Flow Study on the Lower Little Blackfoot River

Final Report

UCFRB Restoration Fund Grant Agreement No. 600206 NRDP Funds: $25,000 Total Funds: 28,500

February 4, 2008

Presented by the

Pat Barnes Chapter of Montana Trout Unlimited

P.O. Box 4404 Helena, MT 59624 406-449-7252

2 Lower Little Blackfoot Flow Study

1) INTRODUCTION:

The Little Blackfoot River (LBR) supports populations of native bull trout and genetically pure westslope cutthroat trout, populations of non-native brook trout and rainbow trout, and more than 6,000 angler days each year and is classified by the Montana Department of Fish Wildlife and Parks (FWP) as an “outstanding fisheries resource.” (NRIS) However, FWP has also determined that dewatering is a significant problem to this important fishery in the reaches of the LBR from Elliston Creek to the confluence with the Clark Fork River. (NRIS) This stretch of the river has also been identified as having temperatures that exceed fish survival recommendations for cold water fisheries at various times during the irrigation season.

To address these concerns, a flow study was designed to measure approximately nine miles of the LBR below the town of Avon over nineteen monitoring weeks beginning July 1, 2007 and ending October 31, 2007. A primary goal of this study was simple collection of the data necessary to quantify total stream flow, water demand, and total return over nine river LBR reaches defined by nine water demand sites. A secondary goal of this study was the analysis of that data.

2) DATA COLLECTION METHODS:

This study began in June, 2007 with an explanatory letter to landowners in the study area, and continued with the establishment of twenty-one monitoring sites selected to best quantify flow on a reach specific basis. Reaches were defined by each of nine different irrigation diversions, and nineteen sites were selected in the main river to measure flow above and below each of these diversions. Site 6 was located in a side channel; measurements were obtained in the channel above the diversion, in the side channel, and in the main river after both channels came back together. An additional two monitoring sites were established to measure tributary flow at the mouths of Spotted Dog and Three Mile Creeks. Staff gages were established at all twenty-one monitoring sites and GPS locations noted. Monitoring weeks correspond generally with calendar weeks, but not exactly, since, depending on weather and other considerations, there wasn’t necessarily 7 days between measurements at any one site. Data collection commenced on July 1, 2007. A map of the study area is attached as Appendix A, and GPS locations of the monitoring sites can be found in Appendix B.

For identification purposes the diversions were numbered in order from Avon down as depicted in Figure 1. Monitoring Sites 1-A and 1-B are the sites above and below the first diversion, 2-A and 2-B are the sites above and below the second diversion, and so on. Flow was then measured weekly at all mainstem locations and bi-weekly on the tributaries using a hand-held Marsh-McBirney current meter using the 6/10 depth method USGS protocol for open channel flow measurements (Buchanan and Somers, 1969).

3 Lower Little Blackfoot Flow Study

Figure 1

Diagram showing relationship of monitoring sites to diversions

Flow direction Diversion 3

Diversion 1 1-A

3-A 2-B

3-B 1-B Diversion 2 2-A

Irrigation Diversion Little Blackfoot River

Possible Monitoring Sites, Above Groundwater Return and Below each diversion

The baseline collection of this flow data is a prime objective of this project, and is tabulated in Appendix D. Initial analysis of the data began with the estimation of total water demand at each of the nine sites, and total recharge in the reaches between these nine sites. This data is also tabulated in Appendix D, and was calculated as follows:

The gain or loss in total river flow (I) at each diversion was calculated by subtracting the discharge below the diversion (Q1-B) from the discharge above the diversion (Q1-A). For example, the total gain or loss in river flow at the first diversion is (I1) = (Q1-A) – (Q1- B).

Total recharge (G) for each reach was calculated by subtracting the total flow at the top of the reach from the total flow at the bottom of the reach. For example total recharge in Reach 1 (G1) below the first diversion was (G1) = (Q2-A) - (Q1-B). Gaining reaches had positive values, losing reaches had negative values, and total recharge is the sum of natural groundwater return, groundwater return from ditch irrigation, and surface return from ditch irrigation. Total flow above Site 6 was the calculated sum of flow in the channel above the diversion (Site A) and the flow in the side channel (Site C). Total flow below (Site B) was measured approximately 200 feet below the diversion in the main river after the channels joined back together, and compared to total flow above using the methods outlined above.

In any given cross-section of the river flow varies both from side to side and top to bottom; the more the flow varies the more difficult it is to obtain accurate flow measurements. Flow varies more in cross-sections of rocky irregular profile, and where the 4 Lower Little Blackfoot Flow Study

river curves. The accuracy of discharge data can be improved by locating monitoring sites in areas of the river that are straight enough to promote parallel velocity threads, free of obstructions such as rocks and weeds that contribute to side-to-side flow fluctuations, and with cross sections of regular depth with a smooth bottom that minimize turbulence and changes in the vertical component of flow velocity.

Overall, 20 monitoring sites were selected according to the above parameters to best represent flow in a given reach of the river. First consideration was given to choosing sites that were most likely to yield accurate flow data, followed by proximity to diversions. As a result monitoring sites varied in distance above and below any given diversion, and the best monitoring cross sections also varied slightly with changing seasonal flows. There was also observed leakage in irrigation dams at Sites 1, 5, 8, and 11 that resulted in immediate returns to the river; flow measurements were taken below these quick surface returns to more accurately reflect the true amount of water demanded. In general, monitoring sites were located within 20 to 300 feet of diversions to best satisfy all conditions and give the best overall flow picture.

As a check on flow data staff gages were installed at each monitoring site. A positive relationship between discharge and staff height was found at Sites 1A, 1B, 2, 3B, 5B, 6A, 6B, 6C, 7A, 7B, 8B, 9A, 9B, 10A, 10B, and 11B. The amount that stage (river level) and discharge (river flow) “vary together” can be described statistically with the correlation coefficient. A correlation coefficient of 1.0 indicates a high level of correlation, and the correlation for the above sites ranged from .91 to .99, averaging around .97. Overall, .97 out of 1.0 can be taken to indicate a 3% (.03) variation in the measured relationship between flow and discharge, within the range of 2% to 5% considered by the USGS to be “good.” A XY graph typical of these 15 sites showing a correlation coefficient of .97 is shown in Figure 2; data is for Site 3B.

