Predicting the distribution of major debris flow hazard using coupled 10Be erosion records and 1m resolution digital topography

On the 6th of August 2010 intense storms triggered widespread debris flows in the Indus Valley centred near Leh, India. Initially over 3000 people were unaccounted for and the final toll was over 200 dead and over 600 houses destroyed. Our group has been working in the area for over a decade and we visited the area in May 2011 to resurvey and resample channels where we had pre-event data. We discovered that debris flows concentrated near the mountain front, somewhat contrary to expectations: channels near the mountain front are on low relief alluvial fan surfaces whereas in the high mountains the main channel is deeply incised and would appear at first glance more active. However, we noted that the hillslopes near the mountain front were rougher (rockier) and were more dissected than the high elevation portions of the catchment; it is from these rough, dissected hillslopes that the debris flows originated. We believe that the rough hillslopes correlate with debris flow activity and seek to test this hypothesis with a combination of detailed field surveys of debris flow channels and previously unavailable high resolution topographic data. We will also quantify if the spatial distribution of debris flows persists over long time scales by measuring the concentration of 10Be in stream sediments. These measurements and our analysis will help us to understand debris flow hazard in remote mountainous areas in the Himalayas and beyond.

This project will provide improved hazard assessment for high mountain regions in general and specifically for the Ladakh region.
The main beneficiaries of knowledge arising from this research are anticipated to be the Ladakh Autonomous Hill Development Council (LAHDC) and the residents of the valleys draining into the Indus valley. We have already discussed this project with the Chief Executive of the LAHDC (Mr Rigzin Spalbar), and he has stated that he will support our efforts to communicate our results to the village communities.

Broader implications of this work will be discussed with contacts at the National Disaster Management Authority (NDMA) in Delhi, where our contact, Dr Mussafa has agreed to discuss implications for policy development from the central government. Knowledge and techniques derived from this proposal may also be applied to other local authorities in high mountain environments (e.g., Pakistan, Nepal, Bhutan) as a guide for debris flow hazard and particularly planning for low -frequency, high-magnitude events and their impact on infrastructure and property.

We will conduct three specific tasks to help inform and educate the people of Ladakh about debris flow hazard in their area.
i) Using our high resolution satellite imagery and topographic metrics developed for this study, we will provide the LAHDC with a hazard map of Basgo valley. The co-I has already met with the Chief Executive and the Executive councillor for Agriculture in the LAHDC and they are keen to obtain hazard maps for planning purposes.
ii) We will author an article to be distributed to the national newspapers such as IndiasNews (there is no Ladakhi newspaper) about debris flow risk and lessons learned from the event. These newspapers are read by English-speaking officials in the area and thus have the potential to affect policy changes in terms of building sites for schools and other public buildings. As part of a local media push, we will also talk on All India Radio which is based in Leh, and is the most popular form of media news in the region - again the LAHDC have encouraged us to do this.
iii) We will produce a pamphlet that contains maps and schematic cartoons depicting debris flow risk and the nature of extreme events. An issue in the villages is that since the 2010 event, many assume that these will now be repeated each summer as a part of the local climate change signal. The text for this pamphlet will be translated into Ladakhi (the dominant language in the area) and distributed to schools.