D2.1 - Inventory of NBS methodologies for slow hydrology (surface water retention, groundwater recharge)

The INTERLAYER Project Deliverable D2.4 presents a detailed catalogue of Nature-Based Solutions (NBS) for Slow Hydrology (SH), targeting improved water retention, groundwater recharge, flood/drought resilience, and ecosystem services. Structured into eight key NBS methodologies, the document details technical implementation, benefits, costs, challenges, and monitoring frameworks: Half-Moon Water Harvesting: Semi-circular bunds used in arid regions (e.g., Sahel) to capture rainwater, enhance soil moisture, and stabilize degraded landscapes. Terrace Farming (Beitang System): Ancient Chinese slope management combining irrigation and drainage for soil conservation, adapted to modern agricultural challenges. Continuous Contour Trenches/Keylines: Contour-aligned trenches (India) and landscape-scale water management (Australia/Germany/US) to slow runoff, recharge groundwater, and prevent erosion. Ridge and Furrow Systems: Medieval European agricultural practice to optimize drainage and moisture retention on heavy soils, still visible in preserved landscapes. Artificial Recharge Systems: Techniques like infiltration basins and riverbed gravel systems (e.g., Gabardine Project, Portugal) to enhance groundwater replenishment in semi-arid regions. Wetland Restoration & Floodplain Reconnection: Danube Delta case study demonstrating habitat restoration, flood risk reduction, and socio-economic benefits through reconnecting rivers to floodplains. Soil and Water Bioengineering (SWBE): Vegetation-based erosion control (e.g., vegetated crib walls) to stabilize slopes, improve water retention, and restore degraded ecosystems. Blue-Green Urban Infrastructure: Copenhagen’s St. Kjelds Quarter model integrating green spaces and stormwater management for urban flood resilience and biodiversity. Cross-Cutting Themes: Co-Benefits: Biodiversity enhancement, carbon sequestration, community engagement, and economic opportunities (e.g., eco-tourism). Challenges: Labor-intensive implementation, site-specific adaptability, maintenance requirements, and initial funding barriers. Monitoring: Emphasis on hydrological metrics (infiltration rates, groundwater levels), ecological recovery (vegetation growth, habitat diversity), and stakeholder feedback.