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PRELIMINARY ENGINEERING REPORT

SUNDOWN ACRESs.w.c. PRoJEGT NO. 576 -27

BURL EIGH COUNTY

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'PRELIMINARY ENGINEERING REPORT

SI,'NDOüIN ACRES

SIIIC Proj ecX #576-27

Nortfr Dakota State [nlater Commission

9OO East Boulevard

Bismarck, ND 58505-0187

Frepared by:

(--,,t Çru* --RanÙal1 Binegar JI¡later Resource Engineer

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A.Dirêctor of EngÍneering

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SUNDOI,ìIN ACRES

State hlater Commission projecl" #576-22

Technio-a1 assistance in the preparati-on of this report wasreceived from John Remus, Corps of Engineers-

TABLE OF CONTENTS

INTRODUCTION.Background..Study Objectives- -Description of the Study Area .. ò..

ÀLTERNATIVE BANK PROTECTION METHODS. . . . . . .Alternative #1 Rebuild Jetty to Original Design-....Alternatíve #2 Extension of Jetty' Structure...Cost Estimate - Alternative #2. -Àlternative #3 - Stoping and Ríprapping the Bank Line-Cost Estimate - Alternative #3ÀCost Estimate - Atternative #38Alternative #4 - Not Sloping the Bank Line Above the

RiprapCost Estimate - ÀIternative .#44Cost Estimate - Alternative #4e

CONCLUSIONS AND RECOMMENDÀTIONSConclusions.Recommendations

FIGURES

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Location Map. .....Topography Map (Station Ll+OO to 27+OO)Topography Map (Station 2B+OO to 43+OO)Topography Map (Station 43+OO to 48+OO)Missouri River FIow Direction.Alternatíve #2 Jetty Extension...Jetty ProfiJ-e and Typical- SectÍon-Typical. Cross-Section - Alternative 3...Riprapped Bank AlignmentRiprapped Bank AlÍgnmentRiprapped Bank ÀIignmentTypical Cross-Section - Alternative 4...

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INTRODUCTION

Background:In L977, the Corps of Engineers constructed a jetty at

Missouri River miJ-e 1328.65, under the Garrison Dam to Lake Oatre

Bank Protection, Program, autfrorized by Pub1ic Law BB-253 of the1963 Flood Control Àct, and amended by Pub1ic Law 9O-483 of the1968 Flood Control Àct. The jetty was constructed along the leftbank for the purpose of directing the Missouri River flows to theright side of the river, thereby protecting the left bank wherethe Sundown Acres subdivision is located. Àccording to the Corpsof Engineers as-built plans, ttre jetty was originaJ-J.y 5OO feetlong and connected with a sandbar which paraJ.J-eJ-ed the bank line.Figure 1- shows the location of the jetty at river miJ-e 1328.65-In recent years, the end of the jetty has deteriorated. Highflows in 1982 and ice actÍon during the 1986 winter causedextensive damages. Ttrere have been conflicting accounts of how

much of the original jetty has been lost, hovrever, most estimatesrange from 20 to 70 feet.

The bank J.ine along the Sundown Acres subdivision hasexperienced severe erosion ín the past few years. In April 1986,the Sundown Àcres homeowners requested the Bur1eígh County IdaterResource Board to establish a special assessment district to funda bank stabilization project for the subdivisíon. The BurleighCounty trlater Resource Board then requested the State lrlaterCommission to provide technical assistance in the deveJ-opment ofan erosíon control project and requested cost participation to

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assist in funding the project. At the June L8, 1986 meeting ofthe State trlater Commission, 5O percent of al-l eligible items, notto exceed S37,5OO, was granted towárds the repair or modificatíonof the jetty to provide immediate protection.

An ÍnÍtial- appraisal report prepared. by the Corps ofEngineers in May l-986 presented seV.eral alternative solutions tothe bank erosion probrem. The corpsr report recommended thatsome form of stone-filr bank revetment be in prace arong thebank. In Ju1y, the area r{as surveyed by the State ûrlaterCommission.

Studv Obiectives:This report considers ttre restoration of ttre damaged jetty to

near its original desÍgn. An evaluation of other erosj-on controlmethods is also addressed and cost estímates for each alternativeare given. Ttre overall objective is to determine a feasible andeffectÍve erosion control method for the bank line in the SundownAcres area-

Description of the Study Area:The project is rocated approximatery nine mires north of

Bismarck in Section 5, Township 14o Norttr, Range Br lrtrest, inBurleigh county. The project is arong the reft river bank atapproximate MÍssouri River mire L328. The project boundariesÍnclude ttre area between revetment 1328.65 and revetment Lg2Z.4S-A topographic map of the project area is shown Ín Figures 2, 3,

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and 4. The sundown Acres subdivision is located within theproject boundaries along the inside bend of the river.

