North Peoria Area Drainage Master Plan - Flood Control District of ...

NORTH PEORIAAREA DRAINAGE MASTER PLANGEOMORPHIC EVALUATIONGeomorphologyis the study oflandforms, thephysical processesthat formsthe land surfaceand the changesthat take place inthe evolution ofthe landform.Geomorphicevaluations conductedfor theNorth PeoriaADMP focusedon watercourse8QQDPHG:DVK&DQ\RQ5HDFK landforms andlateral stability ofa watercourse.Geomorphic evaluations conducted are basedon field observations, aerial photographs(both historic and recent), historical channelposition, stream longitudinal profile andallowable velocity guidelines. The results ofthe evaluation documents physical changes tothe watercourse that have occurred over timeand suggest the types of changes that can beexpected in the future.In general, historical and field evidence suggeststhat the floodplains of the watercoursesin the study area, where not incised in bedrock,are subject to lateral erosion. Thestreams in the study area flow within shallowcanyons comprised of Middle to Late Pleistocenealluvium or bedrock. Within recentgeologic time, the streams appear to havemigrated over the entire canyon bottom, graduallywidening the canyons through lateralerosion. The highest erosion hazards occur onthese canyon bottoms and at the margins ofthe older surfaces that form the canyon walls.The results of the geomorphic evaluation indicatethere is a potential for lateral migration inthe study watercourses and thus a potentialpublic safety hazard. Results of the evaluationsare used to develop erosion hazardzones.6FRXU+ROH8QQDPHG:DVKSEDIMENT ENGINEERINGThe primary objective of the sediment engineeringanalysis for the North Peoria ADMP isto estimate the existing and future sedimentyield, with emphasis on sediment depositionand maintenance requirements upstream ofthe Central Arizona Project (CAP) canal drainagecrossings, and sediment storage for futureregional retention/detention facilities.Sediment yield is the amount of solid materialtransported past a given point in a stream system,or alternately, the amount of materialdeposited in an enclosed basin. Sedimentyield includes particles small enough to becarried in suspension by the flowing water(suspended load) and particles moved alongthe bottom of a channel by rolling, sliding, orbouncing (bed load). When flow velocities arereduced, sediment carried by a stream isdeposited. Flow velocities can be reduced bynatural or manmade changes in channel slopeor channel geometry, or by impoundment inflood control basins. Sediment yield is a majorconcern for public officials in charge of maintainingthe effectiveness of flood control structuresbecause sedimentation behind dams orin floodways reduces the volume of waterthat can be stored or transported through thesystem. A reduction in effective storage volumeincreases the likelihood of a spillover inlarger runoff events, increasing the chances ofinjuries, damage to the structure itself, propertydamage downstream and possible loss ofhuman life.8