Tides and currents can have a significant impact on underwater excavations in several ways, affecting both the safety and efficiency of the operation. Here’s how:
1. Tidal Changes:
- Water Depth Variations: As the tide rises and falls, it changes the depth of the water over the excavation site. Low tide might expose parts of the site, while high tide can submerge the area, which might interfere with the work.
- Timing and Accessibility: In many cases, underwater excavations are planned around low tide, which gives workers better access to the site and may expose areas that are otherwise too deep underwater.
- Increased Work Complexity: If a project spans over a long period (such as weeks or months), workers must account for tidal schedules, as low or high tides can change the work schedule. Excavation efforts might need to pause during unfavorable tidal conditions.
2. Currents:
- Movement of Sediment: Strong currents can disturb loose sediment around the excavation site, which might cause the site to become unstable. It can also make it difficult to maintain visibility underwater, especially if sediment is stirred up and makes the water murky.
- Safety Concerns: Strong currents can pose a serious risk to divers or remotely operated vehicles (ROVs) performing excavation tasks. If the current is too strong, it could cause divers to be carried away from the site or even endanger their lives.
- Slower Progress: The strength of the current affects how quickly and efficiently work can be completed. In high-current areas, progress might be much slower because the equipment (such as dredges or excavators) needs to be more robust to handle the forces of the water.
3. Equipment and Techniques:
- Specialized Equipment: In areas with strong currents or significant tidal changes, specialized equipment like anchors, divers’ surface support systems, or dynamic positioning systems for boats and barges is often necessary to ensure the stability of the excavation process.
- Excavation Techniques: When strong currents are a factor, excavation techniques might have to be adjusted. For example, using an ROV can be helpful in strong currents where human divers might struggle. Additionally, excavation could involve methods like suction dredging, where equipment helps keep the site clear of debris and sediment.
4. Sediment Displacement:
- Erosion and Sedimentation: Currents can cause erosion of the seabed or lead to sediment accumulation over the site. This might bury artifacts, structures, or materials being excavated, making it harder to uncover them.
- Accidental Contamination: If excavations are being done in areas with sensitive environmental concerns, strong currents or tides might spread contaminants or disturb sensitive marine ecosystems.
5. Weather and Seasonal Variations:
- Storms and Weather Events: Tidal surges or increased current strength due to storms can complicate excavations. These events might change the condition of the seabed or delay work.
- Seasonal Patterns: In some areas, tides and currents can vary seasonally. Excavation teams need to account for these patterns to optimize their work windows and ensure safety.
6. Surveying and Mapping:
- Accurate Mapping: Tides and currents need to be factored into the initial surveying and mapping process. Equipment like sonar or lidar mapping devices must be calibrated for varying water levels caused by tidal changes.
- Precision of Work: Tidal effects on water depth must be carefully accounted for in detailed excavation plans to ensure the work is done at the right depth and angle.