Nimpact Academy - Module 10: Environmental Stability & Scoring

Environmental Stability Assessment

The Environmental Stability Assessment synthesizes vegetation health, water level variability, and terrain characteristics to classify how resilient a shoreline is to environmental changes and water level fluctuations.

Why Stability Matters

Two beaches can have similar current conditions but vastly different stability:

High Stability: Dense vegetation, gradual slopes, consistent vegetation—can withstand storms and droughts
Low Stability: Bare slopes, high NDVI variability, steep terrain—vulnerable to rapid changes

Stability vs. Risk Proxy

Shoreline Risk Proxy: Measures how much the waterline has moved historically
Environmental Stability: Measures how resilient the shoreline ecosystem is to future changes

A beach can have low historical variability (low risk proxy) but also low stability if vegetation is degrading—indicating future problems.

The NDVI Variability Method

Nimpact calculates environmental stability using NDVI temporal variability—how much vegetation health fluctuates over time:

# Environmental Stability Calculation
# Step 1: Analyze 10+ years of NDVI data (2018-2025)
# Filter to growing season only (May-Sep Northern / Nov-Mar Southern)

Collection = Sentinel-2 NDVI images
  - 500m buffer around beach
  - Cloud cover < 20%
  - Growing season months only
  - Minimum 10 images required

# Step 2: Calculate statistics
Mean_NDVI = Average across all images
StdDev_NDVI = Standard deviation across all images

# Step 3: Calculate variability ratio
Variability_Ratio = StdDev_NDVI / Mean_NDVI

# Step 4: Classify stability (lower variability = higher stability)
Ratio < 0.15:  HIGH stability (Score: 90/100)
Ratio 0.15-0.25: GOOD stability (Score: 75/100)
Ratio 0.25-0.35: MODERATE stability (Score: 60/100)
Ratio > 0.35:  LOW stability (Score: 40/100)

Why This Works

Stable Ecosystems have consistent NDVI year-to-year:

Mature forests with deep roots
Wetlands with permanent water
Maintained parks and lawns

Result: Low variability ratio (< 0.15) = High stability

Unstable Ecosystems have fluctuating NDVI:

Drought-stressed vegetation
Disturbed or recently cleared areas
Agricultural land with crop rotation
Invasive species outbreaks

Result: High variability ratio (> 0.35) = Low stability

Real-World Example

McGregor West Lake Beach:

Stability Class: Low

Interpretation: The report indicates low environmental stability, suggesting the shoreline vegetation experiences significant year-to-year variation. For a lake beach, this could result from:

Water level fluctuations exposing/submerging vegetation zones
Seasonal drought stress in this semi-arid region
Agricultural land use in the buffer zone

Implication: Structures near the shoreline should be designed with extra resilience—the natural vegetation buffer may not provide consistent protection.

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Topographic Exposure Summary

The Topographic Exposure section provides a quick summary of the physical landscape characteristics that influence beach stability and hazard exposure.

Key Metrics Summarized

Metric	What It Measures	Risk Thresholds
Mean Slope	Average steepness within 100m of shoreline	> 15% requires geotechnical assessment
Mean Elevation	Average height above sea/lake level	Context-dependent (tidal vs inland)

McGregor West Example:

Mean Slope: 1.15° (≈ 2% grade)
Mean Elevation: 874.72 m

Analysis: This is essentially flat terrain (< 2% slope), which is typical for prairie lake beaches. The 875m elevation is absolute elevation above sea level—not relevant for lake flooding risk, but useful for geographic context.

Slope Interpretation

# Slope Categories
0-5%:    Flat - minimal erosion risk, good building sites
5-10%:   Gentle - stable with vegetation, minor runoff concerns
10-15%:  Moderate - increased erosion risk, drainage management needed
15-25%:  Steep - professional assessment required
> 25%:   Very Steep - high hazard, specialized engineering essential

Lake Beaches: Special Considerations

Why "Topographic Exposure" Differs for Lakes

Ocean/Tidal Beaches: Waves, tides, storm surge create significant exposure and erosion forces

Lake Beaches: Minimal wave energy compared to oceans. Primary exposure factors are:

Water level variability (managed releases, drought, seasonal cycles)
Ice scour (freeze-thaw damage in northern climates)
Fetch distance (wind-driven wave heights depend on lake size)

The report notes: "Lake shorelines experience minimal wave energy compared to coastal environments. Topographic metrics shown for reference only."

