Evaluation of open check dams within modelling chains
Authors: Bertoldi Gabriele , Bridi Federico , Cavedon Valentina , Michelini Tamara , Valentinotti Ruggero 
Published: February 2023

&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;Open check dams are widely recognized as &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;effective&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; structural me&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;asures against debris flows&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;. In the last 40 years, the Service for Torrent Control of the Autonomous Province of Trento (&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;Italy&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;) has built around 400 open check dams, which in many cases have made it possible to &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;debris-flow hazard &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;mitigation&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;. &lt;/span&gt;The use of physical-based models and urban planning through hazard maps allow the technicians and scientific community to evolve the hazard assessment methodologies. However, these methodologies require quantitative analyses.&lt;span lang=&quot;en-GB&quot;&gt; The inclusion of a check dam in the modelling chain has several critical issues which are related to hydrological and hydraulic models and the effectiveness of check dams may be underestimated.&lt;/span&gt;&lt;/p&gt;
&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;To overcome these c&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;ritical issues, the Service has adopted an empirical method to &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;evaluate the effect of open check dams on hazard mitigation and the possible design alternatives&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;by &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;defining a reference behaviour and &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;different&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; behaviour &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;s&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;cenarios.&lt;/span&gt;&lt;/p&gt;
&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;The starting data necessary to perform &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;an&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; analysis are: check dam and filter geometries, the geomorphological data of basin (e.g. the volume of expected event), hydrological data, i.e. the peak discharge and the hydrograph of debris flow and an estimate of &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;the&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; largest particle sizes in the reference even&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;t. Preserving the peak discharge and the volume of event&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;s&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;, discharge timestep distribution&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;s&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; are modified to reproduce a debris&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;-&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;flow hydrograph shape consistent with monitored field&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;-&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;site datasets and recorded evidence (Gregoretti et al. 2016, Marchi et al. 2020, Mitchell et al. 2022).&lt;/span&gt;&lt;/p&gt;
&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;The interaction betw&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;een described debr&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;is flow&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;and &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;check dam&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; is analysed by applying the equation of Mizuyama &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;&lt;em&gt;et al. &lt;/em&gt;&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;1996 to each time step until saturation of reservoir capacity &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;and&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;by &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;evaluating the &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;discharge&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; capacity of spillway upon reaching this capacity.&lt;/span&gt;&lt;/p&gt;
&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;To define a confidence interval on the &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;estimate of check-dam&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;efficiency, depending on&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; building &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; characteristics, &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;three&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; other scenarios are also evaluated: the occluded filter hypothesis, the functioning hypothesis with Mizuyama &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;&lt;em&gt;et al.&lt;/em&gt;&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; 1996 &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;using&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; the original hydrograph and the hypothesis of &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;peak &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;lamination &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;by considering&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; the volume of the deposition basin.&lt;/span&gt;&lt;/p&gt;
&lt;p align=&quot;justify&quot;&gt;&lt;span lang=&quot;en-GB&quot;&gt;The debris&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;-&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;flow hydrograph resulting from the reference scenario is used for the physically based simulations downstream of the open check dam. The methodology was applied to &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;several/many&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; case studies, &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;by &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;allowing&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;satisfactorily to evaluate&lt;/span&gt; &lt;span lang=&quot;en-GB&quot;&gt;the behaviour of the open check &lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;dam&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;s&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;. Further advances and refinements of the procedure are desirable with respect to a better and more standardized definition of debrigraph on the basis of the standardization of real debris-flow&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt; hydrograph and on a more refined description of the behaviour of filter&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;s&lt;/span&gt;&lt;span lang=&quot;en-GB&quot;&gt;.&lt;/span&gt;&lt;/p&gt;