Calculator Inputs
Example Data Table
| Scenario | Wave Height (m) | Storm Surge (m) | Slope (deg) | Grain Size (mm) | Dune Height (m) | Vegetation (%) | Historic Erosion (m/year) |
|---|---|---|---|---|---|---|---|
| Calm Reach | 1.20 | 0.60 | 9.0 | 0.80 | 5.00 | 70 | 0.40 |
| Managed Shoreline | 2.40 | 1.30 | 6.0 | 0.40 | 3.50 | 35 | 1.20 |
| Storm Exposed Reach | 4.60 | 2.20 | 3.5 | 0.22 | 1.80 | 10 | 2.80 |
Formula Used
This tool uses a weighted logistic risk model. Each coastal driver is normalized, weighted, and added into one erosion score.
Step 1: Normalize each input into a comparable risk factor.
Step 2: Combine weighted factors into the logistic score.
z = -3.2 + Σ(weight × normalized factor)
Step 3: Convert that score into probability.
Annual Probability = 100 / (1 + e^-z)
Step 4: Extend annual probability across the selected horizon.
Horizon Probability = 1 - (1 - Annual Probability)^Years
Step 5: Estimate retreat from historic erosion and forcing multipliers.
The method is useful for screening, scenario testing, and early engineering review. It is not a replacement for site calibration or full morphodynamic modelling.
How to Use This Calculator
- Enter measured or assumed coastal conditions in every field.
- Use local survey, storm, and shoreline monitoring data where possible.
- Set the analysis horizon to match your planning period.
- Click the calculate button to view probability, retreat, and driver shares.
- Review which drivers dominate the result.
- Test alternative protection, dune, or vegetation scenarios.
- Download the result as CSV or PDF for reporting.
- Use the output as a screening tool before detailed design work.
Beach Erosion Probability in Coastal Engineering
Overview
Beach erosion changes the width, elevation, and stability of a shoreline. A probability calculator helps coastal engineers turn field observations into a clearer risk signal. It combines wave climate, storm surge, sediment size, dune protection, and historic retreat trends. The result is not a guarantee. It is a planning indicator that supports better coastal decisions.
Why Erosion Probability Matters
A beach can look stable during calm months and still fail during one energetic season. High waves move sediment offshore. Storm surge raises water levels and lets waves attack dunes. Sparse vegetation reduces resistance. Weak structures also lower shoreline resilience. Estimating probability helps teams compare sites, rank projects, and justify mitigation budgets.
Inputs That Shape Shoreline Risk
Wave height represents offshore energy reaching the beach. Storm surge describes temporary water level rise during severe weather. Beach slope affects runup and swash response. Grain size reflects how easily sediment moves. Dune crest height adds natural storage and protection. Vegetation cover helps bind surface material. Historic erosion rate anchors the model in local evidence. Storm days per year capture repeated loading. Sea level rise adds chronic pressure. Protection efficiency accounts for seawalls, revetments, or nourished sections.
Reading the Results
The annual probability shows the chance of meaningful erosion under the supplied conditions. The horizon probability expands that risk over several years. The risk index simplifies the weighted drivers into a single percentage. Estimated retreat shows how far the shoreline may move landward if present conditions persist. Driver shares reveal which factors deserve attention first.
Using the Calculator in Engineering Work
Use the tool during concept design, monitoring reviews, or adaptation planning. Test several scenarios instead of one. Compare a present-day case with stormier or higher water conditions. Then adjust dunes, vegetation, nourishment, or structure performance to see how risk changes. This supports resilient design, maintenance scheduling, and clearer communication with coastal stakeholders.
Limits and Good Practice
This calculator is a screening tool. It does not replace detailed morphodynamic modeling, survey control, sediment transport studies, or calibrated local datasets. Always pair results with beach profiles, aerial history, design water levels, and professional judgment. Better input quality improves confidence and project value.
FAQs
1. What does the probability result mean?
It estimates the likelihood of meaningful beach erosion under the entered conditions. It helps compare scenarios and prioritize coastal engineering attention.
2. Is this a replacement for detailed coastal modelling?
No. It is a screening calculator. Detailed design still needs site surveys, sediment studies, hydraulic modelling, and local calibration.
3. Why does vegetation reduce erosion probability?
Vegetation can trap sediment, reduce surface mobility, and strengthen upper beach or dune areas. Better cover generally improves shoreline resistance.
4. Why is grain size included?
Finer sediment usually moves more easily under waves and currents. Coarser grains often provide better resistance to erosion and transport.
5. What should I enter for protection efficiency?
Enter an estimated percentage showing how much existing seawalls, revetments, nourishment, or other works reduce erosion exposure at the site.
6. Can I use projected sea level rise values?
Yes. Scenario testing is useful. You can compare present conditions with higher future sea level rise assumptions for adaptation planning.
7. Why does the horizon probability exceed annual probability?
Because repeated yearly exposure increases cumulative chance over time. A moderate annual risk can become significant across several years.
8. What is the best way to improve result quality?
Use recent surveys, local storm records, shoreline change history, and realistic protection estimates. Better inputs usually produce more useful engineering screening outputs.