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CONTENTS l Abstract .... ........................... ............. .................. ......... ... ........... ....... ..... ............. ........... ............. ....................... Introduction............... .......,.. ........... ................. ... ........... ........... ......... ..... .......... ..................... .... ... ............ .......... Purpose and scope................ ................ ......... ................ ....... ............................... ......... ............................. Description of the study area.............. ........... ..............,........................ ........... ....... ................................... Previous investigations...,............................. .,...............................,......,.................................................... Data collection and analysis.. ........... ...., ............. ......... ................ ......... ........................................ .... ............... ... Hydraulic data. ....... ...................................,...... ..... ........... ......... ..... .............,........................ ............ ... ...... Stream power and shear stress................. ......... .............. ......... .................. ................................. _,............. Vegelation data...... .......... ................... ........... ................. ......... ............. ..... ......... ..... ...... ................. ........... Vegelation-susceptibility index .. ..........., ............,......... ............................. ......... .............................. V egelation- flexibility factor....... ......................... ....... ................ ............. ..... .................................... Vegelation-blocking coefficient .......... ..............,........ ................ ...........,. .......................... ............... Vegelation-distribution coefficient.... .............. ..................................................................,.............. Flow-depth coefficient..... ..... ............. ....................... ......... ....... ......... .......................... .... ......... ........ Relation between stream power and vegetation-susceptibility index ............................................... Vegetation removal............... ..... ............. .........,.... ........... ....... .................. ...................... ......................... Critical shear stress...... .................. ......... .......,........ ,......,. .............. ....,........ .......,. ............................. Flow duration............... ................ ....................... ...........................,............ ..... ................................. Effects of flow-induced vegetation changes on channel conveyance................................................................ Components of Manning's n .......... ........... ......... ....... .................. ..... ...........,.,...............................,.........., Base value of Manning's n .... ........... ......... ... ............. .........,.. .............,..................... ......... ...... ......... Adjustment for vegelation component..... ................ ....... ........................................ .................... ...... Channel-conveyance computations......... ......... ......................................................,........ .......................... Discussion and example case ................ .........,............... n..... .................. ........_.. .........,............................. Assumptions and limilations ...... .................. ...........,............. .........,............... .................................................... Summary ............................................................................................................................................................ Selected references............... .................. ...............,...... ... ....................... ............... ............................................. Basic dala .......................,......................................... ..... .............,...... ..... ............. ......................................... ...... FIGURES 1. Map showing study area and selected sites in central Arizona............................................................ 3 2. Photograph showing dynamometers used to determine vegetation bending-moment values.............. 9 3. Graph showing bending-moment values for four types of vegetation in central Arizona...............,. ........................... ................ ....... .................... ................................ ............., 10 4-7. Photographs showing: 4. A lone willow approximately 15 feet tall in a prone position after the flow of September 10, 1994, Vekol Wash near Stanfield ....................................................................... II 5. An erect, 16-foot-lall palo verde after the flow of January 8,1993, Cave Creek above New River Road ........................................................................................... II 6. Spatial distribution of vegetation in stream channels: A. Vegetation aligned parallel to flow ..................................................................................... 13 B. Randomly distributed vegetation.............. .........,................. ........................ ............... .... ..... 13 7. Saltcedar that was little affected by flow primarily because ofthe relatively low ratio of flow depth to vegetation height............................................................................... IS Contents III Page I 2 2 4 5 5 5 6 6 6 9 12 12 14 14 14 18 18 20 20 20 20 21 21 26 27 27 31