Flow was controlled by natural riffles and stream perimeter in the above 15 sites, and river flow tended to vary with river height in a linear manner. The situation was much different at Sites 3A, 5A, 8A, and 11 A. These Sites were all located in the flowing pools above diversions with dams spanning or nearly spanning the river. Headcutting over time in the LBR has created a system of perched irrigation ditches (direct observation and conversation with landowners.) These dams are necessary to raise LBR stage to ditch levels so water demand can be met, required maintenance over the course of the study period, and staff height at these sites appeared to be controlled by the changing height of the dams as opposed to flow. An XY graph typical of these four sites is shown in Figure 2, data is for Site 11A.

Since stage was almost certainly a function of management activities as opposed to discharge at Sites 3A, 5A, 8A, and 11 A, an alternate method of checking data was required. This was done by comparing flow above and below the diversions when the ditches were closed. Measurements should be the same within the limits of experimental accuracy under these conditions, and measurements were averaged over the period the ditches were closed. At Site 3 flow averaged 58.3 CFS above the closed ditch and 56.7 CFS below, at Site 5 63.9 CFS above and 62.7 CFS below, at Site 8 86.3 CFS above and 84.3 CFS below, and at Site 11 73.1 CFS above and 71.7 CFS below. This is an overall accuracy of about 3% of total flow, again within the range considered to be “good” by the USGS. Indeed, observed major flow 5 Lower Little Blackfoot Flow Study

vectors during measurements at these Sites tended to vary only slightly and in a consistent manner in the tranquil flows at the throats of these pools, and flow data at these Sites seemed in the field to be some of the most accurate due to the lack of turbulence, smooth bottoms, and constant depths characteristic of the cross sections in these smooth flowing pools.

Figure 2

3) DATA:

6 Lower Little Blackfoot Flow Study

Collected flow data is presented in Appendixes C and D. Appendix C is a tabulation of flow over the nineteen week course of the study (July 1-Oct.31) at the monitoring sites above each of the nine major diversions and at the mouth of Spotted Dog Creek, and represents a reach-by-reach summary of LBR flow over the length of the study area throughout the monitoring period. Appendix D includes data on the flow above and below each diversion, the calculated change in the flow above and below each diversion, and the calculated change in flow below one diversion and above the next downstream diversion.

4) DATA ANALYSIS:

It became evident early on that river flow over the mountainous study area was a function of geologic “chokepoints” where bedrock cliffs narrow down from both sides to the river. The LBR tends to gain flow at these chokepoints as water is squeezed out of the ground and into the river, and a major chokepoint at the bottom of the Avon valley divided the study area into two general sections.

Section 1 begins at Monitoring Site Number 1, just downstream from the Avon Café, in the throat of a major chokepoint that defines the head of the Avon Valley. For the next 1½ miles downstream the LBR overall tended to lose flow in the alluvial fill as it spread from east to west across the Avon Valley. Losses were offset to differing degrees depending on season by gains from Spotted Dog Creek, which flowed throughout the period of the study at rates varying from 27 CFS during runoff to 4 CFS in September. Overall losses for Section 1 were greatest during the late summer and early fall, when flows below Site 3, near the lower end of the Avon Valley, dropped as low as 17.8 CFS.

Section 2 begins at the red rhyolite cliffs at the lower end of the Avon valley between Sites 3 and 5. This is the head of the canyon, and these hard igneous cliffs form a major geologic chokepoint that is the major gaining reach for the entire study area, likely the result of flow concentrations from the Spotted Dog and Three Mile drainages which extend south and north respectively from the LBR river valley below the town of Avon. Three Mile Creek did not exhibit measurable surface flow over the course of this study, but standing water observed in the streambed make groundwater contributions likely. In any event, the LBR gained water between Sections 1 and 2 for all 19 weeks (July 1-Oct. 31) of the study. The average gain over that period was 12.5 CFS, the maximum gain was 29.6 CFS on Sept. 18, the minimum gain was 8.8 CFS on Aug. 1, and the nature of that gain was dependent on the time of year.

Section 2 continues downstream from the initial chokepoint through a canyon that alternately narrows and widens over the next six or seven miles of river. Again, geology influences stream flow. In-stream flows tend to increase where the valley is narrow, decrease where the valley is wide, and the magnitude of these effects vary seasonally. Consider the data in Figure 3, the average flows by reach during the last two weeks of this study. Data was averaged to better represent overall flow, for actual values refer to weeks 18-19 in Appendix C. As a reference on baseline conditions consider that water demand ceased at Sites 5, 6, 7, 9, 10 and 11 between Sept. 23 and Oct. 1, at Sites 3 and 8 by Oct. 7, and at Site 1 by Oct. 18. Measurements in Fig. 3 were taken from October 23-24 and Oct. 29-31, generally 7 Lower Little Blackfoot Flow Study

2-5 weeks after the demand for water finished for the season, and the time during this study when flows were most likely to have stabilized into a baseline condition.

Figure 3

Average Baseline Flow by reach, Oct. 23-31

80 70 60 Flow 50 in 40 Section 2 CFS 30 Section 1 20

10

0

1 3 5 6 7 8 9 10 11

Diversion

Baseline flows in Section 1 increased steadily across the Avon Valley from 55 CFS to 70 CFS, with 6.4 CFS attributable to Spotted Dog Creek. Section 2, on the other hand, shows a relatively steady baseline flow through the canyon all the way to above Site 11. Slight flow peaks hint at chokepoints at Sites 6 and 9, but overall water in the river tends to stay in the river under baseline conditions, and flows through the length of the canyon remained relatively steady at about 70 CFS. Steady October baseline flows through the canyon are also described in Figure 2-4 of a Deerlodge Valley Conservation District study (DVCD, 2005) for a length of the LBR closely approximating Section 2 as described in this study, when 5 synoptic flow measurements over 9.4 miles of river varied less than 2 CFS above and below a total flow of 60 CFS.

