D-A192 249 ANALYSIS OF BANK STABILITYI IN THE DEC (DEMONSTRAiTION .'EROSION CONTROL) NATERSHEDS NISSJSSIPPI(U) QUEEN NARYCOLL LOON (ENGLAND) C R THORNE 29 JAN 8

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ANALYSIS OF BANK STABILITYIN THE DEC WATERSHEDS, MISSISSIPPI

By

Colin R. Thorne

Queen Mary College, University of London, UK

Contract Number DAJA45-87-C-0021(R & D 5781-EN-01)

Third Periodic Report

November 1987 - January 1988

The research reported in this document hasbeen made possible through the support andsponsorship of the U.S. Government through

United States Army

EUROPEAN RESEARCH OFFICE OF THE U.S. ARMY.

London England

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DTIC ":S +.SEL E CT7E..-<

MAR 1 8 1988

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L~~~ -CIO!T-z" .JK DONE

Th rcug,-out the tnrd period of study I have been basedjait t)ne W1.1 erwavs Experiment Station, vi cksburg. I h av e:ontinued to aevelop and test criteria for cank s -a[)Ii I ty.for application to tne DEC wa3tersheds. Emphasis has --riftedTr-i d l(ev el.opme nt to testinq durin~g zrns perioa. FIt r 31ifvoiveo rejuction or exist::ng aaz;a s-upplieuo a, tr~e LJIK anI,-ac~uilticn of new dat-a fromn Lon~g Creek and its tlriOutarieZ,Go o d w. n Cree-, and Joh~nson Creek. A~ nal trip to Nortr:%

ssizsipoi was maae for data collection in Decemtoer 7~?"Io numie n t da sections were es-ta::,is-hec at 17 points an Long

.e ak at TC pointz on Goocaw:n Creek and a t 7 aaOnt onr LCIJonnson re e. The Sites on Goodwi n and Jonnson u reeKL

oarr~ zn-ato tose u 1d i my l7/Ostud y fcor t I'll a'zedt,;nerntati,3r Latoratu~rv. 7his gives Lan &added mnsn

to ne:r- u-reui-ess. The fiela dlata supply intormation or-_ a-'~. nion are enerlly steeper than those ruze~

'S U -. evo ana '.Jhich are known fir-om orcerva Zion to( sze clos-eto l~tr g s ta ci11it y Tne f ieid data wil I !e us-ci to .est

t.ne 3-ral.'i procedure for- pradiotin~g bans ta, ltv

vC. zr ac n q ,e r, ~ , n'~ i VC 5

t, r- ~-

eo' a- Di~ acNr forIzeD a.r '.4 t-!,, n 3tt Z' a:i~~rz t 9z~niz en eaneers : trU en z :ns

:3 N0 ran ijK t n i sau nics ad O.ICS

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S - i er- Zr~ nae eter, ur it aOl z ri c c

-i --4L -e a ~rn ; ~n-

2 0r-r' 7 .r C nave 1c 7 1 d'- na~ :Z, tiz e e oc_

a'_l r .n ar ver' a n ~ a et n2 -~ rn Fo

n& b z 4- Bc

rir'~r izr~ ontooflr~~' ~<- ~ ,cs * or

F----or- no~a~o nc-ir inae cen or:.NIP[

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W'hen combined with lateral erosion reducing the value of Mi,tn±s can cause the program to crash, if Hi is reouced tozero before failure occurs. This can be accountea for intne program, but as, usually, the analysis is applied toaegrading channels the problem shoula not arise often. itwould only occur wnen upstream bank failures supply so muchsediment that the bed aggrades even though tne nanKZcontinue to be eroded. Wnether or not this is a realisticscenario reimains to be seen.

A valuable product of the interest shown b'/ wET in tntanK study is a version of tire stabilty analsis for tneSfl-PC micro-computer. Tn is has been Wrltt'n t'/ L'i3 ,4.7evennergen of WET, based on the HP-41CV program and user'smanual zuppliad by me (as reported in tna previou sec:c. .Lyile use.d the LOTUO 1-2-3 saread sheet as the basis for t-,e Z.,ot, rami. ResuLt:s fron hi- proqram are nan oneckea ao lnst

rslta frcm trne HP program to verify that is p rogramr-!73 Ph u ' r -"),, oe rc ze cri,,inai ana lysis. So f 3r no 0 %Cdcreman cles nhave ceen found. r

T,ne ma ,or a '.,antages of the IBM-PC program over- the H.--4i pcoqram are:

i ) Tha ease itn wnion variaoles can e c nanQed. r-0r TU 1-2-3 -pread sneet, any of the input variacies

rHil,pni,c,aamma and ',>) can ce cnanged at wili, and t-neimoa t on the ractor ofI; safety is seen immediately. frni

tn r e .1t;".'en lent to examine tne i nipor tance of eac roar aetr- that I e sr e ns' t Iv.Iy 0a tne , aor or csa t

j e v, a r :ar ablIe an , ; %

.2 Tne orgqr-am runs muCh more ,7uicx~y as oe iari-- n">_

7: ,greater cc:npu ta:.- 3nai ,ower and memory ",nan tne HP -4- .

;c ma ]or- -. _a,ivantaqes are: - .

