Analysis of Aberdeen, ID Groundwater Levels

Jerimiah Fenton

CEE 6440

December 3, 2010

Table of Contents

-Introduction

-Background

-Methods

-Data Collection

-Spatial Representation of Table Data

-Interpolation of Point Data

-Results

-Discussion

-Conclusions

-References

Introduction

Farms located in Aberdeen, ID have been experiencing problems due to flooding. It is believed that this flooding is the result of an Idaho Department of Fish and Game pond rehabilitation project taking place in the area. The ponds may be causing a rise in local groundwater levels. Farmers in the Aberdeen area have requested a groundwater level analysis in order to prove this theory. The analysis of the situation was approached by generating interpolated time series groundwater level maps using ArcGIS 10. Time series water level maps are expected to show how the water levels have changed over time. This should provide a way to determine whether or not the new ponds have actually had any impact on the local water levels. Contained in this report are explanations of the steps and methods used to analyze the Aberdeen groundwater levels.

Background

Aberdeen, ID is an agricultural community located in South Eastern Idaho. During the 1970s, irrigation water was delivered to the area using canals. The large amount of canal water in the area resulted in high water tables and the formation of ponds. Due to the invention and implementation of pressurized irrigation, the Aberdeen area no longer uses as many canals for irrigation. When the canals were replaced with the pressurized irrigation systems, the ponds and wetlands dried up and no longer existed.

Figure 1: Aberdeen, Idaho (Google Earth, 2010)

The Department of Fish and Game desires to bring back the ponds to provide a wetland habitat to the area. To recover the old ponds, Fish and Game dammed up an area located about 2 miles north and 1 mile east of Aberdeen and began pumping water into the area. The ponds are being filled with groundwater that is constantly being pumped out of the aquifer. Figure 2 below shows an image of the ponds now present in the area.

Figure 2: Aberdeen Ponds (Google Earth, 2010)

Since starting the pond rehabilitation process, many problems have arisen in the surrounding area. Frequent flooding in the surrounding fields has resulted in damages to crops and has caused pivots to get stuck in the deep mud. The ponds have also resulted in an increase in the area’s mosquito population. The increased mosquito population has resulted in a decreased livestock birth rate due to the spreading of disease. Farmers in the area have requested a groundwater level analysis to determine whether or not the ponds are the cause of their problems.

Methods

The method used to analyze the groundwater levels in the Aberdeen area was the generation of time series groundwater level maps. Through the generation of the water levels maps, the change of water depths in the area over time can be determined. The steps required to generate the groundwater level maps included the following: data collection, spatial representation of data in ArcMap, and the interpolation of the point data to generate groundwater level maps.

Data Collection

To begin the groundwater analysis, time series groundwater level data were obtained from the USGS Website (USGS, 2010). Using the USGS groundwater level search query, recorded water level data was obtained for Bingham County where Aberdeen is located. The search query produced several well locations where groundwater level measurements had been taken over the years. Only water level data for the last ten years (2000-2010) were of relevance since the pond rehabilitation just started in the last few years. Only wells surrounding the Aberdeen area were used. USGS provides the township and range for each well so it was easy to select wells near the ponds. The ponds are located in the township range of 5S 31E. Wells located in township ranges of 4S 31E, 4S 32E, 5S 30E, 5S 31E, 5S 32E, 6S 30E, and 6S 31E were used to evaluate water table levels in the area. An example of the well chart data provided by the USGS is shown below in Figure 4. Notice that the USGS have provided the date of measurement and the depth to the water level. The location of the well is provided in both township range and lattitude and longitude coordinates.

Figure 4: USGS Well Data

There was not a lot of data for the wells in the area; however, the years of 2001, 2002, and 2008 did have a lot of water level measurement data. For some reason, more measurements were taken during these three years so only well data for the previously mentioned years were used. The time of year the measurements were taken varied for each well. Since lack of data made it impossible to create water level maps for each month, a well’s average water table depth during each one year period was used as the water level at each individual well.

The time series water level data collected from the USGS website was next entered into Excel spreadsheets. Three separate spreadsheets of the time series data were created for the years of 2001, 2002, and 2008. The excel spreadsheets included the well USGS identification number, the water table depth measured at the well, and the location of well in terms of longitude and latitude. The location coordinates were specific to the NAD 83 datum. These coordinates were later used to represent the wells spatially in ArcMap.