There presentry are four homes within the Sundown AcressubdÍvision wtrich, to varying degrees, are endangered by theencroaching river. Ttre home c1osest to the river isapproximately: l-50 feet from the bank rine. Landovrners haveimpremented bank protection measures of their own along smarrsegments of the bank which have been ineffectÍve in stopping theerosion- However, the riprap in the Mohler boat ramp area(Station I7+7O on Figure 2) is providing bank protection becausethe bank was sloped before it was riprapped. This area is arsoreceiving some protection from ttre remaÍning jetty structure.

A surface analysis indicated the entire area consists of anunconsoridated sirty-sand materiat. The area basicarry is asandbar which makes it very susceptable to ctranges as a resutt ofnatural river processes. A remnant channer is rocated nearstation 23+oo, indicating a portion of.the Sundown Àcressubdivísion area was at one tíme heneath the Míssouri River.

Erosíon rates along the bank vary. The averag,e ]-oss is about5 feet per year with losses of 20 feet in one week beingreported. Future losses are impossible to predict except to saythat erosion wilr continue unress preventive measures areÍmplemented. Erosion occurs as ttre resu].t of both water and iceaction. This area is especiarry susceptabre to erosion due toflowing water along the toe of the bank- The depths Ímmediatelyadjacent to the banks are as deep as 25 feet berow ttre normal

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}flSSOIIRI RIVER BANK STASILIZATIONSI^TC PROJECT NO. 576-27

SIINDOT,¡N ACRESToPograPhY l'faP

Stations 43€0 to 481{0Sec. 5, T.140N., R.81w.

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water elevation of 1635 msI. -Figures 2, 3, and 4, show the deepdepressions immediately off the banks. Às the river frows,approach the bank, the flows faII into the depression creatÍng acircurar motion which furttrer increases the potentiar forerosion-

Aerial photographs indicate the f].ow direction of the riverhas changed largety due to the formatÍon of a large new sandbarlocated on ttre west side of the river- The furr force of theriver now flows directly toward the project areas banks as shownin Figure 5.

The damage to the jetty tras a1J-owed additional flows to passbetween the left bank and the sandbar located. approximately 24O

feet from the bank- The addÍtionar flows have increased thevelocities wtrich cause deepening of the riverbed along the bankand further compound ttre erosion problem-

Ttre exact cause for the increase in bank erosion in theproject area is unknown. Factors which.may have contributedinclude: damage to the jetty, unique movement of water and Ícein the past few years, and the natural change in the river courseresultíng from normal fluviaJ- processes. Another factor whichundoubtedly has contributed is the management of the Garrison Dam

and Reservoir which alrows for the rereases of crear, sedimentfree water capabre of eroding and transporting large amounts ofsoi]- from the banks of ttre Missouri Riwer-

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ALTERNATIVE BANK PROTECTION METHODS

Alternative #1 Rebui]-d Jetty to Oriqinat Desiqn:The Corps of Engineers built the jetty at Missouri Riwer míl-e

l-328.65 to divert flows to the west side of the river, therebyprotecting the the banks ín the Sundown Acres area. According tothe Corps as-built plans, ttre jetty was originalty constructed toelevation 164o-0 msr and was 5OO feet in rength- Recent fieldmeasurements indicate that approximately 4Bo feet of the jettyremain in place. Loca1 landowners have estimated that between 50

to 7o feet of the originar jetty is missing. The discrepancybetween the 5O-7O feet of missing dike reported by the 1ocals andthe 20 feet measured ín the fierd may be due to an error in theCorpsr final design p1ans.

The topography map of the jetty area (Figure 2) shows a deepdepression or ctranner on the west side of the jetty which is 14feet berow the normar water surface erevation. tùest of thedepression the riverbed rises to elevation 1630 ms1, 5 feet belowthe normal water surface elevation. Àssuming that 70 feet of thejetty ís missing, reconstructing the jetty to Íts oríginalcondition wourd prace the end of the jetty in the depressionararea. The placement of the end of the jetty in the depressionalarea is an undesirable design which would continue to permit flowthrough the depression and dÍrectly to the bank. The jetty,constructed in this manner, would a].so be very susceptabre tocontinued damage due to ftows through the depressional channel.The reconstructíon of the jetty to near its origina]. design wouldnot be an effective bank protection mettrod and courd again be

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t easily damaged. Therefore, it Ís not considered a feasíbleproject and wiJ-l not ibe studied further.

