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1 Thomas Patton Montana Bureau of Mines and Geology 1300 W. Park Street Butte, Montana (voice) (fax) ( ) 1

2 A well in southeast Montana that had a very well defined response to the very wet winter/spring of

3 Note the distribution of wells in eastern Montana. There is a relative lack of wells where thick shale formations are at or near the land surface. In Western Montana, wells are congregated in the intermontane valleys and along major streams. 3

4 This well failed. When water levels fell in response to dry climate beginning around 2000, the well did not produce enough water to meet demand and had to be deepened. 4

5 This well, even though only 40 feet deep, requires relatively little drawdown to meet demand. It is also located near the center of an intermontane valley remote from most recharge areas. The valley as a collector helps keep it supplied. The annual cyclicity is a response to nearby irrigation practices. 5

6 Montana s statewide monitoring network contains more than 900 wells. At each well groundwater levels are measured quarterly and water samples collected every 8 10 years. The measurements are designed to create multi decadal timeseries records on water levels and inorganic chemistry. There are more than 100 recorders from which hourly to daily measurements are obtained. The distribution of network wells approximates the distribution of water wells in Montana. Data for the monitoring and water wells shown here are available from the Montana Ground Water Information Center (GWIC) web site at 6

7 The statewide monitoring network provides long term water level records that show change in groundwater storage or pressure. Upward trends (increasing elevation and decreasing distance to water) show increased groundwater storage or pressure. Most hydrograph traces portray concurrent high and low frequency signals. The hydrograph above contains a high frequency annual change signal related to pumpage for irrigation near Dillon, Montana. The pumping signal is superimposed on a high amplitude signal that has an apparent >10 yr cycle. Other high frequency signals that may show up on hydrographs include fluctuations caused by tidal forces or barometric pressure. The low frequency (10+/ yr) long term cyclic change in this hydrograph is typical of many hydrographs from the statewide network, particularly from the western third of Montana. For the purposes of this discussion, wells that produce hydrographs with similar slowly varying signals are called climate sensitive and as a group represent the network s response to varying precipitation. Each hydrograph is individual and illustrates the local balance between the numerous signal sources that contribute to a measured water level. The individuality makes portrayal of how a 1,000 well network might respond to climate difficult; it is not feasible to evaluate each hydrograph and then attempt to summarize the results. One way to summarize the network is to evaluate a measurement s net departure from a quarterly average, and group the departures into categories. The categories can be plotted on maps to help visualize the overall network response. Because the mapped well points might be colored by departure category irrespective of location and because of each hydrograph s individual character, the potential always exists that neighboring wells might be in different categories, i.e. a few positive departures in a field of negative departures. 7

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9 The two hydrographs above (approximate well locations are shown on the index map) show differing responses to climate and weather. The hydrograph from western Montana is from a well completed in a shallow sand and gravel aquifer. The rapid, more or less annual, upward fluctuations represent various precipitation events (weather) or stream flow in a nearby stream. The hydrograph, from a well in north central Montana s Blaine County on the Turner Hogeland Plateau, shows response to short term individual recharge events in 1994, 1996, and Water levels rapidly rose but then fell quickly back to their base levels. Climate forced water level response in this unconfined sand and gravel aquifer is shown by relatively sustained water level rises in 1986 and In 2011 groundwater levels rose about 5 ft in response to melt from a heavy winter snow pack (representing above average water accumulation during several months) and a wet spring. 9

10 This synthetic hydrograph shows how signals of differing frequencies and magnitudes can be combined into a single trace that contains elements of all the signal sources. Notice how the influence of the annual signal seems to wash out after 1914 when the ENSO and PDO signals are in phase and moving negative. 10

11 A hydrograph from a well locate in Butte, in southwest Montana shows characteristics when similar to those on the synthetic hydrograph. The annual signal in this Montana hydrograph is more apparent when low frequency signal is flat or rising, but subdued when the low frequency signal is falling. 11

12 About 400 wells in the statewide network appear to show movement likely related to climate. 12

13 Because average groundwater levels generally relate to average (or normal) precipitation, it is appropriate to compare groundwater level changes to departures from average precipitation. There are many ways to depict precipitation departures, but because long term groundwater level response depends in part on the length of time that the climate has been wet or dry, an index that can portray wetness or dryness at different time scales is important. The Standardized Precipitation Index (SPI) (McKee and others 1993) uses only precipitation records and at any calculation time shows departures from average precipitation for different accumulation periods. For more complete explanation of the Standardized Precipitation Index, go to The SPI is usually calculated for accumulation periods of 1 to 72 months. The bell curve depicts how precipitation for an accumulation period relates to SPI values. For example, for an accumulation period of 12 months, a SPI of 0 means that the amount of precipitation received in the current 12 month period is equal to the average for all previous 12 month periods, or in other words 50 percent of previous accumulation periods were wetter, and 50 percent drier. If the SPI is 2, 95 percent of all previous 12 month periods were wetter. If the SPI is +2, only 5 percent of all previous 12 month periods were wetter. McKee, T.B., N.J. Doesken, and J. Kleist, The relationship of drought frequency and duration to time scales. Eighth Conference on Applied Climatology, American Meteorological Society, Jan 17 23, 1993, Anaheim CA, pp

