Hampton Roads Regional Water Quality Monitoring Program Active

Table of Contents

• Hampton Roads: A Unique Region
• Study Overview
  • Study Objectives
  • Monitoring Stations
• Data Collection Approach
  • Continuously-monitored Parameters
  • Discretely-sampled Parameters

Hampton Roads: A Unique Region

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Hampton Roads is a metropolitan region in southeastern Virginia which consists of ten independent cities, six counties and one independent town, all within the Virginia Coastal Plain. Much of Hampton Roads lies within the Chesapeake Bay watershed; therefore, the water quality in Hampton Roads directly impacts the health of Chesapeake Bay. The regulations which govern how much suspended solids and nutrients can be discharged into the Chesapeake Bay are based on results from the Chesapeake Bay Watershed Model. This model uses data from across the Chesapeake Bay watershed, but lacks data from small, urbanized watersheds within the Coastal Plain, such as those found in Hampton Roads. 

The Hampton Roads area is one of the most densely urbanized locations on the East Coast of the United States. Urbanization in the region has led to an increase in impervious surfaces, such as roads, sidewalks, parking lots, rooftops, and compacted soils. This can prevent rainwater infiltration, and instead cause stormwater to rapidly collect on the land surfaces to cause flooding. In order to prevent flooding, which could pose a hazard to residents and property in Hampton Roads, the urban watersheds of Hampton Roads use underground pipes and other stormwater infrastructure to drain water away from inhabited areas as quickly as possible.

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When stormwater flows rapidly as runoff over impervious surfaces and thorough storm drains instead of infiltrating into the ground, it has the potential to transport greater amounts of nutrients and suspended sediments. "However, a second key factor affecting transport is the amount of available nutrients and sediment on the landscape. Nutrient and sediment loadings from small urban watersheds, like those common throughout the densely developed Hampton Roads region, are not well understood due to a lack of historical local monitoring data. This knowledge gap represents a potential limitation for the calibration of regulatory models in the region, such as the Chesapeake Bay Watershed Model. The development of more accurate nutrient and sediment loading rates in Hampton Roads, and a basic understanding of how those rates vary across the land-use types most prevalent in the region is critical to informed decision-making regarding stormwater management, implementing management practices and complying with regulation aimed at reducing contaminant transport to local waterways, and ultimately, Chesapeake Bay.

Study Overview

Our study area, a subset of the greater Hampton Roads region, encompasses the six cities holding Phase 1 municipal separate storm sewer system (MS4) permits: Chesapeake, Hampton, Newport News, Norfolk, Portsmouth, and Virginia Beach.

Twelve monitoring sites, two per jurisdiction, were established in Hampton Roads to measure both water quantity (streamflow) and water quality (levels of contaminants) from water year 2016 onward.

The sampling locations were divided into three land use categories:

• Commercial
• High Density Residential
• Single Family Residential

These stations monitor relatively small watersheds, ranging in area from 30 to 300 acres, with high impervious cover (36-81%). In urbanized areas, watershed boundaries are determined not only by topography but also by networks of stormwater infrastructure such as pipes, culverts, and urban streams.

The dense network of stormwater infrastructure in the Hampton Roads region is critical for preventing flooding after heavy rain events. During storms, rainfall can accumulate quickly on impervious land surfaces. Any area where water falls as precipitation faster than it can infiltrate into the ground or flow out of the watershed as runoff is vulnerable to flooding. This, combined with the region's flat topography and proximity to the Atlantic Ocean and Chesapeake Bay, make the region particularly flood-prone. Hampton Roads' dense network of stormwater pipes and conveyance features allows runoff to quickly drain out of these urban watersheds. To understand how much water is moving through these urbanized watersheds and what this water is carrying (nutrients, suspended solids, etc.), the man-made stormwater conveyance systems that define such watersheds must be monitored.

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Study Objectives

By studying several small urban watersheds in Hampton Roads, we aim to:

1. Operate, and maintain a long-term stormwater monitoring network to collect high-quality, locally relevant water-quantity and quality data in the Hampton Roads Region. ​
2. Use these data to characterize sediment and nutrient loadings from the major types of urban land-uses in the Hampton Roads region.
3. Use annual loads at the 12 monitoring stations to compute an average annual sediment, phosphorous, and nitrogen loading rate for Hampton Roads region. These rates can then be used to assess the accuracy of rates generated by the Chesapeake Bay Watershed Model for the Chesapeake Bay Total Maximum Daily Load and to better calibrate the model in the future. These data can also be used to improve our understanding of the factors affecting spatio-temporal patterns in load. In other words why do watersheds differ from one another, and in any given watershed, why are conditions changing over time? To answer these questions we've investigated the roles of:
   • Hydrology and runoff processes,
   • Land use and land cover attributes,
   • Physical landscape features unique to this region,
   • and other factors the may alter the source, retention, and transport of nutrients and sediment from these small urban watersheds.

