Geomorphology Lab: Stream Flow

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Rafe Parsons
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1 Geomorphology Lab: Stream Flow Destato: Balch Creek Portlad s woderful NW dstrct. The creek s amed after Deholm Balch who lved ear the creek ad 859 was the frst perso to be legally tred ad haged Portlad. He murdered hs so--law. Thgs to brg: Sutable clothg ad footwear for a Portlad park the sprg. You wll eed a pecl ad a hard surface to wrte o. (Feld rule - ever use k the feld, t bleeds o wet or damp paper. Purpose: To measure ad calculate some physcal characterstcs of a stream. Balch Creek s a good example because t accessble, relatvely small ad safe makg t sutable for such a exercse. Although the Columba or Wllamette may be more exctg fluval features, the tme ad effort to make measuremets those rvers far exceeds what extra we mght lear. That s the ce thg about physcs. If you uderstad the fudametal processes, the results ca be appled to other, perhaps more dffcult, stuatos. The ultmate referece: Ratz ad 6 others, 98: Measuremet ad computato of streamflow: Volume. Measuremet of Stage ad Dscharge; ad Volume. Computato of Dscharge. U.S. Geologcal Survey Water Supply paper 75, 63 pp. The Departmet of Iteror's U.S. Geologcal Survey (USGS s the agecy resposble for motorg the ato's stream flow ad groud water levels. Ths s ot to say that other state ad federal make smlar measuremets, but the USGS Water Resource's Dvso s cosdered the lead agecy the subject. For the Orego Dstrct offce, see, FYI: If you ever wat a estmate of stream roughess wthout tryg to measure t, check out the followg referece. It s lke a Peterse's Feld IdetfcatoGude, but for chael roughess: Bares, Jr., H., 967: Roughess characterstcs of atural chaels. U.S. Geologcal Survey Water Supply Paper 849, 3 pp. Assgmet: The feld work wll aswer questos -3,, ad the remag questos ca be doe at home. However, read all questos pror to collectg the feld data, t wll help you gude your feld effort. Ths s lke the real thg. Oe starts develops a feld pla, completes the data collecto, ad typcally aalyzes the data elsewhere. Reports wll be typed (fot pt ad larger ad each aswer wll follow the umberg system of the questos ad be cosecutve order. For mathematcal calculatos, where oe eeds to "show your work", eat hadwrtte calculatos are acceptable. These stuatos are deoted wth a astersk,*. Neatess couts ad all pages eed to be stapled. Graphs eed to be adequately labeled cludg axs labels wth uts. All features a graph or drawg must be

2 detfed. Be careful of uts, make sure that are cosstet. Fally, pay atteto to sgfcat uts. Your book wll be a resource. (8pts Measuremets of stream velocty. Sketch (0pts. Make a rough pla-vew sketch of the stream chael the vcty of the measuremet cross-secto. Iclude about meters above ad below our cross-secto. Note chael shape, shallow areas the water, where rocks mght break the water surface, areas of fast versus slow flow, where plats mght be terferg wth the flow, detfy features draw ad flow drecto. Iclude where the floatg method was performed (start ad stop locatos ad where the measuremet cross-secto s located. Redo the sketch at home ad clude t the report.. Floatg method (5pts. Approxmate the speed of water flow usg a leaf or other debrs that floats o the surface. Your feld otes should clude, elapsed tme, ad dstace traveled. I your report clude these fgures for each ru, the average for all rus ad the average flow speed for all rus. 3. Curret meter. The group wll set up a cross-secto ad measure the flow velocty usg the curret meter at multple postos across the stream. See Fgure. Flow measuremets are made at 0.6H from the surface where H s total depth. Record dstace across stream, depth ad velocty, at each measuremet locato usg the format below. The dscharge wll be calculated later. Your feld otes should be arraged as, Ste. Dstace Depth Velocty.. 3. etc. ( pts Why do you thk we measure at 0.6H ad ot, say, at 0.5H? 4. Dscharge calculato (5pts. The approach towards calculatg dscharge s to use, Q = VA, where Q s the dscharge m 3 /s, V s velocty m/s, ad A s the area m. The specfc uts are ot mportat as log as they are cosstet ad the metrc system. To calculate the dscharge, we dvde the flow cross-secto to subsectos (Fgure, ad measure the velocty ad area for each subsecto. The dscharge s calculated for each subsecto ad summed to estmate the dscharge of the whole cross secto.

