Weather Radar and Hydrology Edited by

Use of weather radar by the water industry in Scotland
STEVEN J. COLE¹, DOMINIC McBENNETT², KEVIN B. BLACK¹ &
robert j. moore¹

1 Centre for Ecology & Hydrology, Wallingford OX10 8BB, UK

[e-mail]

2 Scottish Water, Invergowrie, Dundee DD2 5BB, UK
Abstract Rainfall data are a key source of information used by the UK water industry to perform its diverse regulatory functions. Raingauges have traditionally been used, but radar rainfall data are increasingly being utilised. Within Scotland, the public body Scottish Water has the responsibility for supplying drinking water and the collection and treatment of wastewater. An outline of Scottish Water’s requirements and use of weather radar data is presented along with a brief description of the Hyrad Weather Radar System. A case study illustrates a novel method for post-event analyses of storm events associated with surface water flooding incidents. These analyses combine the analytical capabilities of Hyrad with the Flood Estimation Handbook depth-duration-frequency rainfall model to obtain estimates of rainfall return periods. The estimates are used to assess whether urban drainage systems performed within design specifications or if remedial action is required to comply with the regulatory framework. Finally a look forward is given of future planned applications of weather radar within the water industry in Scotland.

Key words pluvial; flood; radar rainfall; rainfall return period; FEH; urban drainage

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012)., 650-654

Impact of Z-R relationship on flow estimates in central São Paulo
Roberto v. calheiros & Ana m. gomes

Instituto de Pesquisas Meteorológicas – UNESP, Brazil

[e-mail]
Abstract Mean areal radar rainfall over catchments in the State of São Paulo is an operational product under development by the Meteorological Research Institute – IPMet. A pilot project is being carried out which focuses on the important Corumbataí River basin, under surveillance by the IPMet-operated Bauru radar. Previous work on the project explored the relative impact of factors like time resolution of radar data and reflectivity to rain-rate conversion relationships, when the relevance of the latter was verified. This paper deals with the stratification of those relationships by daily intervals and its impact on flow estimates. Daily values of radar mean rainfall using gauges and different conversion relationships are plotted against the corresponding flow at the basin outlet. Flow estimates derived by applying the rainfall from the different relationships to a previously obtained rainfall–runoff curve for the basin is compared to the historical hydrograph. Preliminary results suggest stratification has hydrological significance.

Key words areal radar rainfall; Z-R relationship; Corumbataí River basin; rainfall–runoff relationship

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 655-660.

Derivation of seasonally-specific Z-R relationships for NEXRAD radar for a sparse raingauge network
SAMUEL H. RENDON¹, BAXTER E. VIEUX¹ & CHANDRA S. PATHAK²

1 School of Civil Engineering and Environmental Science, University of Oklahoma, National Weather Center,
120 David L. Boren Blvd. Suite 5340, Norman, Oklahoma 73071, USA

[e-mail]

2 Operations and Hydro Data Management Division, SCADA and Hydro Data Management Department,
South Florida Water Management District, 3301 Gun Club Road, West Palm Beach, Florida 33416-4680, USA
Abstract Radar-based hydrological prediction relies on available raingauges to correct for bias in rainfall estimates. Standard Z-R (radar reflectivity factor against rain-rate) relationships have been developed which are characteristic of storm types, e.g. convective or tropical storms. However, the evolution of storm drop-size distribution and radar-specific factors can affect the accuracy of these standard relationships. Deriving Z-R relationships from raingauge observations for specific radars offers the potential for improved rainfall estimation. The derived Z-R relationship would be more representative of local climatology and radar characteristics, and can be used when raingauges are not available in real-time for bias correction. The purpose of this project is to derive and evaluate regionally- and seasonally-specific Z-R relationships for use in the South Florida Water Management District (SFWMD). These regionally specific relationships are expected to reduce bias in rainfall estimates found when using standard Z-R relationships, and lead to improved rainfall estimation for operational decisions. Validation of the derived Z-R relationships for dry, intermediate, and wet seasons revealed significant bias reduction to essentially 1:1 agreement during the respective seasons. While such relationships are not expected to replace bias adjustment using raingauges on a storm total or real-time basis, they do represent a better starting point for gauge adjustment of the Z-R relationship.

Key words radar; NEXRAD; Z-R relationships; hydrological forecasting; rainfall estimation

Weather Radar and Hydrology

(Proceedings of a symposium held in Exeter, UK, April 2011) (IAHS Publ. 351, 2012), 661-666.

Weather radar to predict bathing water quality
MURRAY DALE¹ & RUTH STIDSON²

1 Halcrow Group Ltd, Ash House, Falcon Road, Exeter EX2 7LB, UK

[e-mail]

2 Scottish Environment Protection Agency, Clearwater House, Heriot Watt Research Park, Avenue North, Riccarton, Edinburgh EH14 4AP, UK
Abstract Weather radar has significant theoretical advantages over raingauges when used for predicting episodes of poor bathing water quality in UK beaches: radar measures rainfall over areas, rather than at a point; radar data are available in real-time and do not require telemetry links; and the detail within a spatial radar image can isolate suspected pollution sources. Poor bathing water quality, characterised by high faecal coliform concentrations, is primarily caused by pollutants mobilised during wet weather in river and urban drainage catchments discharging close to beaches. With a revised Bathing Water Directive (2006/7/EC, repealing current Directive 76/160/EEC), which came into force on 24 March 2006, interest is increasing throughout the UK in developing techniques to predict faecal coliform exceedences. This paper describes the findings of a recent research project in which radar data were used to develop a methodology to improve real-time predictions of faecal coliform concentrations in bathing waters.

Key words radar; rainfall; bathing water quality; prediction