Integrated Strategies for River Restoration and Land Re-Naturalization in Urban Areas: A Case Study in Milan, Italy

Abstract

Densely populated areas are frequently affected by floods, risking people's safety and economic activities. In Milan, Italy, the Seveso river crosses the urban area mainly in close conduits frequently flooding. The sprawling of urban areas combined with the intensification of extreme storm events increase the frequency of floods requiring pursuing a new approach on urban water management. The solutions must be sought not only on structural facilities directly on the river with large-scale dimensions: they present expensive construction and operation costs, and only give an apparent sense of security in a short period. It is necessary to identify natural-based strategies for the fluvial territory management taking a comprehensive view on watershed scale, moving from a traditional local and monothematic approach to a global and multisectoral towards water sensitive cities. This research aim is to assess some effects arising from the applications of river restoration and sustainable urban drainage techniques on a stretch of the Seveso river within Parco Nord, in particular through measures of parking de-waterproofing, improvement of river natural expansion and morphology re-naturalization and diversification of riverbanks and riverbed. To assess the effects, a 2D flow simulation using Hec-Ras and the recalculation of the river functionality index have been conducted. The results show benefits not only in raising better water and environmental quality, thanks to the enhancing of river functionality level, but also in risk mitigation, with the reduction of floodable areas, above all significatively for the storm event with a return period lower than 10 years. This research confirms the validity of the new approach and constitutes the first step towards the creation of a practical guide tool for the watershed management with similar characteristics to that of the Seveso river, to reach the European Directives' requests and to build up a strategy for adapting to climate change.

Urban Flood Risk Management: Impact of Combined Strategies

“…The area chosen as the case study is the subcatchment of river Seveso north of Milan, between the CSNO and the culvert inlet in Via Ornato. A previous study was performed by the Authors for this area, on the effects of possible SuDs strategies [1]. In the present paper additional analyses are presented, to broaden the number of possible scenarios of interventions within the scope of the action plan of the Strategic Sub-Basin Project [18].…”

“…In the present paper additional analyses are presented, to broaden the number of possible scenarios of interventions within the scope of the action plan of the Strategic Sub-Basin Project [18]. In [1], the effects related to the renaturalization of the riverbed and riverbanks in some sections, through the recalculation of the river functionality index (IFF) [19], and the hydraulic risk reduction through the creation of floodplain areas in the northern part of the municipality of Milan and in the neighbouring municipalities, were evaluated, following the hypothesis that no other intervention had been carried out upstream of the study area, including between the CSNO and the beginning of culvert in via Ornato in Milan. The hypothesized actions regarded in particular the morphological diversification of riverbed and riverbanks in five river sections through soil bioengineering operations (fascines, wickers, bush wattles, etc.…”

“…), with the planting of shrub species suitable for the riparian environment or through the hydroseeding techniques; the creation of scrapers and the positioning of triangular boulders deflectors in the riverbed; the construction of four ecotonal buffers, of which two adjoining the water course, with a width of not less than 10 meters and a coverage area of 24,000 m 2 ; the creation of three storage areas (areas A and C, 20,000 and 3,500 m 2 respectively, in the municipality of Cormano, the first one on the hydrographic right, the second one on the hydrographic left and area B, 18,000 m 2 , in the municipality of Bresso) and the de-sealing of four car parking areas for a total of 13,000 m 2 . In [1], the recalculation of the IFF index has shown the enhancement of the river ecologic role while the reduction of the floodable areas obtained after the implementation of storage areas on the Seveso river floodplain was addressed with a 16%, 13% and 26% reduction for 10, 100 and 500 years return period respectively compared to the current situation.…”

“…The comparison between scenarios was held by rainfall-runoff and flow river simulations. With respect to the previous scenarios analysed in [1], the parking lots in the municipality of Cormano and Milan were excluded and three more parking lots were added in the municipality of Bresso for a total of about 13,000 m 2 equal to 0.4% of the municipal area. The case study area remains the same but the conditions for calculating the inlet flows have changed.…”

“…River restoration strategies focus on regain ecological value and while preferring on-site management through the adoption of sustainable urban drainage systems (SuDs) promote stormwater source control and load removal. [1][2][3].…”