14 This illustration shows the statewide SPI for a 30 month accumulation period plotted at the end of each quarter (March, June, September, and December). Each calculation is independent of the others but when viewed in sequence, show increasing or decreasing trends in the amount of water received versus water expected during successive 30 month periods. At this time scale there are distinctive wet (green)/dry (orange) cycles. By this measure, our most recent dry period began in about 2000 and ended in The dashed trace is the statewide SPI for a 12 month accumulation period plotted by calendar quarter. It generally follows the wet and dry pattern shown by the 30 month SPI, but because the accumulation period is only 12 months, the series exhibits more rapid variability. Water level departures in many wells correspond to changes in the SPI at accumulation periods between 24 and 48 months. However, at the statewide monitoring network and precipitation scales, the 30 month accumulation period compares best to long term groundwater level change. 14

15 This map of 30 month SPI values for United States climate divisions shows the extent of the western drought as of February The southwestern Montana climate division was extremely dry ; meaning that 95 to 98 percent of all other 30 month periods between 1895 and 2003 that ended in February were wetter. 15

16 This image shows how the SPI varied relative to various accumulation periods calculated at the end of January 2003 for the Southwest Montana Climate Division. Accumulation periods of less than 12 months were wettest, but the climate division was dry at all time scales. The accumulation periods between 18 and 60 months were extremely dry; meaning that more than 95 percent of periods had been wetter. 16

17 At the end of March 2003, the 30 month statewide SPI was about 1.2; it had averaged 1.54 for the previous year after reaching its driest value in March 2002 at Groundwater levels had generally declined in response to the relatively dry climate. The prevalence of yellow and orange points shows that many wells were 1 to 5 ft, or 5 to 10 ft below their long term first quarter averages. At the end of March 2003, more than 70 percent of wells in the Montana statewide network were below their quarterly averages. The smattering of green points show locations where local conditions near a well caused first quarter 2003 measurements to be above the quarterly average. Conditions that might cause a few above average measurements to seemingly appear to be surrounded by many below average measurements vary from long record periods where large amplitude upward movement is overprinted on the climate signature, to a quarterly measurement capturing response to very immediate local recharge caused by streams, lakes, or ditch systems. 17

18 The maps show October 2011 SPIs for 12, 24, and 30 month accumulation periods. In comparison to the SPI map for February 2003, there are no orange, or red climate divisions anywhere; one climate division in northwestern Wyoming is moderately dry at the 24 month accumulation period. The images show that at the 12 month scale only the southwest Montana climate division has not been moderately to extremely wet. Montana s eastern climate divisions at the 12 and 24 month scales have been very wet; since 1895 only 5 percent of 24 month periods ending in October have been wetter. As the accumulation period lengthens to 30 months, the northern, western, southwestern, and south central divisions received near normal precipitation. The central, northeastern, and southeastern divisions were moderately to very wet. 18

19 At the end of September 2011, the 30 month statewide SPI was about 1.1; it had averaged 1.06 for the previous year and reached its wettest value of 1.55 at the end of June Groundwater levels have risen in response to the relatively wet climate. The prevalence of green and a few purple points shows that many wells were 1 to 5, 5 to 10, or 10 to 20 ft above their third quarter averages. At the end of September 2011, only about 25 percent of climate sensitive wells (see definition on slide 12) were below their quarterly averages. The yellow and orange points show locations where local conditions near a well caused third quarter 2011 measurements to be below the quarterly average. Conditions that might cause a few below average measurements to seemingly appear to be surrounded by many above average measurements vary from long record periods where large amplitude downward movement caused by development or other factors is overprinted on the climate signature, to locally delayed response to the recent relatively wet climate. 19

20 A map of SPI values for the end of February 2013 clearly shows the droughts in the south central and southeastern United States. 20

21 This image shows how the SPI varied relative to various accumulation periods calculated at the end of February 2013 for the Southwest Montana Climate Division. Accumulation periods of less than 5 months have been near normal, but the climate division was moderately to very dry at all other time scales. The accumulation periods between 9 and 14 months were extremely dry; meaning that more than 95 percent of those periods had been wetter. 21

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23 On this page, the top bar chart (blue up and red down bars) is a time series on the 30 month SPI that illustrates how relatively wet or dry the climate was at the end of each calendar quarter. The bottom bar chart is a time series on the percentage of wells below their quarterly averages at the end of each calendar quarter. If the percentage is high, the number of wells below their quarterly averages is greater than if percentages are low. When the climate was driest in late 2001 and early 2002, the number of wells below average was more than 80 percent. As the dry climate slowly moderated towards normal during , the number slowly declined to about 70 percent. Statewide precipitation at the 30 month accumulation period remained near normal from 2006 through early During this time, the number of below average wells fluctuated approximately with changes in the SPI, but the overall trend was downward. In late 2010 and 2011, the climate rapidly became distinctly wetter. In September 2010 the number of wells with below average water levels dropped to less than 50 percent, and by September 2011 had dropped to about 25 percent. 23

