08-22-1988 - Agenda Packet City Council - regular meeting

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Page 4 State Ground Water Levels Under Stress By Dan Zwilling 1:., division of Waters has stepped up monitoring of a num- ber of u.: state's 600 observation wells to better evaluate the ef- fects of the present drought on ground water levels throughout the state. Instead of monthly readings, Soil and Water Conser- vation Districts are taking weekly or bi-weekly measurements in 17 observation wells outstale. The DNR and the U.S. Geological Survey arc recording week- ly levels in 14 additional observation wells prin- cipally in the Twin City area. levels arc being observed primarily in the Prairie du Chien -Jor- dan and Mount Simon -Hinckley bedrock ,r aquifers, and water table (near surface) aquifers. Figure 1 shows haw a shallow wager table level will fluctuate over time. Precipitation z trends, especially when severe and lengthy, [caw m ' noticeable effects on ground water levels. The n r current levels for this observation well arc the a lowest recorded at this site since 1969. Levels .,s will likely continue to decline until next spring's rechargescason. The previous recorded lowoc- curred in 1977 following the severe drought of s 1976. New record lows for water gable aquifers are currenllybeingobserved in cast central Min- .0 nescak extending from Morrison County tojust south of the Twin Cities. Water table levels in Figure I western Minnesota are generally 1 fool above the 1976 levels but arc several feel below the seasonal average. Water table levels in northeastern and southeastern Minnesota are slightly below the seasonal average. The Minneapolis -St. Paul aca is the slate's primary ground water pumping center. Figure 2 shows ground water levels for a Prairie du Chien -Jordan bedrock observation well in West St. Paul. (;round water levels in this area strongly reflect the in- DAKOTA COUNTY w.a Pig c,a,so wurwuwrs Duence of pumping. Water IeveL in Twin Cities bedrock aquifers, in general, are lowered in the summer by large sum- mer appropriations for both irrigation and cooling purposes. Water levels begin to recover after the irrigation and air con- ditioning season and generally return to seasonal levels by mid - fall. Due to this summer's drought and associated high temperatures, appropriations have increased in the Twin Cities area and consequently ground water levels have declined In summary, levels in both the Prairie du ChienJordan and Mount Simon-Hincklvv-nuifers arc near or below recorded seasonal SHERBURNE. JUNTY WELL# 71001 rran — oanwowantauvru lows. The continued lack of precipitation will retard ground water level recovery once summer appropriation ceases. Minnesota's ground water is recharged primarily in the spring and fall. The most significant recharge usually occurs in spring. In summer, when evapotranspiration is at its peak, most rainstorms do not contribute to the ground water supply. The effects of unusually heavy and prolonged sum- mer rainstorms can lessen the rate of ground comer decline or may result in a sporadic rise. However, unless precipitation is significantly above normal, ground water levels will con- tinue to decline this summer. After the return of confer weather in fell, reduced pumping and the onset of the dormant period for vegetation will provide ground l water levels with their first likely chance of reentry. Recwcry during the fall will la: handmapped since rainfall entering the wit must first replenish the depleted wil mowure. Normally, little water is left to perudaic imo A..,�. the ground we- r system and fall rcdtarge is small. Con. mntly, even assuming normal fag precipitatw,a, graend water levels will like. ly remain ky, this year. Dan Zaillsng it a nrgulae connYbaar m Want .. .. Talk and .,b m tare Ground Raw Out