Contrast the reach by reach baseline flow in Figure 4 with the flow in the same reaches measured over a four week period from Aug. 23-Sept. 15 as shown in Figure 4. Flows at any one site generally varied 8-12 CFS over this period, and the data in Fig. 4 was averaged over the four week period to minimize week to week fluctuations in LBR flow due to water management practices and better represent seasonal flow. For actual values refer to Weeks 9-12 in Appendix C. Reach by reach flow comparisons in this study could be misleading as overall LBR flows changed day-to-day due to fluctuating water demand during what was typically a 2-3 day monitoring period each week; therefore data obtained in this study was compared to daily mean discharge data at the USGS gaging station near Garrison as a control. The Aug. 23-Sept. 15 monitoring period was selected as representative of the period of low flow in late summer and early fall due to the overall stability of LBR day-to-day flow as indicated at the USGS gaging station, where mean daily discharge generally varied 2, 2, 3 and 2 CFS over monitoring weeks 9-12 respectively. All LBR USGS daily mean discharge statistics listed in this report can be referenced at the website listed at the end of this report, request the information as daily data in table form.

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Figure 4

Average Flow by reach, August 23-Sept. 15

45 40 35 Flow 30 in 25 CFS 20 Section 2 15 Section 1 10

5

0

1 3 5 6 7 8 9 10 11

Diversion

From Aug. 23-Sept. 15 Section 1 loses a net of over 5 CFS between Sites 1 and 3, despite contributions from Spotted Dog Creek that averaged 4.5 CFS over the period. Once again flow increases significantly at the major chokepoint at the head of canyon above Site 5. Section 2 also shows a losing reach centered on Site 9 in a wide spot in the valley. Flows in Section 2 now decrease about 25% to 30 CFS, flows then gradually increase to 37 CFS as the cliffs narrow down into a final chokepoint at the end of the canyon between Sites 10 and 11. In-stream flows drop below Site 11, as seen in the weekly difference in the blue line (flow above Site 11) and the pink line (flow below Site 11) shown in Figure 6, to a low of 10.5 CFS on Sept. 2 during Week 10. The difference between 37 CFS above and 10.5 CFS below is depicted pictorially in Figure 6.

Figure 5

Above Flow Above and Below Site 11 by week Below

80 70 Flow 60 In 50 CFS 40 30 20 10 0

Week of study 5 6 7 8 9 10 11 12 13 14 Month reference Aug. 1 Sept. 1 Oct. 1 9 Lower Little Blackfoot Flow Study

10 Lower Little Blackfoot Flow Study

Figure 6

Flow above Site 11, 37 CFS, Aug. 23

Flow below Site 11, 10.5 CFS, Sept. 2

11 Lower Little Blackfoot Flow Study

This study was designed to examine how LBR flow changed over space from reach to reach, and this study was also designed to measure how the nature of that flow varied over time. Further examination of Figure 5 shows that this period of lowest flows runs generally from Monitoring Week 6 to Week 13, or Aug.1-Sept. 21, with measured flows of 36.8, 20, 15.2, 14.7, 10.5, 12.4, 12.9, and 14.5 CFS respectively. This period of low flow is typical of the river as a whole, as shown in Figure 7, the daily mean LBR discharge at the Garrison USGS gaging station from May 1-Dec. 1, 2007. That these low flows are a persistent trend from water year to water year is demonstrated by MFWP fisheries biologists who created in 1991, and updated in 1997, 2003, and 2005, a designation on the main-stem LBR from mile 0.0 to 24.9 as “Chronically De-watered,” where the term chronic is applied when dewatering is a significant problem in all years (NRIS). For the purposes of this report the chronic period of low flow is referred to as the “Critical Water Demand Period,” and spans monitoring weeks 6-13, or August 1-Sept. 21. Figure 7 is also generally representative of a typical water year in the LBR, and a typical LBR water year is described briefly in the paragraph following the figure.

Figure 7

Typical early season LBR flows are generally sufficient to support all water demands. In the water year 2007 snowmelt and spring rains kept river flows above 200 CFS from April into May, the river peaked at about 800 CFS in the first week of June in the wake of spring storms. Flows generally drop through June as water demand increases and runoff decreases, then flows stabilize in July as water demand drops as fields are dried for haying. LBR flows drop in late July and early August when irrigation resumes following the hay harvest, forming a trough of low flow in the hydrograph as demand for water goes up. In- 12 Lower Little Blackfoot Flow Study

stream flows remain low as the period of Critical Water Demand continues, and the lowest in-stream daily mean flows were recorded from Aug. 29-Sept. 6 when flows stayed between 18-20 CFS (USGS).The same USGS internet data base shows mean daily mean discharge at Garrison rose from 38 to 83 CFS from Sept. 22-24 in response to the first major storm of the season, signaling an end to the period of Critical Water Demand. LBR flows increased to nearly pre-demand levels, demand dropped between Sept. 23 and Oct. 18 as the irrigation season ended, and over the next several weeks the LBR gradually appeared to return to fall baseline flow conditions which would be expected to fluctuate as a factor of natural precipitation events.

The Period of Critical Water Demand generally represents eight monitoring weeks of the overall lowest LBR flows encountered in this study. Low in-stream flows often reflect high water temperatures, and in one study maximum August water temperatures surpassed suggested trout survival temperatures (67ºF) at 90% of monitoring sites along the main stem LBR, with one downstream site recording a high of 44 days of maximum temperatures exceeding 70ºF (DVCD, 2005). These low flows and high temperatures are likely a function of the demand for water, and the estimated water demand for each monitoring site from Aug. 1-25 and Aug. 29-Sept. 21 is shown in Figure 8.

Figure 8 Estimated Water Demand, Aug. 1-25, and Aug. 29-Sept. 21

Monitoring Site 1 3 5 6 7 8 9 10 11 Water Demand, 8/1-8/25 3.4 1.0 8.1 5.9 2.2 13.7 2.7 NOI 22.0 Water Demand, 8/29-9/21 8.3 10.8 10.3 11.9 3.0 20.0 0.5 NOI 26.7 All measurements in CFS NOI—No Observed Irrigation

The Critical Water Demand Period will vary in duration, intensity, and timing from water year to water year depending on factors like rain fall and snow melt. In addition, demands for water vary on a day to day or even hour to hour basis in a ditch irrigation system of management; the water demands in Fig. 8 were averaged over four weeks of monitoring to minimize short-term fluctuations and give a better idea of overall demand as opposed to a one time demand that may not be indicative of overall use. Specific demands can be found in weekly data tabulated in Appendix D. The data also showed that demand changed from the first half (Aug. 1-Aug. 25) to the second half (Aug. 29-Sept. 21) of the period of Critical Water Demand. Demand increased to the highest levels estimated in this study in the second half of this period, at a time when beneficial plant water use would seem to be limited by the increasing tendency toward colder nights and shorter days as the fall equinox approaches.