3 3 Q = q = where q s the dscharge, v, s the velocty ad a s the area of subsecto,. The area s determed by the depth ad the wdth of each cross-secto, v a a = d + - where, d, s the depth at posto,, ad, b, s the horzotal dstace to that posto from a arbtrarly chose org (Fgure. Thus, q, s estmated by, q = v d + - For the cells at each ed of the cross-secto, where + or - do ot apply, use the followg scheme. At the start use, q = v d ad at the other sde, q = v d (-. b b (- b 3 b 4 b b d (- d d 3 d (-

4 4 Fgure. Defto schematc of a stream cross-secto for calculatg dscharge Take from Ratz et al., 98.. Expla how you calculated the values of wdth at each ed of the cross-secto Create a table of measured ad calculated values for the report usg the followg format. It wll be very helpful to use a spreadsheet for both the calculatos ad producg the table for the report. Make all uts cm ad s. Loc. Dstace Depth Wdth Area Velocty Dscharge.. 3. etc. At the bottom of your table, provde fgures for total area ad stream dscharge. Also covert the total area ad total stream charge to m 3 ad m 3 s Plot (0pts. From your table of values, plot the results of dscharge, velocty, ad stream depth wth dstace across the stream o the same graph. Make the plot such that the water surface s zero ad depth s egatve (drops dow. Plot depth ad wdth at the same scale to help you wth (8 below. O ths same plot, clude velocty ad dscharge. You may wsh to rescale velocty ad dscharge to make them ft better o the graph. Ask, f you do't kow what rescale meas. Velocty Dscharge Depth Ths s what the form of the plot wll look lke. Of course, you wll have to add tck marks, labels, uts, ad a leged of your choce. 6. (5 pts Dscuss the plot referece to frcto of the chael walls ad observatos of flow the feld (sketched fgure. Ca you expla the varato of flow velocty ad dscharge?

5 5 7. ( pts Determe the average velocty of the stream from your calculated value of dscharge ad area questo (4. Do you kow why we use ths value rather tha just the average of all the measured veloctes? 8. (0 pts Usg the Mag equato, calculate the velocty of the stream. Obta slope from the map, usg the slope from the Thurma Brdge to the crossg of the cty boudary le. For the hydraulc radus, use the area calculated questo (4 ad the wetted permeter estmated from your plot. You wll eed a par of dvders to measure alog the chael bottom. For, use a value of 0.06 (mouta stream. Compare that to the velocty oe obtas from a glass surfaced chael (0.0. Show your work* Mag's equato for metrc uts, smply replace the costat.49 wth (5 pts Compare all veloctes (leaf, dscharge, Mag {where, = 0.06} for the stream. Whch value s best for average stream velocty ad why? Iclude a short dscusso of why a dfferece values exsts. 0. Hydraulc characterstcs. Assume the molecular vscosty of the water s,.3x0-3 kg s - m -, ad ts desty s 000 kg m -3. Note that specfc weght s merely the desty tmes gravty. Use the values for velocty as calculated (7. Do ot use depth (a or, use hydraulc radus. a. (5pts Is ths stream flow lamar or turbulet? Show your work cludg how the uts cacel. b. (5pts Is the flow cosdered traqul, crtcal, or rapd (shootg flow? Show your work cludg how the uts cacel. c. (5 pts Calculate the stream power, usg the same slope as foud questo 8. Show your work cludg how the uts cacel.. (pts Paleofloods. What was the sze of some of the paleofloods that moved the surroudg rock? Measure the sze of the largest cobble or boulders or ear the stream you ca fd. If the rock s ot sphercal take a average of the dmesos. What was the velocty of the water eeded to move ths rock? Use the top curve the famly of Hjulström curves. If the rock s larger tha the graph allows, extrapolate the curve.. (pts Suosty. What s the suosty of the stream from the Thurma Brdge to the crossg of the cty boudary le? Show the values used to calculate the suosty. It s calculated by dvdg the path legth of the stream by the legth of a straght le coectg the startg ad edg pots.

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