Laserfiche WebLink
<br />and Costa, 1988). Figure j illustrates a simplified schematic of the kind of evidence gathered for <br />this study. <br /> <br />Figure 5 - Schematic stream cross- ect~.n s owing v . us ~Is. (Source: Jarrett, 1991). <br />~ \,\1 .\ C I..4f\ S . <br />While aging techniques 1st to determine the age of PSIs, this study is onl concerned in <br />d'"-ti~lhe probabl ange of the largest flood in the past !ODor so years t le'ast two cros~ <br />(S"ections of the eh - elwere surveyed wliere PSIs exist and where there was good hydraulic . <br />\ "contro!. TIiecross-sectlonal area at the esfiriiatei:ITIo-odstage can be-estimated using the simple <br />~ioidal rule or other integration routines such as Simpson's rule. Cross-section plots <br />showing the location of PSIs are located in Appendix C. <br /> <br /> <br />Flood sago <br /> <br />The flood flow is determined by assuming the velocity of the flow to be very near a critical <br />condition. More sophisticated techniques exist to determine flow velocity by analyzing the <br />transported sediment, but the assumption of near critical flow yields reasonable estimates <br />(Jarrett, 1997). With the critical flow assumption, mean flow velocity, v, may be calculated by, <br /> <br />v = ~ gD <br /> <br />where g is the gravitational constant and D is the hydraulic depth defined as the cross-sectional <br />area divided by the width of the free surface (Chow, 1959). Caution should be exercised in this <br />simplification as it inherently treats the channel as prismatic. Most natural channels may be <br />abstracted as prismatic to ease computations (Chow, 1959). For complex cross-sections, it is <br />prudent to subdivide the total cross-section into prismatic channels (Davidian, 1984). Figure 6 <br />illustrates how one might subdivide a cross-section. The total channel discharge may then be <br />obtained by superposition. <br /> <br />7 <br /> <br />~ <br />