PUB Working Group 17 (WG17): Low Stream Flows And Hydrologic Drought

Objectives

• To identify a number of study areas with long time series of hydro meteorological data for low stream flow and hydrological drought prediction around the world, to collate data, and create a system to facilitate the transfer of information from these study regions to researchers.
  
  
• To develop and evaluate numerous stochastic and deterministic methods for predicting low stream flow and hydrological drought characteristics at ungauged river sites within the study regions.
  
  
• To identify gaps in our understanding and characterization of low stream flow and hydrological drought processes (e.g. hydro geological characterization), and advance our current methods and estimation tools to improve low stream flow and drought prediction at ungauged river sites.

Range of approaches to be evaluated:
Understanding the frequency and duration of low streamflow events is critical to the efficient management of water resources throughout the world. This is especially important for water quality management, where low stream flows provide the necessary dilution of non-point source and point source pollution discharges, and water quantity management, where low stream flows greatly influence water use policy. The estimation of low streamflow statistics at ungauged river sites is a problem that has received relatively little attention in the hydrologic literature.

The initial focus of this working group will be on the development of a number of low stream flow study areas throughout the world. Of interest will be regions with diverse hydrologic and hydrogeologic properties with a large network of gauged river sites. Such a network will allow for the exploration of various regionalization techniques that have been proposed to improve stream flow prediction. In addition, it is hoped that each study region will contain at least one research catchment where hydrology, meteorology, and internal state conditions (such as soil moisture, groundwater levels, etc.) are monitored. Such watersheds are important to aid in the exploration of deterministic approaches to low stream flow estimation.

We envision a variety of stochastic, deterministic and mixed approaches to low stream flow prediction to be explored within this group. These will include methods which require no stream flow data, as well as techniques which employ some stream flow measurements. Potential techniques will include methods of regional regression, index flow, mapping, and baseflow correlation, as well as watershed modeling. In addition to the ungauged prediction problem, of interest will also be how best to use minimal amounts of stream flow data, and when and how many stream flow measurements should be taken. Some of the study areas will contain urban or urbanizing watersheds, allowing investigators to better assess anthropogenic impacts on low stream flows.

Data availability
As we are in our initial planning phase for this work group, our study areas have not been decided. We are investigating mechanisms for efficient access to necessary streamflow and watershed information within proposed study areas, with the ideal scenario involving free internet access. Restrictions to some data sources may limit this option. Initially proposed study areas include: (1) Southeastern United States, encompassing Tennessee and parts of North Carolina, Georgia, and Kentucky, (2) Northwestern United States, primarily all of Idaho and parts of surrounding states, (3) Southwestern United States, including New Mexico and Arizona, and (4) the Northern South Island of New Zealand. We are also investigating one or two study areas in Europe, as well as an African and/or Asian study area.

Industry partners and user groups
Industry partners are primarily local, state and national agencies who are required to provide advice on low streamflow prediction to their constituents.

As mentioned previously, low streamflow estimation are required for a number of water quality and water quantity management purposes. We envision results from this working group to be integrated into low streamflow prediction methodology which is being developed to help end users, such as those requiring permits for water withdrawals or point and non-point pollution discharges.

Key Participants:

• Chuck Kroll, State University of New York - College of Environmental Science and Forestry, Syracuse, NY, USA
• Lena Tallaksen, University of Oslo
• Henny Van Lanen, Wageningen University
• Richard Vogel, Tufts University
• Zhenxing Zhang, Pennsylvania State University
• Roddy Henderson, NIWA, Christchurch, New Zealand

This working group will also be integrated with the Northern European Flow Regimes from International Experimental and Network Data (NE FRIEND). It is believed that this collaboration will provide more synergies between international researchers and aid in the achievement of the objectives set for this working group.