What Is the Open Channel Water Surface Backwater Profile Calculator?
Backwater profile computation determines how water depth gradually changes upstream or downstream of a hydraulic control structure.
How Does the Open Channel Water Surface Backwater Profile Calculator Work?
Integrates the 1D energy equation between cross sections, balancing bed slope against boundary friction slope Sf calculated via Manning equation.
Open Channel Water Surface Backwater Profile Calculator Formula & Variables
The core mathematical equation utilized by this calculator is expressed as:
Delta x = rac{E_2 - E_1}{S_0 - ar{S}_f}, quad E = y + rac{V^2}{2 g}, quad S_f = left[ rac{n V}{R_h^{2/3}}
ight]^2
Standard step method energy balance for gradually varied open channel flow.
How to Use the Open Channel Water Surface Backwater Profile Calculator
- Input bed slope S0, Manning n, channel width, discharge Q, and depths at Section 1 and Section 2.
Step-by-Step Example Calculation
River Reach Approaching Dam Spillway (M1 Curve)
Input Values:
channelBedSlopeS0:0.0012
manningsN:0.025
channelWidthM:12
dischargeM3S:30
depthUpstreamY1M:1.8
depthDownstreamY2M:2.3
Worked Steps: Reach distance = 654.2 m, Friction head loss = 0.283 m (Subcritical M1 backwater curve).
Understanding Your Result
Displays reach distance Delta_x in meters, friction head loss, specific energy, and flow regime classification (e.g. M1 backwater curve).
Factors That Affect the Result
- Bed slope S0 and normal depth define the curve type (M1, M2, S1, S2); backwater profiles extend kilometers upstream in mild rivers.
When Should You Use This Calculator?
- Floodplain inundation mapping, sizing bridge piers to prevent backwater flooding, and reservoir pool elevation modeling.
Assumptions & Limitations
- Applies to 1D prismatic rectangular channels under steady gradually varied flow.
Frequently Asked Questions
Calculation Accuracy & Reference Note
Standard open channel hydraulics step method.