3.7 Use Suitable Culvert and Bridge Siting and Design Reduce the use of culverts and bridges by careful trail planning, selecting the optimum crossing points, and choosing less intrusive construction techniques where possible. For example drainage dips, cross-slopes, stepping stone crossings and other techniques may reduce or eliminate the need for culverts. Provide for adequate drainage flow. Bridge specifications depend on peak flows and flood cycles. Locate bridge crossings to minimize disturbance to stream beds and banks. Locate bridges where channels are straight and where bank conditions are stable. Use bridges rather than culverts to cross large streams. Culverts may alter flow and cause downstream erosion or silting. They may also disturb fish habitat. Use culverts on small drainage ways. Select an adequate size and set at a level that will not interfere with drainage. (See detailed notes in Construction section).