Thresholds in the storm response of a catchment‐lake system and the occurrence and magnitude of lake overflows: Implications for flood frequency

[1] This model-based study examines the combined effects of catchment and lake thresholds upon the frequency and magnitude of lake-overflow events, and their impacts on flood frequency. A dominant control of lake-overflow events is antecedent storage, which is governed by the climate and by the properties of the contributing catchment. The next major control was shown to be the magnitude of storm depths, and their adequacy to replenish and exceed the lake storage deficit, which are governed by the ratio of catchment to lake areas, AC/AL. When AC/AL is large, lake-overflows can be triggered even at larger antecedent lake storage deficits. This points to the importance of AC/AL as a critical parameter governing the frequency and magnitude of lake-overflow events. As regards the catchment properties, model simulations indicate that fast draining catchments enhance the triggering of lake-overflow events due to the fact that the drainage is rapid and there is the opportunity for faster runoff contributions to combine with direct rainfall on the lakes to exceed antecedent lake storage deficit and overcome the reducing influence of evaporation during inter-storm periods. Slow draining catchments, on the other hand, will not release runoff fast enough to replenish the lake storage deficit before the evaporative effects take hold. The shape of the resulting flood frequency curve captures the dominant lake-overflow generating mechanisms. When the dominant lake overflow generating mechanism is catchment runoff, the shape of flood frequency curve of lake-overflows resembles the shape of the catchment flood frequency curve, including the effects of associated thresholds. On the other hand, when the dominant lake overflow generating mechanism is direct rainfall falling on the lake, the shape of the lake-overflow flood frequency curve exhibits a persistent truncation below a critical return period that is associated with the frequency of flow termination for the given climate in question. These results have provided valuable insights into the relative roles of climate, soil depth, the soil's drainage capacity as well as the ratio of catchment area to lake area on flood frequency of catchment-lake systems in general. The improved understanding of these process controls will be useful in assisting the management of such combined catchment-lake systems. In particular, they can provide valuable guidance towards the monitoring of catchment-lake systems in ways that are targeted towards those controls which are critical to the determination of the magnitude and frequency of lake-overflow events to assist in flood prevention and mitigation.

[1]  M. Sivapalan,et al.  Process controls of water balance variability in a large semi-arid catchment: downward approach to hydrological model development , 2001 .

[2]  M. Sivapalan,et al.  Threshold effects in catchment storm response and the occurrence and magnitude of flood events: implications for flood frequency , 2006 .

[3]  S. Marimuthu,et al.  A field study of hydraulic, geochemical and stable isotope relationships in a coastal wetlands system , 2005 .

[4]  M. Woo,et al.  Snowmelt runoff processes in a headwater lake and its catchment, subarctic Canadian Shield , 2006 .

[5]  Murugesu Sivapalan,et al.  Watershed groundwater balance estimation using streamflow recession analysis and baseflow separation , 1999 .

[6]  H. L. Penman.  Natural evaporation from open water, bare soil and grass , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[7]  Ming-ko Woo,et al.  Hydrology of subarctic Canadian shield: soil-filled valleys , 2003 .

[8]  M. Sivapalan,et al.  Temporal scales of rainfall–runoff processes and spatial scaling of flood peaks: space–time connection through catchment water balance , 2001 .

[9]  S. Manabe.  CLIMATE AND THE OCEAN CIRCULATION1 , 1969 .

[10]  Murugesu Sivapalan,et al.  Conceptual examination of climate–soil controls upon rainfall partitioning in an open-fractured soil II: Response to a population of storms , 2007 .

[11]  M. Sivapalan,et al.  A conceptual investigation of process controls upon flood frequency: role of thresholds , 2006 .

[12]  P. Milly.  Climate, soil water storage, and the average annual water balance , 1994 .

[13]  C. Spence.  The Effect of Storage on Runoff from a Headwater Subarctic Shield Basin , 2000 .

[14]  M. Woo,et al.  Hydrology of subarctic Canadian Shield: heterogeneous headwater basins , 2006 .

[15]  R. Woods,et al.  Climate and landscape controls on water balance model complexity over changing timescales , 2002 .

[16]  Murugesu Sivapalan,et al.  Dominant physical controls on hourly flow predictions and the role of spatial variability: Mahurangi catchment, New Zealand , 2003 .

[17]  Murugesu Sivapalan,et al.  Conceptual examination of climate–soil controls upon rainfall partitioning in an open-fractured soil: I. Single storm response , 2007 .

[18]  Murugesu Sivapalan,et al.  Temporal scales and hydrological regimes: Implications for flood frequency scaling , 1997 .

[19]  Murugesu Sivapalan,et al.  Climate, soil, and vegetation controls upon the variability of water balance in temperate and semiarid landscapes: Downward approach to water balance analysis , 2003 .

[20]  M. Woo,et al.  Catchment hydrology of a High Arctic lake , 1981 .