To avoid the collapse of bridges over rivers during high tides or heavy rainfall, several key considerations and measures should be taken into account during the design, construction, and maintenance stages. 

Here are some strategies to mitigate the risk of bridge collapse in such conditions:
Thorough Site Investigation: 
Conduct a comprehensive site investigation to gather relevant data on the river's hydrological characteristics, including tidal fluctuations, water flow rates, and historical flood levels. This information is crucial for designing a bridge that can withstand the expected hydraulic forces.

Hydrological and Hydraulic Analysis: 

Perform hydrological and hydraulic analysis to determine the design parameters for the bridge. This analysis involves assessing the river's flow patterns, flood levels, and potential scouring effects on bridge foundations. It helps determine the appropriate hydraulic design criteria for the bridge structure.

Bridge Alignment and Elevation: 
Carefully select the bridge alignment and elevation to minimize the risk of flood impacts. The bridge should be aligned to reduce its exposure to high water velocities and potential debris accumulation during floods. The bridge deck elevation should be set above the expected flood levels to ensure clearance and prevent water from submerging critical components.

Bridge Design: 

Employ appropriate design methodologies and standards to ensure the bridge's structural integrity under hydraulic loads. Consider factors such as increased water pressure, dynamic forces from debris, and scouring effects on bridge piers and abutments. Implement robust structural analysis and design techniques to ensure adequate strength, stability, and load-carrying capacity.

Scour Protection Measures: 

Install scour protection measures around bridge piers and abutments to prevent erosion and undermining of the foundation. These measures may include riprap, gabion baskets, or other erosion-resistant materials. Regular inspections and maintenance of scour protection measures are essential to ensure their effectiveness.

Adequate Drainage System: 

Incorporate a well-designed and efficient drainage system to manage surface runoff during heavy rainfall. Properly sized and positioned stormwater drains, culverts, and catch basins should be installed to prevent water accumulation on the bridge deck, which can increase the load and compromise its stability.

Regular Inspections and Maintenance: 

Implement a comprehensive inspection and maintenance program for the bridge structure. Regular inspections help identify signs of deterioration, such as corrosion, cracking, or settlement, that can compromise the bridge's integrity. Address any identified issues promptly through appropriate repairs or maintenance actions.
Emergency Response Plan: 

Develop an emergency response plan in collaboration with local authorities to ensure a swift and coordinated response in the event of extreme weather conditions. This plan should outline evacuation procedures, emergency communication protocols, and contingency measures to safeguard the bridge and its users during floods or severe weather events.

Public Awareness and Education: 

Promote public awareness and education regarding the risks associated with using the bridge during high tide or heavy rainfall. Provide clear signage, warnings, and instructions to users during such events to prevent accidents or potential bridge failures.

Continuous Monitoring: 

Install structural health monitoring systems to continuously monitor the bridge's performance and detect any signs of distress or deformation. These systems can provide real-time data on the bridge's condition, allowing for timely intervention or closure if necessary.

By implementing these measures, the risk of bridge collapse during high tides or heavy rainfall can be significantly reduced. It is crucial to engage experienced bridge engineers, hydrologists, and other relevant professionals throughout the planning, design, construction, and maintenance stages to ensure the bridge's resilience against extreme hydraulic forces.