The applications of remote sensing technology and aerial photography using unmanned aerial vehicles (UAVs) have facilitated the development of large-scale land environment-monitoring technology. When design units are involved in water and soil conservation projects, engineering personnel must take valuable instruments to valleys and streams for mapping purposes; however, obtaining effective and accurate worksite information is challenging. In this study, a remote-controlled helicopter equipped with a digital camera was used to take photographs of riverside slopes that are unreachable by land. Three-dimensional (3D) models of rivers and mountain slopes were constructed through software computation. The results of this study thus provide references for design projects and show how inaccessibility problems, caused by factors such as a difficult terrain, can be solved, thereby avoiding disasters that can occur when surveying dangerous areas. The method effectively saves labor and time to ensure that hillside-related projects can be completed on schedule.