Àlternative #2 Extension of Jetty Structure:This arternative considers the extensÍon of the existing

jetty through the depressionat area and tying it into a sandbarat elevation 1630 msI, as shown in Figure 6. To tie-in with thehigh area, ttre existÍng jetty would need to be extended 220feet. ThÍs wourd effectivery brock the frow through thedepressíonar area, thereby protecting additionar bank rine. Theextended. portion of the jetty woutd be constructed to elevationL637 msl; three feet berow the existing jetty and two feet abovethe normal water surface erevatíon. A profÍre and typicalsection of the jetty extension is shown in Figure 7.

Thre exístÍng jetty protects the bank rine up to approximatetyStation 16+o0. ExtendÍng the jetty 22o feet would lengthen theprotected banktine 4OO feet to StatÍon ?O+OO. Areas downstreamof Station 2O+OO would recieve leSS protection. The further awayfrom the jetty the less protection wourd be provided- rt isestimated that by Station 26+00, Iittle benefit wiII be realizedby the extension of the jetty.

The end of the original jetty tied-in to a sandbar which hassÍnce migrated downstream- The migration of the sandbardownstream probably resulted in the damage to the originaljetty. Ttre sandbar which the jetty extension would tie into may

arso begin to migrate causíng damage to the new jetty structure.l'1.,

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Ì,ÍISSOIIRI RIVER BÆ{K STABTLIZATIONSI.IC PROJECT NO. 576-27

SIJNDO!¡N ACRESAlternatíve lÍz-Jetty Extension

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MISSOURT RIVER BANK STABILIZATIONst,rc PRoJECT N0. 576-27

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cost estimates for the extensíon of the jetty - Arternative#Z are given below:

COST ESTIMÀTEALTERNATTVE #2

item QuantÍty Unit UnitCost Cost

Mobi]-izationRock Riprap 2,960

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79,OOO$82,90016,600

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Alternative #3 S and Ri the Bank Line:This alternatÍve consists of straÍghtening the bank 1Íne and

apptying a continuous rayer of rock riprap material- The stonewould be praced at a rate of. 4 tons per rinear foot with a crownwidth of 4 feet- The bank area above the riprap wourd beback-sloped at 1:3 (J- Verticar to 3 Horizontar) and the riprapwould be praced on a 1:1-s sroped surface- A typicar section ofan Arternatiwe #3 ríprapped bank, ig shown in Figure g. Theriprap would extend down a minimum of B feet to elevation 1630msI -

The irregular shape of the bank rine increases thesusceptibÍlity of the bank to erosion, causes whirlpoors andincreases the flow turbidity which further increases thepotentiar for the flows to erode. straighteníng the bank rinereduces ttre erosion potential and atso reduces the cost becauseress ríprap is required. Figures g, 10, and 11, show thealignment of ttre straightened and riprapped bank line-

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}fiSSOTIRI RIVER BAI.IK STABILIZATIONSI{C PROJECT NO. 576_27

STINDOI{N ACRESRiprapped Bank Alignment

Prefix Elevatlon 1600 nsl 'Contour Interr¡al - 2 feeB .

Sec. 5, T.140N., R.81I{.' Scale: 1"=100tt1t"r tt

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The straightening and sroping of the bank wi1l,-result ín theloss of land along the bank in some areas- The project wouldalso result in the ross of trees arong the bank rine. projectcosts could be reduced Íf the contractor is allowed to stockpilettre downed trees in the project area rather than having totransport and dispose of ttrem.

The project would begin at the boat ramp ]-ocated at StatÍonL7+79. Upstream from the boat ramp ttre bank is protected by bothriprap and the existing jetty structure- Downstream from theboat ramp the bank is rip-rapped for approximatery Bo feet- ThisBO feet of riprapped'bank would receive an additionat 2 feet ofriprap to adequately protect ttre reach. This reach does not needto be re-stoped. Approximately a 4-foot thÍck tayer of ríprapwould be applied to a shaped bank startÍng at Station 1B+SO andextending downstream to ttre end of the project.

Boat ramps arong the bank have compounded the existingerosion problem and would continue to be a maintenance problem ifthey were designed into the project- rt is recommended that noboat ramps other than the Mohler boat ramp be included, hor^rever,íf the landowners insist on including them, provisions should bemade for them during the initial constructíon- The provisj-onsinclude the placement of a windrow refusa]. on thre downstream sideof all boat ramps designed into the project- The additional costof the boat ramps wourd not be incruded in any cost-sharingagreement with the State of North Dakota-

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Cost estimates are given below for Àlternative #3,constructed from Station L7+7O through Station 32+OO (Alternative#3a - 1,430 feet) and from Station L7+7O through Station 45+OO

