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Figure 3 Post-dam annual maximum daily mean discharge at Otowi and Cochiti gages. Table 1 Comparison of the Rio Grande mean daily discharges in m/s before and after closure of Cochiti Dan (November 1973). Pre and post dam values are the mean values for that time period. Average change is the difference between the pre and post dam means expressed as a percentage of the pre-dam value (after Richard, 2001).

Figure 3 Post-dam annual maximum daily mean discharge at Otowi and Cochiti gages. Table 1 Comparison of the Rio Grande mean daily discharges in m/s before and after closure of Cochiti Dan (November 1973). Pre and post dam values are the mean values for that time period. Average change is the difference between the pre and post dam means expressed as a percentage of the pre-dam value (after Richard, 2001).

Related Figures (9)

Figure 1 Location map Cochiti Reach, Rio Grande, New Mexico. Locations of major tributaries and USGS gaging stations are indicated.
Figure 1 Location map Cochiti Reach, Rio Grande, New Mexico. Locations of major tributaries and USGS gaging stations are indicated.
Figure 2 Summary of changes in the water and sediment flow and channel adjustments of the Rio Grande, Cochiti Reach, NM from 1918 to 1992 (after Richard, 2001). Statistical procedures (Richter et al., 1996) were used to compare the water discharge records prior to and following Stream gage data along the Cochiti reach are available from 1895 to 1997 at several USGS gaging stations with the earliest record beginning in 1895 at the Otowi station (Leon ef al., 1999). The water-discharge data were collected by the USGS and recorded as daily mean discharge measurements. Locations of the gaging sta- tions are indicated in Figure 1. The Otowi gage, located upstream from Cochiti reservoir, is used as the non-regulated reference discharge for the post-dam period. No major tributaries enter the Rio Grande between the Otowi gage and Cochiti reservoir. The Cochiti gage is located just downstream from Cochiti Dam and
Figure 2 Summary of changes in the water and sediment flow and channel adjustments of the Rio Grande, Cochiti Reach, NM from 1918 to 1992 (after Richard, 2001). Statistical procedures (Richter et al., 1996) were used to compare the water discharge records prior to and following Stream gage data along the Cochiti reach are available from 1895 to 1997 at several USGS gaging stations with the earliest record beginning in 1895 at the Otowi station (Leon ef al., 1999). The water-discharge data were collected by the USGS and recorded as daily mean discharge measurements. Locations of the gaging sta- tions are indicated in Figure 1. The Otowi gage, located upstream from Cochiti reservoir, is used as the non-regulated reference discharge for the post-dam period. No major tributaries enter the Rio Grande between the Otowi gage and Cochiti reservoir. The Cochiti gage is located just downstream from Cochiti Dam and
dam closure at the Otowi, Otowi/Cochiti combined and Albu- querque gages. The mean daily discharge records were grouped according to water year and divided between pre-dam (prior to 1974) and post-dam (1974-1995) periods for the un-re gulated flow (Otowi gage), the inflow to the study reach downstream of Cochiti dam (Cochiti gage), and the outflow from the study reach (Bernalillo/Albuquerque gages). The results of comparing the mean values of the one-day maximum flow, the mean annual flow and the duration of the high flows for the pre and post dam are presented in Table 1. The one-day maximum (annua periods 1 flood) decreased at all of the gages, with the greatest decrease being just downstream of the dam at the Cochiti gage (38%). The d uration of the high pulse as well as the mean annual flow increased at all gages. Cochiti Dam is operated so that the maximum r discharge is 142 to 170 m/s. As a result, operation of t eleased he dam only affects flood peaks in excess of 142 m/s (Richard, 2001). dam closure at the Otowi, Otowi/Cochiti combined and Albu-
dam closure at the Otowi, Otowi/Cochiti combined and Albu- querque gages. The mean daily discharge records were grouped according to water year and divided between pre-dam (prior to 1974) and post-dam (1974-1995) periods for the un-re gulated flow (Otowi gage), the inflow to the study reach downstream of Cochiti dam (Cochiti gage), and the outflow from the study reach (Bernalillo/Albuquerque gages). The results of comparing the mean values of the one-day maximum flow, the mean annual flow and the duration of the high flows for the pre and post dam are presented in Table 1. The one-day maximum (annua periods 1 flood) decreased at all of the gages, with the greatest decrease being just downstream of the dam at the Cochiti gage (38%). The d uration of the high pulse as well as the mean annual flow increased at all gages. Cochiti Dam is operated so that the maximum r discharge is 142 to 170 m/s. As a result, operation of t eleased he dam only affects flood peaks in excess of 142 m/s (Richard, 2001). dam closure at the Otowi, Otowi/Cochiti combined and Albu-
Figure 5 Double mass curves of suspended sediment discharge at Bernalillo and Albuquerque (after Albert, 2004) Figure 4 Mass curves of suspended sediment discharge at Bernalillo and Albuquerque (after Albert, 2004).
Figure 5 Double mass curves of suspended sediment discharge at Bernalillo and Albuquerque (after Albert, 2004) Figure 4 Mass curves of suspended sediment discharge at Bernalillo and Albuquerque (after Albert, 2004).
