonardo canal Detention costs land The initial idea was to convey the full 190 cms discharge to a single outlet After considering several alternative design schemes, the local water manager ( Consorzio di bonifica ) proposed the reshaping and resizing of an existing canal, the Canale Tagliata, proudly naming this design Canale Leonardo (Benaglia and Domenichini, 2001) Initial cost estimate: approx 6M Euro; modifications in early design phase to swell costs to 12 M Euro.

12 Stakeholders opposition to the Leonardo Canal People were concerned mainly with: Downcurrent coastal erosion following the extension of the canal mouth piers seawards Encroachment of the beach with a considerably wider mouth than in present conditions (25 m in place of 5 m) Water quality deterioration associated to increased local discharge of runoff with significant diffuse pollution loads, and likely impact on bathing waters (presently, discharge through the harbour mouth ensures adequate dilution)

13 The Autorità di bacino steering committee In , the River basin authority asked dr Alberto Pistocchi to coordinate a steering committee, composed of local water managers, land planners, design engineers and academic experts, in charge for the preparation of a report on the feasible alternatives to the Canale Leonardo

14 The steering committee report Consideration of environmental impacts (also with model simulations) Water quality Erosion Socioeconomic impacts Recommendations: A restriction of the canal mouth requires significant detention volumes Costs of a smaller canal mouth are not significantly reduced Detention volumes difficult to plan (due to competing land uses) and requiring long time for implementation; nevertheless necessary, also for reasons of water quality; The economic value of 20 m of beach subtracted to tourism is relatively low and can be compensated by landscaping/accessory works oriented to tourism fruition (cycling paths, walkways, gardens) Recommended to build the canal as designed, but to integrate it with a system of detention areas to be developed in the mid-term Detention areas to be designed with hydraulic as well as ecological and water treatment functions.

15 feasibility study ( ) Based on the outcomes of the steering committee report and the persisting strong opposition of stakeholders to the enlargement of the canal mouth, the Autorità di bacino launched a comprehensive feasibility study on detention areas coordinated by consultants MED Ingegneria srl, with the aim of reducing the flow in need to be discharged through the Canale Leonardo. The feasibility study identified a large extent of areas for flood detention. With such detention volumes, the discharge to sea can be reduced from 190 to 90 cms. This enables a substantial reduction of the mouth width.

16 Suitable flood detention areas as identified by the feasibility study Valle Felici Fossatone Madonnina Montaletto Granarolo Valle Felici Granarolo Fossatone - areas without land use limitations for flood detention - Volumes sufficient for combined flood detention and phytoremediation Montaletto Madonnina

17 SCENARIO DEFINITIVO SCELTO Flood detention 1. Main areas (flood detention): Valle Felici (111,3 ha), Fossatone (21.6 ha) 2. Smaller areas for phytoremediation: Rio Granarolo Rio della Valle Rio Mesola di Montaletto Rio Vena Madonnina

18 Hydraulic functioning LE AREE DI LAMINAZIONE

19 With such detention volumes, the discharge to sea can be reduced from 190 to 90 cms. IL RISULTATO DELLO STUDIO 90 m 3 /s

20 This enables a substantial reduction of the mouth width. Reshaping of the existing canal according with feasibility study coordinated by consultants MED Ingegneria srl Argine in terreno di riporto Argine in terreno di riporto m s.m.m m s.m.m. P.C.: Variabile Variabile Variabile var. 400 var var. 400 var. 4050

21 the mouth is landscaped for mixed use and is 20 m wide according with feasibility study coordinated by consultants MED Ingegneria srl

22 LE AREE DI LAMINAZIONE Final design of canal mouth, after several studies

23 Work in progress LE AREE DI LAMINAZIONE

24 canal mouth after and before works (rendering)

25 Water quality Example of possible realization of a detention/phytoremediation area

26 Socio-economic implications Areas with few residents, planned for ecological rehabilitation and not for urban development Of little agricultural value and no present tourism potential PRG Cesenatico PTCP Ravenna

27 costs framework Emergency works (for built up areas safety) 1) By pass of Tagliata canal across railway and highway ) Resizing Tagliata canal and his sea mouth ) Sluice-gate on Vena canal ) Empowering Tagliata pumping station and his discharge canal Urgent works 5) flood detention areas Valle Felici 1 and flood detention areas Fossatone dx and sn Completion works 6) Resizing banks and n. 8 bridges ) new path for Madonnina canal towards Venarella pumping station ) Remote control management system ) system of along-shore levees on west end ) phytoremediation areas (n. 4)

28 Outcomes of stakeholders lobbying and advocacy A smaller canal mouth Reduced beach encroachment Shorter piers seawards (less downcurrent erosion) More flood detention and water pretreatment Better control of the quality of bathing waters

29 The work under construction Works are funded by the Civil Protection Agency Design by Brath and Binini A different technical solution for the canal mouth Presently no provision for funding of the flood detention/phytoremediation areas. Increased safety for Cesenatico, but still insufficient for the 200yr design event.