Reservoir Sedimentation Overview MIDWEST ELECTRIC CONSUMERS ASSOCIATION 60

Reservoir Sedimentation Overview MID-WEST ELECTRIC CONSUMERS ASSOCIATION 60 TH ANNUAL MEETING DENVER, CO Rollin H. Hotchkiss, Ph. D. , P. E. , D. WRE, F. ASCE Brigham Young University 1

My Roots are in South Dakota • Willard Burton Hotchkiss b. Junius • Samuel Hotchkiss (grandfather) postman during depression • Helen Schuld b. Madison • Esther Schuld (grandmother) cook at Beadle College https: //www. uspostcards. com/media/ecom/prodlg /SD-Q/sd_qq_0989. jpg https: //ap. rdcpix. com/1598710960/03 a 2 d 659 af 4 a 5 b 9 fe 3 d 145 a 92 d 10 a 56 fl-m 0 xdw 480_h 480_q 80. jpg 2

Outline 1 2 3 4 5 6 7 8 How U. S. dams were designed considering sediment Physical impacts downstream Actual sedimentation patterns in reservoirs Physical impacts within reservoir and upstream Ecosystem impacts Looming sediment issues Sediment management alternatives Challenge and opportunity 3

1 How U. S. Dams were Designed Considering Sediment • GIVEN: selected site for a dam • FIND: elevation of lowest outlet https: //img. huffingtonpost. com/asset/56 c 1 e 62 c 1800002 d 0080 bf 19. jpeg? ops=scalefit_720_noupscale 4

SOLUTION 1 Estimate sediment deposition for “economic design life” 2 Conceptually place that volume in the reservoir 3 Place outlet above the stored volume http: //aemstatic-ww 1. azureedge. net/content/dam/HRW/Volume-25/Issue 1/1701 HRWdon_z 01. jpg 5

RESULT • Only very fine sediments pass the dam • You can’t move sediments downstream • Reservoir becomes a “sediment tomb” • Storage below level outlet is called “dead storage” https: //www. researchgate. net/publication/314278964/figure/fig 1/AS: 469317713174528@1488905470178/ Fig-112 -Total-reservoir-storage-volume-capacity-consisting-of-the-sum-of-dead-storage. png 6

2 Physical Impacts Downstream • Channel is sediment starved • Water is “hungry” • Mobilizes sediment from • Streambed • Banks • Channel deepens and widens • Degradation proceeds up tributaries https: //www. researchgate. net/profile/David_Rus/publication/266218139/figure/fig 18/AS: 35627406883635 7 9@1461953765693/Figure-19 -Drop-structure-at-S-Logan-Cr-at-N 15 -ER-12 -Figure-20 -Knickpoint-on-East. png

Typical Degradation Cross Section Missouri River Sediment Range 783. 6 – 1960 River Mile 753. 2

2 Physical downstream impacts, continued • Bridge pier and abutment scour • Abandonment of water intakes • Culvert failures • Loss of riparian land • Groundwater levels lower than root zone 9

3 Actual Sedimentation Patterns in Reservoirs • Typical pattern • Coarse materials upstream • Finer materials closer to dam • Coarse materials propagate upstream deposition From U. S. Bureau of Reclamation Design of Small Dams p. 555 10

4 Physical Impacts within Reservoir and Upstream • Loss of reservoir storage • Inverse of downstream issues • Reduced bridge clearance • Buried water inlets • Groundwater levels rise https: //nm. water. usgs. gov/nawqa/riog/images/15_big. jpg • Crops • Homes • Unstable roadway beds 11

5 Ecosystem Impacts • Complete change in stream channel ecosystem downstream • Colder water temperatures • Less turbid water • Streambed armoring interferes with salmon redds • Upstreambed is smothered and ensuing impacts https: //photos. smugmug. com/Salmonid-Topic/Redd. Superimposition/i-k 8 x. Gz. T 2/1/517 ba 216/L/_DS 37451 L. jpg http: //sonotronics. com/wp-content/uploads/2010/07/First_Trout_Stocking. jpg 12

6 Looming Sediment Issues • Federal agency concern: sediment covers intakes • Most U. S. dams older than “design life” • Unknown but increasing deposition • Much loss of storage is in active pool https: //www. usbr. gov/uc/wcao/progact/ paonia/feature/Intake. Structure. jpg Millsite Dam, Ferron Creek, Utah 13

7 Sediment Management Alternatives • Upstream soil conservation • Check dams, conservation tillage • Bypass sediments around the dam • Channel or tunnel • Pass sediments through reservoir • Density current or flushing (empty the reservoir) • Remove deposited sediments • Hydrosuction • Dredging • Pressure flushing • ASSUMES SEDIMENT IS NOT CONTAMINATED https: //reservoirsedimentation. com/images/COVERsml. jpg 14

7 Upstream soil conservation • Success in • Conservation tillage areas • Construction sites • Challenging in arid areas • Check dams • vegetation https: //encrypted-tbn 0. gstatic. com/images? q=tbn: ANd 9 Gc. SDrn. S 99_Jg 3 a 7 uc. OSv 8 ej. Hr. IFl. Mn 30 lrb. MZq. FDYe 4 qm. BXeb. Tr. AA http: //www. pwcgov. org/government/dept/publicworks /environment/Publishing. Images/Erosion. Control 002. JPG 15

7 Bypass sediment around the dam • Build a low dam at entrance to reservoir • Divert sediment-laden flow into a tunnel • Tunnel discharges downstream • “The dam owner is under no obligation to trap sediment in the reservoir” Sustainable sediment management in reservoirs and regulated rivers: Experiences from five continents G. Mathias Kondolf , Yongxuan. Gao , George. W. Annandale , Gregory L. Morris , Enhui Jiang , Junhua Zhang , Yongtao Cao , Paul Carling , Kaidao Fu , Qingchao. Guo , Rollin. Hotchkiss , Christophe Peteuil , Tetsuya Sumi , Hsiao-Wen. Wang , Zhongmei. Wang , Zhilin. Wei , Baosheng Wu , Caiping. Wu , and Chih Ted Yang 1 5 10 14 2 3 5 5 6 11 7 12 4 5 8 9 5 13 15 16

7 Pass sediment through the reservoir • Density current – turbid water dives to bottom of reservoir, travels to lowlevel outlet • Flushing – empty the reservoir and let water pass through the reservoir http: //images. china. cn/attachement/jpg/site 1007/ 20100729/000 bcdb 95 f 1 d 0 dbb 21 b 013. jpg http: //imgsrv. kbrx. com/image/kbrx/User. Files/Image/Spencer. Dam. jpg 17

7 Remove deposited sediments • Hydrosuction dredging • Uses gravity and suction • No external power needed • Dredging – uses cutterheads and pumps • Pressure flushing- release water at low-level outlet to scour local sediment deposits https: //media. defense. gov/2013/May/13/2000758196/-1/-1/0/900521 -A-CE 999 -001. JPG http: //www. sedicon. no/wp-content/uploads/2017/09/DSC 03671. png Planta Hidroelectrica La Garita, Costa Rica Cherry Creek Reservoir, Denver CO

8 Challenge and Opportunity • Permitting sediment management at reservoirs? Future discussion! • Opportunity for dialog and discussion • We must realize • Eventually all sediment will pass the dam • Wouldn’t we like to manage that now instead of be a spectator later? • Untouched subjects • • Permitting Economics of sustainability Dams in series and polluted sediments Measuring sediment deposition in reservoirs 19