My WebLink
|
Help
|
About
|
Sign Out
Home
Browse
Search
Stimulated Effects of Irrigation on Salinity in the Arkansas River Valley in CO
CWCB
>
Water Supply Protection
>
DayForward
>
4001-5000
>
Stimulated Effects of Irrigation on Salinity in the Arkansas River Valley in CO
Metadata
Thumbnails
Annotations
Entry Properties
Last modified
7/20/2010 2:54:25 PM
Creation date
6/28/2010 4:31:51 PM
Metadata
Fields
Template:
Water Supply Protection
Description
ARCA
State
CO
KS
Basin
Arkansas
Water Division
2
Date
1/1/1998
Author
Ground Water Vol. 36(1), Karin Goff, Michael E. Lewis, Mark A. Person, Leonard F. Konikow
Title
Stimulated Effects of Irrigation on Salinity in the Arkansas River Valley in CO
Water Supply Pro - Doc Type
Report/Study
There are no annotations on this page.
Document management portal powered by Laserfiche WebLink 9 © 1998-2015
Laserfiche.
All rights reserved.
/
13
PDF
Print
Pages to print
Enter page numbers and/or page ranges separated by commas. For example, 1,3,5-12.
After downloading, print the document using a PDF reader (e.g. Adobe Reader).
Show annotations
View images
View plain text
70 <br />60 <br />50 <br />> 40 <br />U <br />a <br />30 <br />o <br />i " 20 <br />10 <br />Range of Error in Water Levels (meters) <br />Figure 6. Frequency distribution of errors in model - simulated wate <br />levels (simulated minus measured) for individual well locations i n <br />1972, 1982, and 1995. <br />Table 1 <br />Average Observed and Simulated Salinity <br />in the Alluvial Aquifer <br />Observed Observed Salinity Simulated Salinity <br />Salinity Spatially Spatially <br />Arithmetic WeightedU Weightedi Percent <br />Date Average (mg/L) Average (mg/L) Average (mg/L) Error <br />February 1972 2262 (25) 2177 (25) 2140 (554) -1.7 <br />February 1982 2269 (24) 2146 (24) 2370 (554) 10.4 <br />February 1995 1779(25) 1983(25) 1770(554) -10.7 <br />( Spatially weighted average computed by the Theissen method with all available data <br />for each event. <br />2 Number in parentheses indicates the number of samples /finite - difference cells used in <br />the averaging procedure. <br />simulated water levels. The frequency of errors in <br />the model - calculated water levels for the 12 individual wells is <br />shown in Figure 6. For 11 of the 12 wells, the errors were relatively <br />small (0 m to 1.2 m) and reasonably unbiased. Model simulations <br />for one of the 12 wells were consistently poor and under pre- <br />dicted, thus making the overall frequency distribution appear neg- <br />atively skewed (Figure 6). <br />The simulated water table at individual locations was in good <br />agreement with measured water levels at individual observation <br />wells through time. Figure 7 shows three snapshots of simulated ver- <br />sus measured water levels for the months of February 1972 (Figure <br />7a), March 1985 (Figure 7b), and March 1993 (Figure 7c). These <br />snapshots are representative of most months throughout the 24 <br />year simulation period. For most wells, there is no consistent bias <br />in the flow calibrations; simulated water levels fluctuate randomly <br />about measured elevations in Figure 7. Small errors in simulated ver- <br />sus measured water levels at individual wells should not have a sig- <br />nificant effect on the calculated regional hydraulic gradients and <br />velocities, which are factors that strongly control solute transport. <br />Dissolved solids concentration data were measured in water <br />samples collected from 25 to 26 wells in February of 1971, 1972, <br />1982 and 1995. An attempt was made to sample the same well net- <br />work that was used throughout the study period. In several instances, <br />we were uwrrvyeu or in a CGnulriuii irrat prevented Sarirpuug. in <br />these instances, new wells that were located near the old wells were <br />sampled. The February 1971 data were the basis for defining ini- <br />tial conditions for the simulation. The simulated salinity (represented <br />as a spatially weighted average computed by the Theissen method) <br />was within 11% of measured values for 1972, 1982, and 1995 <br />(Table 1). A comparison of the measured and simulated spatial dis- <br />tributions of salinity indicates that there is reasonably good agree- <br />ment between the general salinity patterns with some exceptions <br />(Figure 8). In 1972 and 1982, a ridge of high salinity ( >3000 <br />mg/L) existed in the middle of the area (Figure 8a and b). Although <br />this general pattern was well simulated, the model overestimated <br />salinity in some areas for 1982 (Figure 8b). The salinity was found <br />to vary substantially over a short distance in wells sampled during <br />the study period. This is due to differences in pumping rates across <br />the study area, and temporal differences in the salinity of the water <br />leaking into the aquifer from the irrigation canal. The variability in <br />salinity over a short distance and the relatively small number of wells <br />sampled (25 to 26) might account for some of the discrepancy <br />between simulated and measured salinity in areas where the model <br />tended to overestimate. In February 1995, measured salinity had <br />decreased substantially across the study area (Figure 8c), probably <br />in response to decreased ground water pumping and increased irri- <br />gation from surface water sources. The February 1995 salinity <br />pattern was reasonably well simulated by the model (Figure 8c), <br />although the model tended to underestimate salinity at the individual <br />well locations. The frequency distribution of the error in model -cal- <br />culated salinity for individual wells sampled in 1972, 1982, and 1995 <br />is shown in Figure 9. Although some of the errors are rattier large, <br />the errors are reasonably distributed about zero, which indicates rel- <br />atively unbiased estimates. Based on the results of the model cal- <br />ibration, the model satisfactorily reproduces historic spatial patterns <br />of ground water levels and salinity, although prediction errors for <br />some individual well locations are relatively large. Therefore, the <br />obvious strength of the model is to simulate general water level and <br />salinity trends or patterns, which is well suited to its intended use <br />in the study. <br />80 <br />N "o O a l+ -I In rn m cn C., In -I n � O "q N <br />vi i i I? CV CV r+ O O C C-" N m 'r 7 vi <br />Figure 7. Measured and simulated water levels in the alluvial aquifer, <br />February 1972, March 1985, and March 1993. Dark surface is simu- <br />lated water table. Spheres are measured water levels for individual <br />wells. Where the spheres intersect the dark surface, the calculated and <br />measured water levels are the same. <br />
The URL can be used to link to this page
Your browser does not support the video tag.