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North Dakota State Water Commission900 EAST BOULEVARD AVENUE, DEPT 770 • BISMARCK, NORTH DAKOTA 58505-0850

701-328-2750 . TTY 800-366-6888 » FAX 701-328-3696 ■ INTERNET: http://swc.nd.gov

September 15,2015

Roger SauerRenville County Water Resource Board7635 30,h Ave. NWGlenburn, ND 58740

RE: Renville County Study - Tolley Slough

Enclosed is a written report that summarizes the findings of the Tolley Slough study conductedin Renville County and fulfills the responsibilities of the State Water Commission (SWC), asstated in the agreement between the Renville County Water Resource Board and the SWC, datedJune 30th 2013.

As part of this study, the SWC examined the hydrology of the Tolley Slough drainage basin,evaluated potential outlet configurations and other measures to mitigate issues related to elevatedslough, natural outlet, and groundwater levels, and completed a written report with findings andcost estimates.

This report includes survey data collected as part of the study and the hydrologic model of thebasin.

If you have any questions, or would like to meet to discuss the results please contact me at 701-328-4956.

Sincerely,

James Timothy Fay, P.E.Investigations Section Chief

J A C K D A L R Y M P L E , G O V E R N O R T O D D S A N D O , P . E .C H A I R M A N C H I E F E N G I N E E R A N D S E C R E T A R Y

Tolley Slough Investigation Report

SWC Project #1300North Dakota State Water Commission

900 East BoulevardBismarck, ND 58505-0850

Prepared for:Renville County Water Resource Board

June 2015

Prepared by:

Chris Korkowski, E.I.TWater Resource Engineer

Under tte3fiJ;ejtt<supervision of:

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James Jirrio}hy:£af PfEInvestiga^ti6hs;:S0ciij6n Chief

Approved by:

rTodd Sando, P.E.State Engineer

Table of Contents1 . I n t r o d u c t i o n 3

1 . 1 S i t e L o c a t i o n 31 . 2 P r o b l e m B a c k g r o u n d 5

2 . S u r v e y 73 . G e o l o g y 94 . H y d r o l o g y 1 0

4 . 1 C l i m a t e 1 04 . 2 H y d r o l o g y M o d e l 1 14 . 2 . 1 B a s i n 1 14 . 2 . 2 T r a n s f o r m M e t h o d 1 34 . 2 . 3 L o s s M e t h o d 1 34 . 3 F r e q u e n c y S t o r m s 1 4

5 . F l o o d M i t i g a t i o n D e s i g n 1 45 . 1 A l t e r n a t i v e R o u t e S c r e e n i n g 1 85 . 2 A l t e r n a t i v e 1 1 85 . 3 A l t e r n a t i v e 2 2 05 . 5 G r a v i t y F l o w P i p e D e s i g n 2 25 . 6 P u m p D e s i g n : 2 35 . 7 S i p h o n D e s i g n : 2 3

6 . 0 S u m m a r y a n d R e c o m m e n d a t i o n s : 2 47 . 0 R e f e r e n c e s : 2 7

Appendix A Survey (Electronic)

Appendix B Geology (Electronic)

Appendix C Hydrology (Electronic)

Appendix D Outlets (Electronic)

Appendix E Site Photography (Electronic)

Appendix F Investigation Agreement (Electronic)

North DakotaState Water Commission

1. Introduct ion

Tolley Slough is located near the city of Tolley in Renville County. The RenvilleCounty Water Resource Board (Board) contacted the North Dakota State WaterCommission (SWC) about overland flooding on January 24th of 2012. The Boardcommented that the slough used its natural outlet in July of 2011, damagingcounty roads and inundating farmland. Northern Plains Railroad is the mainconnection for Tolley's' grain elevator and has had problems with inundation, iceformation, and saturating the railroad tracks. The Board's investigation requestwas to examine the hydrology and the possibility of lowering the water surface ofthe slough to a more manageable level.