P(: r, i . not :orzaola -rInc cannlot be usec cr-s- ta-1 s i'm1tatio n <ooes not applv to 3erta:n ;:ortable P.-

L. S, O3ut tLhse are comparatv ely ar- Iv ava laO , ,-7

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,3,. -n toda' a ia-r...', .. ,-1 r) o - ,z I ,. "2 z 7;:, r-.* - .-a nD. e" ' . -' e a- a i a t

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1 do wi.s n to recor-d my thanks to Lyle for- w r- i i n, trie3M -PC e r sio n o f tne stability analy/sis and Lo ,Cnes~er.aLson fo)r h~vn im the time to do this.

In Parallel w~ith development of the staboilitv a na ly s~o f sta- a e 0nkS us 1n9g a slab-type failure mode, rav estarted looKing at the analysis of banks with gentler slooes:,i,_Lh re-gard to failure by rotational a-lip. Ina hi 1h.i

mTv graduate student at Colorado S3tate University, Or~ IMha;mos5:%f pr3z3ntaj zaii~tv cnarts f-or rotational failura Df;tza car tr qe n ie s=lopes ( I t,,00) (Osman. >5.

* eh't .)2-in in IcQS. i - 7 hay jetI re-3iitv lu~re o)Iook 1,jt r and failure bioc-K volumie.

~-3PC ti.'l~ :0~.tetney nave not ceen tested or ap~p ieto eal reaoan~.sand so their accuracy and relisolity

.).3~fl ~ nae egu n to ex<amiLne these ctharts with t.-e~t~~t;r~~pyi~ tem to Long vreeK arMc I~.

T :s t~ of t-Ie sltac.Lity analysiS against eaistin .01

re ~ Da t~ r -;cnQ Creek nas orod0uced enoura~iflon 3U Ita

re S imp le-_ prLdr is to pi :t tr0anK neignts andexLs ~<rao~eoi irom the C.orps' surveys or, a grapn tco etrar

-itlte ii ne of linmit ing "t)I i ty de r ivad from Lt2ea nalysS- of initial .'allures. isi plot is snown in,7~

e limiting 13ine delineates two areas of tre ~an ac. -ie 1iZ zne Zone ofr stability iak tho, .~:i

z3s cru w b e s ,t a ev en un dear t r ~o ra;s Lr ooz in at in C 7

_:c.a :,ances, a I tno ugh C'arnkS Lt -i n,; "Ds oa to tre l4oo,~nI, neco. o njy mino-r increases in 1ho.iant 3r- a n,_3i 7 ),o t.

r'm.3: ri< or KC f.3 lurte-. Ba ("ks ' ~n I-ch pl1oDt a b cv/e :n3 I li ,e~r aeay at r;;, o ' ailure. 7 .1 zr ta ltyse r os

.J0r S ao toa. n~ ot: ocourring ard it Dannot tae re L132Tho~' m-~~ou_ C-O eaPezted to fail inm tie i t

~ma earfuture. Unxec3, o data terd, toQ - a i L 2.nr 'sta.ble" zo:ne as Cernea by the present a na s i. n

*'t S~ ou t of 7 3 o o in -,s fal onr or o elIo-)w t h o Lia.) o .

, in:?o iimiri:nq s-taoalitv t.ends to a rma (- r2 'ei'oPe. t* o.Th 1 3 t.a j 1-~~n r3 trn " or :r-3 ac nq :i 22 o, :

~ie T.a it - e F 7

;:r3. .-ur:r' er D znna:o 3 t caa~~~:ctreo O_, anKE 'Ne re a i ic -a rea I r r eac nes Ow n L C C.E

P r Ie n c 1 ng ra Pid nanK retreat. uCn--equently. 1 .3iZ;a:-,a 1a Fe is zjus t as e-'oecoteo. '-

tr test .~5to ~t %O ~ - -> 2e-,C er ,/ed 11 t., e rielI a:;31n~t z;.a:.n e:I n iC..0-;to

~~ ar a U- Lzre eie, r.ri "Za.,

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should be less than Beta, by an amount depending on tn-efriction angle of the disturbed material and the degree otoasal clean-out by the flow. F-ig. S shows a Plot o hversus lower bank angle, with the theoretical curve for Eeta Nadded. The theoretical curve does form an upper tound to %the iata cloud. This suggests that the lower bank anglesare actually equal to or less than Beta, as expected.

2. RESEARCH PLANS

To compiete testing of the s:aolity anal'/sis, repeatsurveys will De carriea out at tne field sites on Long,}oodwin and Jcnnson Creeks in firther field trips to rNortn'12SLs-s~spp1. This viork will supply the detaiied data on tLe•-cocmetrY at; failure needed to test the 4ull analysis, ratr:er-tnan 3ust tne aerivea curves shown here.

Tne nai'i SLs for oanks wi"tn gentle sl as L.Jl I IA evs Ioed and applied to Long Creek ana a user s Ma3-ua.-_;iila r- t:3 tnat for tne stoep banks will ce writtz"-r.

:-)egionalization of the analysis is plannec for'ormer O ' ,3 , after completicn of the _ rr , ztuo'2, and i.

ne'. research contract. The relevant proposal is pre-antl.in or-paration at Quean Nary Collee.

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