Afflux Calculator - Molesworth Formula | Bridge Engineering

Afflux Calculator

Based on Molesworth Formula for Non-Erodible Stream Beds

h = [ (V² / 17.88) + 0.01524 ] × [ (A/a)² − 1 ]

Where:

• h = Afflux in metres
• V = Velocity in un-obstructed stream (m/s)
• A = Un-obstructed sectional area of river (m²)
• a = Obstructed sectional area of river (m²)

Velocity of Stream, V (m/s) Un-obstructed Sectional Area, A (m²) Obstructed Sectional Area, a (m²)

Result

Calculated value will appear here.

Calculation Procedure

Step 1: Calculate velocity head term:

(V² / 17.88) + 0.01524

Step 2: Calculate obstruction ratio term:

(A/a)² − 1

Step 3: Multiply both terms to obtain afflux:

h = Term 1 × Term 2

Disclaimer:

This calculator is developed for educational and preliminary engineering estimation purposes only. The calculation is based on the Molesworth Formula applicable to streams with non-erodible beds. Actual afflux in field conditions may vary due to factors such as sediment transport, river curvature, turbulence, contraction losses, pier obstruction, scour, seasonal variations, and hydraulic boundary conditions.

The designer/engineer must verify all calculations independently and refer to relevant codes, standards, hydraulic studies, and project-specific requirements before using the results for design or construction purposes.

Reference:
IRC / Hydraulic Design Guidelines – Afflux estimation using Molesworth Formula for bridge waterway calculations.

Developed By: Mohan Dangi