Laserfiche WebLink
<br />HYDRAULIC STRUCTURES <br /> <br />DRAINAGE CRITERIA MANUAL (V. 2) <br /> <br /> <br />Photograph HS-9 <br />Close-up of the inside workings of a baffle chute drop after more than three decades of service. <br /> <br />The typical design consists of upstream transition walls, a rectangular approach chute, a sloping apron of <br />2: 1 or flatter slope that has multiple rows of baffle blocks and downstream transition walls. The toe of the <br />chute extends below grade and is backfilled with ioose rock to prevent undermining of the structure by <br />eddy currents or minor degradation of the downstream channel. This rock will rearrange to establish a <br />stable bed condition and produce additional stilling action. The structure is effective without tailwater; <br />however, tailwater reduces scour at the toe. Grouted and concrete basins have been used at the <br />transition to the downstream trickle and main channels. The structure also lends itself to a variety of soils <br />and foundation conditions. <br /> <br />There are fixed costs associated with the upstream transition walls, crest approach section, downstream <br />transition walls and a minimum length of sloping apron (for four baffle rows). Consequently, the baffle <br />chute becomes more economical with increasing drop height. <br /> <br />The potential for debris accumulation and subsequent maintenance must be considered. Caution is <br />advised regarding streams with heavy debris flow because the baffles can become clogged, resulting in <br />overflow, low energy dissipation, and direct impingement of the erosive stream jet on the downstream <br /> <br />HS-30 <br /> <br />06/2001 <br />Urban Drainage & Flood Control District <br /> <br />e <br /> <br />e <br /> <br />e <br />