A NEW FLASHINESS INDEX: CHARACTERISTICS AND APPLICATIONS TO MIDWESTERN RIVERS AND STREAMS¹

Abstract

The term flashiness reflects the frequency and rapidity of short term changes in streamflow, especially during runoff events. Flashiness is an important component of a stream's hydrologic regime. A variety of land use and land management changes may lead to increased or decreased flashiness, often to the detriment of aquatic life. This paper presents a newly developed flashiness index, which is based on mean daily flows. The index is calculated by dividing the pathlength of flow oscillations for a time interval (i.e., the sum of the absolute values of day‐to‐day changes in mean daily flow) by total discharge during that time interval. This index has low interannual variability, relative to most flow regime indicators, and thus greater power to detect trends. Index values were calculated for 515 Midwestern streams for the 27‐year period from 1975 through 2001. Statistically significant increases were present in 22 percent of the streams, primarily in the eastern portion of the study area, while decreases were present in 9 percent, primarily in the western portion. Index values tend to decrease with increasing watershed area and with increasing unit area ground water inputs. Area compensated index values often shift at ecoregion boundaries. Potential index applications include evaluation of programs to restore more natural flow regimes.

Evolución morfo-sedimentaria del tramo medio del río Segre

“…El estudio de la magnitud y frecuencia se realiza a partir de i) la media de los máximos caudales diarios anuales (Q C ) y, si se dispone, de la media de los caudales máximos instantáneos anuales (Q Ci ), ii) el caudal bankfull (Q Bank ) y, iii) el caudal máximo ordinario o caudal de crecida (Q 5 ) correspondiente al percentil 5 (por ej. Clausen y Biggs, 2000;Baker et al, 2004;Batalla et al, 2004), tomado de una curva de caudales clasificados. Para el cálculo del caudal bankfull (Q Bank ) se ha seguido el cálculo propuesto por Villarroya y Xuclá (2003): Para el estudio de la variabilidad, tanto para las variables que se incluyen en el RNC y en el RMC, se ha utilizado el coeficiente de variación de los Q c y el de los Q 5 .…”

The impact of forest regeneration on streamflow in 12 mesoscale humid tropical catchments

“…5). Similarly, studies of the "flashiness" (sensu Baker et al, 2007) of the runoff behaviour of urbanized and forested catchments in Puerto Rico revealed no differences (Ramírez et al, 2009;Phillips and Scatena, 2010). However, Phillips and Scatena (2010) did detect significant differences (p < 0.05) in the frequency of stage change (cf.…”

Hydrology of channelized and natural headwater streams / Hydrologie de cours d'eau recalibrés et naturels de tête de bassin

“…Rate of change provides an indication of how a stream responds to a rainfall event (slowly or rapidly) and how long discharge from that event might be realized. While different from flashiness, rate of change indices, such as time to peak discharge and time to recession, also provide some insight into stream flashiness (Baker et al, 2004). Sixteen hydrology indices representing a subset of the hydrological indices recommended by Olden & Poff (2002) were selected for this study to enable characterization of the magnitude, frequency, timing and rate of change of hydrology in channelized and natural headwater streams.…”

“…Headwater streams tend to be more "flashy" than larger rivers (Baker et al, 2004). Channelization and tile drainage, characteristic of low-gradient midwestern USA streams, also affect the response of the stream to rainfall inputs and tend to produce "flashy" streams Schaller et al, 2004).…”