11 precipitazioni che_innescano_colate_en
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1) Debris flows are triggered by high intensity, short duration rainfall that produces abundant runoff. Rainfall of 9mm over 15 minutes did not produce a debris flow, while 18mm over 10 minutes did. 2) Rainfall characteristics that typically trigger debris flows in dolomitic environments include a core of 10-15mm of rain over 10-15 minutes, with pulses over 5-6mm/5minutes. 3) Two debris flows in July and August 2015 in Italy were examined. The triggering rainfalls had cores of 11.6mm over 5 minutes and 13.8mm over 15 minutes respectively.
11 precipitazioni che_innescano_colate_en
- 1. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University Rainfalls triggering debris flows
- 2. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University Runoff must be abundant to move a large quantity of debris material. In the case of headwater rocky basins rainfall must characterized by high intensity and short duration. 9 mm in 15 minutes No debris flow 18 mm in 10 minutes Debris flow developed downstream Fiames (Cortina d’Ampezzo) channel below Dimai Peak Abundant runoff
- 3. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University Characteristics of rainfalls triggering debris flows - 1 An axiom of hydrology is that rainfall intensity increases/decreases for decreasing/increasing rainfall duration, the other condition being the same. Strictly speaking the peak of rainfall intensity occurs in a short period. Therefore, the high intensity rainfall is characterized by a short duration. The DDF (depth duration frequency) curves corresponding to the Faloria station (Cortina d’Ampezzo, BL) provide the following rainfall depths for the duration 10 and 30 minutes and the return periods 30 and 100 years: 15.1/17.9 mm 26.7/31.8 mm The corresponding intensities, obtained by multiplying the values above by 6 and 2 respectively are: 90.6/107.4 mm/h 53.4/63.6 mm/h
- 4. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University In the left case a rainfall of 3mm/5 minutes occurred while in the right case it was 9 mm/5 minutes Characteristics of rainfalls triggering debris flows - 2 9 mm in 15 minutes No debris flow 18 mm in 10 minutes Debris flow developed downstream
- 5. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University In a Dolomitic environment a debris flow occur if the rainfall has a core of 10-15 mm in 10-15 minutes with a single pulses larger than 5- 6mm/5minutes. This rainfall is able to provide abundant runoff to mobilize enough debris material to form a debris flow. The debris flow occurred the 18th of July 2009 was characterized by two phases: first rainfall event (2:55) triggered a debris flow that stopped during routing on a flat area, while, the second rainfall event (3:35) triggered a debris flow that reached the valley bottom (second event provided a larger amount of runoff becasue the first event saturated the terrain. In the first event, we have a single pulse of 11.6 mm in 5 minutes. In the second event a core of 13.8 mm in 15 minutes. Characteristics of rainfalls triggering debris flows - 3
- 6. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University The rainfalls that triggered the debris flows occurred the 23th of July and the 4th of August 2015 at Rovina di Cancia are examined . There are two rain gauges within the basin with the outlet at the triggering area. Other two rain gauges are located downstream. Characteristics of rainfalls triggering debris flows - 4
- 7. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University RAINFALL OF THE 23 JULY 2015 This rainfall occurred in a 1 km square area. The cumulative rainfall of rain gauge 2 is about 60% that of rain gauge 1 Characteristics of rainfalls triggering debris flows - 5
- 8. Carlo Gregoretti29/05/2017 Debris Flows - Mekele University This rainfall occurred in a wide area and triggered other five debris flows. Characteristics of rainfalls triggering debris flows - 6 RAINFALL OF THE 4 AUGUST 2015 The cumulative rainfall of rain gauge 2 is about 30% that of rain gauge 1