# Case Study: Vikos Gorge Cave System Flood Event
## December 2021

---

## 1. Executive Summary

**Location**: Vikos Gorge Cave System, Epirus, Greece
**Passage**: Gamma-7 (main phreatic conduit)
**Event**: Winter flood pulse
**Date**: December 15-17, 2021
**Key Result**: Successful prediction enabled safe evacuation 18 hours before peak flood

---

## 2. System Characteristics

### Cave System
- **Length**: 4.8 km mapped passages
- **Depth range**: 120 m (entrance) to -85 m (deepest sump)
- **Lithology**: Cretaceous limestone (92% CaCO₃)
- **Fracture density**: 2.3 fractures/m
- **Discharge range**: 0.08 - 7.3 m³/s (seasonal variation)

### Passage Gamma-7
- **Type**: Phreatic conduit
- **Length**: 850 m
- **Typical width**: 3.2 m (pre-flood)
- **Typical height**: 2.8 m
- **Flowstone thickness**: 0.087 mm/yr
- **Survey date**: December 10-13, 2021

---

## 3. Pre-Event Conditions

### Weather Leading to Event
| Date | Precipitation | Temperature | Notes |
|------|--------------|-------------|-------|
| Dec 10 | 5 mm | 8°C | Light rain |
| Dec 11 | 15 mm | 7°C | Steady rain |
| Dec 12 | 25 mm | 6°C | Heavy rain |
| Dec 13 | 40 mm | 5°C | Storm conditions |
| Dec 14 | 35 mm | 4°C | Continued heavy rain |
| Dec 15 | 20 mm | 3°C | Rain turning to snow |

### Pre-Flow Conditions
- **Baseline discharge**: 0.15 m³/s
- **Water level**: 0.45 m above floor
- **CO₂ concentration**: 850 ppm
- **Water temperature**: 11.2°C
- **pH**: 7.3
- **Calcium concentration**: 85 mg/L

---

## 4. CAVORA Predictions

### Initial Prediction (Dec 14, 72h before peak)
```

Time: 2021-12-14 08:00 UTC
Lead time: 72 hours

Predicted:

· Peak discharge: 6.8 m³/s ± 1.2
· Water level rise: 2.6 m ± 0.4
· Passage width change: +1.5 m
· Time to peak: 68 hours ± 6

Confidence: 89%
Recommendation: EVACUATE within 24 hours

```

### Updated Prediction (Dec 15, 48h before peak)
```

Time: 2021-12-15 08:00 UTC
Lead time: 48 hours

Predicted:

· Peak discharge: 7.1 m³/s ± 0.8
· Water level rise: 2.7 m ± 0.3
· Passage width change: +1.6 m
· Time to peak: 46 hours ± 4

Confidence: 92%
Recommendation: IMMEDIATE EVACUATION

```

### Final Prediction (Dec 16, 24h before peak)
```

Time: 2021-12-16 08:00 UTC
Lead time: 24 hours

Predicted:

· Peak discharge: 7.3 m³/s ± 0.4
· Water level rise: 2.8 m ± 0.2
· Passage width change: +1.7 m
· Time to peak: 22 hours ± 2

Confidence: 95%
Recommendation: EVACUATION IN PROGRESS

```

---

## 5. Actual Event Measurements

### Flood Progression
```

Date/Time Discharge Water Level Width Notes
Dec 15 00:00 0.35 0.62 3.3 Rising slowly
Dec 15 12:00 0.85 0.95 3.5 Accelerating
Dec 16 00:00 2.2 1.45 3.9 Caution level
Dec 16 12:00 4.8 2.35 4.5 High risk
Dec 17 00:00 7.3 3.25 4.9 PEAK
Dec 17 12:00 4.2 2.15 4.7 Receding
Dec 18 00:00 1.8 1.25 4.2 Stabilizing

```

### Peak Conditions
- **Peak discharge**: 7.3 m³/s (48.7× baseline)
- **Maximum water level**: 3.25 m above floor (+2.8 m)
- **Maximum width**: 4.9 m (+1.7 m, +53%)
- **Peak CO₂**: 3,200 ppm (during flood)
- **pH during flood**: 6.8 (more acidic)
- **Duration above caution level**: 36 hours

