Zero-flow Days Research Articles

Regionalization of patterns of flow intermittence from gauging station records

Abstract. Understanding large-scale patterns in flow intermittence is important for effective river management. The duration and frequency of zero-flow periods are associated with the ecological characteristics of rivers and have important implications for water resources management. We used daily flow records from 628 gauging stations on rivers with minimally modified flows distributed throughout France to predict regional patterns of flow intermittence. For each station we calculated two annual times series describing flow intermittence; the frequency of zero-flow periods (consecutive days of zero flow) in each year of record (FREQ; yr−1), and the total number of zero-flow days in each year of record (DUR; days). These time series were used to calculate two indices for each station, the mean annual frequency of zero-flow periods (mFREQ; yr−1), and the mean duration of zero-flow periods (mDUR; days). Approximately 20% of stations had recorded at least one zero-flow period in their record. Dissimilarities between pairs of gauges calculated from the annual times series (FREQ and DUR) and geographic distances were weakly correlated, indicating that there was little spatial synchronization of zero flow. A flow-regime classification for the gauging stations discriminated intermittent and perennial stations, and an intermittence classification grouped intermittent stations into three classes based on the values of mFREQ and mDUR. We used random forest (RF) models to relate the flow-regime and intermittence classifications to several environmental characteristics of the gauging station catchments. The RF model of the flow-regime classification had a cross-validated Cohen's kappa of 0.47, indicating fair performance and the intermittence classification had poor performance (cross-validated Cohen's kappa of 0.35). Both classification models identified significant environment-intermittence associations, in particular with regional-scale climate patterns and also catchment area, shape and slope. However, we suggest that the fair-to-poor performance of the classification models is because intermittence is also controlled by processes operating at scales smaller than catchments, such as groundwater-table fluctuations and seepage through permeable channels. We suggest that high spatial heterogeneity in these small-scale processes partly explains the low spatial synchronization of zero flows. While 20% of gauges were classified as intermittent, the flow-regime model predicted 39% of all river segments to be intermittent, indicating that the gauging station network under-represents intermittent river segments in France. Predictions of regional patterns in flow intermittence provide useful information for applications including environmental flow setting, estimating assimilative capacity for contaminants, designing bio-monitoring programs and making preliminary predictions of the effects of climate change on flow intermittence.

Predicting effects of plantation expansion on streamflow regime for catchments in Australia

Abstract. The effect of plantations on mean annual streamflow is well understood and, there are robust methods available for assessing the impact. Plantations also affect streamflow regime, leading to reductions in low flow and increased number of zero-flow days. Understanding changes in streamflow regime following plantation expansion is important for developing water resources and environmental flow strategy. This study evaluated the impacts of plantations on streamflow regime from 15 catchments in Australia. The selected catchments range in size from 0.6 to 1136 km2 and represent different climatic conditions and management practices. The catchments have at least 20 yr and in most cases 35 yr of continuous daily streamflow data and well documented plantation records. Catchments with perennial streamflow in the pre-treatment periods showed relatively uniform reductions in most flows after plantation expansions, whereas catchments with ephemeral streamflow showed more dramatic reductions in low flows, leading to an increased number of zero-flow days. The Forest Cover Flow Change (FCFC) model was tested using the data from the selected catchments and comparison of predicted and observed flow duration curves showed that 14 of the 15 catchments have coefficients of efficiency greater than 0.8. The results indicate that the model is capable of predicting plantation impacts on streamflow regime.

Incorporating land-use changes and surface–groundwater interactions in a simple catchment water yield model

Pressure on limited water resources and the environment requires better understanding of how landscape change impacts river flow. Rainfall-runoff models have traditionally focused on estimating total river flows with less emphasis on modelling the groundwater component or the consequences of different land-use change scenarios. In this paper, we present the GWlag model, a water-generation model that predicts river flows with explicit accounting of the impacts of catchment land-use change and surface–groundwater interactions. The paper firstly describes the theory that underpins the model and its calibration then presents a case study application in the Tarcutta Creek catchment of the Murray–Darling Basin, Australia. The case study aims at: (i) demonstrating the ability of the model to predict daily river flows; (ii) modelling the impacts of hypothetical plantation forestry expansions on river flows; and (iii) showing the impacts of reduced recharge on the low-flow regime using three indices, namely, Q90/Q50 (where Qn refers to nth percentile flow), slope of low-flow part of flow duration curve, and % of zero-flow days. Results showed that predicted flows agreed favourably to those observed at the gauge especially during low-flow conditions. The hypothetical plantation expansion from 32% to 87% of the catchment area has resulted in reductions of 48% and 32%, in Q50 and Q20, respectively. The low-flow indices demonstrated the great sensitivity of low flow to reductions in recharge with the trend of the low-flow response changing to non-linear for recharge reductions beyond 10%. GWlag daily river flow predictions compared favourably to those obtained from four other rainfall-runoff models in terms of the Nash–Sutcliffe model efficiency (E). However, GWlag produced the highest E-value for log-transformed flows thus highlighting the model's superior predictive capability during low-flow conditions.

