A Single-Nozzle Pressurized Rainfall Simulator for Post-fire Infiltration and Runoff Studies

Marketing Paragraph: Statement of Purpose: Rainfall simulators are commonly used to study hydrological processes such as soil infiltration, runoff, and erosion in response to rainfall. However, they not only vary in type, size, and features, but also in the methods in which they are calibrated. This work aims to develop a low-cost, portable, and pressurized rainfall simulator capable of replicating an average rainstorm in San Diego, California for post-fire infiltration and runoff studies. Many simulators are not designed to produce low-intensity events like those of southern California. Additionally, direct measurements of key rainfall characteristics like drop size, velocity, and kinetic energy require sophisticated and costly instruments, increasing the overall project expense. When faced with limited space and funds, alternative approaches include those that relate a variable to another that is more easily measured or those of simplified theoretical expressions. These alternative approaches require relationships derived from comparable experimental conditions or data that falls within available calibration curves. With these methods, the rainfall simulator will be analyzed and adjusted to provide reliable experimental conditions in varying field settings, particularly sensitive environments like post-fire landscapes. While high-intensity rainfall is crucial for understanding extreme runoff and erosion, lower intensity rainfall, characteristic of San Diego's climate, can also provide valuable insights on the more gradual hydrological processes.

Full Abstract: Complete Proposal for Your Session:Given the increasing frequency and intensity of wildfires in southern California, it is critical to understand the hydrological changes that can occur in post-fire environments in order to inform effective restoration and management strategies. Rainfall simulators are invaluable tools for investigating hydrological processes, such as soil infiltration, runoff, and erosion, in response to rainfall events. Therefore, the goal of this research is to build and calibrate a low-cost, portable, and pressurized rainfall simulator capable of replicating an average rainstorm in San Diego, California, including lower intensity rainfall events. However, the design and calibration of these simulators can be complex and resource-intensive. While direct measurement of rainfall characteristics like drop size, velocity, and kinetic energy provides precise data, it often requires sophisticated and expensive instrumentation. For example, projects including specialized tools like photogrammetry or disdrometers used for rain drop measurements can total up $10,000 or more.

To address these limitations, researchers have explored alternative manual calibration methods. One approach involves relating key rainfall parameters to more easily measurable variables, such as rainfall intensity. Another method relies on simplified theoretical expressions to estimate rainfall impact and terminal velocity. While less precise than direct measurements, these indirect methods can still provide useful insights into water cycle dynamics, especially in regions experiencing increased wildfire activity where water resources are often scarce.

To calibrate the simulator, we will implement a combination of direct and indirect methods. Direct measurements, such as rainfall intensity, will be recorded using a standard tipping bucket rain gauge. Indirect methods, including the use of theoretical, experimental, and empirical relationships, will be used and compared to estimate key rainfall characteristics like drop mass, velocity, and the corresponding kinetic energy.

By combining these approaches, we will provide a reliable and affordable rainfall simulator that can be adjusted to varying field slopes and settings to investigate the impacts of post-fire disturbances on hydrological processes. The insights gained from this research can then contribute to our understanding of hydrological changes and inform water resource management strategies.