**1. Introduction**

The problem of watersheds is the problem of ecological balance related to the carrying capacity of the environment and its components [1–3]. The environment is defined as a region (region, etc.) as a boundary of economic activity, which influences the development of life in it [4, 5]*.* Dwelling or hydrological containers of economic activity based on environment are described as watersheds [4, 6].

The conversion of lands of an area of a watershed is due to population pressure on the land indicating there is a role for the community, both on a spatial scale

and in general that affects the sustainability of natural resources [7–9]. Population pressure on this land is driven by the unbalanced rate of population growth with the availability of land resulting in increased activity and intensity on existing land or opening new land [10]. Conversion of lands without regard to topographic geological, and carrying capacity of ecosystems causes natural disasters such as landslides, floods and drought [11].

Land conversion is always associated with erosion [12]. Brantas watershed is one of the priority watersheds facing erosion problems [13, 14]. Lesti subwatershed as part of the Brantas watershed plays a very important role in the preservation of the Sengguruh Reservoir. The Sengguruh Reservoir affects the supply of irrigation water for flood control, and generates most of the electricity in the East Java Province [15]. Erosion from upstream of the Lesti Sub-watershed sub-impacted a reduction in the storage capacity of the Sengguruh Reservoir resulting in an accelerated reduction of water storage from the original plan [16]. The interesting thing is that the upstream area of the Brantas watershed, especially the Lesti Sub-watershed is contributing a large river water flow to the downstream of the Sengguruh Reservoir [16–18].

Previous studies of erosion in the Lesti Sub-watershed show a significant upward trend in erosion rates. Yupi [19] has calculated the rate of erosion in the average of each hectare of land in the Lesti Sub-watershed, which is 30.57 tons/ha/ year. The results of the Setyono and Prasetyo studies in 2012 stated that the average erosion rate in each hectare of land in the Lesti Sub-watershed was 105.763 tons/ ha/year [20]. Meanwhile, the study of Ma'wa *et al.* [16] got an average erosion rate/hectare of 131,098 tons/ha/year. This research increasingly shows that areas with a high level of erosion hazard are also getting wider, especially in the current conditions.

Analysis of erosion associated with population pressure has not been much discussed in the Lesti Sub-watershed. This needs attention because the rate of erosion that affects sedimentation in the Sengguruh Reservoir as an outlet of the Lesti Sub-watershed cannot be separated from the activities of the residents therein. The activities of the population and the choice of how to use land in fact suppress the land so that it affects the carrying capacity of the watershed. Measuring land strength is usually known from the value of existing population pressures and their effects on vulnerability or the level of erosion hazard.

Research related to erosion in the Lesti Sub-watershed so far has only been influenced by physical factors of the watershed such as slope, vegetation, and soil erodibility [21]. Linkages between population pressures and the extent of the erosion hazard area in determining the most priority areas for conservation are rare [22–26]. The linkage and determination of the most priority areas for environmental conservation are interesting things to be studied further based on environmental science.