An important component of LBR ditch irrigation is the amount of water originally demanded that returns to the river as groundwater flow. This water isn’t lost to the river, it’s stored in the aquifer beneath the hay field. The answers to the questions of how much water is stored, and how long it takes for that water to return to the river, are notoriously difficult to answer, yet some trends were noted in this flow study. As previously discussed average flow in the canyon stretch from Sites 5-11 remained fairly constant during baseline conditions (Fig. 4). Contrast this relatively steady baseline flow with the data in Figure 9, the 13 Lower Little Blackfoot Flow Study

adjusted flow difference between Site 5 at the top of the canyon and Site 11 at the bottom of the canyon over the nineteen week period of the study (July 1-Oct. 31).

Figure 9 Adjusted Flow Difference Between Site 11 and Site 5 Net Gain/Loss Over Canyon by Week

15 10 5 Net Gain/Loss 0 (CFS) -5 -10 -15 1 357 9 11 13 15 17 19 7/26-28/07 Week 10/29-31/07

The nature of the river flow through the canyon changes dramatically over the course of the 19 week study period. Three distinct periods emerge in Figure 9: weeks 1-5 (approximately July1-Aug 1) when the river gains overall from top to bottom, weeks 6-13 (approximately Aug. 1-Sept. 21) when the river loses overall, and weeks 14-19 (approximately Sept. 21-Oct. 31) when the river gains then stabilizes. Note that the middle period, Aug. 1-Sept. 21, a period of eight monitoring weeks when the river loses overall, corresponds closely with the period of Critical Water Demand.

It wasn’t possible to visit all monitoring sites in one day, so weekly monitoring generally occurred over a two to three day period. As previously stated, daily real-time flow data at the USGS station in Garrison shows that overall river flow could change over the course of any given two to three day period, a factor that had to be accounted for when comparing relative flows at the beginning and end of the weekly monitoring period. For the purposes of comparison in Figure 9, whenever the daily mean discharge at the USGS station varied by more than 3 CFS over the weekly monitoring period, then the measured flows were adjusted by the difference in the daily mean USGS flows over the same monitoring period, generally a two day period. Changing flows over any given monitoring week were most evident in the early weeks of this study on the falling hydrograph as runoff tapered off, and in Week 14 following a storm. The weeks when flow was adjusted are presented in Figure 10, including the dates of measurements, the flow at Site 5 at the top of the canyon, the flow at Site 11 at the bottom of the canyon, the gain or loss in the flow from Site 5 to Site 11, the adjustment factor (the difference in the mean daily flow over the same monitoring period as given in USGS real time data tables referenced at the end of this document), and 14 Lower Little Blackfoot Flow Study

the adjusted flows shown graphically in Figure 9. Flows for Weeks 4, 7, 8, 9, 10, 11, 13, 16, 17, and 18 were not adjusted, and flows for these weeks are shown as measured in Figure 9.

Figure 10 Adjustment flow factors by week used in data for Figure 9

Week 1 2 3 5 6 12 14 15 19 Date 7/1-3 7/5-7 7/10-14 7/26-28 8/1-8/3 9/13-15 9/25-27 10/2-4 10/29-31 Site 5, flow 125.5 102.1 106 82.4 63.9 48.1 67.9 55.5 67.6 Site 11, flow 105.9 110.7 102.2 71.6 55.5 41.6 60.3 57.1 64.3 Flow Change, -19.6 +8.6 -3.8 -10.8 -8.4 -6.5 -7.6 +1.6 -3.3 Site 5 to Site 11 Adjustment +26 -4 +7 +14 +5 +2.5 +13 +4 +5 Adjusted +6.4 +4.6 +4.2 +3.2 -3.4 -4 +5.4 +5.6 -1.7 Flow

As an example of modification methodology, consider week 1 in Figure 10. Flow on July 1 at Site 5 was 125.5 CFS, and flow at Site 11 on July 3 was 105.9 CFS, for an apparent loss over the reach of 19.6 CFS. However, over that same time period, daily mean discharge at the USGS gaging station dropped 26 CFS (from 121 to 95 CFS.) Since the river as a whole dropped 26 CFS (the adjustment factor) over the monitoring period, and the river between Site 5 and Site 11 only dropped 19.6 CFS over the monitoring period, this was taken to mean the river actually gained 6.4 CFS between Site 5 and 11 during the monitoring period (26 CFS - 19.6 CFS = 6.4 CFS). By week 7 (Aug. 9-11) flows had stabilized, and daily mean USGS discharge varied only 1 CFS from the beginning to the end of the monitoring period (31-32 CFS). All USGS daily mean discharge data is available in tabular form at the USGS website referenced at the end of this paper.

The overall gains the river through the canyon from Site 5 to Site 11 apparently shows in monitoring weeks 1-5 (July 1-July 28) are likely the lingering results of runoff. The amount of gain tapers off as seasonal rain and snowmelt contributions to flow decrease, and water demand decreases as fields are dried for haying. In the study area demand as irrigation ditches closed had dropped to zero by July 26 at Sites 1, 3, 6, 8, 9, and 11. Demand resumed by the week of Aug. 1 at Sites 8 and 11, where demand was 18 and 18.9 CFS respectively. Demand continued to increase, and by the monitoring week of August 9-11 Sites 5, 6, 7, 8, 9, and 11 demanded an estimated 10.6, 8.4, 4.4, 14.7, 6.4, and 25.6 CFS respectively.