At the local level the findings of this study can be used to inform decision-making regarding implementation of future stormwater management practices, and at the state and federal level, to inform future versions of regulatory models by improving the loading estimates for urbanized regions of the Virginia Coastal Plain and other similar areas.

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Data Collection Approach

At each station, a data logger, satellite transmitter, and refrigerated automated sampler are housed in a rugged enclosure located alongside or above the stormwater conveyance feature. These instruments collect data continuously, including flow rate, water temperature, specific conductance, and turbidity. Additionally, discrete water samples are collected by the automated sampler during storm events and retrieved for analysis of total suspended solids and nutrients by our partners at the Hampton Roads Sanitation District. Samples are also collected by hand on a fixed day each month to characterize the chemistry of groundwater discharges that sustain baseflows in these pipes year-round. 

Continuously-monitored parameters:

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Specific Conductance: The concentration of ions in a water sample. Specific conductance is a good proxy for salinity, as salts dissolve into ions in water. Specific conductance is often elevated in urban waters, and common sources of dissolved ions include de-icing road salts applied before winter storms and carbonates from concrete infrastructure. Specific conductance can also be used as a proxy for other dissolved constituents of interest such as nitrate and orthophosphate.

Stream Stage: The depth of the water in a pipe or channel. Stream stage and discharge are linked, so measuring stream stage allows researchers to construct models that let us estimate discharge at a given monitoring location.

Turbidity: A measure of water clarity. The more turbid the water, the less light can penetrate, and in very turbid waters, aquatic plants may die due to decreased light availability. High amounts of suspended sediment increase turbidity, so these measurements can be used as a proxy for total suspended solids or particulate bound nutrients such as phosphorus or organic nitrogen.

Water Velocity: The speed of the water flowing through the pipe or stream. When combined with stream stage and the cross-sectional area of a pipe or channel, this can be used to compute total streamflow, or discharge, at a given time.

Water Temperature: Buried concrete pipes are insulated from seasonal fluctuations in temperature, unlike surface streams. Biological processes that affect water quality, such as microbe activity, can be influenced by water temperature.

Discretely-sampled parameters:

Nitrogen: A nutrient required for life, but in excess can degrade water quality and harm aquatic organisms. In addition to measuring total nitrogen, researchers also measured total organic nitrogen (TON), total Kjeldahl nitrogen (TKN), ammonia plus ammonium (NH₃/NH₄⁺), and nitrate plus nitrite (NO₃^-/NO₂^-).

• The inorganic forms of nitrogen (nitrate, nitrite, ammonia, and ammonium) are bioavailable, meaning that they can be used by plants in order to grow. These forms of nitrogen can therefore have a large impact on aquatic environments and are themselves toxic to aquatic animals in high enough concentrations.
• Total organic nitrogen is already bound up in organic matter, and therefore has less of an impact on the environment than inorganic nitrogen; however, high levels can still cause problems. Organic nitrogen can be transformed into the more bioavailable forms of inorganic nitrogen under the right conditions.
• Total Kjeldahl Nitrogen is a combined measurement of total organic nitrogen, ammonia, and ammonium, but excludes other inorganic forms of nitrogen such as nitrate and nitrite.

Phosphorus: Like nitrogen, phosphorus is a nutrient required for life, but in excessive amounts it is harmful to the environment. Excess phosphorus can lead to nutrient pollution, which can have devastating impacts on downstream aquatic ecosystems like Chesapeake Bay. In addition to total phosphorus, researchers also measured orthophosphate (PO₄ ^3-), which is the primary dissolved inorganic form of phosphorus.

Total Suspended Solids: the amount of fine sediment and coarse particles contained in a water sample. In addition to contributing to turbidity, fine suspended sediments can transport contaminants (nitrogen, phosphorus, metals, pesticides, poly-chlorinated biphenyls, and other organic contaminants) that are bound to these particles downstream.

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