Hydrology is an important aspect of civil engineering that deals with the study of water in the earth's system. It plays a crucial role in predicting, managing, and designing water-related infrastructure. The correct answer to the question is option 'E', which means that hydrology helps in predicting maximum flows, deciding the minimum reservoir capacity, forecasting the availability of the quantity of water at reservoir sites, predicting the effects on the river water level on completion of dams, and all the above.

Prediction of Maximum Flows
Hydrology helps in predicting the maximum flows of water in a river or stream. This information is useful in designing and building structures that can withstand the maximum flow of water and prevent flooding.

Deciding the Minimum Reservoir Capacity
Hydrology helps in deciding the minimum reservoir capacity required to meet the water demand of an area. This information is crucial in designing and building reservoirs that can store enough water to meet the water demand of an area.

Forecasting the Availability of Quantity of Water at Reservoir Sites
Hydrology helps in forecasting the availability of the quantity of water at reservoir sites. This information is useful in determining the amount of water that can be stored in a reservoir and the amount of water that can be used for irrigation, drinking, and other purposes.

Predicting the Effects on the River Water Level on Completion of Dams
Hydrology helps in predicting the effects on the river water level on completion of dams. This information is useful in designing and building dams that can effectively control the flow of water and prevent flooding.

Conclusion
In summary, hydrology plays a crucial role in predicting, managing, and designing water-related infrastructure. It helps in predicting maximum flows, deciding the minimum reservoir capacity, forecasting the availability of the quantity of water at reservoir sites, predicting the effects on the river water level on completion of dams, and all the above.