As demand increased during the monitoring week of Aug. 1 the LBR went from gaining water between Sites 5 and 11 to losing water between Sites 5 and 11 as shown in Figure 9. During the three monitoring weeks 6-8 (Aug. 1-Aug. 18) the LBR over this stretch loses 3.4, 12.3, and 12.6 CFS respectively, for an average loss of 9.4 CFS; these losses are most likely a result of increased evapotranspiration and short term recharge going to fill the groundwater aquifer beneath the hay fields. Once an aquifer is full, it takes less water to keep it full. Imagine a glass with a small hole drilled into the bottom. You can fill the glass as fast as you can add the water, but once the glass is full, you can only put in as much water as trickles out the hole in the bottom. It’s the same with saturated gravels beneath the hayfields. Water can seep into the ground only as fast as it can trickle back into the river. Under these 15 Lower Little Blackfoot Flow Study

conditions it should take less water to recharge the aquifer, and the flows necessary to maintain the aquifer once it was saturated would be expected to drop and stabilize.

This condition is apparently represented in the flows in Figure 9 for monitoring weeks 9-13 (Aug. 23-Sept. 21). First, losses decrease significantly from 12.6 CFS to 4 CFS from monitoring week 8 to monitoring week 9 (between Aug. 18-23), beginning a five monitoring week period (Aug. 23-Sept. 21) when the LBR from Site 5 to Site 11 showed losses of 4, 2.7, 1.7, 2.5, and 4.7 CFS. This is an average loss of 3.1 CFS, with a maximum variation of 1.6 CFS from that average, and appears consistent with the relatively low and steady flows that would be expected for maintenance of a saturated aquifer.

If this data does point to a saturated aquifer, then a reverse effect should be noted in the fall. The river from Site 5 through Site 11 should gain as the aquifer drains; again the data supports this theory. In weeks 14-17 (Sept. 25- Oct. 19), coinciding with decreased demand as outlined earlier, the river over the canyon stretch gains 5.4, 5.6, 7.3, and 13.2 CFS, for an average gain of 7.9 CFS over the 4 week period, before tapering off to the baseline flow shown in Figure 3. The first storm of the season came at the end of week 13 (Sept. 23), and certainly added to the gains shown from Sept. 25-Oct. 19. Even so, the similarity between the average losses shown in weeks 6-8 (9.4 CFS over a 3 week period), and the average gains shown in weeks 14-17 (7.9 CFS over a 4 week period) points to, as a first approximation, a groundwater storage capacity through the canyon reach from Site 5 to Site 11 equal to the flow of approximately 8-9.5 CFS over a 3-4 week period. This approximation indicates a fairly quick recharge that does not seem unreasonable based on the proximity of the hayfields to the river, the steep terrain, the size of the fields, the generally narrow water course, generally shallow soils, and the generally coarse gravels observed in the cut river banks that form the aquifer beneath the hayfields. A discernable increase in qualitatively observed ponding and sheet surface flow as September progressed is also observed evidence pointing to a saturated aquifer beneath the fields during the second half of the Critical Water Demand Period.

Preliminary information from this report was presented at a meeting of the Little Blackfoot Watershed Group, where it was noted that the summer of 2007 was unusually hot and dry in the LBR watershed; an observation that landowners believed important to consider in any further use of this report. In this same vein it is equally important to note that while the trends indicated in the data collected for this report are likely to persist from year to year; actual numbers should be expected to vary.

4) Conclusions and Recommendations

1) Seasonal LBR water demand is an important component of groundwater recharge and a controlling factor on stream flow. The highest demands for water came in September, at a time when consumptive use for plant growth and groundwater recharge appear to be declining, and this high late season demand is a promising area in which to continue talks developing a shared shortage and common water management vision between consumptive and nonconsumptive water users.

16 Lower Little Blackfoot Flow Study

2) Further monitoring is warranted, as noted at meetings of the Deer Lodge Valley Conservation District, the Natural Resource Damage Program advisory council, and the Little Blackfoot Watershed Group. Further monitoring in succeeding water years would 1) check and further quantify the ground and surface water interactions indicated in this report, 2) provide baseline data to measure the effects of future changes in demand if they develop, 3), measure the effects of changes in demand if they do develop, and 4) address important landowner questions as they develop.

Sources Sited

Buchanan and Somers, 1969, “Discharge Measurements at Gaging Stations,” Techniques of Water-Resources Investigations of the United States Geologic Survey.

NRIS, Montana Natural Resource Information System, water information is available at http://nris.mt.gov/wi.asp

USGS, all USGS data in this report is available as daily flow data on the LBR at http://waterdata.usgs.gov/mt/nwis/uv/?site_no=12324590&PARAmeter_cd=00060,00065, 00010

DVCD, 2005, Deerlodge Valley Conservation District, “Little Blackfoot River Stream Flow and Thermal Assessment Project.”

Resources:

All activities and work associated with this study was performed by Dave Ames, GeoScience Services, Box 205, Elliston, MT, 59728, on behalf of the Pat Barnes Missouri River Chapter of Trout Unlimited.

17 Lower Little Blackfoot Flow Study

18 Lower Little Blackfoot Flow Study

Appendix B

GPS Locations of Monitoring sites

Station NAD 83 Location 1A 46 35.785 N 112 35.198 W 1B 46 35.725 N 112 35,472 W 2 46 35. 591 N 112 36.395 W 3A 46 35.712 N 112 36.680 W 3B 46 35.728 N 112 36.689 W 4 46 35.910 N 112 37.542 W 5A 46 35.834 N 112 38.253 W 5B 46 35.834 N 112 38.327 W 6A 46 35.751 N 112 39.031 W 6B 46 35.690 N 112 39.094 W 6C 46 35.719 N 112 39.044 W 7A 46 34.954 N 112 39.926 W 7B 46 34.920 N 112 39.934 W 8A 46 34.460 N 112 39.906 W 8B 46 34.402 N 112 39.871 W 9A 46 33.818 N 112 40.804 W 9B 46 33.654 N 112 40.831 W 10A 46 32.668 N 112 40.837 W 10B 46 32.432 N 112 41.329 W 11A 46 32 416 N 112 41.717 W 11B 46 32.412 N 112 41 845 W

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Appendix C

Flow in CFS at Monitoring Sites above diversions over the Nineteen Week Study Period (7/1/2007--10/31/2007)

Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Date 7/1- 7/5- 7/10- 7/20- 7/26- 8/1- 8/9- 8/16- 8/23- 8/29- 9/6- 9/13- 9/18- 9/25- 10/2- 10/8- 10/18- 10/23- 10/29- 7/3 7/7 7/14 7/21 7/28 8/3 8/11 8/18 8/25 9/2 9/8 9/15 9/21 9/27 10/4 10/9 10/19 10/24 10/31