The SWC agreed to conduct a study investigating the hydrology of the basin andevaluate mitigation alternatives.

Tolley Slough is much like other pothole regions; it receives inflows from directprecipitation and runoff from snowmelt and rainstorms. The area around theslough has dramatically changed since 2010, when the slough was relatively dry.Figure 1 compares the 2010 National Agricultural Imagery Program (NAIP) withthe 2012 NAIP.

Figure 1. Tolley Slough, 2010 on the left compared to 2012 NAIP on the right.

1.1 Site Location

6^^\ North Dakota~^\ State Water Commission

Tolley Slough is located in central Renville County in north central North Dakota,adjacent to the city of Tolley. The slough is located with Sections 19, 20, 29, 30,31, 32, 33 of Township 161 North, Range 86 West; Sections 6 of Township 160North, Range 86 West; and Sections 1, 2, 12 of Township 160 North, Range 87West. Currently the surface area of the slough is approximately 2.9 square milesand is situated within a contributing basin of 58.8 square miles.

Tolley Flats

Richland

Figure 2. Tolley Slough, Site Location.

North DakotaState Water Commission

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I Tolley Slough

Figure 3. Tolley Slough, 2012 NAIP.

1.2 Problem Background

The city of Tolley experienced overland flooding from the slough every year sincethe summer of 2010. The flooding from the slough is currently consumingfarmland, inundating roadways, and has temporarily inundated the railroad.However, prior to 2010, the slough was typically dry or it only inundated smallamounts of farmland, but seldom reaches the level of its natural outlet.

Northern Plains Railroad has also witnessed ice on the slough exerting stress onthe railroad track. Ice formation in the fall of 2014 caused delays in the railroad'soperation due to the ice bending the rails and moving them out of alignment.

The current water surface, near the natural outlet elevation, is one of the maincauses of concern. Once the water surface increases, the slough begins todischarge over its 15-mile long natural outlet, damaging roadways and inundatingfarmland. Figure 4 shows the natural outlet of the slough drainage throughMackobee Coulee into Lake Darling.

Culverts along the outlet path are undersized and silted in, increasing flowsacross county roads. Existing culverts along the natural outlet, when cleaned,would provide insignificant flow during an outlet event.

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Figure 4. Natural Outlet, Tolley Slough.

An elevation capacity curve is shown in Figure 5. The digital elevation modelused to compute the elevation capacity curve came from the National ElevationDataset (NED) and any data derived from the NED should only be used as anapproximation.

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Figure 5. Tolley Slough elevation-capacity curve.

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The elevation capacity curve shows the slough's maximum water surface to benearly 1840 ft before it discharges through its natural outlet. At 1840 ft the sloughholds approximately 7500 acre-ft of water. Since it has recently discharged, it isassumed the slough is currently at its maximum capacity, having no additionalstorage.

2. Survey

A survey of the surrounding water surface elevations, railroad track elevation,and possible drainage route were completed on June 2nd of 2012. The verticaldatum for the survey was North American Vertical Datum 1988 (NAVD 88) andthe horizontal datum was North American Datum 1983 (NAD 83). Figure 6 showsthe water surface elevations from the survey conducted on June 2nd 2012. Thesurvey data collected is available in Appendix A.

Light Detection And Ranging (LiDAR) data was collected for the area east ofTolley, ND. The LiDAR data is a 1-meter collect in horizontal datum NAD83 andvertical datum NAVD88.

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Legend■M Natural Outlet

• Water Surface ElevationsI I Slough 2012 NAIP

Figure 6. Water Surface Elevations, June 2nd 2012.

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3. Geology

Tolley Slough hasn't been known to have strong groundwater connection to otherbodies of water. The surface geology suggests that the slough bed is composedof silt surrounded by glacial till. Figure 7 depicts a geologic surface map createdfrom the Soil Survey Geographical Database (SSURGO).

Figure 7. Tolley Flats Geologic Surface Map (SSURGO).

