Hazem et al. (2025) Hybrid storm water management for water conservation in cities nearby surface water streams

Identification

• Journal: Innovative Infrastructure Solutions
• Year: 2025
• Date: 2025-09-08
• Authors: Nahla Hazem, Ayman Mohamed Mostafa, Sherine Ahmed El Baradei
• DOI: 10.1007/s41062-025-02252-y

Research Groups

• Civil Engineering, Cairo University, Giza, Egypt
• Irrigation and Hydraulics Department, Cairo University, Giza, Egypt
• Civil Engineering Program, German University in Cairo, Al Tagamoa, Gamal Abdel Nasser, New Cairo 3, Cairo, Egypt

Short Summary

This study proposes a smart, cost-efficient approach to urban stormwater management by optimizing existing combined sewer networks and utilizing surface runoff pathways. It demonstrates that for large catchments, combined systems are often sufficient, while smaller, denser areas require dedicated surface runoff solutions to prevent overflows and maximize existing infrastructure capacity.

Objective

• To propose a practical, low-cost approach for stormwater management by optimizing existing combined sewer networks and utilizing surface runoff pathways.
• To reduce pressure on sewer pumping stations during winter and maximize the capacity of existing sewer pipes.
• To provide design thresholds and planning strategies based on local numerical modeling applied to Egyptian cities.

Study Configuration

• Spatial Scale: Two distinct urban areas in Egypt: Alexandria (specifically Borg Al Arab region) and Cairo (New Administrative Capital). Catchment areas ranging from less than 20 feddan (approximately 0.084 km²) to over 400 feddan (approximately 1.68 km²), considering various land uses, population densities, and topographies.
• Temporal Scale: Analysis of dry and wet weather flows, considering seasonal variations (winter vs. summer) and daily precipitation values for return periods of 2 and 5 years. Historical rainfall data (e.g., 2016 storm in Cairo) was also referenced.

Methodology and Data

• Models used: A numerical model developed using an Excel spreadsheet to calculate maximum dry weather flow and maximum wet weather flow. The Soil Conservation Service (SCS) method was used for rainfall-runoff calculations. Hydraulic equations were applied to determine flow and ensure compliance with design standards.
• Data sources: Daily precipitation values for Alexandria (based on Awadallah et al. [28]) and Cairo (calculated using the new administrative capital code for sewerage networks). Data inputs included drainage area, population density, land use patterns (roads, buildings, green areas), land slopes (0.03% to 7%), curve numbers (CN) based on USDA 1986 classifications (98 for roads, 94 for buildings, 89 for green areas), and average sewage flow (160 L/d/capita) as per the Egyptian Code for design water and wastewater Networks.

Main Results

• For catchments larger than 100 feddan (approximately 0.42 km²), dry weather flow exceeds wet weather flow by up to 45%, making combined sewerage systems cost-effective.
• In smaller, denser catchments (e.g., less than 190 feddan or approximately 0.798 km² in luxurious areas), wet weather flow can exceed dry weather flow by up to 40%, necessitating design based on maximum wet weather flow.
• Proper grading of roads and streets allows most stormwater to be drained via surface runoff, which can be directed to safe outfalls or detention ponds, reducing pressure on the sewer network.
• The impact of slopes is significant in small catchments, and luxurious areas, with larger road areas, experience higher peak storm flows than domestic flows.
• In Cairo, dry weather flow generally exceeds wet weather flow, except in luxurious cities with drainage areas less than 20 feddan (approximately 0.084 km²), where wet weather flow is larger.

Contributions

• Proposes a novel, cost-effective stormwater management strategy by optimizing existing combined sewer capacity and surface runoff pathways, avoiding expensive pipe expansion.
• Provides practical design thresholds and planning strategies tailored to different catchment sizes and land uses in rapidly urbanizing cities, particularly in arid regions like Egypt.
• Demonstrates that effective stormwater management can be achieved through adaptive planning and strategic utilization of existing infrastructure, rather than solely relying on large-scale new construction.
• Offers valuable insights for urban planners to improve flood resilience and optimize drainage without costly upgrades, by aligning stormwater inflows with seasonal sewage flow variations and integrating surface runoff routes.

Funding

Open access funding provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Citation

@article{Hazem2025Hybrid,
  author = {Hazem, Nahla and Mostafa, Ayman Mohamed and Baradei, Sherine Ahmed El},
  title = {Hybrid storm water management for water conservation in cities nearby surface water streams},
  journal = {Innovative Infrastructure Solutions},
  year = {2025},
  doi = {10.1007/s41062-025-02252-y},
  url = {https://doi.org/10.1007/s41062-025-02252-y}
}