Comprehensive Assessment Scoring

The Executive Summary presents four category scores that synthesize multiple observations into single metrics:

                The Four Assessment Categories
                Recreation – Beach usability for swimming, walking, leisure activities
Marine Ecology – Biodiversity and health of marine/aquatic life
Beach Quality – Cleanliness, absence of pollution and litter
Natural Features – Scenic value, unique characteristics

            

Data Source: Community Ground Truth

These scores are derived from crowd-sourced observations collected via the My BeachBook app—they're based on what visitors actually experience, not satellite data.

Why Combine Satellite + Ground Truth?

Satellites excel at: Water quality, temperature, vegetation, development, historical trends

Ground observers excel at: Beach substrate (sand vs rocks), presence of wildlife, litter, aesthetic features

Nimpact integrates both for comprehensive assessment!

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How Category Scores Are Calculated

1. Recreation Score (0-100)

Based on beach substrate quality and walkability:

# Recreation Components (from ground truth observations)
Components measured (0-5 scale each):
  - Sand abundance
  - Pebbles/cobbles (texture)
  - Beach Walk suitability

# Calculation
For each component with data:
  Component_Score = (Observed_Value / 5) × 100

Recreation_Score = Average of all component scores

Example:
  Sand = 3/5 → 60 points
  Beach Walk = 4/5 → 80 points
  Recreation Score = (60 + 80) / 2 = 70/100

McGregor West: Recreation = 60/100 (Good)

This indicates the beach is suitable for recreation but not exceptional—likely has mixed substrate or limited amenities.

2. Marine Ecology Score (0-100)

CRITICAL: This score is water-type dependent:

# Marine Ecology - TIDAL BEACHES ONLY
Components (0-7 scale each):
  - Anemones, Barnacles, Clams, Limpets
  - Mussels, Oysters, Snails, Starfish

Marine_Ecology_Score = Average of observed components

# LAKES AND RIVERS
Marine_Ecology_Score = 0 (cannot support marine life)

Why Lakes Score 0 for Marine Ecology

Marine organisms (barnacles, starfish, sea anemones) require saltwater and tidal cycles—they cannot survive in freshwater.

McGregor West: Marine Ecology = 0/100

This is NOT a quality judgment—it simply reflects that this is a prairie lake, not an ocean. A "0" for marine ecology at a lake beach is correct and expected.

3. Beach Quality Score (0-100)

Primarily based on absence of litter and pollution:

# Beach Quality Calculation
Garbage_Level = Observed value (0-9 scale)
  0 = pristine, 9 = heavily polluted

# Invert the scale (less garbage = higher quality)
Quality_Score = 100 - (Garbage_Level / 9) × 100

Example:
  Garbage = 1/9 (minimal litter)
  Quality = 100 - (1/9 × 100) = 89/100 (Excellent)

McGregor West: Beach Quality = 89/100 (Excellent)

This indicates very low litter—observers reported minimal garbage, suggesting good stewardship or low visitor impact.

4. Natural Features Score (0-100)

Based on scenic and unique characteristics:

# Natural Features Components (0-5 scale each)
  - Islands (visible offshore)
  - Trees (vegetation aesthetic)
  - Lookout points (scenic vistas)
  - Caves (geological features)

Natural_Features_Score = Average of component scores × 20

Example:
  Trees = 1/5 → 20 points
  Others = 0 (absent)
  Natural Features = 20/100

McGregor West: Natural Features = 20/100 (Poor)

The beach lacks notable scenic features—no offshore islands, dramatic terrain, or unique geology. This doesn't mean it's "bad," just unremarkable scenically.

Putting It All Together

Category	McGregor West	Interpretation
Recreation	60 - Good	Functional for swimming/walking but not premium
Marine Ecology	0 - N/A	Freshwater lake—no marine life possible
Beach Quality	89 - Excellent	Very clean, minimal pollution
Natural Features	20 - Poor	Unremarkable scenery, few unique features

                Overall Assessment: McGregor West is a clean, functional beach suitable for casual recreation, but lacks exceptional scenery or unique ecological features. Perfect for a quiet day by the water, not a destination beach for tourists.
            

Page 3 of 3 - Ready for Final Quiz

🎯 Module 10: Environmental Stability & Scoring