North DakotaState Water Commission

This map suggests silt lining on Tolley Slough, which could be preventing theslough infiltration into the subsoil. The silt lining also makes it unlikely that TolleySlough would have a strong ground water connection.

Boring logs (Appendix B) near Tolley Slough also indicate that the first 30 feet ofsoil is clay. Thick clay layers do not typically allow strong groundwaterconnections supporting the geologic surface data showing a poor groundwaterconnection.

The surveyed water surfaces of neighboring water bodies appear to be similar inelevation to the slough of interest near Tolley. Since the survey was collectedafter the outlet's discharge, the similar water surfaces are primarily caused by thenatural discharge over flat ground and not a strong groundwater connection. Thisassumption can be justified by the boring logs and geologic surface map.

4. Hydrology

The climatic conditions of the area were examined to determine hydrologic inputsto the study area. These inputs were used in a HEC-HMS model to determine theeffect of certain events at Tolley Slough.

4.1 Climate

North Dakota's geographic location lends itself to extreme variability inprecipitation. As a result, the state's history includes many drought and floodevents. Since 1993 much of the state has received above average precipitation.

Yearly precipitation data was obtained from the National Climate Data Center(NCDC) for North Central North Dakota, also known as North Dakota ClimateRegion 2. Figure 8 shows the average yearly precipitation data collected since1990 for North Central North Dakota.

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North Dakota, Climate Division 2. Precipitation, January-July

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Figure 8. NCDC's annual precipitation plot for North Central North Dakota.

4.2 Hydrology Model

The U.S. Army Corps of Engineers' Hydrologic Engineering Center HydrologicModeling System (HEC-HMS, version 4.0) was used to model the hydrology ofthe Tolley Slough Basin. Spatial analysis and the calculation of some hydrologymodel parameters were performed using ArcMap (versions 9.3 and 10.0) andQuantum GIS (version 2.0.0). Inputs for the HEC-HMS model include basin area,transform parameter, and a loss parameter.

4.2.1 Basin

Terrain preprocessing was performed using the Spatial Analyst tools in ArcMapon a 10-meter resolution DEM from the NED. The basin was kept as onecontinuous sub-basin, as shown in Figure 9.

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Figure 9. Tolley Slough, Contributing Watershed.

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4.2.2 Transform Method

The Soil Conservation Service (SCS) unit hydrograph model was selected as thetransform method. The time of concentration (TOC) was calculated using a GIStravel time tool. A more detailed discussion on the travel time tool is provided inAppendix C. Land class and wetland data were required for use of the traveltime tool. Land class data was obtained from the National Land Cover Database2006 (NLCD2006). Wetland data was acquired from U.S. Fish and WildlifeService's National Wetland Inventory. The calculated TOC value for the basin isprovided in Table 1.

Table 1. Tolley Slough time of concentration.

Drainage Area(Square Miles)

TOC Lag Time(min)

Tolley SloughBasin 58.8554 120 7200

4.2.3 Loss Method

The Green-Ampt loss model was used as the loss method in the hydrologymodel. A more detailed discussion on the Green-Ampt algorithm is provided inAppendix C. The calculated Green-Ampt parameters are provided in Table 2.

Table 2. Tolley Slough HEC-HMS loss parameters.

PorosityHydraulic Conductivity

(in/hr)Suction

(in)%

ImperviousTolley Slough

Basin 0.47436 0.16776 19.58058

North DakotaState Water Commission

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4.3 Frequency Storms

The frequency storms used in the Tolley Slough Basin HEC-HMS model werecreated using Atlas 14 point precipitation data. The data collected was partialduration series data.

Table 3. Runoff generated from frequency storms.

Frequency Event(Year)

Percent Chance ofReoccurrence

Runoff(acre-ft)

10 10 2,28625 4 3,24150 2 3,927100 1 4,738500 0.2 6,840

5. Flood Mitigation Design

A stable outlet from Tolley Slough will reduce damages to Renville County roadsand Northern Plains Railroad, while also lowering the water surface to allowaccess to currently inundated farmland. The county roads along the naturaloutlet could be affected depending on the severity of the event. Figure 10 is amap of the roads that could be affected when the outlet is discharging. The list ofthe county roads that could be affected during outlet discharge is located inappendix C.

