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Aquifers in Alluvial Sediment PowerPoint PPT Presentation


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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

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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)

  • Mississippi embayment


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: 0.01-0.1 km

  • Outwash deposits, alluvial plain

    • planar sheets

      10s km horizontally

      Thickness: 0.01-0.1 km

1:10


Aquifer Types

  • Unconfined

  • Confined

  • Both, unconfined with local confining unit

Deposits

  • Channel fill in modern valley

  • Buried channel

  • Outwash plain

  • Alluvial plain


Confining unit where fine grained

Sand and gravel,

Primary aquifer

Idealized setting

Channel fill in modern valley

substratum


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?

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


Infiltration through floodplain

Losing stream

including tributary

Stormflow off uplands

Recharge to alluvial aquifers


Irrigation return flow

Rise in river stage,

Bank storage

Rise in river stage,

Flood


Discharge from basement

Main channel losing due to pumping


  • Discharges from Alluvial Aquifers

  • To main channel or tributaries

  • Lakes on floodplain

  • Wetlands

  • Wells


Streambed conductance effects on gw/sw interaction

Fine-grained seds on streambed

Fine-grained seds in topstratum


10

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.


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?

Regional GW flow patterns?

Where are thr recharge and discharge areas? What controls?

Expected fluxes?

GW discharge area?

30 miles


Baseflow rate related to T of surficial aquifer

Composition of GW and SW similar


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


Flow-through lake


Another major outwash deposit


Conceptual Model

Recharge

Streams

Cape Cod Bay

Fine-grained

Sand/Silt

Groundwater Flow Paths

Saline

Groundwater

Bedrock

Glacial Till

Freshwater/Saltwater

Interface

South

North


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.


1 mile

5 miles


4000

1:40 aspect ratio


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.


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


Hardness = 2.5 Ca(mg/l) + 4.1 Mg(mg/l)

<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


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.

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.


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 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


Some other alluvial aquifers


Relative sizes of example alluvial aquifers

100 miles


Dissolution of underlying evaporites forms deep troughs in Pecos River Basin


80 Mgpd

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

  • TDS

  • Hardness

  • Major ions


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