Aquifers in Alluvial Sediment River valley draining glaciated area Fault bounded basins Partially dissected alluvial plain (High Plains) Mississippi embayment Unconsolidated sands and gravels deposited by rivers. Must be large enough to produce significant rates and volumes of water from wells

Sea vs. Closed Basin as Drainage Destination 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

Alluvial aquifers in glacial deposits

Large Glacial Lakes

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)

Alluvial sediments in glaciated areas, Cont Sea level rises, glaciers recede, hydraulic gradient diminishes, discharge diminishes, carrying capacity drops. Style changes from braided to meandering. 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. Complex facies distributions

Gravel lens within a silty-clay till

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

1:100 Geometry Channel deposits –Elongate, tabular bodies, sinuous Length: many km Width: 0.1-several km Thickness: km Outwash deposits, alluvial plain – planar sheets 10s km horizontally Thickness: km 1:10

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

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

Hydraulic conductivity of some major alluvial aquifers

Storativity of major alluvial aquifers confined unconfined

Fining upward sequences in major alluvial aquifers Estimate how K varies with depth in alluvial aquifers? Log(20)-Log(3)=0.82 b=Slope=2/0.82=2.4 d 50 =C*Z b Straight line on log*log plot d 50 =C*Z 2.4 Hazen method K=C 1 d 10 2 Alluvial: K=C 2 Z 4.8

Recharge to alluvial aquifers Infiltration through floodplain Losing stream including tributary Stormflow off uplands

Irrigation return flowRise in river stage, Bank storage Rise in river stage, Flood

Main channel losing due to pumping Discharge from basement

Discharges from Alluvial Aquifers 1.To main channel or tributaries 2.Lakes on floodplain 3.Wetlands 4.Wells

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

Gaining reach 10 9 Stream-parallel flow, Neither gain nor lose Losing reach Gaining losing Preliminary interpretations of gw-sw interactions using head contours

Draw a Hydrogeologic Conceptual Model of Alluvial Aquifers

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

Wisconsin Dome

140 miles 20 miles Fox-Wolf River Basin

Buried pre-glacial valley, now covered by till and lacustrine deposits

What does this map tell you about the Fox- Wolf River aquifer? 30 miles Regional GW flow patterns? Where are thr recharge and discharge areas? What controls? Expected fluxes? GW discharge area?

Composition of GW and SW similar Baseflow rate related to T of surficial aquifer

Ground water flow through surficial aquifer, Paleozoic sandstones, and discharge to river

Flow-through lake

Another major outwash deposit

Conceptual Model North South Bedrock Groundwater Flow Paths Freshwater/Saltwater Interface Saline Groundwater Recharge Streams Cape Cod Bay Fine-grained Sand/Silt Glacial Till

Chemung river valley, Corning, NY Limestone and shale bedrock on rounded hills 800 ft or more above the sand and gravel aquifer on the valley floor.

5 miles 1 mile

1:40 aspect ratio 4000

3000 ft 1.Determine the horizontal head gradient at each location 2.Estimate the ground water fluxes at each location 3.Estimate the average flow velocities 4.Estimate the volumetric rate per unit length of river that the aquifer is contributing to the rivers at each location. 5.Provide an explanation for the differences between the two locations Corning Aquifer Exercise A. B.

Water Balance Info given in GW Atlas ET=0.5 P 0.6Recharge is from uplands What is the total baseflow flux to streams? Water Balance from Conceptual Model Recharge = Infiltration + Upland Runoff I=0.5P UR=0.6Re Re=0.5P+0.6Re Re=1.25P From map, P = 40 inch/yr, so Re=50 in/yr

Water is magnesium bicarbonate type. Note the hardness. The region is underlain by limestone and shale Hardness = 2.5 Ca(mg/l) Mg(mg/l) <60 mg/l = soft >150 mg/l = very hard

16 Mgpd

Fine-grained marine sediments underlie glacial outwash in the Little Androscoggin aquifer in Maine.

Glacial valley partially inundated by the sea

5000 ft

Water Balance Info given in GW Atlas P=43 in/yr, ET=23 in/yr (0.53), Ru=20in/yr (0.46) Also given: Recharge as infiltration over 16 mi2 aquifer accounts for 16.4 cfs, overland from uplands 11.2 cfs, from river 1.4 cfs. 29 cfs total Re to aquifer Area of aquifer = 16 mi2 Are these consistent? Demonstrate with water balances. Watershed Balance: P+OU=ET+Ru different from above Aquifer: Infilt+OU+RiverLoss=Baseflow Infiltration = 16.4 cfs; convert to flux over aquifer: 14 in/yr Overland from Upland= 11.2 cfs; 9 in/yr Total Recharge=baseflow= 29 cfs: 24 in/yr Ru=P+OU-ET= =29 in/yr different from above Ru=Base+Storm, So, stormflow must be 5 in/yr; Ru=Baseflow+Storm=Recharge+Storm Total Recharge=baseflow= 29 cfs: over 16 mi2= 24 in/yr 20 in/yr= 24 in/yr+Stormflow, Negative stormflow?? Problem In general, the water flux values seem to be inconsistent. Always make certain your water balances can be closed.

Hydraulic head in glacial outwash, Little Androscoggin Aquifer, Maine

7 Mgpd production

4 miles Aquifer filling a valley once occupied by fresh water glacial lake

Structural Contours on Bedrock

4.3 Mgpd

Corning Aquifer. Ca, Mg, HCO3; Hardness: 225 ppm; TDS: 212 ppm 16 Mgpd Little Androscoggin, Na, K, Ca, HCO3; Hardness: 24-68ppm TDS ppm Irondogenesee Aquifer, Ca, Na, HCO3, Cl, SO4; TDS 665, Hardness: Mgpd alluvium bedrock

Some other alluvial aquifers

100 miles Relative sizes of example alluvial aquifers

Dissolution of underlying evaporites forms deep troughs in Pecos River Basin

80 Mgpd Water Quality: mg/L common due to underlying evaporites and recharge from saline surface water and irrigation return flow where evaporation has increased salt content

Water Quality Summary TDS Hardness Major ions