UNIVERSITY OF KWAZULU-NATAL EXAMINATIONS: JUNE 2007

Transcription

1 EXAMINATIONS: SUBJECT, COURSE AND CODE: HYDROLOGY 20 DURATION: HOURS TOTAL MARKS: 00 Internl Exminer : Ms ML Wrburton : Prof RE Schulze : Ms KT Chetty : Mr MJC Horn Externl Exminer : Prof PJT Roberts STUDENTS ARE REQUIRED IN THEIR OWN INTERESTS, TO WRITE LEGIBLY NOTES: This pper consists of 5 pges of questions. Plese see tht you hve them ll. Answer ll questions. Clcultors my be used. QUESTION : Rinfll (5 mrks) () Currently in South Afric three techniques of rinfll mesurement re used, viz. ringuges, wether rdr nd stellite. (i) Briefly discuss the use of wether rdr in mesuring rinfll, giving both the dvntges nd disdvntges. (4) (ii) With the id of sketch, explin the differences between hydrologicl nd meteorologicl rinfll. () (iii) Nme two fctors of ringuge s exterior which ffect its ccurcy, giving short resoning for ech fctor nmed. (2) (b) Does the rel reduction fctor (ARF) increse or decrese with (i) re? (ii) storm durtion? (iii) storm intensity? () Discuss the three () bsic ssumptions behind design rinfll studies. ()

2 QUESTION 2 : Interception nd Systems (5 Mrks) () Why, for given durtion of rinfll event, is the interception loss higher for higher rinfll intensities? Answer with the id of n nnotted sketch. (6) (b) Prepre sketch of the interctions of n ecosystem nd for ech component, explin how ech of the interctions is importnt in hydrology. (9) QUESTION : Evportion (20 Mrks) () When considering vegettion fctors which ffect totl evportion, explin the importnce of reflectivity, nd how it vries with plnt colour, wetness, seson nd time of dy. (6) (b) Both the Blney-Criddle nd the Thornthwite equtions for the estimtion of reference potentil evportion contin correction fctors for dylength. How, respectively, re the correction fctors clculted? (4) In the shortwve eqution of the Penmn formul for reference potentil evportion, clculte wht frction of extrterrestril rdition would rech the erth on dy when the sun shines for hlf the time, given n lbedo of 20%. Show ll working steps. (5) (d) In the versions of the Lincre eqution for n extended wter surfce nd wet vegetted surfce, wht re the differences between the equtions nd why do the respective constnts used chnge in the wy they do? (5) [20] 2

3 QUESTION 4 : Soil Wter (5 mrks) () Derive n expression for prticle density, P s, given lbortory setup where you re provided with four identicl flsks, some soil, some wter nd scle. Use digrms to explin your derivtion. (4) (b) Explin the processes of sorption nd desorption in the hysteresis effect. (2) (d) Explin, with the id of digrm, how one would mesure verticl flow in cylindricl smple. Add in your explntion how you would clculte sturted hydrulic conductivity nd the verge velocity. (5) If the bulk density of the soil smple is mesured s 600kg.m -, the prticle density is 2650 kg.m - nd the wter content is 0.2, determine the percent sturtion of the smple. (4) QUESTION 5 : Runoff (5 mrks) () Criticlly discuss ny two ssumptions of Horton s runoff theory. (4) (b) Explin the two theories used to describe interflow contribution to the hydrogrph. (6) Briefly explin the impct of (i) Overgrzing on sediment yield nd, (ii) Afforesttion on bseflows (4) (d) Define the term rting curve. () QUESTION 6 : Wter Budget (20 Mrks) () (b) Complete the monthly wter budget tble on pge 4. (Hint: All the necessry informtion is contined in the tble) (7) Explin briefly how, in given month there my be more net precipittion (Pn) thn totl evportion (E) nd yet no runoff my be generted? (4) Knowing the Men Annul Precipittion of n re is of no vlue to wter prctitioner, frmer or home owner. Discuss this sttement with reference to the vrious spects of the wter budget you hve studied. (9) [20]

4 Do Not forget to hnd in this pge Student Number (mm) Jn Feb Mr Apr Pn Em Pe - Em 28 Actul SM 200 chnge 0 SM E D 0 S 28 Avil Q 56 Q 28 Detention 28 4

5 EQUATION SHEET P % n 0 = ( n+ m) 00 n+ RH ed = 00 e P T t =.(0.27 lnt )(0.54t )( M 2 +.9L) = (0.5 lnt +0.76)(0.54t )(.M 0.6 R 0.20 ) E p = /γ Rn + E /γ+ P n - o = ( - / T) n r = R+ Rtn tn i cos( B W ) 2 V = d. 02 d d t d 50 =.28I E = ( u)( 00 RH ) e 7. 5T /( T) e = R = R ( α )( n / N) sw R = [ ε ( σt 4 )][ c( e RH ) 0.5 ][ f + ( f) n / N ] lw k E = 0.5mv 2 = / I = log 0 I h= 2σ cos ά rρg A 0 = (π / 4) D 0 E p = [0.05+4x0-4 T +0-6 z][480(t z)/(84 - φ) u(T -T d )] = [0.05+4x0-4 T +0-6 z][80(t z)/(84 - φ) u(T - T d )] = [60(T z)/(84 - φ) u(T - T d )] / [ (γ / ) ] where (T - T d ) = 0.002z+0.7T+0.5(T mx - T mn ) + 0.5T r f = ψ cr / E s l r i m( i ) = E = k E FRAC If Ө (i-) > [(f s PAW ) + LL ], then FRAC = else A e = A 0 cos i FRAC = ( LL ) θ ( i ) PAW f s 5