Two major summer floods within 3 days

Stage = 0.437 m, Q = 0.615 m3/s

After an enforced break of 2 months, we finally managed to visit Takiya River to carry out a routine discharge measurement, and download both the stage recorders. The river channel seemed to be filled with an abundance of fine gravel, and indeed we found that the stage-rating curve had shifted to reflect this channel aggradation (higher stage level for a given rate of discharge).

Our previous visit (30 July) came just after a major flood on 28 July of stage 1.8 m, while a second major flood occurred soon after during 31 July to 1 August. Although both floods were of similar magnitude, the first flood was due to prolonged rainfall, while the second was due to very intense rainfall of short duration. At Takane Amedas gauge peak rainfall intensity reached 56 mm/h, and 71 mm fell over two hours. At Miomote Amedas gauge peak rainfall intensity reached "only" 19 mm/h, indicating the localized nature of the most intense rainfall.

These back-to-back floods appear to have introduced a larger amount of fine sediment to the channel than it can transport downstream, and hence the channel aggradation and shift in the rating curve.