Statistical procedures (Richter et al., 1996) were used to investigate the impact of the dam on the daily mean suspended sediment concentration data from the Otowi, Cochiti, Bernalillo and Albuquerque gage records. The results of the compari- son of the pre-dam with post-dam conditions are presented in Table 2. The greatest impacts of the dam were seen at the Cochiti gage located directly downstream from the dam, where the sediment concentration decreased an average of 99%. Prior to construction of the dam, the suspended sediment concentration at Bernalillo/Albuquerque was typically about 2 times greater than the concentration at Otowi. Following construction of the dam, The active channel width was measured from digitized cover- ages of the active channel delineated by the USBR’s GIS and Remote Sensing Group from aerial photos and topographic sur- veys (USBR, 1998). The non-vegetated active channel width is the total channel width between the outermost banklines minus the width of the mid-channel vegetated bars and islands. The
Statistical procedures (Richter et al., 1996) were used to investigate the impact of the dam on the daily mean suspended sediment concentration data from the Otowi, Cochiti, Bernalillo and Albuquerque gage records. The results of the compari- son of the pre-dam with post-dam conditions are presented in Table 2. The greatest impacts of the dam were seen at the Cochiti gage located directly downstream from the dam, where the sediment concentration decreased an average of 99%. Prior to construction of the dam, the suspended sediment concentration at Bernalillo/Albuquerque was typically about 2 times greater than the concentration at Otowi. Following construction of the dam, The active channel width was measured from digitized cover- ages of the active channel delineated by the USBR’s GIS and Remote Sensing Group from aerial photos and topographic sur- veys (USBR, 1998). The non-vegetated active channel width is the total channel width between the outermost banklines minus the width of the mid-channel vegetated bars and islands. The
Table 2 Comparison of Rio Grande suspended sediment concentration (mg/L) before and after closure of Cochiti Dam (November 1973). Pre and post dam values are the mean values for that time period. Average change is the difference between the pre and post dam means expressed as a percentage of the pre-dam value. reach shifted as flow energy and sediment supply changed from 1918 to 1992 (Richard, 2001). active and total channel widths were measured at cross sections every 500 meters along the channel and then reach-averaged using one-half the distance to the nearest upstream and down- stream cross sections as the weighting factor. Figure 2 illustrates the changes in active channel width with time and distance down- stream. The width of the Cochiti reach decreased with time since 1918 (Richard, 2001).
Table 2 Comparison of Rio Grande suspended sediment concentration (mg/L) before and after closure of Cochiti Dam (November 1973). Pre and post dam values are the mean values for that time period. Average change is the difference between the pre and post dam means expressed as a percentage of the pre-dam value. reach shifted as flow energy and sediment supply changed from 1918 to 1992 (Richard, 2001). active and total channel widths were measured at cross sections every 500 meters along the channel and then reach-averaged using one-half the distance to the nearest upstream and down- stream cross sections as the weighting factor. Figure 2 illustrates the changes in active channel width with time and distance down- stream. The width of the Cochiti reach decreased with time since 1918 (Richard, 2001).
Figure 6 Example of planform adjustments of the Cochiti Reach, Rio Grande, New Mexico (after Richard, 2001). Using the overlay GIS coverages of the active channel for dif- ferent years, the percentage of the active channel that remained Planform maps of the Cochiti reach active channel are presented in Figure 6. These maps show the non-vegetated active channe from 1918 through 1992 and illustrate the decrease in number and size of mid-channel bars and islands as well as the size of the active channel. Increased sinuosity is evident following dam construction and is most pronounced in reach 2. Channel pat tern is often considered to be a function of stream power, or of a slope-discharge relationship combined with sediment supply (Bledsoe, 1999). Accordingly, the channel pattern of the Cochiti a slope-discharge relationship combined with sediment supply
Figure 6 Example of planform adjustments of the Cochiti Reach, Rio Grande, New Mexico (after Richard, 2001). Using the overlay GIS coverages of the active channel for dif- ferent years, the percentage of the active channel that remained Planform maps of the Cochiti reach active channel are presented in Figure 6. These maps show the non-vegetated active channe from 1918 through 1992 and illustrate the decrease in number and size of mid-channel bars and islands as well as the size of the active channel. Increased sinuosity is evident following dam construction and is most pronounced in reach 2. Channel pat tern is often considered to be a function of stream power, or of a slope-discharge relationship combined with sediment supply (Bledsoe, 1999). Accordingly, the channel pattern of the Cochiti a slope-discharge relationship combined with sediment supply
Figure 7 Lateral stability index = Unchanged active channel area/previous active channel area (after Richard, 2001).
Figure 7 Lateral stability index = Unchanged active channel area/previous active channel area (after Richard, 2001).
Figure 8 Cross-section surveys of the Rio Grande downstream from Cochiti dam. Surveys prior to November 1973 are prior to dam construction (after Leon et al., 1999).
Figure 8 Cross-section surveys of the Rio Grande downstream from Cochiti dam. Surveys prior to November 1973 are prior to dam construction (after Leon et al., 1999).
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Environmental ScienceRiver Basin ManagementStream RestorationDam RemovalChannel Geometry
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