文档介绍：Hortonian Flow ? Sheet flow described by Horton in 1930s ? When i<f , all i is absorbed ? When i > f , ( i-f ) results in rainfall excess ? Applicable in – impervious surfaces (urban areas) – Steep slopes with thin soil – hydrophobic pacted soil with low infiltration Rainfall, i Infiltration, f i > q Later studies showed that Hortonian flow rarely occurs on vegetated surfaces in humid regions. Subsurface flow ? Lateral movement of water occurring through the soil above the water table ? primary mechanism for stream flow generation when f>i – Matrix/translatory flow ? Lateral flow of old water displaced by precipitation inputs ? Near surface lateral conductivity is greater than overall vertical conductivity ? Porosity and permeability higher near the ground – Macropore flow ? Movement of water through large conduits in the soil Saturation overland flow ? Soil is saturated from below by subsurface flow ? Any precipitation occurring over a saturated surface es overland flow ? Occurs mainly at the bottom of hill slopes and near stream banks Streamflow hydrograph ? Graph of stream discharge as a function of time at a given location on the stream Perennial river Ephemeral river Snow-fed River Direct runoff Baseflow Excess rainfall ? Rainfall that is neither retained on the land surface nor infiltrated into the soil ? Graph of excess rainfall versus time is called excess rainfall hyetograph ? Direct runoff = observed streamflow - baseflow ? Excess rainfall = observed rainfall - abstractions ? Abstractions/losses – difference between total rainfall hyetograph and excess rainfall hyetograph ?-index method ??????? Mm m dtR r 1?? Goal: pick ? t, and adjust value of M to satisfy the equation ? Steps 1. Estimate baseflow 2. DRH = streamflow hydrograph – baseflow 3. Compute r d , r d = V d /watershed area 4. Adjust M until you get a satisfactory value of ? 5. ERH = R m - ?? t SCS method ? Soil conservation service (SCS) method is an experi