## 1 Introduction
However, impervious cover alone has proven an insufficiently sensitive measure of river health [23], as significant aquatic assemblage degradation has been observed across a wide range of watershed imperviousness [24]. Recognition that the spatial configuration of impervious cover relative to stream channels may be an important moderator of the magnitude of stream ecosystem response to urbanization [25; 26] has led to development of alternative metrics for measuring urbanization effects on stream ecosystems. Measures of effective imperviousness (EI, impervious cover directly adjacent to a stream channel [27; 28]) and directly connected impervious area (DCIA, impervious surfaces that route stormwater runoff directly to streams via stormwater pipes [29]) have been shown to better integrate the multiple stressors of urban development, relative to TI. However, these methods also have shortcomings; they either fail to explicitly capture piped and concrete-lined stream channels (e.g., EI) or necessitate detailed information on stormwater conveyances to determine runoff routing and specific on-lot drainage patterns (DCIA). Most importantly, neither approach directly quantifies the impact of urbanization on stream habitat, and instead relies on indirect measures such as changes in sedimentation and hydrology. Stream habitat is most directly impacted when impervious surface completely covers the stream channel. Previous research has shown a relationship between stream size and the probability of burial, with the smallest, headwater streams of the urbanized Gunpowder-Patapsco watershed, Maryland, USA, exhibiting disproportionately high rates of burial in relation to larger streams [2]. Whether this pattern remains consistent in other watersheds or across broader geographic scales is unknown. Local topographic patterns, such as slope, are also known to affect the probability of urbanization [30; 31], by making some places inaccessible or unstable for building [32]. It remains unclear whether these same physiographic constraints may limit, or necessitate, the burial of streams. Insights into both the spatial and temporal patterns of stream burial, particularly with respect to stream size and topographic slope, are critical for gauging the effectiveness of land-use policies meant to foster development, while protecting the health of stream ecosystems. Historical patterns of stream burial also provide insight into the characteristics of streams that remain, information that is potentially useful for describing and understanding patterns of watershed exports, ecosystem functions, and remaining aquatic biodiversity [33; 34]. Recent advancements in stream mapping, remote-sensing of impervious cover, and predictive models now make it possible to predict stream burial at a relatively high level of detail and accuracy across large areas. To enhance our understanding of the phenomenon of stream burial, we developed a novel analytical approach using improved headwater stream maps [35], moderate resolution impervious cover data [36], and recursive partitioning models [37] to map the extent and magnitude of burial across an urban gradient in the Mid-Atlantic United States. We then analyze the spatial patterns of stream burial within the context of watershed area, topography, and impervious surface area. We expect these new burial maps and analysis of burial response to physiographic parameters to provide a fresh perspective into land use decision-making processes, and the development pressures facing critical headwater stream ecosystems, past, present, and future.