Delaware’s water, both ground and surface, is one of its most important natural resources. It is essential for meeting the needs of all segments of our society and for maintaining economic growth and agriculture. At this time, all water used for public and domestic supply and more than 98% of water used for irrigation south of the Chesapeake and Delaware Canal is groundwater. North of the canal, approximately 70% of public water supplies are obtained from four surface-water sources (creeks) and 30% from groundwater resources.

Because of the importance of groundwater to the State, hydrogeologic programs and studies are a major focus of DGS staff. Recent and ongoing efforts include such subjects as ambient and targeted groundwater level and quality monitoring, mapping of aquifer extents and hydraulic properties, assessing the impacts of artificial drainage and wastewater disposal practices, developing methods for remote sensing of groundwater discharge areas, and development of techniques for storage, analysis, and distribution of groundwater information by geographic information systems. The DGS is the lead agency for collection and analysis of data on groundwater levels and stream discharges in Delaware. The importance of water conditions monitoring has been highlighted in the last several years by a series of droughts and floods. We operate and monitor a variety of systems that provide water-conditions data and capture these data in an Oracle-based hydrological data management system. Groundwater conditions are monitored by a statewide water-level monitoring network of 69 wells. In addition, in 1985 the DGS implemented a water level and chloride monitoring program for 25 wells along the Atlantic Coast to evaluate the potential for salt-water intrusion in aquifers used for public and domestic water supplies. Surface-water conditions are tracked for 15 stream-gage and 10 tide-gage stations around the state. The stream-gaging network was begun by the USGS in 1931 and is now operated cooperatively between the DGS and the USGS. DGS staff participate in programs and projects related to surface water resources of Delaware and the Delaware River Basin. For example, the DGS coordinates these efforts for the state and facilitates acquisition of streamflow and tide-gage data for Delaware stakeholders. Staff members have also been principal investigators in multi-disciplinary, multi-agency studies to evaluate the fluxes of water, plant nutrients, and other dissolved and suspended sediments in the Inland Bays and Nanticoke River watersheds. As Delaware's lead earth science agency, the Delaware Geological Survey provides information to inform and educate resource managers and the public to better understand and manage our water resources. The Delaware Geological Survey, by statute, manages and provides liaison for all state-federal projects related to the DGS-USGS Joint-Funded and Partnering Programs.

Data and Graphs about Water in Delaware

• Current Water Conditions Report
• Delaware Geological Survey - US Geological Survey Stream and Tide Gaging Program
• Data and Graphs of Water Level Summaries for Wells for 20+ years or 100+ observations
• Water Level Summary Table for Index Wells with 20+ years of data
• Spreadsheet table of all wells with 4 or more observations
• Weather, Stream, and Tidal data from the Delaware Environmental Observing System (DEOS)
• Stream Gage Height and Discharge Graphs from the United States Geological Survey (USGS)

Because of its "renewability" water is unique among earth resources that sustain and enhance life. No other mineral resource that we extract on a long-term and continuous basis can be counted on for at least some degree of replenishment within a human lifetime. This attribute allows a great deal of flexibility in management of the resource. In Delaware local rainfall, approximately 44" to 46" per year, renews part or all of our water supply on a regular basis. However, not all of the rain that falls is available for use. From this total rainfall must be subtracted the water that evaporates (about 20"/year), the amount that is used by plants (about 3 to 6"/year), and the amount that runs overland to surface streams during storms (about 4 to 5"/year). The remainder, approximately 13" to 15" is Delaware's bank of water for the year. This water is stored in a system of groundwater reservoirs, or aquifers, that underlie most of the state. Not only do these groundwater reservoirs provide water to wells, but thyey also maintain the flow in surface streams during times of no rainfall. Streamflow between rainfall events is nothing more than the discharge of excess groundwater.

Precipitation: Condensed water vapor that falls to the Earth's surface. Most precipitation occurs as rain, but also includes snow, hail, and sleet.

Runoff: The variety of ways by which water moves across the land. This includes both surface runoff and direct runoff. As it flows, the water may seep into the ground, evaporate into the air, become stored in lakes or reservoirs, or be extracted for agricultural or other human uses.

Infiltration: The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

Groundwater Flow: The flow of water underground, in the vadose zone and aquifers. Subsurface water may return to the surface (e.g. as a spring or by being pumped) or eventually seep into the oceans. Water returns to the land surface at lower elevation than where it infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to move slowly, and is replenished slowly, so it can remain in aquifers for thousands of years.

Evaporation: The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere. The source of energy for evaporation is primarily solar radiation. Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to as evapotranspiration.

Transpiration: The release of water vapor from plants and soil into the air.

The following table displays the correlation of hydrologic units to geologic units recognized by the Delaware Geological Survey in the Atlantic Coastal Plain. PDF version is also available below.

Groundwater levels recorded in Qb35-08, a 14-foot deep monitoring well located approximately 5 miles west of Laurel, DE show a remarkable response to tropical storms Irene and Lee, which occurred in August and September, 2011, respectively. Groundwater levels and temperatures in Qb35-08 were collected with an automated pressure-temperature datalogger system. At the same time, rainfall and soil moisture data were recorded by the DEOS Laurel Airport station located approximately 5 miles from the well. In the following illustrations daily mean groundwater levels and groundwater temperatures, total daily rainfall, and daily maximum volumetric soil water content are plotted to show how groundwater, rainfall, and soil moisture are related.

Note the two big storms were 6.6 (Irene, August 27-28) and 3.7 (Lee, September 8) inches. In response, groundwater level (gwl) rose more than 9-1/2 feet, with the largest rise occurring after the second storm. Though a 9-1/2- foot rise in groundwater level within a few weeks is remarkable, long term the gwl are within the range of previously observed gwl. The shallowest groundwater levels observed in this well, about 3 feet below land surface, are very common in this part of Delaware and a primary reason why there are very few homes with basements in the area. Daily mean groundwater temperatures do not show a noticeable affect from the storm events. The timing and magnitude of groundwater level rise is related to the rainfall amount and the antecedent maximum daily volumetric water content (VWC) or soil moisture conditions. Prior to the first storm VWC was less than 0.1 indicating a significant soil moisture deficit. Increase of VWC to values above 20 percent (0.2) and onset of gwl rise appear to be strongly correlated with a delay of one day or less. Rates of increase in gwl slow within two days and reverse within 3-4 days after the VWC drops below 20 percent. The rapid rates of rise in VWC and gwl reflect rapid infiltration and groundwater recharge and are consistent with the sandy soil at the DEOS station and sandy aquifer material at the well site. Rapid recharge is one reason why the shallow aquifer is especially vulnerable to pollution from contaminants released at or just beneath land surface. These data provide an example of why it is important to monitor groundwater conditions. Well Qb35-08 is operated by the Delaware Department of Agriculture as part of their Pesticide Compliance Monitoring Network (PCMN, http://dda.delaware.gov/pesticides/gwater.shtml). Construction, maintenance, and instrumentation are done in cooperation with the Delaware Geological Survey. Additional groundwater and well data can be obtained from this web site or from the PCMN web site.

The Water Conditions Summary is an online monthly summary of water conditions in Delaware. Principal factors in determining water conditions are precipitation, streamflow, and groundwater levels in aquifers. Data from rain gages, stream gages, and observation wells located throughout Delaware have been collected and compiled since the 1960s by the Delaware Geological Survey. These data are displayed as hydrographs and are also available for download. In general, water is abundant in Delaware, but supply is restricted by natural geologic conditions in some areas, by contamination in others, and is dependent on precipitation.

• Summary of Water Conditions in Delaware