TRACKING SEDIMENT MOVEMENT ALONG CAVE STREAMS: LESSONS LEARNED (Invited Presentation)

The movement of sediment along cave streams can provide insight into the stability of streambed habitat. Initially, predicting whether the streambed material was stable (or not) was the focus of the research that showed that the studied cave streams could transport 50-85% of the streambed material during bankfull discharge conditions with a recurrence interval of 11.7 months (based on d₈₅). Meaning the habitat of aquatic species that dwell within the streambed material was disturbed annually. Subsequently, the research focused on documenting movement of both bed load and suspended load. The suspended load research has relied on using cosmogenic radioisotopes, beryllium-7 and cesium-137. Based on sampling at a spring during a storm event, fresh surface material was as much as 96% of the initial flush of sediment discharged at the spring. In addition, sediment from erosion of the surface was 23% of the total sediment flux during the 4-day runoff event. This research showed that movement of suspended load can be by direct transfer from the surface, into and along the cave stream, to the discharge point within one storm event. The continued research on the movement of the bed load is based on measuring the movement of radio-tagged cobbles while simultaneously documenting streamflow conditions. In one studied cave stream, the average movement of the tagged cobbles ranged from 0.24 m to 8.8 m per event. This long-term research has shown that sediment, both suspended and bed load, can be mobilized and moved significant distances within individual storms events.