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EPANET Leakage Implementation Summary

Overview​

This document summarizes the implementation of leakage calculations in the EPANET results gathering system based on the FAVAD model specifications provided.

Completed Implementation​

1. EPANET API Constants (EPANET_OWA/include/epanet2_enums.h)​

  • Added EN_LEAK_AREA = 25 to EN_LinkProperty enum
  • Added EN_LEAK_EXPAN = 26 to EN_LinkProperty enum
  • Added EN_LEAKAGEFLOW = 29 to EN_NodeProperty enum

2. C# Wrapper Enums (EpanetWrapper/EpanetEnum.cs)​

  • Added corresponding leakage constants to C# enums:
    • EN_LEAK_AREA = 25 in EN_LinkProperty
    • EN_LEAK_EXPAN = 26 in EN_LinkProperty
    • EN_LEAKAGEFLOW = 29 in EN_NodeProperty

3. EpanetWrapper Methods (EpanetWrapper/EpanetWrapper/)​

  • EpanetWrapperLinks.cs: Added leakage methods for links:

    • GetLinkLeakage(int index) - Gets leakage area
    • GetLinkLeakArea(int index) - Gets leak area property
    • GetLinkLeakExpansion(int index) - Gets leak expansion property
    • SetLinkLeakArea(int index, double value) - Sets leak area
    • SetLinkLeakExpansion(int index, double value) - Sets leak expansion

  • EpanetWrapperNodes.cs: Added leakage method for nodes:

    • GetNodeLeakageFlow(int i) - Gets computed leakage flow at node

4. Model Integration (EpanetWrapper/ENModelReferenceCodeRemoved.cs)​

  • Implemented leakage property retrieval in GetLinkByIndex() method
  • Implemented leakage coefficient retrieval in GetPipeByIndex() method:
    • pipe.LeakArea - Leak area (sq mm per 100 units of pipe length)
    • pipe.LeakExpansion - Leak expansion rate (sq mm per unit of pressure head)

5. Results Builder Integration (NetworkManager/Builders/ResultsBuilder.cs)​

  • PipeHydr Results: Added result.Leakage = wrapper.GetLinkLeakage(pipe.Index)
  • JunctionHydr Results: Added result.LeakageFlow = wrapper.GetNodeLeakageFlow(junc.Index)

FAVAD Model Implementation​

The implementation follows the FAVAD (Fixed and Variable Area Discharge) model:

Formula​

Ql = Cd * Ao * (H^0.5) * (1 + m*H)^0.5

Where:

  • Cd = discharge coefficient (handled by EPANET engine)
  • Ao = area of cracks under zero pressure conditions (EN_LEAK_AREA)
  • H = pressure head (computed by EPANET)
  • m = rate at which crack area expands as pressure increases (EN_LEAK_EXPAN)

Property Definitions​

  • Leak Area (EN_LEAK_AREA): Area of leak openings in square millimeters per 100 units of pipe length
  • Leak Expansion (EN_LEAK_EXPAN): Rate of leak expansion in square millimeters per unit of pressure head (ft or m)
  • Leakage Flow (EN_LEAKAGEFLOW): Computed leakage flow rate at nodes

Required Next Steps​

1. Database Model Updates​

The following model classes need to be updated to include leakage properties:

PipeHydr Model​

public class PipeHydr
{
    // ... existing properties
    public double Leakage { get; set; }  // Leakage flow rate
}

JunctionHydr Model​

public class JunctionHydr
{
    // ... existing properties
    public double LeakageFlow { get; set; }  // Leakage flow at junction
}

Pipe Model​

public class Pipe
{
    // ... existing properties
    public double LeakArea { get; set; }      // Leak area property
    public double LeakExpansion { get; set; } // Leak expansion property
}

2. Database Migration​

Create Entity Framework migration to add leakage columns to database tables:

  • PipeHydrs table: Add Leakage column
  • JunctionHydrs table: Add LeakageFlow column
  • Pipes table: Add LeakArea and LeakExpansion columns

3. EPANET Engine Integration​

The EPANET engine (EPANET_OWA) needs to be updated to:

  • Implement the FAVAD model calculations in the hydraulic solver
  • Store leakage results in the output file
  • Handle leakage property setting and retrieval

4. Input File Support​

Update EPANET input file parser to handle leakage properties in the [PIPES] section:

[PIPES]
;ID    Node1   Node2   Length  Diameter    Roughness    MinorLoss    LeakArea    LeakExpansion
PIPE1  NODE1   NODE2   1000    12          130          0            0.1         0.001

5. Testing and Validation​

  • Test leakage property setting and retrieval
  • Validate FAVAD model calculations
  • Test results gathering and storage
  • Verify database persistence

Usage Example​

Setting Leakage Properties​

// Set leak area for a pipe
wrapper.SetLinkLeakArea(pipeIndex, 0.1); // 0.1 sq mm per 100 units

// Set leak expansion for a pipe
wrapper.SetLinkLeakExpansion(pipeIndex, 0.001); // 0.001 sq mm per unit head

Retrieving Leakage Results​

// Get leakage flow for a pipe
double pipeLeakage = wrapper.GetLinkLeakage(pipeIndex);

// Get leakage flow at a junction
double nodeLeakage = wrapper.GetNodeLeakageFlow(nodeIndex);

