Dry Creek Monitoring - 2015
Monitoring streamflow, temperature, turbidity, and the fishery within Dry Creek began in mid-May of 2015. Streamflow was monitored continuously using a TruTracks recording device, recording water depth every 30 minutes—this was used in conjunction with a mounted staff gauge where water depth measurements were taken manually during times of discharge measurements. Discharge measurements were taking periodically (approximately every two weeks, for the lower two gauge locations; intermittently for the upper gauge) using a current meter and wading rod (detailed measurement instructions can be found in the Broadwater County Sampling and Analysis Plan: field methods). Turbidity was measured using a portable turbidimeter when discharge measurements were made.
Dry Creek was monitored at three locations during the 2015 water year: near the mouth, above the Broadwater-Missouri Canal, and below Timber Gulch. Discharge measurements and water depth measurements were used to create a rating curve for each monitoring location. These rating curves allow for a continuous discharge to be calculated from the water depth measured by the TruTracks continuous recorder.
Streamflow was measured continuously on Dry Creek from 5/12/15 to 9/30/15 at the two lower gauge locations, and measured continuously from 7/10/15 to 9/30/15 at the upper gauge location. The continuous logger at the Dry Creek near Mouth gauge exhibited some technical malfunction, and daily discharge data from this logger was interpolated in some cases. Water users and infrastructure influence the water quantity in Dry Creek significantly throughout the summer and irrigation seasons. When temperatures increase and there is less water storage available, irrigation demand increases and flows decrease.
Starting in late June water demand increases and decreased flows are observed at the above BM Canal gauge site. The two upper gauge sites accumulated water over the monitoring season in a similar pattern, with the lower of the two accumulating more
water as would be expected given few diversion or creek alterations upstream. The lower gauge, near the mouth, accumulates water more quickly starting in June, this accumulation increases even more in mid-August, and beginning in September slows to match the upper two gauge’s accumulation pattern. This rate of accumulation suggests there is an input into the creek between the above BM gauge site and the near Mouth site which delivers water to the creek sporadically from June to September, this input could be the Spring Ditch or some other large source of water. This water source contributes a significant volume of water to the lower site. Below Timber Gulch was monitored for only half the period of the lower two gauges, and accumulated water at above BM is double that of the below Timber Gulch site, while volumetric accumulation at the lower site (which was monitored for the same period as above BM) is triple that of the middle site. Higher velocities at the near Mouth site aid in sediment transport and erosion.
Turbidity was measured during discharge measurements using a portable turbidity meter. The portable turbidity meter measures light reflected back through a water sample, this gives a scale of suspended sediment present in the water sample. This scale is measured in Nephelometric turbidity units, or NTUs—the higher the value, more light is reflected back to the sensor and the higher sediment load present in the water sample. The color and other physical properties of sediment present within the water sample can influence the turbidity readings. Due to the influence of sediment type on the reading, comparing turbidity readings between sites can be challenging without knowing the physical properties of the sediment present at each location—due to this uncertainty caution should be taken when comparing these data.
Turbidity measurements in Dry Creek show a typical high spring sediment load, following spring runoff and a peak in sediment load during mid-August. Typically, sedimentation should increase moving down stream (as occurred in mid-August), peaking during times of runoff, high discharge, and other sediment loading incidents. Several factors along Dry Creek can influence the movement of sediment downstream; being infrastructure, bank stability, riparian vegetation, and geomorphic properties. The Dry Creek siphon, which transports the creek below
the Broadwater-Missouri Canal is an example of infrastructure that can influence suspended and bedload sediment. Along with infrastructure, there are many actively eroding banks along Dry Creek that increase sediment load. EPA and MT DEQ turbidity standards vary dependent on stream classification and use. For a stream like Dry Creek, turbidity standards are 10 NTUs for domestic use and 25-50 NTUs for commercial use (EPA). For the majority of the summer season Dry Creek turbidity remains around the domestic standard, but during high flow situations turbidity increases and can exceed these commercial standards. Aside from turbidity and sediment load, high bedload transport was observed at the Dry Creek at Mouth gauge location, where a gravel bar formed throughout the summer season above the gauge site, and large particles were often observed moving along the stream bed.
Stream temperature in Dry Creek was measure during times of discharge measurements at all three locations (Figure 14) by placing a thermometer in the stream and recording after completing the discharge measurement. Continuous temperature measurements were recorded using a HOBO datalogger from 5/20/2015 to 10/07/15. Data collected from the HOBO
datalogger was summarized into minimum, maximum, and mean daily temperatures. Ideal temperatures for fresh water fisheries are below 73 degrees Fahrenheit, and creeks like Dry Creek provide cold water refuge from the warmer temperature of the Missouri River. Water Temperatures within the Missouri River have generally increased, approaching the 73 degree threshold—undesirable for fresh water fisheries. With increased Missouri River temperature, tributaries of the Missouri—like Dry Creek—provide critical refuge. Where 73 degrees is
exceeded, low flows are often observed. Similarly, in Figure 18, when flow decreases at the above BM site, water temperature increases. Further monitoring to develop an average temperature trend will provide further insight into Dry Creek in-stream temperature and suitability for fresh water fishery and refuge. Further monitoring can also provide the opportunity to assess temperature improvement projects.
Fishery health within a stream is a good indicator to the overall health of the stream. To assess the fishery within Dry Creek, it is important to recognize how streamflow and temperature impact trout. High temperatures and low flows will reduce the resident fishery and decrease spawning and juveniles. Electrofishing techniques were used to measure trout populations in Dry Creek. Electrofishing sampling was also done in Dry Creek above the Broadwater-Missouri Canal in 2015; at this location no juveniles of brown or rainbow trout were captured. However, a majority
of the fish captured above the Dry Creek Sipon were diseased, showing signs of whirling disease—a deformity that presents on the operculum of the fish and is often fatal to juveniles—66% of the capture fish showed whirling deformations, suggesting that the disease is still present and widespread in the creek. The Dry Creek siphon may present a fish passage issue to juveniles, though the presence of adults above the siphon indicates that adult fish may be able to pass through.
This report can be downloaded below, along with 2015 mean daily discharges measured in Dry Creek as both .pdf and .exl files.