Site 1 95.1 81.7 92.7 73.7 67 49.2 42.4 34.6 41.8 32.7 32.3 34.7 36.3 54.5 43.9 50.5 51.8 58 51.8 2 22.5 19.6 17 11 10.6 6.7 4.7 4 4.9 7.1 7.3 6.4 7 5.8 3 105. 87.2 98.6 72.9 70.2 54.6 47 35.2 30.6 26.5 27.8 30.6 35 46.9 44 49.6 54.6 60.3 58.6 1 5 125. 102. 106 86.8 82.4 63.9 57.9 49.5 40.7 33.8 40 46.1 50.9 67.9 55.5 61.8 61.3 72.4 67.6 5 1 6 117. 103. 108.5 94.9 81.9 60.8 53.6 44.8 37.2 44 39.2 42.2 48.3 71.7 57.9 66.4 70.9 76.9 66.7 1 7 7 117. 94.3 90.9 84.1 83.8 61.7 52.1 41.4 37 33 38.8 45.2 45.8 59.3 56.2 60.6 66.4 75.3 63.7 7 8 116. 99.6 94.2 85.3 82.6 69.3 51.7 45.4 37.8 35.1 40.8 45 52.4 57.7 58.5 67.1 72.8 71.2 64.5 9 9 103. 100. 100.1 86.6 72 57 46.5 32.8 32 24.6 27.6 32.1 39.5 46.6 46.8 62.6 70.3 73.9 61.1 6 4 10 108. 106. 95.5 86.7 68.2 60 45.9 36.2 33.2 27.8 35.1 38.5 43.1 54.4 54.8 66.8 73.2 73.7 64.7 3 6 11 105. 110. 102.2 82.4 71.6 55.5 45.6 36.9 36.7 31.1 38.3 41.6 46.2 60.3 57.1 69.1 74.5 74.8 64.3 9 7

Date: These are the dates during which data was collected for each weekly division

Flow: All flow is in CFS

Note: Site 4, the mouth of 3 Mile Creek, does not appear in this table because no measurable flow was noted at this tributary over the course of the study 20 Lower Little Blackfoot Flow Study

Appendix D—Flow data, weeks 1-19

Week 1 Week 2

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 7/2/07 1A 95.1 7/5/07 1A 81.7 7/2/07 1B 79 16.1 7/5/07 1B 71.4 10.3 7/2/07 2 27.5 7/5/07 2 19.6 7/2/07 3A 105.1 26.1 7/5/07 3A 87.2 15.8 7/2/07 3B 98.7 6.4 7/5/07 3B 80.4 6.8 7/2/07 4 NSF 7/6/07 4 NSF 7/1/07 5A 125.5 26.8 7/6/07 5A 102.1 21.7 7/1/07 5B 120.1 5.4 7/6/07 5B 96.5 5.6 7/1/07 6A 49.4 -3 7/6/07 6A 45.5 7.2 7/1/07 6B 27.3 22.1 7/6/07 6B 36.1 9.4 7/1/07 6C 67.7 7/6/07 6C 58.2 7/2/07 7A 117.7 22.7 7/6/07 7A 94.3 0 7/2/07 7B 117.4 0.3 7/3/07 8A 116.9 -0.5 7/6/07 7B 96.4 -2.1 7/3/07 8B 104.1 12.8 7/6/07 8A 99.6 3.2 7/3/07 9A 103.8 -0.3 7/6/07 8B 97.9 1.7 7/3/07 9B 106.5 -2.7 7/7/07 9A 100.4 2.5 7/3/07 10A 108.3 1.8 7/7/07 9B 106.8 -6.4 7/3/07 10B 106.2 2.1 7/7/07 10A 106.6 -0.2 7/3/07 11A 105.9 -0.3 7/7/07 10B 100.9 5.7 7/3/07 11B 82.6 23.3 7/7/07 11A 110.7 9.8 7/7/07 11B 89.9 20.8

21 Lower Little Blackfoot Flow Study

Week 3 Week 4

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 7/10/07 1A 97.7 5.5 7/20/07 1A 73.7 5.7

7/10/07 1B 92.2 7/20/07 1B 68

7/10/07 2 17 7/20/07 2 11

7/10/07 3A 98.6 11.8 6.4 7/20/07 3A 72.9 9.1 4.9 7/10/07 3B 86.8 7/20/07 3B 63.8 4 NSF 7/20/07 4 NSF 7/11/07 5A 106 6.2 19.2 7/20/07 5A 86.8 5.2 23

7/11/07 5B 99.8 7/21/07 5B 81.6

7/11/07 6A 48.5 9.3 8.7 7/21/07 6A 37.3 3 3.3

7/11/07 6B 99.2 7/21/07 6B 81.9 7/11/07 6C 60 7/21/07 6C 47.6 7/14/07 7A 90.9 0.7 -8.3 7/21/07 7A 84.1 5.8 2.2 7/14/07 7B 90.2 7/21/07 7B 78.3 7/14/07 8A 94.2 0 4 7/21/07 8A 85.3 DC 7

7/14/07 8B 94.2 7/21/07 8B 84.3

7/14/07 9A 100.1 1.6 5.9 7/22/07 9A 86.6 DC 2.3 7/14/07 9B 98.5 7/21/07 9B 84.4 7/14/07 10A 95.5 -6 -3 7/21/07 10A 86.7 3.5 2.3 7/12/07 10B 101.5 7/21/07 10B 83.2 7/12/07 11A 102.2 13 0.7 7/21/07 11A 87.4 DC 4.2

