Water Stewardship Information Sources
| ID | 1790 |
|---|---|
| Citation | Toews. MW., Allen, DM. 2007. Aquifer characterization, recharge modeling and groundwater flow modeling for well capture zone analysis in the Oliver Area of the Southern Okanagan, BC. Final Report submitted to BC Ministry of Environment. |
| Organization | SFU |
| URL | http://a100.gov.bc.ca/appsdata/acat/documents/r16069/Oliver_Modeling_Report_SFU_1241461559877_1889edcbf8a3343a99a8beb2d78e2d33c46d56443ce38cc5f184042428abba86.pdf |
| Abstract/Description or Keywords | Aquifer characterization, recharge modeling and groundwater flow modeling are undertaken for the arid region of the south Okanagan Basin near Oliver, British Columbia. The primary objectives of the study are to map the distribution of geologic units in the study area with the aim of constructing a 3-dimensional architecture model of the aquifer(s); to quantify and map the spatial distribution of recharge to the aquifer(s) within the sub-region; to construct and calibrate a three-dimensional groundwater flow model that can be used to simulate groundwater conditions in the Oliver region; and to construct a local scale groundwater model for the Town of Oliver to obtain well capture zones for municipal wells. The study region is located between Lake Vaseux and Lake Osoyoos; the Town of Oliver is in the center of the region. Okanagan River is the main surface water body in the region, which flows from Vaseux Lake, southward to Lake Osoyoos. The river is controlled near the outlet of Vaseux Lake by McIntyre Dam, which also diverts water into the SOLID irrigation channel. The majority of the streams entering the Oliver region are ephemeral, and do not extend far down into the valley. It is assumed that some of these small streams directly recharge to groundwater at the bedrock/valley-fill interface, since they disappear partway down the valley over unconsolidated material. There are also many small (~1 km) lakes along the valley bottom and valley sides. These water bodies do not have any major streams flowing in or out of their surface (with the exception of Tugulnuit Lake, which has a gravity-fed pipe down to Okanagan River), and are interpreted to be sustained through groundwater. In the Oliver region, there is only a limited number of valley-bottom boreholes that reached bedrock through the valley fill. The spatial definition of the bedrock surface was approximated from a GIS analysis of borehole, digital elevation, slope, and orthophoto data. From the available data, the maximum depth of the bedrock surface ranges from approximately 0 to 100 m above sea level. There are no indications that the bedrock is eroded as deeply as in the northern Okanagan, where the bedrock contact is below sea level in many parts of the Valley. The valley fill within the Oliver area consists of Pleistocene-aged glaciolacustrine silt and clay overlain by glaciofluvial sand and gravel. The main aquifer in the study region is the upper unconfined sand and gravel aquifer adjacent to Okanagan River. Deep confined sand and gravel aquifers are found along the valley margins, which are in alluvial deposits. Many of these alluvial fan deposits interfinger the glaciolacustrine deposits at depth, and likely extend less than several hundred metres toward the valley center. Spatial recharge is modelled using available soil and climate data with the HELP hydrology model. Irrigation was added to precipitation in irrigation districts located in the Oliver region using proportions of crop types, and daily climate and evapotranspiration data generated from a stochastic weather generator (LARS-WG). Mean annual recharge rates have a median of 45 mm/yr, with first and third quartiles of 15 and 60 mm/yr, respectively. These values are approximately 20% of the annual precipitation. Recharge simulations using irrigation yield significant increases in net recharge in the irrigation districts, from 250 mm/yr to 1000 mm/yr. A regional scale deterministic model is developed for the region extending from Vaseux Lake to Osoyoos Lake. Estimates of the hydraulic properties of the hydrostratigraphic units are obtained from available pumping tests or estimated from the literature. Model boundary conditions are established for existing rivers, streams, lakes and recharge (including irrigation return flow). Both a steady-state and transient model are run and calibrated to observed hydraulic head data. Model results suggest that groundwater in the Oliver region is regulated and maintained from Okanagan River and the bounding lakes. The water table is generally flat throughout the region, and ranges in elevation from 280 to 355 m.a.s.l. along the Vaseux Lake to Osoyoos Lake corridor. The water table rises up slightly in proximity to the benches. A large proportion of the water budget is sustained through recharge, and much of the recharge is from irrigation return flow. A local scale stochastic model was developed for the Oliver area in which the aquifer properties in the upper two layers were generated stochastically using transition probabilities determined from the borehole data. This stochastic model was used to derive probabilistic capture zones for major production wells in the Oliver area. The stochastically-generated capture zones are similar to zones determined using the calculated fixed radius method (circular) where pumping rates are relatively low, and appear more elliptical where the groundwater flow rates are greatest, such as where there is a high hydraulic gradient and/or hydraulic conductivity. |
| Information Type | report |
| Regional Watershed | Okanagan |
| Sub-watershed if known | |
| Aquifer # | 193; 254; 255; 256; 257 |
| Comments | |
| Project status | complete |
| Contact Name | Diana Allen |
| Contact Email | [email protected] |