Surface Water and Drainage (Leaving Cert Construction Studies): Revision Notes
Surface water and drainage
Introduction
Understanding the difference between surface water and wastewater is essential for proper site management. Surface water comes from rainfall, whilst wastewater originates from household use. Both types of water require different handling approaches.
Site owners have legal responsibility for managing all water on their property. Rainwater and surface water must be directed to appropriate soaking areas, whilst household wastewater needs connection to sewerage systems or septic tanks.
Surface water management
Surface water refers to rainwater that collects on and around buildings. The main collection points are rooftops and paved surfaces where precipitation gathers.
Urban development has made surface water management increasingly challenging. When buildings cover natural land, the ground absorbs less water than it would naturally. This reduction in absorption capacity increases the total volume of surface water that requires management.
The two primary areas where surface water accumulates are:
- Building roofs
- Paved areas surrounding properties
Guttering systems
Purpose and installation
Guttering collects rainwater from roof edges and channels it away from buildings. Proper installation requires positioning gutters as close to roof edges as possible, allowing roofing felt to extend slightly into the channel.
The roof edge must not extend beyond the gutter's centreline. If positioned incorrectly, water will overshoot the gutter and spill onto surrounding ground areas.
Installation requirements
Guttering can be installed either level or with a slight downward slope. Adding a gentle fall helps reduce silt accumulation and enables the system to handle larger roof areas effectively.
Regular cleaning maintains proper function and prevents blockages that could cause system failure.
System components
Brackets and fixings:
- Fascia brackets attach to the building's fascia board and hold guttering in position
- Union brackets join separate gutter sections together
- Angle brackets change the guttering's direction around building corners
- Stop ends prevent water spillage from gutter terminals
Downpipes and connections:
- Downpipes carry water vertically from gutters to ground-level drainage
- Offset bends connect downpipes to guttering systems
- Pipe brackets secure downpipes to exterior walls
- Rainwater shoes can divert water away from foundations
- Adaptors extend pipes to drainage channels when required
Soak pits
Soak pits are underground chambers designed for rainwater collection and gradual drainage. These structures are typically positioned downslope from buildings to utilise natural water flow.
Construction
Soak pits consist of large holes or precast concrete chambers filled with stone materials. The stone filling serves two purposes:
- Collects incoming rainwater
- Allows slow, controlled drainage into surrounding soil
Access covers enable inspection and maintenance of the system. The surrounding area uses hard stone materials sized between 100-150mm for optimal drainage performance.
Paved area drainage
Surface water from paved areas requires systematic removal to prevent accumulation and potential property damage.
Urban vs rural approaches
In cities and large towns, surface water connects directly to drainage channels for rapid removal. However, rural areas cannot access these centralised systems and must use alternative approaches.
French drain systems
Rural properties typically employ soakaway pits for paved area drainage. Two main methods achieve this:
Trench systems: Dig trenches that direct water away from buildings towards soakaway areas.
Perforated pipe systems: Install sloped, perforated pipes underground. The pipe gradient ensures water flows efficiently to soakaway pits whilst allowing gradual soil infiltration along the route.
These systems are often called French drains and provide effective surface water management for properties without access to municipal drainage networks.
Water reuse options
Surface water collection can be redirected to rainwater harvesting systems rather than disposal, providing sustainable water management alternatives.
Drainage system basics
Drainage describes the pipework network that removes wastewater from residential properties. This wastewater flows to either mains sewerage systems or private septic tanks.
Types of wastewater
Wastewater: Contaminated water from sinks, showers, dishwashers, and washing machines. This water contains chemicals, food particles, and other waste products.
Soil water: Water specifically from toilets, channelled directly to sewers or septic tanks.
Foul water: Combined wastewater and soil water mixture, directed to sewers or septic tanks.
System requirements
Effective drainage systems must meet several critical requirements:
Access provision: All pipework must remain accessible for maintenance and repairs.
Leak prevention: Pipes and fittings require sound construction to prevent both inward and outward leaking. Underground pipe gaps allow root penetration and debris accumulation.
Solid prevention: Systems must prevent solid material build-up that could block pipework.
Corrosion resistance: Materials must withstand chemical damage from transported waste and external environmental factors.
Correct gradient: Proper slope ensures efficient flow. Excessive steepness causes liquids to flow too quickly, leaving solids behind. Insufficient gradient prevents effective waste transport.
Domestic drainage divides into above-ground and below-ground systems. Above-ground drainage includes all visible pipework associated with the dwelling, whilst below-ground drainage refers to underground installation.
Key Points to Remember:
- Surface water comes from rainfall whilst wastewater originates from household use - each requires different disposal methods
- Guttering must be positioned close to roof edges with proper gradient to collect rainwater effectively
- Soak pits use stone-filled chambers to collect and gradually drain surface water into surrounding soil
- Rural areas need French drains with perforated pipes leading to soakaways for paved area drainage
- Drainage systems require proper access, leak prevention, correct gradient, and corrosion resistance to function effectively