reducing flow. in the creek for downstream users having priority surface. At the request of Mr. H.D. DeBeck, Comptroller of Water Rights, an

Transcription

1 .., Dr. J.C. Foweraker, Head Groundwater Sect i on Hydrology Division Water nvestigations Branch Date: September O, 1979 File: 2,9'2 1/10 Fr: A.P. Kohut Sr. Geologi cal Engineer Groundwater Section Re: Cherry Creek - Groundwater versus Surface Water Use At the request of Mr. H.D. DeBeck, Comptroller of Water Rights, an investigation was undertaken in the above area to obtain information on groundwater-surface water relationships. This information is required to assist in water management decisions aimed at resolving the conflict between grohdwater and surface water users in the valley. A major point of contention is whether or not wells located upstream of the Cherry Creek Ranch are diverting water from Cherry Creek, thereby reducing flow. in the creek for downstream users having priority surface water rights. All available data, including existing well logs, geo- 1 ogi c reports and air photographs, were reviewed to ascertain the groundwater conditions. A field inspection was carried out on August 13, 1979, to verify the local geologic conditions, to observe the current situation of water withdrawals, and to carry out some preliminary testing and monitoring. This memorandum summarizes the geologic and groundwater condi tions of the Val 1 ey, provides comments on the probable surf ace water-groundwater relationships and makes recommendations for further monitoring. GENERAL GEOLOGY The Cherry Creek'Valley is underlain principally by Tertiary volcanic rocks comprised of rhyolite, andesite, basalt and associated tuff, breccias and agglomerates (Cockfield, 1948). Older (Triassic) volcanic and sedimentary rocks occur in the upland areas south of Cherry Creek. According to Fulton (1963), ice overrode the entire map area, depositing a mantle of glacial till up to 70 feet thick over the region. The ice sheet retreated largely by downwasting with tongues of ice remaining in the main valleys after the surrounding uplands were bare. During this phase of partial deglaciation, glacio-fluvial, fluvial, e- glacio-lacustrine and lacustrine deposits formed in valleys tributary to the Thompson Valley (Fulton, 1963). During this time, a large glacial lake referred to as Lake Thompson formed in the Thompson Valley east of Kamloops and thick sections of lacustrine silt were deposited in the Val ley. Meltwaters from the retreating ice, cut ice-margi nal me1 twater channels in the glacial till, depositing coarser fractions of the eroded till as glacio-fluvial deposits with the silt and finer-grained fractions being deposited in Lake Thompson (Fulton, 1963).... 2

2 - 2 - The Cherry Creek Valley in part represents a meltwater channel feature. Figure 1 modified after existing surficial geologic mapping (Fulton, 1963) and air photograph analysis shows the distribution of surficial deposits in the area. From a point approximately %-mile downstream of the Beaton Road crossing, the upstream portion of the Cherry Creek Valley is relatively narrow and incised in glacial till and the bedrock. Downstream of this point where bedrock is exposed on either side of the valley close to creek level, the valley widens appreciably, following the eastern edge of a terraced glacial-flucial deposit comprised of sand and gravel. Downstream beyond the glacial-fluvial deposit in the vicinity of the Cherry Creek Ranch, the valley broadens further and Cherry Creek flows over alluvial floodplain and lacustrine deposits comprised of silt, sand and gravel, overlying clay. GROUNDWATER CONDTONS Available well log information in the vicinity of the Cherry Creek Ranch, shown in the generalized geologic cross-section AA' (Figure 2) indicates the valley at this location is infilled by a sequence of silt, clay and glacial till up to 120 feet thick overlain by an aquifer zone comprised of sand and gravel wihich in turn is overlain by clay, till and alluvial sand and gravel. Maximum thickness of the valley fill material is greater than 200 feet. The aquifer zone ranges in thickness from less than 5 to 70 feet in thickness and varies in composition from highly permeable sand and gravel to less permeable si1 ty sand phases. On the north side of Cherry Creek, groundwater occurs under flowing artesian conditions in the thin aquifer zone which lies directly on the bedrock. The well drilled at this location in 1963 originally flowed at % gprn and was rated at 6 gprn by the driller. The aquifer zone appears to thicken towards the south flank of the valley where the large capacity irrigation well of Cherry Creek Ranch is sited. This 10-inch diameter well completed with slotted casing was originally tested at 600 gprn with only 8 feet of drawdown. The nonpumping water level in 1963 was 11 feet below ground surface. ndications are that properly screened, large diameter wells capable of supplying 1,500 to 2,000 gpm could be constructed -- in this aquifer. Recently (May 1979), a moderate capacity well was completed upstream in the valley near the Beaton Road crossing. At this location the valley is relatively narrow and infilled with up to 95 feet of valley fill deposits (Figure 3). The main aquifer zone is a minimum of 20 feet thick, lying 75 to 95 feet below ground and overlain by glacial till containing thin layers of gravel and silty sand. The 8-inch diameter well completed on the south side of the creek on the Patterson property was screened with 1.0feet of 100 slot screen set 81 to 91 feet below ground. The nonpumping water level was 7 feet and the well was rated by the driller at 100 gpm on the basis of a bail test. A 6-inch diameter well is located on the north side of the Creek, 110 feet from.... 3

