Aquifers in Alluvial Sediment

1. Aquifers in Alluvial Sediment Unconsolidated sands and gravels deposited by rivers. Must be large enough to produce significant rates and volumes of water (b>5 to 10m) • River valley draining glaciated area • Rivers draining area in west with high Pleistocene rainfall • Fault-bounded basins in west • Partially dissected alluvial plain (High Plains)

2. Sea vs. Closed Basin as Deposition Site for Alluvial Sediments Sea • Suspended load possibly removed • Salts possibly removed • Sea level change important • Closed Basin • Fine-grained seds in system • Salts remain • Isolated from effects of sea level change • Affected by local climate

5. Alluvial aquifers in glacial deposits

7. Alluvial sediments in glaciated areas • Glaciers advance, scour seds., modify river course. Sed comp. depends on location/source material. Large range of grn size. Till=clay-boulder beneath glacier. • Sea-level drops as ice advances. Hydraulic gradient increase. Erosion, velocity, carrying capacity increase. Valleys incised into bedrock, older glacial sediments (cover earlier channel deposits) • Glaciers recede. Discharge increases. Erosion. Braided rivers, large sediment capacity. Outwash plain (sands and gravels). Lakes in front of receding glaciers. Lacustrine=clay-silt (varved)

8. Alluvial sediments in glaciated areas, Cont • Sea level rises, glaciers recede, hydraulic gradient diminishes, discharge diminishes, carrying capacity drops. Lakes. • Coarse-grn seds deposited in incised valleys. Gravel on bottom, fining upward. Thickness depends on conditions during/following glaciation. Glacial landforms • Region adjusts to interglacial. Discharge decreases. Sediments reworked. • Important materials: Till, lacustrine, outwash, alluvial valley fill, diamicton, drift.

12. Gravel lens within a silty-clay till

13. AlluvialAquifer Systems • Geometry • Aquifer type • Properties • Recharge/Discharge • Flow pattern • Chemistry • Examples

14. Geometry • Channel deposits • Elongate, tabular bodies, sinuous Length: many km Width: 0.1-several km Thickness: 0.01-0.1 km • Outwash deposits, alluvial plain • planar sheets many km horizontally Thickness: 0.01-0.1 km

15. Aquifer Types • Unconfined • Confined • Both, unconfined with local confining unit Deposits • Channel fill in modern valley • Buried channel • Outwash plain • Alluvial plain

16. Confining unit where fine grained Sand and gravel, Primary aquifer Idealized setting Channel fill in modern valley substratum

17. substratum

19. Hydraulic conductivity of some major alluvial aquifers

20. Fining upward sequences in major alluvial aquifers

21. Storativity of major alluvial aquifers confined unconfined

22. Infiltration through floodplain Losing stream including tributary Discharge from basement Recharge to alluvial aquifers

23. Irrigation return flow Rise in river stage, Bank storage Rise in river stage, Flood

24. Main channel losing due to pumping

25. Discharges from Alluvial Aquifers • To main channel or tributaries • Lakes on floodplain • Wetlands • Wells

27. Streambed conductance effects on gw/sw interaction Fine-grained seds on streambed Fine-grained seds in topstratum

28. Some examples • Fox-Wolf River Basin, WI. Outwash • Corning aquifer, NY. River valley • Andruscoggin. ME. Alluvial valley once inundated by seawater • Irondogenese, NY, Alluvial valley once filled with fresh water lake • Others

30. 140 miles 20 miles

36. Another major outwash deposit

39. Chemung river valley, Corning, NY

40. 1 mile 5 miles

42. 4000 1:40 aspect ratio

46. 16 Mgpd

47. A. Corning Aquifer Exercise 3000 ft • Determine the horizontal head gradient at each location • Estimate the ground water fluxes at each location • Estimate the average flow velocities • Estimate the volumetric rate per unit length of river that the aquifer is contributing to the rivers at each location. • Provide an explanation for the differences between the two locations B.

49. Glacial valley partially inundated by the sea