ارزيابي اثر مقياس نقشه هاي مبتني بر روشهاي سنجش از دور و برداشت هاي زميني بر عملكرد مدل بارش- رواناب HEC-HMS

Evaluating Scale Effect of Maps Derived via Remote Sensing and Ground Surveying on the Performance of HEC-HMS

مدل‌هاي هيدرولوژيكي بارش-رواناب يكي از روش‌هاي مناسب براي برآورد سيلاب به ويژه در مناطق فاقد آمار است كه مدل را به شدت به اطلاعات برداشت شده از حوضه وابسته مي‌كند. از مهم‌ترين مسائل مورد توجه در به‌كارگيري مدل‌هاي رياضي بارش-رواناب، اثر توان تفكيك مدل ارتفاعي رقومي (DEM Resolution) و مقياس نقشه (Data Resolution) بر پارامترهاي ژئومورفولوژيكي حوضه مانند شبكه آبراهه‌ها، مساحت زيرحوضه‌ها، شيب زيرحوضه‌ها و آبراهه‌ها مي‌باشد. در پژوهش حاضر به ارزيابي اثر مقياس و توان تفكيك نقشه مورد استفاده جهت تهيه DEM بر پارامترهاي ژئومورفولوژيكي و عملكرد مدل بارش- رواناب HEC-HMS پرداخته شده است. نتايج بدست آمده در دو حوضه آبريز كسيليان و كارده بيانگر اين مطلب است كه دبي اوج هيدروگراف سيلاب بدست آمده از DEMهاي SRTM همواره بالاتر از نتايج بدست آمده از نقشه‌هاي زميني (نقشه‌هاي 1/25000) است. همچنين با افزايش ابعاد سلول DEM، عملكرد دو منبع در شبيه‌سازي سيلاب و پارامترهاي ژئومورفولوژيكي به علت يكسان شدن محتوي اطلاعاتي آنها، اختلاف اندكي را نشان مي‌دهد. همچنين دبي اوج هيدروگراف و زمان پايه و شيب شاخه صعودي بدست آمده از دو منبع تامين DEM متفاوت بوده و اين تفاوت در حوضه كارده قابل توجه مي‌باشد. اين امر لزوم توجه به مقياس نقشه مورد استفاده جهت مدل‌سازي سيلاب به ويژه در حوضه‌هاي فاقد آمار را بيش از پيش آشكار مي‌نمايد.

Rainfall Runoff modeling especially in ungauged watersheds is almost dependent on hydro-geomorphologic data. In this regard, the effects of data and DEM resolution on deriving watershed’s geomorphologic data such as subbasins area, channels and subbasins’ slope should be well realized in modeling. In this research, HEC-HMS as the rainfall runoff model and two subbasins with different areas, geomorphologic properties and climate were selected for studying. By reducing the cell size of the DEM derived from a topo map, simulated peaks increased. For DEM cell sizes less than 100 m, the differences in simulated peak were limited to 2 to 5%. Using SRTM DEMs against the topo DEM at the scale of 1:25000, representing the effects of data resolution in rainfall runoff modeling, led to obtaining higher flood peaks at the two watersheds. Such an outcome was obtained for time to peak, hydrograph base time, and the slope of hydrograph rising limb. Change of SRTM DEM resolution affected the model output more than the case of using topo DEM. Decreasing DEMs resolution by decreasing information content of the topo DEM reduced differences in the model output when using two different sources of DEM. Furthermore, it is concluded that the extent of scale effect in modeling could not be inferred by watershed size. It was illustrated that HEC-HMS application in a watershed of more diversity was more sensitive to data resolution. Using cell size of 100 m and less could guaranty the result of the HEC-HMS application regardless of DEM origin and size of watersheds. Rainfall Runoff modeling especially in ungauged watersheds is almost dependent on hydro-geomorphologic data. In this regard, the effects of data and DEM resolution on deriving watershed’s geomorphologic data such as subbasins area, channels and subbasins’ slope should be well realized in modeling. In this research, HEC-HMS as the rainfall runoff model and two subbasins with different areas, geomorphologic properties and climate were selected for studying. By reducing the cell size of the DEM derived from a topo map, simulated peaks increased. For DEM cell sizes less than 100 m, the differences in simulated peak were limited to 2 to 5%. Using SRTM DEMs against the topo DEM at the scale of 1:25000, representing the effects of data resolution in rainfall runoff modeling, led to obtaining higher flood peaks at the two watersheds. Such an outcome was obtained for time to peak, hydrograph base time, and the slope of hydrograph rising limb. Change of SRTM DEM resolution affected the model output more than the case of using topo DEM. Decreasing DEMs resolution by decreasing information content of the topo DEM reduced differences in the model output when using two different sources of DEM. Furthermore, it is concluded that the extent of scale effect in modeling could not be inferred by watershed size. It was illustrated that HEC-HMS application in a watershed of more diversity was more sensitive to data resolution. Using cell size of 100 m and less could guaranty the result of the HEC-HMS application regardless of DEM origin and size of watersheds.