## 3 Results
### Relationship between Predicted Burial Rates and Impervious Cover  
Predicted, county-level stream burial increases linearly with total impervious cover (Figure 6), in an approximately 1:1 relationship (Y = 1.135 \(\times\) X \(-\) 0.572; R\({}^{2}\) = 0.99; \(p\) \(<\) 0.001), with a few exceptions (i.e., deviations from the 1:1 line). Several Tier 1 counties and independent cities exhibited a higher proportion of stream burial than expected based on a 1:1 relationship with impervious cover. The largest discrepancies exist in the oldest municipalities with the greatest levels of urban development, including Washington, DC (1.26), the independent cities of Falls Church, VA (1.22), and Alexandria, VA (1.19), and Arlington County, VA (1.17). Conversely, counties that developed more recently, but still exhibit high levels of development (mostly Tier 2), were found to have lower levels of predicted burial than expected based on the 1:1 relationship. The Virginia independent cities follow the same pattern as counties, where cities that developed earlier exhibited higher predicted rates of burial per unit of impervious cover than did the more recently developed cities. All the Virginia cities exhibit very high predicted burial rates per unit imperviousness, with the exception of Manassas, VA, which falls directly on the 1:1 line, and Manassas Park, which is the only independent city to show a significantly lower burial to impervious ratio (0.79).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multicolumn{5}{c}{**Accuracy (\%)**} \\ \cline{2-5}  & **Intact** & **Buried** & **Overall** \\ \hline Iterative & 92.7 & 55.8 & 83.1 \\ Full & 88.0 & 71.0 & 83.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Accuracy values for iterative and full burial models.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Tier 1**} & \multirow{2}{*}{**Counties and Independent Cities**} & **Area** & **Potential Stream Length** & **Impervious Cover** & **Stream Burial** \\  & & **(km\({}^{2}\))** & **(km)** & **(\%)** & **(\%)** \\ \hline \multirow{4}{*}{**Tier 2**} & Washington, DC & 177.0 & 325.8 & 37.6 & 47.3 \\  & Arlington County, VA & 67.3 & 170.9 & 33.6 & 39.4 \\  & City of Alexandria, VA & 39.9 & 95.7 & 42.8 & 51.1 \\  & City of Fairfax, VA & 16.3 & 40.9 & 28.9 & 31.3 \\  & City of Falls Church, VA & 5.1 & 11.2 & 26.6 & 32.4 \\  & City of Manassas, VA & 25.8 & 49.1 & 32.0 & 31.7 \\  & City of Manassas Park, VA & 6.5 & 16.4 & 29.1 & 22.9 \\ \hline \multirow{2}{*}{**Tier 3**} & Prince George’s County, MD & 1291.0 & 2984.5 & 16.4 & 18.5 \\  & Montgomery County, MD & 1313.5 & 3830.8 & 10.2 & 11.0 \\  & Fairfax County, VA & 461.5 & 2803.9 & 15.2 & 14.3 \\ \hline \multirow{2}{*}{**Tier 3**} & Frederick County, MD & 1728.4 & 4146.2 & 3.3 & 4.4 \\  & Loudon County, VA & 1053.1 & 3555.3 & 5.5 & 4.9 \\  & Prince William County, VA & 902.3 & 2566.7 & 8.0 & 7.5 \\ \hline \multirow{2}{*}{**Tier 4**} & Washington County, MD & 1210.9 & 2151.0 & 3.7 & 4.4 \\  & Jefferson County, WV & 548.0 & 733.0 & 2.5 & 4.5 \\ \cline{1-1}  & Clarke County, VA & 1349.6 & 658.4 & 0.9 & 1.6 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Area, stream length, impervious cover and stream burial statistics for the 16 study units. Development ‘tier’ designations correspond with those shown in Figure 2, above.