Responsibility for landslide management is undertaken by a range of organisations, with significant variations between jurisdictions. It is important to identify the key organisations to contact.
In many cases, national or state geological surveys maintain databases of landslides, which can include maps of known landslides, case studies of significant landslide events and a timeline of when major landslides have occurred. This provides important information about the local conditions (such as slope angle, geological materials and land use) in which landslides have occurred. This information can be used to see whether sites with similar conditions to those at the project site have suffered from landslides, or whether the project site (and its adjacent slopes) may have been subject to instability in the past.
The data can also be used to consider the conditions under which landslides have been triggered. For example, what is the level of rainfall intensity and duration that led to landslides, and/or what was the nature of earthquake shaking that led to landslides occurring? In such cases, determine how large the landslides were, and examine how far they travelled.
It is important to note that many such datasets are not complete because of the complex nature of collecting, curating and portraying landslide information. Thus, the absence of known landslides in similar conditions to those at the sites under consideration does not necessarily indicate that the sites will not be subject to landslides.
More detailed information is often held by local government organisations. The format of these data can be variable – in some cases a detailed map of landslides might be available, whilst in others there might be a portfolio of case studies. This can provide insight into the problems that might be encountered at the sites under consideration, and of the processes that lead to landslides occurring.
National and local government officials in planning and/or engineering departments, often have strong knowledge of specific local or site conditions (for example the types of materials and or slope gradients) that have been associated with landslide problems in the past. Seek their insight and advice where possible.
However, every site is different, such that landslides can occur in areas that have not be prone to instability before. Thus, remember that this type of desk study does not remove the need to understand the likelihood of slope instability at a particular site.
Weblinks:
The USGS provide useful information on signs that might indicate that instability is developing: http://landslides.usgs.gov/learn/prepare.php