Stormwater Management with EPDM Membrane
Control urban flooding and comply with RJUE and the Water Framework Directive with retention basins, bioswales and SuDS systems waterproofed with EPDM — 50-year service life, root resistance certified to EN 13948, and Membriko's 20-year warranty.
The Urban Flooding Challenge in Portugal
Portugal has a difficult relationship with rain: long dry summers, compacted and sealed soils, then intense and concentrated autumn and winter precipitation at a rate that the land and drainage networks cannot absorb. The consequences are visible and growing — flooding in Lisbon, Setúbal, Évora and dozens of medium-sized cities during extreme rainfall events, with erosion, watercourse contamination and aquifer degradation. Climate change intensifies this trend, with extreme precipitation events becoming increasingly frequent.
- Intense rainfall events (T=10-25 years) cause urban flooding with growing economic and public health damage
- Drainage networks sized for historical rainfall are structurally insufficient for 21st-century extreme events
- Unmanaged runoff carries hydrocarbons, heavy metals and suspended solids to watercourses and coast
- European (WFD) and national regulations (RJUE, PDM) impose peak flow limits on new developments — limitation to pre-urbanisation flow
- Concrete retention basins crack with differential embankment settlement; compacted clay desiccates in Alentejo summers; rigid HDPE does not follow settlement
- Stormwater runoff from car parks carries oils and fuels that contaminate sensitive aquifers in recharge zones
The EPDM Solution for Stormwater Management
Retention basins, bioswales and SuDS systems waterproofed with EPDM membrane are the reference solution for stormwater management in Portugal. EPDM membrane ensures total watertightness (EN 1928 — 60 kPa), accommodates embankment settlement with 400% elongation, withstands Portuguese summer desiccation without cracking, is biologically inert for aquatic ecosystems, and has root resistance certified to EN 13948/FLL. Membriko installs EPDM in retention basins for road infrastructure, business parks, residential developments and constructed wetlands across Portugal.
- Total certified watertightness (EN 1928) — basin retains 100% of volume without controlled infiltration
- 400% elongation accommodates embankment settlement of 50-100 mm in early years without creating leaks
- Certified root resistance (EN 13948/FLL) — bioswales with vegetation function for 50 years without puncture
- Total ecological compatibility — zero toxins for aquatic and riparian ecosystems
- Chemical compatibility with urban runoff: hydrocarbons, heavy metals, pH 2-12
- Eligible for RJUE licensing conditions and Infraestruturas de Portugal technical specifications for road basins
EPDM Benefits
Total Watertightness — 100% Retention
EPDM membrane of 1.0-1.5 mm withstands 60 kPa hydrostatic pressure (EN 1928) — equivalent to a 6-metre water column. Typical retention basins have depths of 0.5 to 3 m. Watertightness is the primary membrane function and EPDM guarantees it for 50 years without intervention.
RJUE and WFD Compliance
Stormwater management systems with EPDM comply with RJUE (Urban Planning and Building Legal Framework) requirements, municipal drainage regulations and Water Framework Directive obligations for peak flow limitation to pre-urbanisation values. Membriko provides complete technical documentation for licensing processes.
Aquifer and Riparian Ecosystem Protection
In areas with contaminated soils, sensitive aquifers or proximity to protected watercourses (Natura 2000 Network), EPDM basin waterproofing prevents contaminated urban runoff from infiltrating the water table. EPDM is biologically inert — zero toxins for aquatic flora and fauna.
Economically Viable Alternative to Drainage Network Upgrades
An EPDM retention basin can replace public drainage network capacity increases at much lower cost. For a 5 ha residential development, the required retention basin (500-1,500 m³) costs €30,000-80,000 — a fraction of the cost of enlarging municipal sewers.
Landscape Integration in Parks and Gardens
EPDM basins integrate into green spaces, parks and recreational areas — functional for stormwater management but appearing as a natural garden or wetland. The black membrane is completely invisible under vegetation and substrate.
Stormwater Reuse
Retained water can be pumped for use in irrigation of green spaces, surface washing and other non-potable uses, turning stormwater management into a reusable water source. EPDM preserves the quality of retained water without contamination.