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Figure 10: Roads that could be affected by Tolley Slough's natural discharge.

A water surface elevation of 1835.5 ft would alleviate damages to roads,railroads, and decrease the inundation area of the surrounding farmland.Reducing the slough to this level would leave nearly 800 acre-feet of water in the

IS North DakotaState Water Commission

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wetlands, conditions similar to those prior to 2010.

Reducing water levels to 1835.5 ft. requires that the outlet would be able toremove nearly 6700 acre-feet of water. Designing an outlet to remove 10 cfswould be equivalent to removing 20 acre-feet per day, taking roughly 335 days.Since the average open water season in North Dakota is between April andNovember it would take nearly two years to reduce the water surface in theslough, providing no new inflows would enter. If however, the allowable rate forthe outlet increased to 20 cfs, or 40 acre-feet per day, the outlet would be able tohandle inflows and reduce the time needed to lower the water surface elevationof the slough. Increasing the flow to 20 cfs would decrease the slough elevationto desired levels in 188 days, providing no new inflows enter Tolley Slough. Anoutlet with a discharge capacity of 20 cfs was then created in the HEC-HMSmodel. The reservoir representing Tolley Slough in the HEC-HMS model's watersurface was then lowered to an elevation of 1835.5. These modifications to theHEC-HMS model can show the affects of creating the proposed outlet structures.Each of the frequency events were then re-run with the modifications in place toview the outcomes of each event. Figure 11 shows the behavior of Tolley Sloughequipped with a 20 cfs outlet during a 10, 25, 50, and 100 year event.

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5.1 Alternative Route Screening

The alternative alignments for possible outlets were evaluated to determine theoptimum route. As a screening tool, an open channel gravity outlet wasevaluated to reduce the water surface elevation to 1835.5 ft. Evaluating routeswith gravity outlets emphasizes selecting the most optimum route for conveyanceregardless of what outlet system is put into place.

5.2 Alternative 1

After determining the flows needed to reduce the water surface elevation of theslough, routes for possible outlets were examined. During initial talks with arearesidents, it was suggested to build an outlet along the right of way of the railroadtracks. Thus, defining Alternative 1. In the city of Tolley, the right of way is 100 fton each side of the track; out of Tolley the right of way is only 50 ft on each sideof the tracks. The width of the right of way would require land acquisition alongthis route, depending on which type of outlet is designed. Alternative 1 wasexamined due to local input. It extends from the slough through the city of Tolley,ultimately flowing into Lake Darling. Figure 10 is the plan view of Alternative 1.

Figure 10. Tolley Slough, Outlet Alternative Route 1.

C&^5 North DakotaState Water Commission18

Alternative 1 was the preferred route by local residents due to the perceivedminimal land acquisition needed to complete the project. The city of Tolleyoccupies one of the highest points between Tolley Slough and Lake Darling. Thisrequires extensive excavation for many outlet systems and increases the amountof land acquisition required to complete the project, however, this is only one ofthe several challenges facing Alternative 1. Figure 11 is the ground profile viewfor Alternative 1 extracted from the LiDAR collect.

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Figure 11. Alternative 1's ground profile plot.

Challenges facing Alternative 1:

• Topography (high ground near Tolley requiring increased excavation/landacquisition)

• Proximity to the railroad and elevator (soil stability during and afterconstruction requires specialized construction techniques and safetyconcerns)

• Proximity to Tolley (open channel accessibility is unacceptable inside citylimits due to safety concerns)

• Possibility of post-construction leakage (could cause soil instability, whichcombined with continued dynamic loadings, could have catastrophicconsequences)

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5.3 Alternative 2

After considering the topography, proximity to the railroad, elevator, and city ofTolley, and the possibility of leakage along Alternative 1, other outlet paths wereinvestigated. Alternative 2 is an outlet path to the north of Tolley that follows thelowest points between the slough and the Mouse River. By following the lowestpoints the route takes advantage of the natural grade. This reduces the amountof earthwork required to move water out of the slough. Figure 12 is the plan viewof Alternative 2.