7/12/07 11B 89.2 7/21/07 11B 85.3

22 Lower Little Blackfoot Flow Study

Week 5 Week 6 DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 7/26/07 1A 67 DC 8/1/07 1A 49.2 DC 7/26/07 1B 64.8 8/1/07 1B 50.7 7/26/07 2 10.6 8/1/07 2 7/26/07 3A 70.2 DC 5.4 8/1/07 3A 54.6 DC 3.9 7/26/07 3B 68.9 8/1/07 3B 55.1 7/26/07 4 NSF 8/1/07 4 NSD 7/26/07 5A 82.4 7.7 13.5 8/1/07 5A 63.9 DC 8.8 7/27/07 5B 74.7 8/2/07 5B 62.7 7/27/07 6A 36.8 DC 7.2 8/2/07 6A 25.4 DC -1.9 7/27/07 6B 84 8/2/07 6B 65 7/27/07 6C 45.1 8/2/07 6C 35.4 7/27/07 7A 83.8 2 -0.2 8/2/07 7A 61.7 DC -3.3 7/27/07 7B 81.8 8/2/07 7B 63 7/27/07 8A 82.8 11.3 1 8/2/07 8A 69.3 18 6.3 7/27/07 8B 71.5 8/2/07 8B 51.3 7/28/07 9A 72 DC 0.5 8/2/07 9A 57 DC 5.7 7/28/07 9B 70.5 8/2/07 9B 58.8 7/28/07 10A 68.2 -1.7 -2.3 8/2/07 10A 60 7.3 1.2 7/28/07 10B 69.9 8/3/07 10B 52.7 7/28/07 11A 71.6 DC 1.7 8/3/07 11A 55.5 18.9 2.8 7/28/07 11B 71.4 8/3/07 11B 36.6

23 Lower Little Blackfoot Flow Study

Week 8 Week 7

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 8/16/07 1A 34.6 DC 8/9/07 1A 42.4 DC

8/16/07 1B 34 8/9/07 1B 41.6 8/16/07 2 8/9/07 2 6.7 8/16/07 3A 35.2 DC 1.2 8/9/07 3A 47 DC 5.4 8/16/07 3B 35.7 8/9/07 3B 46.3 8/16/07 4 NSF 8/9/07 4 NSF 8/16/07 5A 49.5 11.7 13.8 8/9/07 5A 57.9 10.6 11.6

8/16/07 5B 37.8 8/9/07 5B 47.3

8/17/07 6A 18.8 7.9 7 8/9/07 6A 23.5 8.4 6.3 8/17/07 6B 36.9 8/9/07 6B 45.2 8/17/07 6C 26 8/9/07 6C 30.1 8/17/07 7A 41.4 0.6 4.5 8/10/07 7A 52.1 4.4 6.9 8/17/07 7B 40.8 8/10/07 7B 47.7 8/17/07 8A 45.4 13.6 4.6 8/10/07 8A 51.7 14.7 4

8/17/07 8B 31.8 8/10/07 8B 37

8/18/07 9A 32.6 2.2 0.8 8/10/07 9A 46.5 6.4 9.5 8/18/07 9B 30.4 8/10/07 9B 40.1 8/18/07 10A 36.2 1.2 5.8 8/10/07 10A 45.9 0.8 5.8 8/18/07 10B 35 8/11/07 10B 45.1 8/18/07 11A 36.9 21.7 1.9 8/11/07 11A 45.6 25.6 0.5

8/18/07 11B 15.2 8/11/07 11B 20

24 Lower Little Blackfoot Flow Study

Week 9 Week 10

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 8/23/07 1A 41.8 13.7 8/29/07 1A 32.7 6.7

8/23/07 1B 28.1 8/29/07 1B 26 8/23/07 2 4.7 8/29/07 2 4 8/23/07 3A 30.6 4.1 2.5 8/29/07 3A 26.5 7.7 0.5 8/23/07 3B 26.5 8/29/07 3B 18.8 8/23/07 4 8/29/07 4 8/23/07 5A 40.7 10 14.2 8/29/07 5A 33.8 6.1 15

8/23/07 5B 30.7 8/29/07 5B 27.7

8/24/07 6A 15.5 7.1 6.5 8/30/07 6A 23.8 16.3 16.3 8/24/07 6B 30.1 8/30/07 6B 27.7 8/24/07 6C 21.7 8/30/07 6C 20.2 8/24/07 7A 37 3.3 6.9 8/30/07 7A 33 3 5.3 8/24/07 7B 33.7 8/30/07 7B 30 8/24/07 8A 37.6 8.4 3.9 9/1/07 8A 35.1 17.8 5.1

8/24/07 8B 29.2 9/1/07 8B 17.3

8/25/07 9A 32 2.1 2.8 9/1/07 9A 24.6 2.1 7.3 8/25/07 9B 29.9 9/1/07 9B 22.5 8/25/07 10A 33.2 -1.3 3.3 9/1/07 10A 27.6 0.4 5.1 8/25/07 10B 34.5 9/2/07 10B 27.2 8/25/07 11A 36.7 22 2.2 9/2/07 11A 31.1 20.6 3.9

8/25/07 11B 14.7 9/2/07 11B 10.5

25 Lower Little Blackfoot Flow Study

Week 11 Week 12

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 9/6/07 1A 32.3 8.4 9/13/07 1A 34.7 10.2 9/6/07 1B 23.9 9/13/07 1B 24.5 9/6/07 2 9/13/07 2 4.95 9/6/07 3A 27.8 10 3.9 9/13/07 3A 30.6 11.8 6.1 9/6/07 3B 17.8 9/13/07 3B 18.8 9/6/07 4 9/13/07 4 9/6/07 5A 40 7.8 22.2 9/13/07 5A 48.1 14.1 29.3 9/6/07 5B 32.2 9/13/07 5B 34 9/6/07 6A 15.5 9.5 7 9/14/07 6A 16.6 10.8 8.2 9/6/07 6B 29.7 9/14/07 6B 31.4 9/6/07 6C 23.7 9/14/07 6C 25.6 9/7/07 7A 38.8 2.4 9.1 9/14/07 7A 45.2 4.7 13.8 9/7/07 7B 36.4 9/14/07 7B 40.5 9/7/07 8A 40.8 18.6 4.4 9/14/07 8A 45 20.3 4.5 9/7/07 8B 22.2 9/14/07 8B 24.7 9/7/07 9A 27.6 -0.3 5.4 9/14/07 9A 32.1 DC 7.4 9/7/07 9B 27.9 9/14/07 9B 31.3 9/7/07 10A 35.1 -1.1 7.2 9/14/07 10A 38.5 -0.8 7.2 9/7/07 10B 36.2 9/15/07 10B 39.3 9/7/07 11A 38.3 25.9 2.1 9/15/07 11A 41.6 28.7 2.3 9/7/07 11B 12.4 9/15/07 11B 12.9

