Rain-on-Snow Load refers to the additional load exerted on snow-covered surfaces when rain falls onto the existing snowpack. This phenomenon can significantly increase the weight and stress on structures, posing a potential risk of structural damage or collapse.
There are different types of Rain-on-Snow Load, categorized based on the characteristics of the rain and the existing snowpack:
- Rain-on-Fresh Snow: This type of Rain-on-Snow Load occurs when rain falls on a fresh, uncompacted layer of snow. The rainwater percolates into the snowpack, increasing its weight and density. As a result, the load on the underlying surfaces, such as roofs or structures, intensifies. Rain-on-Fresh Snow can be particularly hazardous since the newly fallen snow may not have had time to settle or consolidate, making it more prone to compression and saturation.
Example: Suppose a region experiences a heavy snowfall, resulting in a fresh layer of snow with a significant depth. Following the snowfall, a warm front moves in, causing rain to fall on the freshly accumulated snow. The rainwater infiltrates the snowpack, increasing its weight and density. As a result, the load on roofs and structures in the area is considerably amplified, potentially surpassing their design capacities. This increased load can strain the structural elements and pose a risk of failure.
- Rain-on-Old Snow: This type of Rain-on-Snow Load occurs when rain falls on an existing, compacted snowpack that has undergone partial melting and refreezing cycles. The rainwater may not be readily absorbed by the denser snowpack, leading to runoff and ponding. However, if the rain is persistent or the snowpack is saturated, the water can gradually penetrate the snowpack, further increasing its weight and saturation.
Example: Consider a scenario where a region has a deep snowpack accumulated over the course of winter. Subsequently, a warm weather system moves in, bringing rain. The rainwater falls onto the old, compacted snowpack, some of which may have undergone partial melting and refreezing cycles. The rainwater initially forms puddles on the snow surface and may gradually penetrate into the snowpack, increasing its density and adding additional load to structures. The weight of the rainwater on the snowpack, combined with the existing snow load, can pose a significant risk to roofs, especially if the snowpack is already near its capacity.
Rain-on-Snow Load poses a unique challenge in structural design, as it involves the interaction of rainwater and an existing snowpack. The weight and distribution of the rainwater on the snowpack can vary depending on factors such as the temperature, duration of rain, snowpack characteristics, and the ability of the snowpack to absorb or retain water. When designing structures in areas prone to Rain-on-Snow Load, engineers must consider the potential for this additional load and ensure that the structures can withstand the combined effects of rain and snow on the surfaces.
