Water Resources Professional Project Reports

Document Type

Technical Report

Publication Date



In the Albuquerque/Rio Rancho area in central New Mexico, the Arid-Lands Hydrologic Model (AHYMO) has been used for more than a decade by land developers, municipalities and flood control agencies to simulate the effect of urban development on storm water runoff. An effort is underway to switch from the proprietary AHYMO program to the public domain model HEC-HMS. The majority of watersheds in the greater Albuquerque area are un-gauged, but more than ten years of experience show that AHYMO produces reliable results for the region. New guidelines that exist for the use of HEC-HMS were therefore developed to closely match AHYMO results. This paper presents a case study comparing AHYMO and HEC-HMS results for a small urban watershed in central New Mexico, testing specifically the influence of sub-basin size, impervious surfaces and modeling time steps on differences in model results. The methodologies used in AHYMO and HEC-HMS were based on the above mentioned guidelines. Out of twelve model scenarios created as part of this study, six resulted in significant differences between AHYMO and HEC-HMS peak flow rates computed for individual sub-basins. Sub-basin size appears to play an important role in explaining those differences. Four out of six model runs with small sub-basins (between five and 30 acres) yielded significantly different results, compared to only two out of six runs with larger sub-basins (between 60 and 75 acres). In addition to sub-basin size, imperviousness appears to influence differences between AHYMO and HEC-HMS. For all sub-basin sizes modeled in this study, HEC-HMS peak flow rates were significantly higher for scenarios with low imperviousness. Scenarios with high imperviousness and small sub-basins resulted in significantly higher AHYMO peak flows. Differences between the two models can be reduced by adjusting the storage coefficient R in HEC-HMS.

Language (ISO)



Arid-lands hydrologic model, AHYMO, HEC-HMS, watershed, sub-basin, peak flow rates


A Professional Project Report submitted in partial fulfillment of the requirements for the Degree of Master of Water Resources, Water Resources Program, University of New Mexico.