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

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Aquifers in alluvial sediment l.jpg
Aquifers in Alluvial Sediment

Unconsolidated sands and gravels deposited by rivers. Must be large enough to produce significant rates and volumes of water from wells

  • River valley draining glaciated area

  • Fault bounded basins

  • Partially dissected alluvial plain (High Plains)

  • Mississippi embayment


Sea vs closed basin as drainage destination for alluvial sediments l.jpg
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 sediments in glaciated areas l.jpg
Alluvial sediments in glaciated areas Sediments

  • 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)


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Alluvial sediments in glaciated areas, Cont Sediments

  • 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



Alluvialaquifer systems l.jpg
AlluvialAquifer Systems Sediments

  • Geometry

  • Aquifer type

  • Properties

  • Recharge/Discharge

  • Flow pattern

  • Chemistry

  • Examples


Geometry l.jpg

1:100 Sediments

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

      10s km horizontally

      Thickness: 0.01-0.1 km

1:10


Aquifer types l.jpg
Aquifer Types Sediments

  • Unconfined

  • Confined

  • Both, unconfined with local confining unit

Deposits

  • Channel fill in modern valley

  • Buried channel

  • Outwash plain

  • Alluvial plain


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Confining unit where fine grained Sediments

Sand and gravel,

Primary aquifer

Idealized setting

Channel fill in modern valley

substratum



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Storativity of major alluvial aquifers Sediments

confined

unconfined


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Fining upward sequences in major alluvial aquifers Sediments

Estimate how K varies with depth in alluvial aquifers?

Straight line on log*log plot

d50=C*Zb

Log(20)-Log(3)=0.82

b=Slope=2/0.82=2.4

d50=C*Z2.4

Hazen method K=C1d102

Alluvial: K=C2Z4.8


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Infiltration through floodplain Sediments

Losing stream

including tributary

Stormflow off uplands

Recharge to alluvial aquifers


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Irrigation return flow Sediments

Rise in river stage,

Bank storage

Rise in river stage,

Flood


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Discharge from basement Sediments

Main channel losing due to pumping


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Streambed conductance effects on gw/sw interaction Sediments

Fine-grained seds on streambed

Fine-grained seds in topstratum


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10 Sediments

Stream-parallel flow,

Neither gain nor lose

9

Losing reach

10

9

Gaining losing

Gaining reach

Preliminary interpretations of gw-sw interactions using head contours

10

9

10

2.

3.

9

1.

4.



Some examples l.jpg
Some examples Sediments

  • 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


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Wisconsin Sediments

Dome


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140 miles Sediments

20 miles

Fox-Wolf River Basin



What does this map tell you about the fox wolf river aquifer l.jpg
What does this map tell you about the Fox-Wolf River aquifer?

Regional GW flow patterns?

Where are thr recharge and discharge areas? What controls?

Expected fluxes?

GW discharge area?

30 miles


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Baseflow rate related to T of surficial aquifer aquifer?

Composition of GW and SW similar


Ground water flow through surficial aquifer paleozoic sandstones and discharge to river l.jpg
Ground water flow through surficial aquifer, Paleozoic sandstones, and discharge to river


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Flow-through lake sandstones, and discharge to river


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Another major outwash deposit sandstones, and discharge to river


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Conceptual Model sandstones, and discharge to river

Recharge

Streams

Cape Cod Bay

Fine-grained

Sand/Silt

Groundwater Flow Paths

Saline

Groundwater

Bedrock

Glacial Till

Freshwater/Saltwater

Interface

South

North


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Chemung river valley, Corning, NY sandstones, and discharge to river

Limestone and shale bedrock on rounded hills 800 ft or more above the sand and gravel aquifer on the valley floor.


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1 mile sandstones, and discharge to river

5 miles


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4000 sandstones, and discharge to river

1:40 aspect ratio


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A. sandstones, and discharge to river

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.


Water balance l.jpg
Water Balance sandstones, and discharge to river

  • 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


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Hardness = 2.5 Ca(mg/l) + 4.1 Mg(mg/l) sandstones, and discharge to river

<60 mg/l = soft

>150 mg/l = very hard

Water is magnesium bicarbonate type. Note the hardness. The region is underlain by limestone and shale


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16 Mgpd sandstones, and discharge to river


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


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Glacial valley partially inundated by the sea the Little Androscoggin aquifer in Maine.


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5000 ft the Little Androscoggin aquifer in Maine.


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Water Balance the Little Androscoggin aquifer in Maine.

  • 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.

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

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=43+9-23=29 in/yr different from above

Ru=Base+Storm, So, stormflow must be 5 in/yr;

In general, the water flux values seem to be inconsistent. Always make certain your water balances can be closed.



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7 Mgpd production Aquifer, Maine


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4 miles Aquifer, Maine

Aquifer filling a valley once occupied by fresh water glacial lake



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4.3 Mgpd Aquifer, Maine


Corning aquifer ca mg hco3 hardness 225 ppm tds 212 ppm 16 mgpd l.jpg
Corning Aquifer. Ca, Mg, HCO3; Hardness: 225 ppm; TDS: 212 ppm16 Mgpd

Little Androscoggin, Na, K, Ca, HCO3;

Hardness: 24-68ppm

TDS 67-128 ppm

alluvium

bedrock

Irondogenesee Aquifer, Ca, Na, HCO3, Cl, SO4; TDS 665, Hardness: 373

4 Mgpd





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80 Mgpd in Pecos River Basin

Water Quality: 1000+ 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 l.jpg
Water Quality Summary in Pecos River Basin

  • TDS

  • Hardness

  • Major ions


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