// Get leakage properties for a pipe
double leakArea = wrapper.GetLinkLeakArea(pipeIndex);
double leakExpansion = wrapper.GetLinkLeakExpansion(pipeIndex);

Integration Points​

Energy Calculations​

Leakage flows should be included in energy balance calculations:

  • Leakage energy = Ql H Dt where Ql is leakage flow, H is head, Dt is time step

Results Storage​

Leakage results are stored in the same pattern as other hydraulic results:

  • Link leakage stored in PipeHydr.Leakage
  • Node leakage stored in JunctionHydr.LeakageFlow

Notes​

  1. Units: All leakage properties use EPANET's internal units and are converted to user units by the wrapper
  2. Compatibility: This implementation maintains backward compatibility with existing EPANET models
  3. Performance: Leakage calculations are performed by the EPANET engine, not the wrapper
  4. Validation: The FAVAD model implementation follows the specifications provided in the original documentation

Files Modified​

  1. EPANET_OWA/include/epanet2_enums.h - Added leakage constants
  2. EpanetWrapper/EpanetEnum.cs - Added C# enum constants
  3. EpanetWrapper/EpanetWrapper/EpanetWrapperLinks.cs - Added link leakage methods
  4. EpanetWrapper/EpanetWrapper/EpanetWrapperNodes.cs - Added node leakage method
  5. EpanetWrapper/ENModelReferenceCodeRemoved.cs - Implemented leakage property retrieval
  6. NetworkManager/Builders/ResultsBuilder.cs - Added leakage to results gathering

Files Requiring Updates​

  1. Database model classes (EN2Models project)
  2. Database migration scripts
  3. EPANET engine source files (EPANET_OWA/src/)
  4. Input file parser (EPANET_OWA/src/input*.c)
  5. Output file handling (EPANET_OWA/src/outfile/)

Model Support for Leakage​

Nodes - LeakageFlow Support​

✅ Junctions - YES​

  • Physical Reality: Junctions can have leakage from connecting pipes
  • EPANET Support: EN_LEAKAGEFLOW property works for all node types
  • Implementation: Already implemented in JunctionHydr

✅ Tanks - YES​

  • Physical Reality: Tanks can have leakage from walls, connections, or overflow
  • EPANET Support: EN_LEAKAGEFLOW property works for tanks
  • Implementation: Should add to TankHydr

⚠️ Reservoirs - TECHNICALLY YES, but...​

  • Physical Reality: Reservoirs typically have minimal leakage (they're usually large bodies of water)
  • EPANET Support: EN_LEAKAGEFLOW property works for reservoirs
  • Implementation: Could add to ReservoirHydr but may not be meaningful

Links - Leakage Support​

✅ Pipes - YES​

  • Physical Reality: Pipes are the primary source of leakage in water systems
  • EPANET Support: EN_LEAK_AREA and EN_LEAK_EXPAN properties designed for pipes
  • Implementation: Already implemented in PipeHydr

❌ Pumps - NO​

  • Physical Reality: Pumps themselves don't typically leak (they're sealed mechanical devices)
  • EPANET Support: Leakage properties don't apply to pumps
  • Implementation: Don't add to PumpHydr

❌ Valves - NO​

  • Physical Reality: Valves are designed to be leak-tight when closed
  • EPANET Support: Leakage properties don't apply to valves
  • Implementation: Don't add to ValveHydr

High Priority (Essential)​

// Node Results
public class JunctionHydr { public double LeakageFlow { get; set; } }
public class TankHydr { public double LeakageFlow { get; set; } }

// Link Results
public class PipeHydr { public double Leakage { get; set; } }

// Network Definition
public class Pipe {
    public double LeakArea { get; set; }
    public double LeakExpansion { get; set; }
}

Medium Priority (Optional)​

public class ReservoirHydr { public double LeakageFlow { get; set; } }

Don't Implement​

// Don't add leakage to these - not physically meaningful
public class PumpHydr { /* no leakage */ }
public class ValveHydr { /* no leakage */ }

Database Tables to Update​

You'll need to add columns to these database tables:

  1. PipeHydrs table: Add Leakage column (double)
  2. JunctionHydrs table: Add LeakageFlow column (double)
  3. Pipes table: Add LeakArea and LeakExpansion columns (double)
  4. TankHydrs table: Add LeakageFlow column (double) - if implementing tank leakage
  5. ReservoirHydrs table: Add LeakageFlow column (double) - if implementing reservoir leakage

EPANET API Behavior​

The EPANET API treats leakage differently:

  • EN_LEAKAGEFLOW: Available for ALL node types (junctions, tanks, reservoirs)
  • EN_LEAK_AREA and EN_LEAK_EXPAN: Only meaningful for pipes (PIPE and CVPIPE link types)

Summary​

Add LeakageFlow to:

  • JunctionHydr ✅ (already done)
  • TankHydr ✅ (recommended)
  • ReservoirHydr ⚠️ (optional, low priority)

Add Leakage to:

  • PipeHydr ✅ (already done)

Don't add leakage to:

  • PumpHydr ❌ (not physically meaningful)
  • ValveHydr ❌ (not physically meaningful)

The FAVAD model is specifically designed for pipe leakage, which is why the leakage properties only apply to pipes, while the computed leakage flow can be retrieved at any node.

Last updated on by Jake, Cursor