Spatial Representation of Table Data

After the groundwater levels for each of the three years were imported into Excel, it was necessary to represent the data spatially in ArcMap. By right clicking on the spreadsheets and selecting “Display X, Y Coordinates” the data could be represented as point data based on the provided longitude and latitude coordinates. The resulting point feature class for the well data is displayed below in Figure 3. A reference base map obtained from ARCGIS.com was used as a base for the wells.

Figure 3: Aberdeen Well Point Spatial Representation

Interpolation of Point Data

The Aberdeen well point feature classes only represented point data of groundwater depths. The ultimate goal of the groundwater level analysis was to develop groundwater maps. In order to develop groundwater level maps it was necessary to interpolate between the points. To interpolate between the points the IDW spatial analyst tool was used. The IDW tool interpolates a raster surface from point data. In this case, IDW was used to generate interpolated groundwater level maps based on the point water levels. In this way, three groundwater depth maps were generated for each of the three years under analysis.

Figure 5: IDW Spatial Analyst Tool in ArcMap

Results

The generated groundwater level maps for 2001, 2002, and 2008 are shown below in Figures 4, 5, and 6 on the following three pages. Notice the minor differences between the three maps. The particular area of interest on the maps is the area about two miles north and one mile east of the town of Aberdeen where the ponds are located. This area is highlighted by a blue circle on each of the maps. These groundwater level maps should provide some information about how the groundwater levels in the area have changed with respect to time.

Figure 4: 2001 Aberdeen Groundwater Depths

While the 2002 groundwater level map is very similar to the 2001 map, there has been a slight reduction in groundwater levels over the entire area. Also, notice that the water level at the well in the area of the ponds has also decreased.

Figure 5: 2002 Aberdeen Groundwater Depths

The 2008 groundwater level map also shows a similar trend in the general decrease in water levels over the entire Aberdeen Area. However, notice that the groundwater level at the well near the ponds has increased according to the IDW interpolation. Further investigation of the well near the pond site was required to determine whether or not an increase in water level at the pond location was in fact the case.

Figure 6: 2008 Aberdeen Groundwater Depths

To determine whether the water level around the well near the ponds had in fact increased, it was necessary to look at the well’s point data. The point data of the well at this location provided the average depth to the water table at the well. The depth to the water level at the well had actually increased from 23.3 feet to 24.4 feet between 2002 and 2008. This means that the water level near the ponds had actually decreased between the years of 2002 and 2008.

Discussion

The interpolated water level maps should provide a fairly accurate estimation of the water level depths throughout the Aberdeen area. The same wells were used to create each of the maps, so the data used was consistent. The reduction of water table levels over the entire area is most likely accurate. This is expected in areas where water is being pumped out of the aquifer for irrigation. However, further analysis of the well located near the new ponds showed that the water table level at this particular well had actually decreased as well. Therefore, the interpolated water table maps can be a little misleading in this respect. However, the maps were correct in showing a general decrease in the average groundwater levels throughout the area.

Conclusion

While the interpolated water level maps gave a general representation of the groundwater levels in the Aberdeen area, they did not represent what was going on with the groundwater near the recently constructed ponds. Therefore, the ground water level maps do not really show any conclusive evidence that the ponds are the cause of an increase in groundwater levels. However, this may be a result of the data not being up to date. More recent groundwater level data may reveal more information about how the groundwater levels are changing around the ponds. This would require field work to obtain more groundwater levels at wells close the ponds. Until more data is collected it looks like the farmers will have to put up with their flooding fields.

References

ARCGIS.com. Physical Base Map. <arcgis.com>. Path: Search for Data: Base maps: Physical. (Oct 30, 2010).

Aqueveo. “ARC Hydro Groundwater Tutorials: Wells and Time Series.” [Electronic Version].

Google Earth. (2010).

USGS.gov. NWIS: Ground Water Levels For Idaho. < http://nwis.waterdata.usgs.gov/id/nwis/gwlevels >. (Oct 15, 2010).

Water Well Consultants. Verbal Contact.