(Arternative #3s - 2,730 feet). station 32+oo Ís immediatelydownstream of the Oswald house which is the l_ast home inimmediate danger from the bank erosion. station 45+oo is justupstream from the jetty located at Missouri River mile L327.45-

COST ESTIMATEÀLTERNÀTIVE #3A1,43O Feet, Station L7+7O to 32+OO

UnítCostItem

Mobi]-izationRock RiprapFi11Excavate

ItemMobi]-izatÍonRock RiprapFiIlExcavate

anti Unit

2,3BO1, OOOL,42O

Subtota]-2OZ Contingencies & EngineeringTotal

COST ESTIMÀTEALTERNATIVE #382,73O Feet, Station L7+7O to 45+OO

Quantitv Unit UnitCost

L.S. s4,300 c.Y. 27 .OO1,590 c.Y- 2.OO2,870 c. Y- 2.OOSubtotal20å Contingencies å EngineeringTotaI

SYYY

Lccc

Þ27.OO

2.OO2 -OO

Costs 3,000

64,3002,OOO2,goo

s72,LOOL4,400

s86,500

Costs 3,ooo

116,1003 ,2005,700

s128, OOO25,600

s153,600

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A]-ternative - Not SI the Bank Line Above ttreThis arternative is essentially the same as Arternative #3

except that ttre bank above the riprap would not be sloped in mostareas and thre riprap would have a frat top rather than sroped. Atypical section of an Alternative #4 riprapped bank, is shown inFÍgure L2. Arternative #4 would be less expensive thanAlternative #3, but wourd provide tess protection during highrunoff. Àlternative #3 would provide an average of 2 feet ofadditionaJ. coverage on the top portion of the riprap.Arternatíve #4 would be more of a hazard in some areas due to thesudden drop off of ttre bank onto the riprap. ÀIternative 3 wouldprovide easier access to the river and would be more estheticallypleasÍng ttran Alternative #4. Cost estÍmates for Alternative #4constructed from Station L7+7O through Station 32+OO (ÀIternative#4e' - r,43o feet) and from station LZ+zo through 45+oo(Alternative #4e - 2,230 feet) are given below.

COST ESTIMÀTEÀLTERNÀTIVE #4AL,43O Feet, Station LT+ZO to 32+OO

ItemMobi].ÍzationRock RiprapFj-I]-Excavate

anti Unit UnitCost

L.S. S2 ,2LO c - Y- 27 .OO930 c.Y. 2.OO1,l_BO c-Y. 2-OOSubtotal

20å Contingencíes å EngineeringTotaI

Costs 3,OOO

59, 700l_,9o02,400

$67, OOO13,400

sBo,400

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ExistingBqnk Line

l. MISSOURT RI\TER BANK STABILIZATIO}Tsl{c PROJECT NO. 576-27

SIINDOT.¡N ACRESTypl-cal Cross-Sedtloa : Alternatfve 4

Scale: 1rto5 r

Figure 12-22-

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. COST ESTIMATEÀLTERNÀTIVE #482,730 Feet, Station L7+fg to 45+OO

temMobi]-izationRock RÍprapFiI1Excavate

s27 .AO

2.CIO2 -OO

$ 3,0oo105, 600

2,gao4r7OO

$1L6,20023,2AO

$L39,400

t Cost

3,9101,45O2,360

Subtotal2Oå Contingencies å EngineeringTota]-

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CONCTUSIONS AND RECOMMENDATIONS

Conc]-usj-ons:

The jetty constructed at Missouri River mile ].328.65 by theCorps of Engineers has been damaged and does not provide adequatebank erosion protection in the Sundown Äcres area- The banl<s arecurrently very susceptibre to erosion and. are in need ofimmediate protection-

Reconstruction of the jetty to its original design wourd notprovide an adequate amount of bank erosion protection and therebuirt structure would rikely be damaged again during hÍghflows -

Alternatj-ve #2 considers extending the jetty 22o feet andtying it into a sandbar- Ttre amount of bank 1ine protected would.not substantially increase- Ttre extended jetty wourd be moresusceptible to damage due to high flows than Alternatives 3 or 4wourd be. The expected life span of the jetty extension wourd befrom 1 to 20 years-

Alternative 3 offers the most effective form of bankprotection- Both Àlternatives 3 and 4 have expected rífe spansof 20 years, hovrever, no form of bank protection can provideguaranteed protection from the erosive forces of the MissouriRiver-

RecommendatÍons:

Due to the rimited amount of protection provided byArternatives 1 and 2, and. the smatr difference ín costs betweenAlternatives 3 and 4, it is reconmended that AlternatÍve 3, be

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I

impremented. The decisÍon to proceed with the project must bemade by the Bur1eígh County hlater Resource Board-

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