Figure 12. Tolley Slough outlet alternative route 2.

The benefit of Alternative 2 is that it requires the least amount of earthwork toremove water out of the slough. This means that any outlet option that isconsidered on Alternative 1 would also work on Alternative 2. The route wouldrequire land acquisition along most of the route depending on what type of outletis put into place. Figure 13 is the ground profile view for Alternative 2 extractedfrom the LIDAR collect. The ground profile plots for both Alternative 1 andAlternative 2 are compared in Figure 14.

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Figure 13: Alternative 2's ground profile plot.

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Figure 14: Tolley alternatives ground profile plot.

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Although Alternative 2 is the most efficient route hydraulically, each alternativehas high velocities through the coulees into Lake Darling. HEC-RAS modelswere created for each alternative route (Appendix D) to calculate channelvelocities. The velocities calculated for each alternative were reasonable in mostof the channel, but became significantly higher when moving through the couleesto Lake Darling. Energy dissipation structures or other techniques must beapplied to both alternatives. Energy dissipation structures were not included incost estimates due to the large variability in price.

Each of the alternatives would require modifications to several roadways. Themodifications examined for the open channels for each alternative route wereculverts at each crossing. The standard culvert size determined to be adequatewas a 42-inch or 3.5-foot diameter culvert. This size allows an open channelgravity flow of nearly 33 cfs, more than enough flow to account for natural runoffinto the open channel. Each alternative would have a control structure on themost upstream crossing to control the discharge through the channel.

Construction of either alternative may require a Section 404 permit. The CleanWater Act (CWA) Section 404 regulates the discharge of dredged and fill materialinto waters of the United States, including wetlands, and any fill brought into theslough to construct the outlet may be subject to regulation. Therefore, obtaininga permit from the United States Army Corps of Engineers (USACE) to place fillduring the outlet construction may be required. Additionally, wetlands impactedalong the outlet alignment may be under the jurisdiction of the USFWSeasements and may require mitigation.

5.5 Gravity Flow Pipe Design

Alternative 1 and 2 were also examined as closed gravity flows pipe systems.These pipe systems would follow the same grade as the open channel design,but would restore the surface after construction.

Alternative 1 would be more desirable as a piped system due to minimum landacquisition costs and the shorter route. Due to the load on the pipe system fromthe railroad track, reinforced concrete pipe was examined for this alternative.Reinforced concrete pipe is a rigid pipe that only carries the load of the soildirectly above the pipe. This means that the rigid pipe could be placed within theright of way of the railroad track without taking the load from trains and therailroad. Placing the rigid pipe within the right of way of the railroad would stillrequire special safety equipment, increasing the cost of the pipeline.

Alternative 2 is a slightly longer route, requiring around 2,000 feet of extra pipe.The benefit to Alternative 2 is that the pipe system be made of high strengthHDPE or reinforced concrete pipe. HDPE is a slightly less expensive pipe systemthat would reduce some costs. HDPE is also extremely variable in cost, whichcan change drastically over short periods of time.

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Alternative 1 and 2 would both require control structures on the upstream end ofthe system to ensure a maximum discharge capacity of 20 cfs.

5.6 Pump Design:

Traditionally, pumping is viewed as a drainage method with one of the smallestfinished footprints. Even though pumping initially sounds like a suitable method ofwater removal, it is typically one of the most expensive options. Pumpingsystems have higher operation and maintenance costs than other outlet options,along with having higher construction costs.

