The Kavalan offices build the walls and the moats of Yilan areas in 1810s. As time goes by, it became obstacles for the street expansion and the commercial development during the transfer of governance power between the Qing Dynasty and the Japanese colonial government. Finally, the modern urban planning gradually eliminate the landscape of the Kavalan city walls and the moats. The construction of the walls and the institution allocation inside the city had been well discussed in the previous studies, but the description of the moats remains the lost fragment in the spatial narratives of the city. Some study issues can be rise as: where the water came from and where to outflow; the change of the Kavalan city moat's identity during the last century; when and how each part of the moats disappeared in the landscape of the city. In order to solve the above mentioned issues, we first identify the flow of water ways and the irrigation canals before the appearance of Kavalan moats with the reference of “Kavalan Prefecture Chronicles (噶瑪蘭廳志 )". Then, we overlay a series of large-scale maps including the “Yiland Town's Overview Map (宜蘭城略圖)",“Yiland City's Postal telegraph Summary Map (宜蘭郵便電信局市內略圖 )",“Taiwan Bao Map (臺灣堡圖 )", and “Yiland City's Amendment Map (宜蘭街市區改正圖 )"as references to contrast the historical documents related to the river improvement, sewer development and the urban planning. Thus, we frame a complete story of the Kavalan city moats from a protection function to a sightseeing river, then covered by the road and disappeared in the memory of citizens. In this study, we represent the spatial process of the change of the Kavalan city moats that effectively fills up the missing link of the development of Yilan city. By the long term investigation of the Kavalan city moats during the past 2 centuries, it also provides important references for local government's urban landscape projects.