Option 1: Rooftop recharge pit is a suitable method for urban rainwater harvesting. It involves collecting rainwater from rooftops and directing it into a pit or storage tank for recharge.
Option 2: Recharge wells are also a suitable method for urban rainwater harvesting. They involve drilling a well and directing rainwater into it for groundwater recharge.
Option 3: Gully plug. This method is not suitable for urban rainwater harvesting. A gully plug involves blocking a drainage gully or ditch with a barrier to collect rainwater. However, in urban areas, it may not be feasible or practical to block existing drainage systems as it can lead to flood risks and waterlogging.
Option 4: Recharge trench is a suitable method for urban rainwater harvesting. It involves digging a trench and directing rainwater into it for infiltration into the ground.
In summary, Option 3 - the gully plug is not suitable for urban rainwater harvesting due to the potential complications it may cause in existing drainage systems. Alternative options such as rooftop recharge pits, recharge wells, and recharge trenches are preferred for effective rainwater harvesting in urban areas.