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Home My WebLink AboutGrading Plans - 12/17/2020City of Fort Collins Approved Plans Approved by: Wes Lamarque �� Date: 12/17/2020 � -o �� I i iil lil�! II�� III �� Sorensen Engineering & Construction, Inc. Civil/Environmental Engineering December 4, 2020 Mr. Wes Lamarque Development Review Engineer Water Utilities Engineering City of Fort Collins Subject: 65 Circle Drive Fort Collins, Colorado Drainage Letter for Proposed Home Addition and Garage Dear Wes, Sorensen Engineering & Construction, Inc. (SEC) was retained by Mr. Craig Ellsworth, owner of the above referenced property, to evaluate drainage conditions on his property and prepare this drainage letter as required by the City of Fort Collins. This letter is prepared in accordance with requirements as presented in your email of November 3, 2020 to Taylor Meyer of Vaught Frye Larson Aronson, architects for the home addition and garage project. It is our understanding that the relative drainage assessment or analysis requirements are dependent on the amount of increase in impervious area as a result of the proposed project, as well as nearby drainage conditions. EXISTING AND PROPOSED IMPERVIOUS AREAS As shown on the attached existing and proposed impervious area drawings (SEC Sheets C101 and C102, respectively), and as summarized in the attached Impervious Area Calculations spreadsheet, the following conditions are defined: IMPERVIOUS AREA (SF) CHANGE IN IMPERVIOUS AREA PERCENT (SF) IMPERVIOUS AREA EXISTING 1,815.3 24.83 `Yo PROPOSED 2,273.9 +458.6 31.10% As shown, the increase in impervious area is greater than 350 square feet, but less than 1,000 square feet. Moreover, the area of the proposed improvements drains to an unimproved alley. Accordingly, we understand that a Drainage Assessment, with Professional Engineering (PE) certification is required. 1901 Bear Court / Fort Collins, Colorado 80525 (970) 590-1579 / paul(�secen�ineerin�.net SITE AND ALLEY TOPOGRAPHIC MAP The Site and Alley topographic map is attached, showing both surveyed contours on a 0.1-foot contour interval due to the flatness of the site, as well as elevation data points. Although the elevation data points may be difficult to discern on this copy, they do demonstrate that the subject property and alley are quite flat, but they show that the alley slopes very gently to the north. Drainage patterns are depicted on the topo map, including building downspouts. It is SEC's contention that the site conditions are more conducive to infiltration rather than off site discharge, and in fact the topo date indicate a minor closed basin in the back yard within the 4984.2 contour; the adjacent elevation in the alley is shown at 4984.4, with the southeast and northeast property corners at 4984.8 and 4984.2, respectively. ALLEY CONDITION The alley is an unimproved dirt alley. A number of existing garages line the alley near the subject property, many with flow-restrictive fencing adjacent to the alley that would serve to minimize any additional onsite flow from the alley. Accordingly, the precedence exists for approvals of similar projects on adjacent and near-by properties. OPINION Because of the extreme flat condition, the existence of garages and fences adjacent to the alley in both directions, and the infiltrative nature of the subject property and the alley dirt surface, SEC's professional opinion is that the proposed home addition and the new garage on the subject property will not cause any adverse effects on adjacent properties. Accordingly, we request that the City of Fort Collins approve this project as submitted. Please do not hesitate to contact me if you have any questions with respect our engineering analysis or the corresponding opinion we have rendered. Sinc r ly, � / Paul C. Sorensen, PE Attachments 2 Address : Owner 65 Circle Drive Fort Collins, Colorado Craig Ellsworth Existing and proposed impervious Area Calculations Total Lot Area: Existing Impervious Area: Concrete: Hom e: 7,312.10 square feet 527.2 square feet 1,288.10 square feet TOTAL 1,815.30 square feet % Impervious: Proposed Impervious Area: Concrete: Hom e: Garage: TOTAL % Impervious: Net increase in impervious area: 24.83 % 410.5 square feet 1,518.40 square feet 345 square feet 2,273.9 31.10% 458.6 square feet (existing sidewalk in rear to be removed) „” �'°a'°,s""'=��"e' v�v snoinxa� �ntr.csn�a � 6<s� �s o�s 3�o�d � W � SLSO80�'SNIIIOJltlO� p 5_ 8 O iano� av3a �os� m _ oavxo�oo�sNrr�oo.ixoi > � � DNRIHHf.fl'JN87tlJNHV3t3021IAN9/'77AIJ w•� z a � S 3 U s a JM'NOISJ(IN.LSNO� �8 �JM2I33.IIDt3ff NflSNHT10S y�� 3AIUQ 9Z�T� s9 � s� x _ w$ +�9 �H'�' 9 iWZZP OZOZ 60-�'-"9� %�H� fiw'r.�b� 6�Is�goi�JS9l�/5Y< A3xV59?hiq�%AU�O �'�N�µW � ufiuuaauiBuwxs�IneO � BLSL9650[6-3NOHd SZSOHOJ SNIIIO�ia01 1tlf10� 11b3B 1084 ONRI3�II'JN3'Itl.LNH31NO2UAN9 /'IIAIJ � �NI `NOIS�f1NJ.SI�OJ �,4 7NIN33AII'JNY N95NeN05 - � I II'I II I��"'ii%�v� _ II �� I I ��r.T�- �-� 'i I �� j � z � � �� a � t o� � � ° -'au � � � w � J u w W N G w u w L�S � � I I I I I I I I � I -- — — — — —� - �— — -- / -- — � � — — — d�x�a snoinxa�nu aasoaoxa � e 3 o � �_' �3 N b- O N oanao�o��swno�.cnoa > � � � � ��o a�m� s9 � U � : � r� w �a � � � � �h 7 y�� N � 7 O K W a " � g s ❑ -w c�n '�a O °�� i � a �aIIV lanea� AZ (�vM-30-3NR?N �96) a1.wQ aj�,n� N — � — —� _ — _ — — � �z✓nB <A'�'/a' .'�B v✓Y6/�'B 0.�OZ i0+�'-ro %�J /+M'�+M�%F�N-a'm.�S9l 51�tlH'y'.�5' J3Gim+"a4A:0 .'�N��tl �au 6uiaau 6ua�as��ned � ses��ossoes aNONa �no�Cc-j a.inl�a�2��.id t{�im s�uiod � I � szweoosNmoolaod o ` ianoo avae �os� - 3� ...aay, � onvnmo.�'sw�no.>.irod w .Q . .):11NSi'dNL)4�'IVLti111.\f1ll1nN3/11AIJ �� ' ` � ��I \OiLJrIiIiS�OJ F;JNiTI f tM'l�il N75hL78()S +3�Q'�7�2IIJS9 _� ' � . � '. olI �� I- oI� i � o� � \ ,� � �lx � � / ��O O?i _�o �so 0 � J � ,�;LL. �� i , ��, �, _ � � i�i � :� �� m �� aa�� <�� _ � , < =ae�s�w�� g ` E� E� aa8888 3 S 8 S II go >� I ro w'�p o�o I_— —_ _ . 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