Technical Specifications
Thickness — bioswale and SuDS systems
1.0 mm
Thickness — retention and detention basins
1.0 mm to 1.5 mm
Hydrostatic watertightness (EN 1928)
Passed at 60 kPa — 6 m column
Elongation at break (EN 12311-2)
≥ 400%
Tensile strength (EN 12311-2)
≥ 9 N/mm²
Puncture resistance (EN 12691)
≥ 200 N
Root resistance
Certified EN 13948 / FLL
UV resistance (EN ISO 4892-3)
No cracking at 2,000 hours
Compatible pH range
pH 2 to 12 (urban runoff)
Hydrocarbon resistance
Good — up to ~500 ppm typical runoff
Service temperature
-45°C to +130°C
Vegetation substrate compatibility
Excellent — biologically inert
Product standard
EN 13956
CE marking
Yes
Membriko warranty
20 years on installation
Installation Process
- 1
Hydrological Design and Basin Sizing
Hydrological calculation of peak flows for return periods of 10, 25 and 100 years (rational method or SCS-CN). Sizing of required retention volume to limit outflow to the pre-urbanisation flow rate. Design of calibrated discharge structure (orifice + safety flood spillway). Regulatory verification against RJUE and municipal PDM.
- 2
Excavation and Topographic Shaping
Excavation and topographic shaping of basin per execution design. Bank and base compaction in 200 mm layers at optimum moisture content. Stable slopes at ≤ 1:2 (V:H) gradient. Perimeter access and maintenance platform above maximum storage level.
- 3
Lower Protective Geotextile Installation
Installation of 300 g/m² non-woven polypropylene geotextile over all compacted substrate. Geotextile protects the EPDM membrane from residual aggregates in the soil and from roots growing from natural ground. Verification that the geotextile surface is free of stones, debris and irregularities before the membrane.
- 4
EPDM Membrane Installation
EPDM panels unrolled with minimum possible seams — 15.25 m wide panels cover most Portuguese basins with few seams. Seams executed with QuickSeam system with 300 mm overlap. Perimeter anchoring in 300 mm × 300 mm compacted trench. Full inspection of installed surface before upper geotextile.
- 5
Upper Protective Geotextile Installation
Installation of 200 g/m² non-woven geotextile over EPDM membrane for protection during rapid filling with sediment transport. Upper geotextile distributes sediment load and impacts over the membrane. In dry detention basins with prolonged UV exposure, light-coloured geotextile to reflect solar radiation.
- 6
Controlled Discharge Structure
Installation of calibrated discharge orifice for the pre-urbanisation flow and surface spillway for the safety flood (T=100 years). Sealing of membrane penetrations with certified EPDM accessories and adhesive. Membrane protection at discharge structure with stainless steel plate or concrete headwall.
- 7
Stormwater Inlet Integration
Connection of urban runoff collectors to basin with EPDM transitions at membrane penetrations. For high-velocity inlets, membrane protection with stone riprap or gabion mattress over EPDM in the energy dissipation zone. Hydraulic verification that arrival velocities do not damage the membrane.
- 8
Landscape Integration and Final Verification
Substrate and vegetation placement on basin banks above the maximum flood line. For basins with permanent pool: introduction of aquatic plants and macrophytes for biological treatment and algae control. For dry detention basins: grass seeding on banks. Test filling and discharge structure verification. Photographic record for licensing process.
Installation Techniques
Retention Basin with Permanent Pool
Basin with permanent water level up to the discharge structure level. Above this level there is flood storage volume used during and after precipitation events. EPDM membrane covers the entire basin surface — the permanently submerged zone and the flood storage zone periodically exposed to air and UV. Recommended for business parks, quality residential developments and urban infrastructure where landscape value is important.
Vantagens
- Very attractive landscape appearance — integrable in parks and gardens as natural lake
- Permanent pool supports aquatic biodiversity (birds, amphibians, macrophytes)
- Aquatic macrophytes improve water quality through natural biological treatment
- Lower colonisation by invasive vegetation than dry basin — permanent level creates specific conditions
- Flood storage volume always available in zone above permanent level
Desvantagens
- Ongoing permanent pool water quality management — algae and macrophyte control
- Slightly higher installation cost from greater excavated volume
- Risk of eutrophication in basins receiving runoff from agricultural areas with nutrients
Dry Detention Basin
Basin that retains water only during and after precipitation events, remaining dry between events. The entire basin surface is covered by EPDM and exposed to UV when dry. EPDM's native UV resistance is critical in this application — the material withstands surface temperatures of 60-80°C in Portuguese summers without degradation. Recommended for road infrastructure, car parks and industrial zones where permanent pool management is not appropriate.