3 ' '.' -3-. the 8-inch well. This well was completed to a depth of 62 feet encountering 5 feet of aquifer material lying on bedrock. Under nonpumping conditions the well is flowing artesian. t was rated at 40 gprn by the well driller on the basis of a bail test. Due to well interference between these two wells it is not possible to utilize both wells simultaneously at their maximum individual capacities. Close to the area of these wells a seepage zone was observed at the toe of the upland along the southern side of the valley (Figure 1). Groundwater from this zone may be originating from the bedrock along the valley wall. At the time of the field visit a new 6-inch diameter well was being drilled on the Penner property downstream of the Patterson wells. Dri 11 i ng had proceeded to 62 feet encounteri ng water-beari ng gravel from 53 to 62 feet, overlain by 37 feet of glacial ti 11 and 16 feet of silty sand and gravel. Other wells above the Cherry Creek Ranch include a 4-inch diameter well, approximately 46 feet deep, completed 35 feet from the creek, on the Moorcroft property (Figure 1). The well normally flows slightly under nonpumping conditions. Two wells are located downstream of the Moorcroft we1 1, including a 14-foot dug we1 1, 1 ined with a 3-fOOt diameter culvert casing and a newly completed 5-inch (D) drilled well, 50 feet in depth. Water level in the drilled well measured on August 14, 1979 was 38 feet below ground or approximately 20 feet below the creek level. the drilled well is presently not available. A log of Shallow dug wells completed in the thin sand and gravel, surface deposits adjacent to Cherry Creek can be considered to be under water table conditions and in direct hydraul ic connectionwi t h the creek. PRELMNARY FELD TESTNG n order to determine whe(her or not the Patterson irrigation well could be affecting the flow of Cherry Creek, arrangements were made with Mr. Brian Patterson to stop his pump for a four-hour period. Three marker stakes, a, b and c, were set up in the creek channel, opposite the we1 1 and at points upstream and downstream (Figure 1 ), to monitor any changes in creek flow 'during the shutdown period. Prior to shutdown Mr. Patterson estimated that he was pumping at about 100 gpm, providing water for 28 sprinkers. He had been pumping continuously for about 23 hours since last ishutting off the pump to move the sprinklers. He apparently had been operating the well more or less continuously in this manner for the last few weeks. Water level measurements were taken in the irrigation well and the neighbouring 6-inch well prior to shutdown and during the shutdown period. This recovery information is shown in Table 1. A level survey was carried out to tie in the relative elevations of the two wells and the creek. Conductivity and temperature measurements were also made in the creek and on a water sample from the irrigation well to determine any differences in water quality between the sources.... 4

