The most suitable binder for carrying out bituminous patch work during the rainy season is bituminous emulsion.

**Bituminous Emulsion:**
Bituminous emulsion is a mixture of bitumen and water along with emulsifying agents. It is a liquid form of bitumen that can be easily applied in wet conditions. The emulsion is made by dispersing bitumen droplets in water with the help of an emulsifying agent.

**Advantages of Bituminous Emulsion:**
Bituminous emulsion offers several advantages for carrying out patch work during the rainy season:

1. **Ease of Application:** Bituminous emulsion can be easily applied in wet conditions, making it suitable for rainy seasons. The presence of water in the emulsion helps in faster adhesion and setting of the patch material.

2. **Better Bonding:** Bituminous emulsion forms a strong bond with the existing pavement surface, ensuring good adhesion and preventing water infiltration. This helps in maintaining the integrity of the patch and preventing further damage.

3. **Quick Setting Time:** Bituminous emulsion has a quick setting time, which is beneficial during the rainy season when longer setting times can be a disadvantage. The patch material sets quickly and can be opened to traffic sooner.

4. **Improved Workability:** Bituminous emulsion provides better workability compared to other binders like road tar or hot bitumen. It can be easily mixed with aggregates and applied as a patch material without the need for heating.

5. **Cost-effective:** Bituminous emulsion is a cost-effective option for patch work during the rainy season. It requires less energy and resources for production and application compared to hot bitumen or road tar.

6. **Environmental Benefits:** Bituminous emulsion is a more environmentally friendly option as it reduces emissions and energy consumption during production and application. It also reduces the use of natural resources like aggregates.

Overall, bituminous emulsion is the most suitable binder for carrying out bituminous patch work during the rainy season due to its ease of application, better bonding, quick setting time, improved workability, cost-effectiveness, and environmental benefits.