Vantagens
- Lower management cost — no permanent pool to monitor
- Can be integrated in normal green space with grass seeding on banks
- Simpler to size and licence than basin with permanent pool
- No risk of eutrophication or mosquito breeding
- Natively UV-resistant EPDM withstands decades of sun exposure without degradation
Desvantagens
- Less attractive appearance when dry — apparently empty basin
- Can be colonised by invasive vegetation in the wetted zone if not managed
- Prolonged UV exposure requires EPDM with 2,000-hour UV certification (EN ISO 4892-3)
Bioswale (Biofiltration Channel) with EPDM
Vegetated channel that slows, treats and infiltrates stormwater as it flows from impermeable surface to the receiving watercourse. EPDM membrane waterproofs the base of the channel when soil permeability is inadequate for natural infiltration or when outlet flow must be controlled. Vegetation (Phragmites, Carex, Iris pseudacorus, riparian grasses) filters solids and biologically treats hydrocarbons and heavy metals.
Vantagens
- Biological treatment of urban pollutants — hydrocarbons, heavy metals, nitrogen, phosphorus
- Completely natural appearance — vegetated channel integrated into the landscape
- Certified root resistance (EN 13948) — 50-year vegetation does not puncture EPDM
- Lower construction cost than retention basin for equivalent volumes
- Compatible with WFD runoff treatment requirements
Desvantagens
- Lower storage capacity per linear metre than retention basin
- Requires sufficient linear area — not suitable for very constrained sites
- Vegetation maintenance required (annual cutting, invasive species removal)
Comparison with Other Membranes
| Característica | EPDM | Earth basin with bentonite | Reinforced concrete basin | HDPE geomembrane basin |
|---|---|---|---|---|
| Watertightness and guaranteed retention | 100% — no infiltration (EN 1928, 60 kPa) | 80-95% — desiccates and cracks in Alentejo summers | 90-99% — joints crack in 15-25 years | 99% — good but thermofusion seams are brittle |
| Adaptation to embankment settlement | Excellent — 400% elongation, 50+ years | Good — but prolonged drought desiccation is irreversible | None — cracking from 5-10 mm settlement | Poor — rigid, permanent folds |
| Ecological compatibility (WFD) | Total — zero toxins, EN 13948 | Good — natural, but can increase turbidity | Acceptable — but alkalinises contact water | Acceptable — but residual plasticisers possible |
| UV resistance (dry detention basins) | Native — no degradation in 50 years | N/A — no UV-exposed surface | Good — concrete resists UV but cracks thermally | Poor — HDPE requires additional UV protection |
| Root resistance (bioswales) | Certified EN 13948 / FLL | Poor — roots penetrate compacted clay | Good — roots enter through cracks | Acceptable — but no EN 13948 certification |
| Repair without emptying | Yes — underwater patch possible | Limited — dry bentonite addition only | No — requires emptying and structural repair | Limited — thermofusion welding in situ |
Performance in the Portuguese Climate
Lisbon, Setúbal and Greater Metropolitan Area — Intense Rainfall on Sealed Soil
Greater Lisbon has the highest density of sealed surfaces in the country and faces recurrent flooding in rainfall events exceeding 30 mm/hour. New Lisbon PDM licensing requires retention of 100% of pre-urbanisation runoff. EPDM basins in new condominiums and business parks on the south bank of the Tagus are an increasingly mandatory regulatory requirement.
Porto and North — Extreme Rainfall Events and Saturated Soil
The humid North combines high annual rainfall (>1,000 mm) with extreme autumn and winter events (>50 mm in 24 hours). Saturated soils after dry summer have very low infiltration capacity, worsening flood peaks. EPDM bioswales in Greater Porto business and industrial parks are technically required by municipal PDMs.
Alentejo and Algarve — Concentrated Precipitation on Dry Soil
Southern Portugal combines the lowest average rainfall with the greatest peak intensity — 40-80 mm rains in 1-2 hours after months of drought. Dry, compacted soils with near-zero infiltration capacity create quasi-total runoff during these events. Dry detention basins with EPDM are the solution: native UV resistance withstands 2,800+ sun-hour summers without degradation.
