Hydrologic Telemetry System
The Las Vegas Valley Groundwater Management Program Hydrologic Telemetry System (HTS) was put in place to help educate well owners about water levels in the valley and allow well owners to see fluctuations in water levels near their wells in "real-time."

What's the purpose of water level networks?
Water level networks are established and maintained to observe long-term changes in water level over time. The changes that are observed may be natural variations or may be caused by anthropogenic activities. Some of the changes may be so slow that the presence of long-term trends cannot be observed without decades of measurement. Others are nearly instantaneous but the magnitude of the change may be small.

Weather stations are a more common example of a network. Each station collects data that allows meteorologists to predict future weather patterns and explain weather-related phenomenon. Data are collected on a minute, hourly or daily schedule to predict the weather tomorrow or next week near the station. When data are analyzed from all the stations in the network, the weather can then be predicted over a much wider area.

Once the station has established a historical record, the site can become a climate station where long-term weather predictions can be made. Water level networks observe the "weather" conditions near the well, and long-term sites help explain the "climate" in a given aquifer or system of aquifers. The most important characteristic of any monitoring network is good spatial coverage that not only represents the area but also is capable of observing significant local variations.

Well Selection
The HTS well network is designed to augment the existing water level monitoring networks. Several networks currently exist and are measured by different agencies and for different purposes. These networks are designed by the investigating hydrologist to be representative of aquifer conditions at a given location and are measured at regular intervals. The physical construction specifications of the well, the location of the well and the characteristic (i.e. water quality, or water level or both) that is being monitored all determine how often the well is measured.

The wells within the network may include:

• Dedicated monitor wells
• Unused/inactive wells
• Active wells where the activity of the wells does not significantly effect the parameter that is measured

The construction of the well determines the various aquifers and aquitards in communication with the wellbore. The aquitards or aquifers may be large or small depending on the complexity of the alluvium. The proximity of the well to local stresses (wells producing water out of the same zone) is also an important consideration when selecting the well site. In some wells, this will have a strong effect on the local flow patterns. Monitoring the flow patterns is the very purpose of water level networks and therefore the wells are best located where flow patterns are undisturbed.

Data collection and analysis
The frequency of data collection and the accuracy of the equipment determine the type of hydrologic event that can be investigated. These hydrologic events can be as normal as seasonal water level changes or as unique as water level changes associated with earthquakes.

The water levels within the confined part of the Las Vegas Aquifer System are very active. Hourly, daily, monthly, seasonal, yearly and decade-long variations can all be observed. Hourly and daily data can record variations in barometric pressure and cyclic daily production of nearby wells. This type of data is usually measured with units less than a foot. Monthly and seasonal water levels usually vary by tens of feet, reflecting seasonal stress induced by natural and artificial recharge and production.

How are the wells monitored?
The wells are equipped with instruments and data loggers to allow the water level and water temperature or barometric pressure to be monitored continuously. Water levels and the secondary parameter readings are taken hourly. The data are then transmitted from the HTS site daily and the data are updated every 24 hours.

Figure 1. Hydrograph showing the influence of barometric pressure on water levels.

Water temperature and water level
Some sites monitor water temperature and water level. Wells in the extreme southern and southeastern portions of Las Vegas Valley have a higher water temperature than do the wells in other locations of the valley. This is due to the subsurface geologic conditions. These wells are in closer proximity to volcanic rocks, which at depth, still heat the water.

Barometric pressure and water level
Other sites collect barometric pressure and water level. Depicted on the hydrograph, the relationship between water level and barometric pressure are easy to see. When the barometric pressure is lower, the water level will rise and when the pressure is higher, then the water level will fall.

Several local, state and federal agencies maintain water level networks for the confined portion of the Las Vegas Valley Aquifer System (LVVA Aquigroup). Also, a few agencies maintain water level monitoring networks for the shallow, unconfined part of the LVVA Aquigroup. The wells proposed for this network were selected to be representative of the conditions in specific areas and provide good spatial coverage of the entire Las Vegas Valley.

Twelve sites in the deeper confined system were selected to complement six wells that are currently continuously monitored (but not telemetered) by the United States Geological Survey. All owners of wells used for water supply directly benefit from this type of information but the magnitude of the benefit is usually a function of the distance from the monitor well to the site of interest.

All of the wells selected were previously existing and unused because of both the cost of drilling new wells and the lack of historical record on new wells. The likelihood of subdivision development was also an important consideration because several long-term (20+ years) monitoring wells have been lost to residential development in the last five years.