Rainy season arrives

Stage = 85cm

Today brings typical rainy season conditions as the seasonal front passes over Niigata Prefecture, bringing very unstable conditions with heavy rain and thunder storms. Miomote Amedas gauge records up to 13mm/h while just to the north Takane Amedas gauge records 19mm/h, with total rainfall of 76mm and 110mm respectively by 4pm.

We arrived at 10am and set about making a discharge measurement using the float method. The flow was too high to try the wading method with current meter. Using a distance along the bank of 25m, we used branches as floats to measure surface velocity with a stop watch. We used six points across the width of the channel from the bridge. We estimated the mean surface velocity was about 1.5m/s, giving a mean profile velocity of about 1.2m/s (multiply by 0.8). Multiply this by mean depth (0.63m, estimated from current stage and the most recent channel cross-section), and channel width (11.6m), gives total discharge of about 8.75m3/s. Although this estimate is very approximate, it does fit within the bounds of the current stage-rating curve.