4 - 4 - During the 4-hour shutdown period, the water level in the irrigation well recovered 26.1 feet from 64.3 to 38.2 feet below.the top of the casing while the level in the nearby 6-inch well recovered 5.3 feet from 34 to 28.7 feet below the top of the casing. t is evident that due to the slow rate of recovery (Figure 4) it would require several days for the water levels to stabilize at their natural "static" levels. From a plot of the recovery data in the irrigation well (Figure 5), boundary conditions are evident from the change in slope of the recovery curve and it is apparent that the aquifer is of limited extent. Significant well interference (34 feet) is shown in the 6-inch well 110 feet from the irrigation well. Transmissivity values calculated from the recovery data (Figures 5 and 6) indicate values ranging from 1,500 to 7,000 USgpd/ft. The higher values are perhps more representative of the formation transmissivity in the vicinity of the well while the lower values observed result from the boundary effects. The storativity of the confined aquifer calculated from the limited recovery data of the 6-inch well and utilizing transmissivity values of 7,000 and 2,300 varies from 3.7 x lom3 to 3.2 x respectively. Observations taken on the three marker stakes during the shutdown period showed that there was no significant change in the flow of the creek. A slight drop in creek level of 1/8 inch was actually recorded at each of the sites. This reduction in flow may have been due to increased usage from creek intakes upstream during the supper time period. t is not surprising on the other hand that the creek flow did not increase due to shutdown of the irrigation well. This was probably due to the fact that the water levels in the wells were recovering at a very slow rate, and after 4 hours, were still 28 feet or more below ground and creek level. t would have been necessary, therefore, to have the well shut down for several days in order to observe any possible change in flow of the creek. Conductivity and temperature measurements taken on the creek and on a sample from the irrigation well indicated the conductivity of the creek was 500 pmhos/cm at T = 17 C while the conductivity of the groundwater was pmhos/cm at 13 C. This difference in chemistry, combined with the fact that the aquifer is confined and overlain by glacial till of 1 ow permeabi 1 i ty indicates the irrigation we1 1 is not in direct hydraulic connection with the creek and the well is not drawing water directly from the creek at this locale. The possibility of an indirect connection between the well and the creek, however, was examined in the manner outlined below. ANALYSS OF THE POSSBLE NDRECT RELATONSHP BETWEEN WELLS AND SURFACE WATER As evidence indicated that the water being pumped from the Patterson irrigation well was not coming directly from Cherry Creek, the following a1 ternati ve sources were examined :... 5

5 - 5 - e A. Groundwater storage of the confined aquifer. B. nterception of the' natural groundwater flow component. C. Groundwater discharge from the bedrock. A. Groundwater Storaae of the Confined Aauifer The amount of groundwater released through lowering of the hydraulic head in the aquifer by pumping of the Patterson irrigation well was calculated assuming for discussion purposes only that the cone of influence extended the full width of the channel (200 feet) to an average depth of 60 feet and along the channel for distances 2,000 feet upstream and downstream of the well. The theoretical volume affected can be approximated by a body of triangular cross-section area, 4,000 feet'in length. 7 3 Volume = 100 x 60 x 4,000 = 2.4 x 10 ft. This volume, of.course, would be exaggerated as the actual depth of the cone decreases longitudinally away from the we1 1. Applying a storativi ty value of 3.7 x 10-3 indicates the amount of water released from storage from such an affected area would be: 2.4 x lo7 ft. x 3.7 x = 88,800 ft.3 = 664,224 US gals. This volume of water would be equivalent to supply from a 100-gpm well for only 4% days of continuous pumping. t is inconceivable, therefore, that the main irrigation well could be pumping entirely from storage and must therefore be receiving recharge from some source. B. ntercedtion of the Natural Groundwater Flow ComDonent The natural flow component through the aquifer can be approximated using Dlarcyls Law in the form: Q = KA... 6

6 - 6 - where: Q is the flow through the aquifer in USgpd K is the aquifer permeability or hydraulic conductivity in USgpd/f t. is the hydraulic gradient A is the cross-sectional area of the aquifer in ft.2 Assuming an hydraulic gradient of 200 feet/mi le from topographic considerations, a cross-section area of (200 x 20) ft.2 and a permeability of 350 USgpd/ft.2 suggests up to 37 USgpm on a continuous basis could be flowing through the aquifer. t would appear therefore that a portion of the water pumped from the aquifer could be derived from natural groundwater through flow in the aquifer. Recharge of the component of flow would presumably come from areas upstream along Cherry Creek. C. Groundwater Discharge from the Bedrock Under natural conditions any natural discharge of groundwater into the valley would be incorporated into the downgradient component of groundwater flow discussed under B above or would augment creek flow directly. t is possible that under pumping conditions a component of recharge may be induced from the.bedrock adjacent to the valley. As the bedrock storati vi ty Val ues and bedrock permeabi 1 i ties would be expected to be very low in comparison to the hydraulic properties of the confined aquifer, it is unlikely that recharge from the bedrock would contribute more water than that released from storage of the confined aquifer as determined in A above. Since it does not appear possible that groundwater in storage or interception of the natural groundwater flow component could maintain the production of the Patterson well for an extended period of time at a rate of 100 gpm, some leakage from the creek would have to be occurring to recharge the confined aquifer. n order to determine whether or not pumping of the Patterson well is inducing recharge of the aquifer from Cherry Creek, two weirs to monitor creek flow would have to be established at sites upstream and downstream of the well (Figure 1). f a significant change (i.e., loss) in creek flow less withdrawals from licensed intakes is recorded over this portion of the valley, these flow losses may be attributable to pumping from the Patterson well. SUMMARY AND RECOMMENDATONS Preliminary field testing and monitoring has indicated that the 8-inch diameter Patterson irrigation well is not drawing water directly from Cherry Creek. Pumping from the well on the other hand may be affecting the creek flow indirectly through the lowering of the artesian head in the aquifer, thereby inducing recharge from the creek into the aquifer.... 7