Power costs alone can be large enough to remove pumping as an acceptableoutlet option. Based on area power cost averages, running a pump of this sizetypically costs between $15 and $17 (values based off of the Devils Lake Outletoperations, 2014) dollars per acre-ft removed in power costs. This means thatwithout any new inflows into Tolley Slough, it would cost nearly $114,000 inpower to drop the water surface to its desired level. Based on the area'shydrology, millions of dollars could be spent just in power costs trying to maintainthe slough's elevation. With operating, maintenance, and power costs creatingthis expense; a pumping option is not suggested as an outlet method for TolleySlough.

5.7 Siphon Design:

Residents inquired about the use of a siphon to remove water from the TolleySlough. Siphons work by creating a suction head that lifts water out of areservoir to a point of lower elevation. The suction head is created by primingthe siphon with a pump, priming the siphon displaces the air in the systemcreating the suction head.

Siphons are an efficient way to move water out of a reservoir. However,construction and operation of a large siphon can be difficult. The system must beair tight, any air leaks will cause the siphon to fail. Siphons are limited in theamount of total lift required. If the forces of gravity and friction losses are greaterthan the suction head required, the siphon will fail and need to be primed.Maximum siphon lift equation can be used to determine if a siphon ishydraulically possible at a site. It was determined, through initial calculations thata siphon would fail due to friction losses within such a large structure. The siphoncould however become hydraulically possible by notching through the highground in order to reduce the maximum lift. Creating a notch that wouldeffectively reduce the maximum siphon lift would have similar cost implicationsas creating an open channel with the added cost of pumps to prime the siphonand pipe. Calculations used to determine if a siphon operation would behydraulically feasible are located in Appendix D.

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6.0 Summary and Recommendations:It is recommended that a permanent outlet be placed along Alternative 2,preferably a gravity flow open channel outlet with 3.5 ft culverts at each of thefour crossings. The route along Alternative 1 should be avoided if possible due tothe close proximity to the elevator and railroad, proximity city of Tolley,topography, and possibility of leakage, but if an outlet is most desirable throughthe city, it is recommended that the outlet be open channel with a piped sectionthrough Tolley. The section through Tolley would have to be piped due to thespace restrictions. Table 4 & 5 are cost estimates for the two recommendedalternatives described above. The cost estimates in Tables 4 & 5 do not includeland acquisition for the project or energy dissipation controls through the couleeinto Lake Darling.

The recommended alternatives would reduce the risk of further damages causedby the natural outlet flows and would control the water surface elevation of TolleySlough. If nothing is done to reduce the water surface elevation of Tolley Slough,the slough could continue to use its natural outlet if the current wet cyclecontinues. If the wet cycle ends, the sloughs water surface elevation coulddecrease by infiltration and evaporation.

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7.0 References:

Evan, G.( 2011, The National Elevation Dataset December 2011 Release NotesU.S. Geological Survey (USGS), Earth Resources Observation and Science(EROS) Center, p. 16.

Gesch, D.B., 2007, The National Elevation Dataset, in Maune, D., ed., DigitalElevation Model Technologies and Applications: The DEM Users Manual, 2ndEdition: Bethesda, Maryland, American Society for Photogrammetry and RemoteSensing, p. 99-118.

Fry, J., Xian, G., Jin, S., Dewitz, J., Homer, C, Yang, L, Barnes, C, Herold, Nand Wickham, J., 2011. Completion of the 2006 National Land Cover Databasefor the Conterminous United States, PE&RS, Vol. 77(9):858-864.

U.S. Department of Agriculture, [n.d.], Hydrology manual for North Dakota: U.S.Department of Agriculture, Soil Conservation Service, Bismarck, N. Dak., 230 p.

North Dakota Geologic Survey, (n.d.). Retrieved September 10, 2014, fromhttps://www.dmr.nd.aov/ndqs/surfacegeo/

Fortier, R. (Ed.). (2014). RSMeans Heavy Construction Cost Data (28th ed., p.738). Norwell: Reed Construction Data.

I^S$^ North Dakota^^^ii State V/ater Commission