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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Unconsolidated sands and gravels deposited by rivers. Must be large enough to produce significant rates and volumes of water from wells
Sand and gravel,
Channel fill in modern valley
Estimate how K varies with depth in alluvial aquifers?
Straight line on log*log plot
Hazen method K=C1d102
Stormflow off uplands
Recharge to alluvial aquifers
Rise in river stage,
Rise in river stage,
Main channel losing due to pumping
Fine-grained seds on streambed
Fine-grained seds in topstratum
Neither gain nor lose
Preliminary interpretations of gw-sw interactions using head contours
Buried pre-glacial valley, now covered by till and lacustrine deposits
Regional GW flow patterns?
Where are thr recharge and discharge areas? What controls?
GW discharge area?
Composition of GW and SW similar
Cape Cod Bay
Groundwater Flow Paths
Limestone and shale bedrock on rounded hills 800 ft or more above the sand and gravel aquifer on the valley floor.
1:40 aspect ratio
Corning Aquifer Exercise
0.6Recharge is from uplands
Water Balance from Conceptual Model
Recharge = Infiltration + Upland Runoff
From map, P = 40 inch/yr, so Re=50 in/yr
<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
Fine-grained marine sediments underlie glacial outwash in the Little Androscoggin aquifer in Maine.
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
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
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
Aquifer filling a valley once occupied by fresh water glacial lake
Little Androscoggin, Na, K, Ca, HCO3;
TDS 67-128 ppm
Irondogenesee Aquifer, Ca, Na, HCO3, Cl, SO4; TDS 665, Hardness: 373
Dissolution of underlying evaporites forms deep troughs 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