Evaluating the SWAT Model for a Low-Gradient Forested Watershed in Coastal South Carolina

Modeling the hydrology of low-gradient forested watersheds on shallow, poorly drained soils of the coastal plain is a challenging task due to complexities in watershed delineation, microtopography, evapotranspiration, runoff generation processes and pathways including flooding and submergence caused by tropical storms, and complexity of vegetation species. The main objective of this study was to calibrate and validate the GIS-based spatially distributed hydrologic model SWAT for the 72.6 km2 low-gradient, third-order Turkey Creek watershed within the Francis Marion National Forest in the South Carolina Coastal Plain. Model calibration used GIS spatial data of the watershed and 2.75 years (2005-2007) of streamflow and climate data, and the model was validated with 2.5 years (2008 -2010) of data. Based on limited field measurements, results showed that the SWAT model with an improved one-parameter depletion coefficient for plant evapotranspiration in the SCS curve number (CN) estimate can predict the daily and monthly streamflow processes of this watershed reasonably well and better than the CN method. The model performance was good (E = 0.68; RSR = 0.56) to very good (E = 0.90; RSR = 0.31) for the monthly calibration and validation periods but only satisfactory (E = 0.59; RSR = 0.64) to good (E = 0.70; RSR = 0.55) for the daily calibration and validation periods. Better predictions were found for the validation period that included two wetter years than the calibration with two drier years. The model's predictions of the zero or near-zero flow days of summer were also in agreement with the measurements for 60% of the time. However, it was concluded that the refined SWAT model was still unable to accurately capture the flow dynamics of this forest ecosystem with shallow, high water table soils for events preceded by wet saturated conditions during the dry summer and wet winter periods, warranting further investigations on these forest systems. The five-year average annual runoff coefficient of 19% with a baseflow amount of 27%, on average, of the runoff (streamflow) and ET of 987 mm predicted by the model were found reasonable compared to the estimated values and other published data for the region. Further improvements in estimates of forest potential evapotranspiration, rainfall spatial variability, and antecedent moisture as a function of water table should reduce uncertainties in flow predictions, allowing the model to be used in hydrologic impact assessments of land use change, land management practices, and climate change in coastal landscapes.

Responses of water yield to changes in vegetation at a temporal scale

The effect of vegetation on the water recycling of a land ecological system is considerably significant. Understanding the relationship between vegetation and runoff changes will benefit regional eco-environmental and water resources management. Based on paired catchments and time trend studies, a number of studies had been undertaken to establish the relationship between vegetation cover and water yield. We obtained some results from paired watersheds by focusing on changes at various time scales. At the mean annual scale the runoff changes resulting from vegetation alteration can be predicted using Zhang’s curves. The absolute change of runoff due to vegetation alteration in a humid area is larger than that in the dry region, while the relative change is reverse. At the annual scale, it takes 15-20 years or longer in the arid region for catchments to reach a new equilibrium after afforestation, and under natural restoration, it takes about a hundred years. The vegetation changes have a proportionally larger impact on low flow at the seasonal scale. For catchments in arid regions, relative changes in low flow sections of the flow duration curve will be much more significant compared with that in the high flow section, leading to increased number of zero-flow days. However, in humid regions, changes in runoff tend to be much more uniform.

Variability of Water Resource in the Yellow River Basin of Past 50 Years, China

We use Mann-Kendall trend test and Lepage method to study spatial and temporal variations of the streamflow series over the past 50 years based on daily hydrologic data from six gauging stations in the Yellow River basin. Research results indicate that: (1) The streamflow of the Yellow River basin is decreasing and water resource deficit tends to be more serious from the upper to the lower Yellow River basin; (2) Zero-flow days are observed after 1970 and overwhelmingly prevail during 1990-2000. Moreover, zero-flow events are observed mainly during spring and summer; (3) Low flow events are more sensitive to climatic changes and human activities when compared to the high flow events, which is mainly reflected by larger fluctuation of timing of change points. Furthermore, the timing of change point of hydrologic events tends to be earlier from the upper to the lower Yellow River basin, indicating more intensive impacts of human activities on water resource in the lower Yellow River basin. The current research will be greatly helpful for sound and effective water resource management in the Yellow River basin, being characterized by serious water deficit.

Response of coastal marine eco-environment to river fluxes into the sea: A case study of the Huanghe (Yellow) River mouth and adjacent waters

The impact of the Huanghe (Yellow) River outflows on its estuary was investigated with river gauging and shipboard hydrographic observations. The river flux has been decreasing dramatically; the discharges of water and sediment in the 1990s dropped to 27.4% and 31.9% of those in the 1950s, respectively, resulting in frequent and lengthy events of downstream channel dry-up since the 1970s. There were accumulatively 897 zero-flow days during the 1990s in the river course below the Lijin Hydrological Station, 100 km upstream from the river mouth, which is 82.4% of that in 1972. As freshwater input decreases, river-borne nutrients to the estuarine increased significantly. Concentration of dissolved inorganic nitrogen (DIN) in the 1990s was four times of that in 1950s. Changes in amount and content of the riverine inputs have greatly affected the estuarine ecosystem. Over the past several decades, sea surface temperature and salinity in the estuary and its adjacent waters increased and their distribution pattern altered in response to the reduction of freshwater inflow. The distribution of and seasonal succession in nutrient concentrations in the surface layer have also changed with a shift of river outlet and the decrease in riverine nutrient loads. Furthermore, deterioration of estuarine ecosystem by less river input has decreased primary productivity in the deltaic region waters, and in turn depressed the fishery.