24 This plot illustrates the quarter to quarter relationship between the 30 month statewide SPI and the number of wells below their quarterly average. The green diamond is the oldest (March 1996), the yellow is the 2 nd most recent (September 2012), and the red is the most recent (December 2012) comparison. An implied correlation between the SPI (departure from precipitation averages) and the percentage of wells below average is illustrated by the linear trend line; how well the line fits data is shown by the R 2 value. An R 2 of 0.78 says that 78 percent of change in the percentage of wells could be explained by the change in precipitation departures. Since 1996, most points have negative SPI values showing that the climate has mostly been dryer than average. Consequently the relationship portrayed above is biased towards dry conditions. The lower right to upper left distribution also appears slightly curved and it is likely that the relationship will ultimately not be linear. If a curved line is fitted to the data set, the R 2 value increases to about 0.8. Groundwater levels decline below their averages as the SPI becomes more dry, and rise above their averages as the SPI becomes wetter. The relationship is continuous and suggests that wells are not necessarily dried up by drought but that as the climate dries water levels decline. Therefore, the number of individual wells that might not be able to meet required water production volumes increases. 24

25 What happened to cause the large, abrupt changes in ? 25

26 The well sets differ but comparison of wells measured before and after each jump have similar percentages of negative departures. 26

27 A large percentage of wells moved through the relatively narrow 1 to +1 category to the +5 to +10 and +10 to +20 categories between first and second quarters in

28 Between second and third quarters 2012, wells jumped across the relatively narrow 1 to +1 category from the +5 to +10 and +1 to +5 ft categories to categories below the central average. 28

29 Because Montana has maintained a statewide monitoring well network since the early 1990s, it has observed how groundwater levels respond to climatologically wet and dry periods. Without the monitoring network, Montana s citizens would have little data about how much, and where groundwater storage changed during the drought. There would be no way to verify reports of dewatered aquifers and dry wells. The hydrograph from southwest Montana shows groundwater response in the Boulder Batholith (fractured bedrock aquifer) near Butte, Montana in which water levels have risen about 10 ft since Strong upward groundwater level response in resulted from the wetter than average climate. The hydrograph from northeast Montana near Scobey is for a well completed in the sand and gravel Flaxville Formation that caps local plateaus. Water levels rose about 6 ft in in response to recharge from an above average snowpack and a wet summer. 29

30 Wells on the east side of the Kalispell Valley often show response to the wetter climate on the west side of the mountains. 30

31 Wells on the relatively dry west side of the Kalispell Valley show a much more muted response to the current climate. 31

32 In the Blacktail Deer Creek Valley southeast of Dillon, Montana groundwater levels respond to climate as well as pumping signals. 32

33 Monitoring wells on the East Bench east of the Beaverhead River, monitoring wells tell a complex story dating back to before the irrigation project was in place. The climate response in occurred because Clark Canyon Reservoir was not able to supply water to the irrigation district. 33

34 The Madison Limestone is ft below land surface near Great Falls. It is widely used to supply good quality water to wells. Water levels fell about 30 ft between 1997 and Since 2003, water levels have stabilized and have risen up to 15 ft. 34

35 A very similar hydrograph to that in well 2394 (previous slide) occurs in an unused monitoring well at Belt, Montana. 35

36 A similar pattern occurs in monitoring wells near Giant Springs. 36

37 An eastern Montana example from The Foxhills Hell Creek Formation shows that water levels in this part of this aquifer may be showing a climate signature. The relationship of monitoring points to the outcrop of the formation is shown by the placement of monitoring wells. 37

38 In northeast Montana near Scobey, a shallow Fort Union Formation well shows good response to the wet period. 38

39 A relatively shallow Fort Union Formation well north of Glendive showed good response to the recent wet period. 39

40 A well completed in the Fox Hills Hell Creek aquifer north of Terry, Montana shows a consistent downward trend during its entire period of record beginning in The trend is caused by longterm pressure loss in the aquifer possibly related to nearby wells that are allowed to flow under artesian pressure. The decline could also be caused by long term water use for purposes such as providing water for Bakken hydrofracturing operations in Montana and western North Dakota. The latter possibility would take much additional work to prove up and there are other Fox Hills wells closer to the oil and gas development that do not show this signature. 40

41 Future monitoring will help determine if the downturn in water levels in this Hell Creek Formation well is significant. 41

42 Much of the information I discussed today is available at the website portrayed above. 42

43 The Mapper portrays the current locations of more than 230,000 water wells located in Montana at scales closer than 1:288,895. Clicking on a well symbol will bring access to the well log information. Clicking on a green triangle will produce monitoring well information including the static water level record. 43

44 Water level data from the wells included in this presentation as well as data from many other monitored points are available from the Ground Water Information Center at the Montana Bureau of Mines and Geology. You can access the MBMG Mapper through the link right above the web address for the Ground Water Information Center. 44

45 Montana s Ground Water Assessment Program provides systematic collection and distribution of ground water information through the Ground Water Information Center (GWIC) at 45

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47 Thomas Patton Montana Bureau of Mines and Geology 1300 W. Park Street Butte, Montana (voice) (fax) ( ) 47