In order to directly obtain quantitative data on debris flows, and to study the movement characteristics and laws of debris flows, debris flow observation stations should be established when conditions are possible. Through the field observation of debris flow, the perceptual understanding of debris flow is enriched. Observatories should be located in mudslide basins where outbreaks are more frequent, so that there are more opportunities for field observations.
First, the selection of observation sections
The debris flow observation section should be selected on the relatively straight ditch section above the debris flow accumulation fan, and the distance between the two sections is generally between 30-50 meters. If there is a debris flow floodway in the basin, the ideal observation section is to be set on the flood channel.
2. Observation items and methods
1. Cross-sectional flow velocity
The surface velocity of the debris flow was measured by throwing buoys; If there is a particularly viscous debris flow, large boulders floating on its surface can also be observed to replace the buoys and thus derive the surface distribution of the flow velocity.
2. Mud position
The mud level is required to determine the flow rate of the debris flow. Due to the formation characteristics of debris flow, the mud level changes greatly, so special attention should be paid to the observation. In order to quickly record the change of mud level, a small wooden stake can be nailed every 10cm on the slope on the side of the observation section from bottom to top. Nail a larger stake at 50cm and 1m. When the mud level of the debris flow changes, the mud level can be determined by recording the number of the wooden piles affected by the debris flow at that time.
3. Samples were taken for analysis tests such as bulk density, viscosity and shear of debris flow to determine various physical and mechanical characteristics of debris flow.
4. Observation of scouring and silting
Due to the strong erosion and siltation of debris flows, the cross-section of the debris flow is measured once before and after each debris flow eruption.
5. Observation of other elements
Observations were made on the amount of precipitation (especially the intensity of heavy rainfall) and the recharge of solid matter in the observed watersheds. This information is indispensable for a comprehensive analysis of debris flows.
6. Make a comprehensive description of the debris flow eruption process
The start and end time of rainfall, the outbreak time of debris flow, the "dragon head" situation, the change of debris flow regime, the transformation of debris flow type, the occurrence of scouring and silting, the end time of debris flow and other special circumstances, etc. Whenever the flow pattern of debris flow changes and the type begins to change, the flow velocity, mud level, sampling and other items should be observed, so as to understand the change of debris flow and the relationship between it and various elements.