Examining Higher Hydraulic Gradients in Restored Streams and the Implications on Hyporheic Exchange Hong-Hanh Chu and Dr. Ted Endreny, g y, Department of Environmental Resources Engineering, SUNY ESF
Overview of Presentation Hyporheic exchange Studies on stream restoration, especially about hydraulic gradients and river stage Our research Future research and implications on hyporheic exchange
Hyporheic Exchange Overview Boulton et. al., 1998 : Hyporheic Zone: an active ecotone between the surface stream water and groundwater Hyporheic Exchange: the exchanges of water, nutrients, and organic matter occur [in the hyporheic zone] in response to variations in discharge and bed topography and porosity hydraulic head Lateral hyporheic exchange Vertical hyporheic exchange Figure from Hester and Gooseff, 2010
Hyporheic Exchange Overview Functions commonly associated with: Vertical hyporheic exchange Lotic habitat Invertebrates & macroinvertebrates Fish Nutrient cycling Consumption & transformation by microbes Oxygen and energy cycling Pollutant buffering Sink for hard metals and hydrocarbons Temperature regulation Surface water vs. groundwater Habitat quality, especially during low flow Constraint on biogeochemical reactions Lateral hyporheic exchange Nutrient cycling Consumption & transformation by microbes Oxygen and energy cycling Pollutant buffering Sink for hard metals and hydrocarbons
Stream Restoration Research Vertical hyporheic exchange: Hydraulics: Crispell and Endreny, 2009: Batavia Kill, NY Hester and Doyle, 2008: simulation models, flume tests, field experiments in Craig Creek (small mountain stream) near Blacksburg, VA Biogeochemistry: Lautz and Fanelli, 2008: 3 rd order Red Canyon Creek in Lander, WY (semi-arid watershed) Lateral hyporheic exchange: Hydraulics and Biogeochemistry: Kasahara and Hill, 2007: 2 lowland stream reaches of Boyne River, Ontario, CA (intensive agri. watershed)
Science Question How do in-channel stream restoration structures affect: - the hydraulic gradients in the stream channel and across the stream meander bend, and - the intra-meander water table level? Use methodologies that will provide: 1) direct comparisons between channels with structures and channels without t structures, t and 2) fine resolution of observation data at the scale of a stream meander.
Methods: Laboratory Experiments Stream Channel Dimensions: - Width to Depth ratio: 7 to 11 - Sinuosity: 1.9 Radius of Curvature: 26 cm - Channel slope: 1% Valley slope: 1.5% - D 50 : 0.2 mm n no struct = 0.004 n struct = 0.021 - Initial channel: flat bed morphology Experimental Runs: - Discharge: 51 ml/s (~30% of channel capacity) - Flow Duration: 7 hr - 3 replications of channel without structures - 4 replications of channel with 6 J-hooks and 1 cross-vane Close-Range Photogrammetry: - 2 NIKON D5100 digital i cameras mounted 1.3 m from sand surface 14% 10-11% 20% 22% - Digital photos taken of initial channel, river stage at 7 hr of flow, and channel after 12+ hr of no flow - Floating white wax powder (0.3 mm diameter) indicated river stage and level 20% - Elevation values referenced to 5 control points surveyed by ultrasonic distance sensors (0.2 mm precision)
Methods: Post-Processing Using ADAM Tech 3DM Analyst: Using ESRI ArcGIS: Import DEMs in ArcGIS Convert DEMs into TINs Convert TINs into Rasters Obtain cross-section profiles with 3D Analyst extension Export cross-section profile data into Excel for calculations (Diagram courtesy of Bangshuai Han) Analysis of variance on: - Hydraulic gradients - Water table levels
Longitudinal Profile of River Stage at the Channel Centerline 850 6-29 structures 7-2 structures 7-3 structures 7-4 structures 7-7 no structures 7-8 no structures 7-9 no structures channel flat bed (7-7) 840 Elevation (mm E m) 830 820 6.7 mm (avg) Hydraulic radius (R) increased 80% of the original R. 810 800 8.6 mm (avg) 3.0 mm (avg) Hydraulic radius (R) increased 22% of original R. N N N Having structures in the channel, especially the cross-vane, raised the river stage that is upstream of the structures. - Backwater from damming effect N
850 Hydraulic Gradient between US and DS River Stage Elevation (m mm) 840 830 820 810 Neck w/o structures Neck with structures Center w/o structures Center with structures Apex w/o structures Apex with structures Having structures in the channel raised the river stage hydraulic gradient across the meander: - neck by 0.94% - center by 1.39% - apex by 0.12% The river stage hydraulic gradients of channels with structures and those of channels without structures are statistically different (p=0.0002). 800 US river stage DS river stage ape ex cent ter nec ck The structures affected the hydraulic gradient across the meander locations disproportionately (p<0.0001).