Interior and Embankment Zones — High Differential Settlement
Retention basins in recent embankment zones (motorway embankments, logistics platforms) undergo 50-100 mm settlement in the first 5 years. EPDM's 400% elongation absorbs this settlement without leaks — impossible with concrete (10 mm settlement cracks concrete) or rigid HDPE (permanent folds creating pores).
Industrial Zones and Car Parks — Aquifer Protection
Retention basins for car park and industrial zone runoff concentrate hydrocarbons, heavy metals and microplastics. EPDM membrane prevents infiltration of these pollutants into the aquifer. EPDM has good resistance to hydrocarbons at typical runoff concentrations (up to 500 ppm) — superior to bentonite which degrades under prolonged hydrocarbon contact.
Frequently Asked Questions
Yes. Basins waterproofed with EPDM guarantee the runoff coefficient and outlet flow required by the RJUE (Urban Planning and Building Legal Framework) and municipal drainage regulations. The certified watertightness of EPDM membrane (EN 1928, 60 kPa) guarantees the required hydrological control. Membriko provides complete technical documentation — descriptive report, hydrological calculation note, material datasheet and CE certificates — for municipal licensing processes.
Yes, with verification of typical concentrations. EPDM has good resistance to aliphatic hydrocarbons (diesel, petrol) at typical urban runoff concentrations, which rarely exceed 100-500 ppm in diluted car park runoff. For basins receiving undiluted accidental fuel spills (filling stations, fuel warehouses), we recommend a specific compatibility test and potentially specifying thicker EPDM (2.0 mm).
Yes — with the correct EPDM. Membriko exclusively uses EPDM certified for root resistance to EN 13948 (European standard) and FLL (German green roof standard). These tests subject the membrane to accelerated root growth conditions for 2 years, proving that Phragmites, Typha, Salix and other riparian species roots do not penetrate the membrane. This certification is not optional in bioswales — it is the difference between a membrane that lasts 50 years and one punctured in 8-10 years.
Yes. EPDM has native UV resistance — built into the molecular composition of the elastomer and not dependent on additives that deplete. UV accelerated aging test at 2,000 hours (EN ISO 4892-3) without cracking confirms that EPDM does not degrade even under intense solar exposure. In Portuguese summers, membrane surface temperatures reach 60-80°C — within the EPDM service temperature range (-45°C to +130°C). Membriko's EPDM has this test certified as standard.
For a 5 ha residential development in Lisbon with 60% impermeabilisation and peak flow limited to pre-urbanisation flow (C=0.2 for T=10 years), the required retention volume is typically 800-1,500 m³ depending on design rainfall, terrain slope and hydraulic capacity of the outlet system. This volume corresponds to a basin of 30-60 m length by 20-30 m width with maximum depth of 1.5-2.5 m. Membriko sizes and installs basins of this scale with a specialist team.
For small damage below the permanent water level (up to 50 mm diameter), underwater repair is possible with an EPDM patch and underwater-cure adhesive — without emptying. For larger damage, partial emptying (lowering the level 50-100 cm below the damage) is sufficient in most cases. For dry detention basins, waiting for the next dry period. In all cases, repair is localised and permanent — unlike concrete which requires disruptive structural repair.
Yes. EPDM membrane with CE marking (EN 13956) is accepted in the technical specifications of Infraestruturas de Portugal (IP) for geomembranes in road retention basins. It is also accepted in municipal infrastructure tender documents for stormwater basins. Regarding funding, stormwater management systems are eligible for PT2030 funds (climate change adaptation component) and for municipal water infrastructure financing. Membriko provides technical eligibility documentation and specifications for European fund application processes.
The controlled discharge structure is a hydraulic element sized independently of the membrane but critical to basin function. It includes: (1) calibrated bottom discharge orifice for the pre-urbanisation flow (Q_out = C_pre × i × A), (2) safety flood spillway sized for the T=100 year flood without storage, and (3) debris protection grating. Membriko collaborates with the hydraulics designer to ensure compatibility between EPDM membrane penetrations and the hydraulic devices of the discharge structure.
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