Slide 1

Alternative Check Dams for Polyacrylamide Dosing Melanie M. McCaleb, CPESCNorth Carolina State University, Soil Science Departmentmelanie_mccaleb@ncsu.edu919-513-1419

Richard A. McLaughlin, Ph.D.North Carolina State University, Soil Science Departmentrichard_mclaughlin@ncsu.edu919-515-7306

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE

Sediment is the #1 pollutant in NC waterways!NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEWe all probably know that sediment is the #1 pollutant in NC waterways- including lakes, rivers, streams, and reservoirs. This sedimentation comes primarily from active construction sites including the development of roadway and housing developments.2EPA Rules and Regulations

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEWith those heavy loads of sediment plaguing our water ways comes high (unmanageable) turbidity levels. It seems the only real way to treat turbidity is by chemical treatment. By the end of this year EPA will tell us what turbidity levels we will be able to discharge from our construction sites. Hopefully we all had a chance to listen to Jesse Pritts talk yesterday and are a little more informed about the upcoming ELG.3Effects of Baffles: Velocity

inletoutletNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE4Here is some data from a study that we did. It shows different types of material in a basin acting as a baffles the affects they have on slowing down the velocity of water. Regardless of the material used there was a reduction when compared to no treatment. The same is true when looking at water flowing through a conveyance. Check dams should help prevent erosion and scour and promote grass growth!

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEOur research is looking at different check dams used in ditch lines to see how efficient they are at slowing the velocity of water. When installed properly you can see that the weir, or lowest point in the check dam, is in the center of the ditch line where the flow of water will go over the dam and not around it.5

We dont want to create erosion!NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCESo its really important, whatever type of dam you use that you are getting good ground contact and that you are making your smiley face (or low point) in the middle of the device. This, obviously, doesnt cut it.6

Excelsior wattlesRockRock w/ ExcelsiorRock w/ coir

Coir logsNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEWe wanted to take a look at different types of check dams and measure their performance (measured turbidity and tss). We wanted to know the clarity of water as well as the amount of sediment that each type of device could capture given aRock dams were installed with a weir at 18 in the middle and a tail extending 3 downslope. For the fabric-covered rock dams, the fabric was laid on the bottom, the rocks piled on top as with the standard rock dam, and the fabric was pulled back over the rocks and anchored with rock on the downhill side. The excelsior and coir logs were cut to fit snugly into the sides of the ditch and stapled down using 8 landscape staples. Instead of installing wood stakes on the downhill side as would be the normal practice, we placed several large rocks below each device to avoid compromising the tarps too much. certain flow rate.74 minutes at each 0.5, 1.0, 2.0, 1.0, and 0.5 cfs soil added at 6,000 mg/L4 samples were collected in each bottle- 5 bottles total3 consecutive runssediment depth and length was measuredLIDAR scan was taken

soilNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEAn 80 foot ditch was constructed on a 5-7% slope and lined with plastic tarps (Fig. 1). It was 2 wide and 2 deep with an H-flume installed at the lower end to measure flows.

A test consisted of three consecutive runs. For each run, water was introduced from our uphill storage pond through a 12 pipe at the rates of 0.5, 1.0, and 2.0 CFS. A run consisted of 4 minutes of flow at 0.5, 1.0, 2.0, 1.0, and 0.5 CFS in sequence to simulate a storm event. Soil was added to the water at a rate to maintain a constant concentration of approximately 6,000 mg L-1. On the downhill side of each dam, a sampler intake was anchored with a rock and the sampler was programmed to obtain a sample every minute. Four samples were collected into each bottle, which represented a composite for the period of flow.After three consecutive runs, the depth and length of accumulated sediment was measured at each of the three dams and pictures taken of the accumulation. Then the sediment was shoveled out of the ditch and the devices removed. After washing the remaining sediment from the ditch, the check dams were reconstructed with the same rock with new fabric, or with new sections of excelsior or coir logs, and the series of three runs resumed. Three replications of the series of three runs were completed for all but the rock with excelsior blanket check dam, which has only had one set of three runs completed to date. The samples were analyzed for turbidity and total suspended solids in the laboratory.8Ideal BMP SpacingBMPs theoretically spaced such that flow goes from pool to pool This slows water velocity down and gives more time for water to infiltrate into the ground and causes sediment to fall out of suspension!NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE9At three points in the ditch, check dams were installed so that the top of the lower one was even with the bottom of the upper one. Ground-based LIDARLIDAR LIght Detection And RangingUses reflected laser pulse todetermine 2-way travel time(X,Y,Z) coordinates from the scanner headRecords 50,000 points/second360 degree field of view

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEScanning Site (SECREF)

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCELIDAR Data (Down Channel)

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEMethodologyTake LIDAR scans before and after testInterpolate points to 3-D surfacesCalculate the difference in the 2 surfacesReveals total volume and spatial distribution of sediment captured within the basin

First Scan (bottom layer)3-D View of Before and After SurfaceFinal Scan (top layer)NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE3D Channel

Rock Check DamFlow DirectionNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE

Coir3 Sediment DepthCoir Location Sediment In Front of First Coir Check DamNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEMethod ComparisonIn Front of First TrapRUN NAMEmax depth(in)Volume (m3)Volume (ft3)Coir311.190.1304.58RC27.880.2308.12RC38.010.2207.77RX19.690.1836.46X28.800.0531.87In Front of Second TrapRUN NAMEmax depth(in)Volume (m3)Volume (ft3)Coir33.520.0381.35RC24.560.0150.52RC34.470.0321.13RX13.110.0170.61X26.150.0491.72NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEBehind first check dam

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEBehind second check dam

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCETotal Suspended Solids

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEIntroduction of PAMRock with PAM

Rock with Excelsior wrap with PAM

Excelsior wattle with PAM

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCESprinkle 60 grams of APS 705 PAM over the check dam where the water is going to flow over.

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE21

Flocs sticking to rocksNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEComparison of TreatmentsNC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEExcelsior with PAM was the clear winner in these different treatments with an average NTU of 109 (remember this is after shaking the sample and reading at the 30 sec mark) but on the next slide well see comparisons among the testing.23Comparison of Treatments

NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCEJust looking at the comparison of treatments we can look at what effect the small amount (60 g) of APS 705 PAM has on clearing up the turbidity issue we are certainly having to deal with. Just remember that in the end this type of treatment chain should eventually be dumping into some sort of sediment basin where the velocity of the water will settle even more which will allow for the settling of the flocs. With even just a 5 minute resting period we could see upwards of NTUs in the single digits. We are also sampling from the bottom of the ditch and when the samples are analyzed in the lab they are shaken and read at 30 seconds.24

There is a rainbow on our horizon! NC STATE UNIVERSITYDEPARTMENT of SOIL SCIENCE