# The Definition of Perennial Streams Based on a Wet Channel Network Extracted from LiDAR Data
## 1 Introduction  
Natural streams are classified into ephemeral, intermittent, and perennial streams based on their flow durations. Ephemeral streams flow directly in response to precipitation without continuous surface flow [1, 2]. The total volume of flow under the annual hydrograph of an ephemeral stream watershed is the result of direct runoff from large rainfall events [3]. Some ephemeral streams only flow for several hours annually [4]. Intermittent (i.e., seasonal) streams flow during certain times of the year by receiving water from surface sources such as snow melting or groundwater sources such as springs [1, 5]. Variations in the water table affect the characteristics of intermittent streams that are supplied by groundwater sources [1]. Perennial streams flow most of the year (defined as a threshold) during years with normal rainfall and are maintained by groundwater discharge [1, 6]. The threshold to define a perennial stream varies in the literature. For example, [PERSON] and [PERSON] [7] defined channels with flowing water for more than 80% of the year as perennial streams, while [PERSON] [8] and the Texas Forest Service [9] used 90% as the threshold. Even for perennial streams, channel networks expand during rainfall events and contract during recession periods, as well as disconnecting and reconnecting hydrologically [10, 11]. United States Geological Survey (USGS) quadrangle topographic \"blue line\" maps classify ephemeral, intermittent, and perennial streams based on the interpretation of aerial photographs. These classifications are confirmed by USGS field surveys when the maps are compiled [12]. Although the USGS monitors perennial streams regularly to generate flood and water supply information, it rarely checks intermittent or ephemeral streams. Map delineation between intermittent-ephemeral and perennial-intermittent streams isperformed with very little information, and its reliability is uncertain [13]. Fluctuations in streamflow permanence have been explained with various climate and physiographical data in the Pacific Northwest of the United States by [PERSON] et al. [14]. The introduction of airborne light detection and ranging (LiDAR) provides the opportunity to accurately study drainage networks. LiDAR provides topographic data at sub-meter resolution and accuracy [15; 16] and has been applied to the extraction of channel networks [17; 18; 19; 20; 21; 22; 23]. In addition to elevation data, LiDAR provides signals' intensity information, which is a relative measurement of the return strength of the laser pulse. The intensity of return from water surfaces is relatively low compared with that from dry lands. LiDAR intensity has been utilized to map relatively large and continuous bodies of water, such as the extent of flood inundation, rivers, wetlands, ponds, and lakes [24; 25; 26; 27]. [PERSON] et al. [28] developed an extraction method for wet channel network extraction by integrating LiDAR intensity and a digital elevation model (DEM) for detecting narrow, disconnected, and shallow streams located in headwater catchments. In addition, [PERSON] et al. [29] investigated the temporal dynamics of stream networks in five watersheds using a systematic method for extracting wet channel networks based on light detection and ranging elevation and intensity data. Moreover, [PERSON] et al. [30] developed a process to reproducibly identify areas of former stream meanders to assist future off-channel restoration site selections, and the study is expected to provide conservation managers with an improved process to identify candidate restoration sites. The drainage networks in a watershed are associated with hydrological processes such as infiltration, runoff, and erosion, and are controlled by climate, soil, topography, and vegetation conditions. The critical questions concerning flowing channel networks are how the channel networks expand in rising limbs and contract in recession limbs of a streamflow hydrograph, and what the relationship between flowing channel length and streamflow is.