---

## 6. Comparison: Predicted vs Actual

| Parameter | Predicted | Actual | Error |
|-----------|-----------|--------|-------|
| Peak discharge (m³/s) | 7.3 | 7.3 | 0% |
| Water level rise (m) | 2.6-2.8 | 2.8 | +0-7.7% |
| Passage width (m) | 4.7-4.9 | 4.9 | +0-4.3% |
| Time to peak (hours) | 68-72 | 70 | +2.9% |
| Event duration (hours) | 42-48 | 48 | 0% |

**Overall prediction accuracy: 96%**

---

## 7. Operational Response

### Timeline of Actions
```

Dec 14, 08:00 - Initial prediction received
Dec 14, 10:00 - Team briefing, evacuation planning
Dec 14, 14:00 - Begin moving equipment to safe height
Dec 14, 18:00 - All non-essential gear staged
Dec 15, 08:00 - Updated prediction, evacuation ordered
Dec 15, 10:00 - Team begins exit
Dec 15, 14:00 - All personnel out of cave
Dec 15, 18:00 - Water level reaches caution threshold
Dec 16, 08:00 - Final check of equipment placement
Dec 16, 14:00 - Water reaches pre-placed sensors
Dec 17, 00:00 - Peak flood
Dec 20, 10:00 - Safe re-entry, damage assessment

```

### Resources Used
- **Personnel evacuated**: 7 team members
- **Equipment moved**: 85% of gear (15% lost)
- **Sensors deployed**: 8 loggers (all recovered)
- **Communication**: Radio check every 30 minutes
- **Surface support**: 3 people at base camp

### Success Factors
1. Early warning (72h lead time)
2. Clear decision protocols
3. Pre-planned evacuation route
4. Equipment staging areas
5. Continuous communication

---

## 8. Post-Flood Assessment

### Passage Changes
- **Permanent widening**: +0.4 m (14% increase)
- **New ceiling features**: Scalloping, pockets
- **Flowstone damage**: Minor scouring
- **Sediment redistribution**: New deposits in lower passages

### New Limit Cycle
Pre-flood amplitude: 2.31 m
Post-flood amplitude: 2.67 m (+15.6%)
Convergence time: 3 weeks

### Equipment Status
- **Sensors**: All 8 recovered, 6 functional
- **Survey markers**: 60% destroyed, need replacement
- **Rigging**: All anchors intact
- **Emergency caches**: 2 of 3 intact

---

## 9. Lessons Learned

### What Worked Well
- **72-hour prediction**: Provided adequate evacuation time
- **Tiered response**: Progressive actions matched risk level
- **Equipment staging**: Pre-placed gear above flood level
- **Communication**: Regular check-ins maintained situational awareness
- **Team training**: All members knew protocols

### What Could Be Improved
- **More sensors**: Additional water level loggers needed
- **Faster data transmission**: Real-time telemetry would help
- **Equipment protection**: Better waterproofing for critical gear
- **Evacuation drills**: Practice scenarios before real events

### Protocol Updates
1. Install continuous water level monitoring in all active passages
2. Pre-stage emergency caches at 30-minute intervals
3. Mark flood levels on passage walls for reference
4. Develop automated alert system for rapid response

---

## 10. Scientific Significance

### Research Contributions
- Validated flood prediction model with 96% accuracy
- Documented passage response to 50× discharge increase
- Measured post-flood limit cycle transition
- Collected rare data on flood chemistry changes

### Publications
- Baladi, S. (2022). "Flash flood dynamics in Mediterranean phreatic conduits." *Journal of Cave and Karst Science*, 84(2), 45-62.
- Data contributed to Cavora validation dataset (Event #FL001)

---

## 11. Acknowledgments

**Survey Team**:
- Nikos Karstidis (Leader)
- Maria Papadopoulou
- Georgios Antoniou
- Elena Vlachou
- Dimitris Alexandrou

**Support Team**:
- Base camp: Andreas Pappas
- Weather forecasting: Dr. K. Makris
- Cave management: Vikos-Aoos National Park

**Equipment**:
- CPDL systems provided by UIS grant #2021-08

---

## 12. References

1. Vikos Gorge Cave Survey Data 2021 (Cavora database)
2. Hellenic Meteorological Service, December 2021 records
3. Cavora Flood Prediction System validation report
4. Emergency response after-action review

---

**Report Date**: January 15, 2022
**Author**: Samir Baladi, Principal Investigator
**Status**: Final

*For more information: vikos@cavora.org*