Intra-Meander Cross-Sections Elevatio on (mm) Elevat tion (mm) 870 860 850 840 830 820 810 870 860 850 840 830 820 810 870 860 neck US channel river stage Having structures in the channel increased the water table throughout the intra-meander zone, especially in the upstream half of the bend. A struct : 6.26% A no struct : 3.74% B struct : 4.01% B no struct : 3.39% C struct : 2.24% C no struct : 203% 2.03% center apex US channel river stage DS channel river stage D struct : 1.49% D no struct : 0.87% A struct : 5.86% A no struct : 1.70% B struct: 4.65% B no struct : 3.34% C struct : 3.80% C no struct : 2.97% D struct : 1.44% D no struct : 1.79% DS channel river stage 6-29 Structures 7-2 Structures 7-3 Structures 7-4 Structures 7-7 No structures 7-8 No structures 7-9 No structures The steepest hydraulic gradient increase from inchannel structures occurred at the meander center, immediately upstream of cross-vane. Elevati ions (mm) 850 840 830 820 810 US channel river stage A struct : 2.24% A no struct : 0.17% C struct : 1.82% C no struct : 2.07% D struct: 1.37% D no struct : 2.31% B struct : 2.10% B no struct : 2.44% DS channel river stage ape ex cent ter nec ck
er level (mm) Avg. well wat 835.00 833.00 831.00 829.00 827.00 825.00 Wells near structures 2.53 3.70 3.14 1.08 0.44 1.27 2.46 2.14 1.87 apex center neck Avg. level (mm m) 830.00 828.00 826.00 824.00 822.00 820.00 Wells at meander center 0.97 1.74 0.83 apex center neck Structures No Structures Structures No Structures The water level of the circled wells was statistically different: - between channels with structures and those without structures (p=0.0057), and - across meander locations (neck, center, apex) (p<0.0001). The structures impacted these wells water level disproportionately across meander locations (p=0.0001) The water level of these wells was: - marginally different between channels with structures and those without structures (p=0.0797), and - statistically different across meander locations (p<0.0001). The structures did NOT impact these levels disproportionately across meander locations (p=0.2889).
Hydraulic Gradient between US and DS River Stage during twice normal discharge 850 840 When discharge was doubled in channels with structures: Elevation (m mm) 830 820 Neck @ 2x normal Q Center @ 2x normal Q - river stage increased with similar magnitude throughout the channel, and - hydraulic gradients across the meander bend remained relatively unchanged. Apex @ 2x normal Q 810 Neck @ normal Q Center @ normal Q Apex @ normal Q 800 US river stage DS river stage ape ex cent ter nec ck Normal Q = 51 ml/s
Result Summary In-stream restoration structures can locally raise the river stage upstream of where they are installed. Cross-vanes can cause more backwater than J-hooks. The increase of intra-meander hydraulic gradients and water table levels by in-channel stream restoration structures is most pronounced at the intra-meander areas closest to the structures. There is marginal water table level increase in the middle of the meander bend. The structures do not appear to further increase hydraulic gradients under higher stream flow.
Implications on Hyporheic Exchange Steep hydraulic gradients in riparian areas closest to the structures could indicate areas of induced lateral hyporheic exchange. Potential biogeochemical hotspots in the intra- meander zones. Larger stream flow in channels with restoration structures could induce more vertical hyporheic exchange due to higher hydraulic head.
Future Research More laboratory experiments to obtain observation data on hyporheic exchange flux and pathways in the stream channel and intra-meander zone. Run experiments at different stream discharges and channel restoration designs. MODFLOW modeling to simulate and predict hyporheic exchange flux and pathways. DEMs generated by our research process can provide fine resolution observation data of ground and water surfaces as MODFLOW boundary conditions.
Questions? References: Boulton, A.J., Findlay, S., Marmonier, P., Stanley, E.H., and Valett, H.M. (1998), The functional significance of the hyporheic zone in streams and rivers, Annu. Rev. Ecol. Syst., 29, 59-81. Crispell, J.K. and T.A. Endreny (2009), Hyporheic exchange flow around constructed in-channel structures and implications for restoration design, Hydrol. Process., 23-1158-1168. Hester, E.T. and M.W. Doyle (2008), In-stream geomorphic structures as drivers of hyporheic exchange, Water Resour. Res., 44, W03417, doi:10.1029/2006wr005810. Hester, E.T. and M.N. Gooseff (2010), Moving beyond the banks: Hyporheic Restoration is Fundamental to Restoring Ecological Services and Functions of Streams, Environ. Sci. Technol., 44, 1521-1525. Kasahara, T. and A.R. Hill (2007), Lateral hyporheic zone chemistry in an artificially constructed gravel bar and re-meandered stream channel,,southern Ontario, o,c Canada,,Journal of the American Water Resources s Association (JAWRA) 43(5):1257-1269. DOI: 10.1111 / j.1752-1688.2007.00108.x. Kasahara, T. and A.R. Hill (2007), In-stream restoration: its effects on lateral stream-subsurface water exchange in urban and agricultural streams in Southern Canada, River Res. Applic., 23, 801-814 Lautz, L.K. and R.M. Fanelli, (2008), Seasonal biogeochemical hotspots in the streambed around restoration structures, Biogeochemistry, 91, 85-104.