No abstract

No abstract

Gullies contribute high sediment loads to receiving waters and significantly degrade landscapes. In drylands, low annual rainfall and resultant poor ground cover, coupled with high-intensity storms and dispersive soils, predispose these landscapes to gully erosion. Land management, such as grazing, exacerbates gully-forming processes by degrading ground cover and compacting soils, thereby increasing and concentrating overland flow. Current surface erosion models do not adequately represent sediment export from gullied terrain due to lack of distributed data and complex hydrogeomorphic processes, such as overland flow concentration, waterfall erosion, soil pipe collapse, and mass wasting. Here, we outline the strengths and weaknesses of past modelling approaches in erodible terrain and focus on how gully erosion processes can be better simulated at appropriate scales using newly available remote-sensing techniques and databases, coupled with improved understanding of relevant hydrogeomorphic processes. We also discuss and present examples of challenges related to assessing land management practices in drylands that affect gully erosion.

No abstract

No abstract

The Central Java region is one of the most seismically active regions in Indonesia. Each year, the region experiences an average of more than 20 medium-tolarge magnitude earthquakes. Hence, reliable hazard analysis is necessary for the region, and we undertook this study in order to conduct a probabilistic seismic-hazard analysis to estimate and map peak ground acceleration (PGA) and spectral response at 0.2 and 1 s periods, with 10% probability of exceedance in 50 years corresponding to the return period of 475 years. Maps presented in this study are intended for regional purposes only and may be useful for emergency response planning and urban development. The database used in this study is compiled from the Indonesian Meteorological, Climatological, and Geophysical Agency, the U.S. Geological Survey, and the Incorporated Research Institutions for Seismology. The compiled catalog covers an area between latitude 5°-12°S and longitude 105°-115°E and includes moment magnitude 5 and greater from 1900 to February 2011. We used a standard logic-tree approach that included systematic allowances for various seismicity models. Because a region-specific empirical ground-motion model is lacking, we used Next Generation Attenuation ground-motion relations. We calculated PGA and spectral response at 0.2 and 1 s periods for all cities across Central Java. We found that the city of Pati is subject to the highest seismic hazard with a PGA of 0:45g, and the city of Kendal has the lowest hazard with a PGA of 0:13g. This study provides a basis upon which to design maps for building codes and emergency planning.

No abstract

No abstract