26 Lower Little Blackfoot Flow Study

Week 13 Week 14

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 9/18/07 1A 36.3 7.9 9/25/07 1A 54.5 6.6 9/18/07 1B 28.4 9/25/07 1B 47.9 9/18/07 2 9/25/07 2 7.1 9/18/07 3A 35 13.7 6.6 9/25/07 3A 46.9 7.8 -1 9/18/07 3B 21.3 9/25/07 3B 39.1 9/18/07 4 9/25/07 4 9/18/07 5A 50.9 13.1 29.6 9/25/07 5A 67.9 17.9 28.8 9/18/07 5B 37.8 9/25/07 5B 50 9/20/07 6A 18.9 10.9 10.5 9/25/07 6A 29.6 13.8 21.7 9/20/07 6B 37.4 9/25/07 6B 57.9 9/20/07 6C 29.4 9/25/07 6C 42.1 9/20/07 7A 45.8 1.8 8.4 9/26/07 7A 59.3 6 1.4 9/20/07 7B 44 9/26/07 7B 53.3 9/20/07 8A 52.4 23.1 8.4 9/26/07 8A 57.7 21.7 4.4 9/20/07 8B 29.3 9/26/07 8B 36 9/21/07 9A 39.5 0.1 10.2 9/26/07 9A 46.6 DC 10.6 9/21/07 9B 39.4 9/26/07 9B 45.9 9/21/07 10A 43.1 -0.9 3.7 9/26/07 10A 54.4 -6.6 8.5 9/21/07 10B 44 9/27/07 10B 61 9/21/07 11A 46.2 31.7 2.2 9/27/07 11A 60.3 DC -0.7 9/21/07 11B 14.5 9/27/07 11B 58.5

27 Lower Little Blackfoot Flow Study

Week 15 Week 16

DATE STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 10/2/07 1A 43.9 7.1 10/8/07 1A 50.5 8.3 10/2/07 1B 36.8 10/8/07 1B 42.2 10/2/07 2 10/8/07 2 7.3 10/2/07 3A 44 11.3 7.2 10/8/07 3A 49.6 DC 7.4 10/2/07 3B 32.7 10/8/07 3B 49.6 10/2/07 4 NSF 10/8/07 4 NSF 10/2/07 5A 55.5 DC 22.8 10/8/07 5A 61.8 DC 12.2 10/2/07 5B 55.5 10/8/07 5B 61.8 10/4/07 6A 57.9 DC 2.4 10/8/07 6A DC 4.6 10/4/07 6B 57.9 10/8/07 6B 66.4 10/4/07 6C 0 10/8/07 6C 10/4/07 7A 56.2 DC -1.7 10/9/07 7A 60.6 DC -5.8 10/4/07 7B 56.2 10/9/07 7B 60.6 10/4/07 8A 58.5 18.8 2.3 10/9/07 8A 67.1 DC 6.5 10/4/07 8B 39.7 10/9/07 8B 67.1 10/4/07 9A 46.8 DC 7.1 10/9/07 9A 62.6 DC -4.5 10/4/07 9B 46.8 10/9/07 9B 62.6 10/4/07 10A 54.8 DC 8 10/9/07 10A 66.8 DC 4.2 10/4/07 10B 54.8 10/9/07 10B 66.8 10/4/07 11A 57.1 DC 2.3 10/9/07 11A 69.1 DC 2.3 10/4/07 11B 57.1 10/9/07 11B 69.1

28 Lower Little Blackfoot Flow Study

Week 17 Week 18

10/18/07 STATION DISCHARGE DIVERSION RETURN DATE STATION DISCHARGE DIVERSION RETURN 10/18/07 1A 51.8 DC 10/23/07 1A 58 DC 10/18/07 1B 51.8 10/23/07 1B 58 10/18/07 2 6.38 10/23/07 2 7 10/18/07 3A 54.6 DC 2.8 10/23/07 3A 60.3 DC 2.3 10/18/07 3B 54.6 10/23/07 3B 60.3 10/18/07 4 NSF 10/23/07 4 10/18/07 5A 61.3 DC 6.7 10/23/07 5A 72.4 DC 12.1 10/18/07 5B 61.3 10/23/07 5B 72.4 10/18/07 6A DC 9.6 10/23/07 6A DC 4.5 10/18/07 6B 70.9 10/23/07 6B 76.9 10/18/07 6C 10/23/07 6C 10/18/07 7A 66.4 DC -4.5 10/23/07 7A 75.3 DC -1.6 10/18/07 7B 66.4 10/23/07 7B 75.3 1019/07 8A 72.8 DC 6.4 10/24/07 8A 71.2 DC -4.1 1019/07 8B 72.8 10/24/07 8B 71.2 1019/07 9A 70.3 DC -2.5 10/24/07 9A 73.9 DC 2.7 1019/07 9B 70.3 10/24/07 9B 73.9 1019/07 10A 73.2 DC 2.9 10/24/07 10A 73.7 DC -0.2 1019/07 10B 73.2 10/24/07 10B 73.7 1019/07 11A 74.5 DC 1.3 10/24/07 11A 74.8 DC 1.1 1019/07 11B 74.5 10/24/07 11B 74.8

29 Lower Little Blackfoot Flow Study

Week 19

DATE STATION DISCHARGE DIVERSION RETURN 10/29/07 1A 51.8 DC

10/29/07 1B 51.8 10/29/07 2 5.8 10/29/07 3A 58.6 DC 6.8 10/29/07 3B 58.6 10/29/07 4 NSF 10/29/07 5A 67.6 DC 9

10/29/07 5B 67.6

10/29/07 6A DC -0.9 10/29/07 6B 66.7 10/29/07 6C 10/31/07 7A 63.7 DC -3 10/31/07 7B 63.7 10/31/07 8A 64.5 DC 0.8

10/31/07 8B 64.5

10/31/07 9A 61.1 DC -3.4 10/31/07 9B 61.1 10/31/07 10A 64.7 DC 3.6 10/31/07 10B 64.7 10/31/07 11A 64.3 DC -0.4

10/31/07 11B 64.3