7 - 7 - Presumably this leakage would occur through the overlying till layer, along the valley walls at the bedrock-till contact or in areas where the till may not be present. Weirs would have to be established at points upstream and downstream of the we1 to ascertain the magnitude of any flow losses in the creek. Shallow dug wells completed in the surface sand and gravel deposits adjacent to the creek can be considered to be under water-table conditions and in direct hydraulic connection with the creek. Development of additiona wells in the valley near the Patterson well is limited due to mutual interference between wells and limited capacity of the narrow aquifer due to boundary effects. Additional groundwater development is feasible in the vicinity of the Cherry Creek Ranch irrigation well and in the glacial-fluvial deposit to the south. n these downstream areas it is probable that Cherry Creek may be naturally recharging the groundwater regime in the glacial-fluvial deposits. The large storage potential and high permeability of these deposits on the other hand suggests large capacity wells completed in this area could be used to augment the creek flow. A.P. Kohut Sr. Geol ogi cal Engineer Groundwater Section Hydrology Division APK/ j s REFERENCES Cockfield, W.E Geology and Mineral Deposits of Nicola Map-Area, British Columbia. Geological Survey of Canada, Memoir 249. Fulton, R.J Surficial Geology, Kamloops Lake, British Columbia. Geological Survey of Canada, Map

8 Province of British Columbia Ministry of the Environment ENVRONMENTAL AND ENGNEERNG SERVCE WATER NVESTlGATlONS BRANCH SCALE: VERT.... DATE HOR 1" uu,1320' Aug TO ACCOMPANY REPORT ON CHERRY CREEK....a.f?k... ENGNEER FLE NO DWG. N ~ qur.e... bcil 6660 wrs

9 GEOLOGC CROSS-SECTON 1 / \ 500 /ooo /5m 2000 FE T BEDROCK Province of British Columbia., Ministry of the Environment ENVRONMENTAL AND ENGNEERNG SERVCE WATER NVESTGATONS BRANCH SCALE: VERT s.ho.w.n.... DATE As shown Aug HOR... TO ACCOMPANY REPORT ON CHERRY CREEK A.P. Kohut... ENGl NEER 82 1/10 Figure 3 FLE No... DWG. No...

10 ~~ ~ GEOLOGC CROSS-SECTON A U '", 'u \1 h F k 7! '0-500 /OOO FE T /SO0 s ll7 Cf4Y ~~~ ~ Province of British Columbia Ministry of the Environment ENVRONMENTAL AND ENGNEERNG SERVCE WATER NVESTGATONS BRANCH As shown As-"'s hown ~ SCALE: VERT... HOR... DATE hs TO ACCOMPANY REPORT ON CHERRY CREEK A.P. Kohut 82 /lq Figure 2... ENGNEER FLE No... DWG. No... bcil 6660 wrs

11 \ L SEM-LOGARTHMC 5 CYCLES X 70 DVSONS H*E KEUFFEL & ESSER CO. MADE N U.S.A O 20 30

12 TME 0 SEM-LOGARTHMC. 3 CYCLES X 70 DVSONS KEUFFEL LL ESSER CO. MADE N US.& r ON ELL O ~ N MNUTES AFTER PUMPNG STOPPED figure

13 figure 6 TME N MNUTES AFTEP~PUMPNG STOPPED - SEM-LOGARTHMC 5 CYCLES X 70 DWSONS 0 k@k KEUFFEL 8: ESSER CO. MADE 18 U.S.A

14 . 4 TABLE 1 RECOVERY MEASUREMENTS TME TME AFTER PUMPNG STOPPED (minutes) WATER LEVEL N FEET BELOW TOP OF CASNG rrigation We1 1 6-inch We